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Papers by Dale Gelman

Research paper thumbnail of Aedes aegypti TMOF modulates ecdysteroid production by prothoracic glands of the gypsy moth,Lymantria dispar

Archives of Insect Biochemistry and Physiology, 2000

Trypsin modulating oostatic factor (TMOF) is a decapeptide that inhibits the biosynthesis of tryp... more Trypsin modulating oostatic factor (TMOF) is a decapeptide that inhibits the biosynthesis of trypsin-like enzymes in the midgut of several insect species and, as such, serves as a dipteran oostatic hormone. In vitro incubation of lepidopteran prothoracic glands with Aedes aegypti TMOF revealed that this decapeptide, in the presence of brain extract, modulates ecdysteroid production. The modulatory effect was highly dependent on both the concentration of TMOF and brain extract. Typically, TMOF was stimulatory in the presence of lower concentrations of Lymantria dispar brain extract (0.01 and 0. 025 brain equivalent), and either neutral or inhibitory at higher concentrations (0.25, 0.5, and 1.0 brain equivalent) of extract. In the presence of European corn borer (Ostrinia nubilalis) brain extract, TMOF also exhibited modulatory effects, effects that again were dependent on the concentrations of both brain extract and TMOF present in the incubation medium. At 1.5 brain equivalents, TMOF was inhibitory at all but the highest concentration tested (5x10(-6) M), at 1.0 brain equivalent, TMOF was stimulatory at 10(-6) M and at 0. 5 brain equivalents, TMOF did not significantly affect PTG synthesis of ecdysteroids. Results suggest the presence of a modulatory peptide(s), which fine tunes the synthesis and release of ecdysteroids by PTGs in accordance with the insect's developmental/physiological requirements.

Research paper thumbnail of Age-specific interaction between the parasitoid, Encarsia formosa and its host, the silverleaf whitefly, Bemisia tabaci (Strain B)

Journal of Insect Science, 2003

The effect of hostage, the instar of Bemisia tabaci (Gennadius) parasitized, on the growth and de... more The effect of hostage, the instar of Bemisia tabaci (Gennadius) parasitized, on the growth and development of Encarsia formosa (Gahan) was studied. E. formosa was able to parasitize and complete its life cycle no matter which instar of B. tabaci (Strain B), [also identified as B. argentifolii (Bellows and Perring)], was provided for oviposition, but parasitoid development was significantly slower when 1st or 2nd instar B. tabaci rather than 3rd or 4th instars were parasitized. Host age influenced the day on which E. formosa nymphs hatching from eggs was first observed. Mean embryonic development was significantly longer when 1st (5.4 days) rather than 2nd, 3rd or 4th instars (4.1, 3.4 and 3.5 days, respectively) were parasitized. The duration of the 1st instar parasitoid and the pupa, but not the 2nd or 3rd instar parasitoid, were also significantly greater when 1st instars were parasitized than when older host instars were parasitized. Interestingly, no matter which instar was parasitized, the parasitoid did not molt to the 3rd instar until the 4th instar host had reached a depth of about 0.23 mm (Stage 4-5) and had initiated the nymphal-adult molt and adult development. Histological studies revealed that whitefly eye and wing structures had either disintegrated or were adult in nature whenever a 3rd instar parasitoid was present. It appears, then, that the molt of the parasitoid to its last instar is associated with the host whitefly's nymphal-adult molt. However, the initiation of the host's final molt, while a prerequisite for the parasitoid's 2nd-3rd instar molt, did not necessarily trigger this molt. In contrast to its significant effect on various aspects of parasitoid development, host instar did not significantly influence the mean size of the parasitoid larva, pupa, or adult. Larval and pupal length and adult head width were similar for all parasitoids, regardless of which host instar was parasitized as was adult longevity. Adult parasitoid emergence was more synchronous when 2nd, 3rd and 4th instars were parasitized than when 1st instars were parasitized. Results are compared with those reported when the greenhouse whitefly, Trialeurodes vaporariorum, was parasitized by E. formosa, and provide possible explanations for why T. vaporariorum is a more suitable host than B. tabaci for E. formosa.

Research paper thumbnail of Host plant pubescence: Effect on silverleaf whitefly, Bemisia argentifolii, fourth instar and pharate adult dimensions and ecdysteroid titer fluctuations

Journal of Insect Science, 2003

BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access t... more BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access titles in the biological, ecological, and environmental sciences published by nonprofit societies, associations, museums, institutions, and presses.

Research paper thumbnail of Host-parasitoid interactions relating to penetration of the whitefly, Eretmocerus mundus

Journal of Insect Science, 2005

It has been reported that the aphelinid wasp Eertmocerus mundus parasitizes all four nymphal inst... more It has been reported that the aphelinid wasp Eertmocerus mundus parasitizes all four nymphal instars of the sweet potato whitefly, Bemisia tabaci (Biotype B), with 3 rd instars being the preferred hosts. The parasitoid lays its egg on the leaf underneath the host nymph. First instars hatch and later penetrate the whitefly. Previous studies have shown that the initiation of parasitoid penetration induces the host to form a cellular capsule around the parasitoid. As described here, females never oviposited once the 4 th instar whitefly nymph had initiated adult development. First instar E. mundus larvae were observed under 2 nd , 3 rd and 4 th instar whitefly nymphs, however, penetration did not occur until the whitefly had reached the 4 th instar. The non-penetrating E. mundus larva almost always induced permanent developmental arrest in its 4 th instar whitefly host and also caused a reduction in whole body host ecdysteroid titers. Therefore, unless there is a peak in molting hormone titer in the area local to penetration, it appears that the induction of capsule formation is not due to an increase in ecdysteroid titer. As the capsule formed around the penetrating parasitoid, host epidermal cells multiplied and became cuboidal and columnar, and relatively thick layers of new cuticle were deposited within the developing capsule, particularly near its ventral opening. The newly formed host cuticle was thinner in the dorsal part of the capsule and appeared to be absent at its apex. These results provide new information regarding the timing and dynamics of parasitoid oviposition and egg hatch as related to larval penetration, parasitoid-induced changes in whitefly development, molting hormone titers and the process of capsule formation.

Research paper thumbnail of Critical periods for the brain and prothoracic glands of 5th instars of the European corn borer, Ostrinia nubilalis hubner

Comparative Biochemistry and Physiology Part A: Physiology, 1982

1. 1. Classical ligation techniques were used to determine the critical periods for the head and ... more 1. 1. Classical ligation techniques were used to determine the critical periods for the head and the prothoracic glands in the larval-pupal molt of the European corn borer. 2. 2. Most larvae reared under LD 16:8 and 30°C released sufficient PTTH between lights on + 13 hr and lights on — 3 hr to stimulate the prothoracic glands to produce ecdysone. 3. 3. Ecdysone was first released just before lights on, with almost all larvae having produced sufficient ecdysone to elicit a molt by lights on + 6 hr. 4. 4. Critical periods for the brain and prothoracic glands of Ostrinia are compared with those of other lepidopterans.

Research paper thumbnail of Critical Feeding Periods for Last Instar Nymphal and Pharate Adults of the Whiteflies,Trialeurodes vaporariorumandBemisia tabaci

Journal of Insect Science, 2007

A critical feeding period is the time after which 50% of a given species of insect can be removed... more A critical feeding period is the time after which 50% of a given species of insect can be removed from its food source and complete development by undergoing adult eclosion. The critical feeding period was determined for the greenhouse white fly, Trialeurodes vaporariorum, and the sweet potato whitefly, Bemisia tabaci (Biotype B) (Homptera/Hemiptera: Aleyrodidae). Fourth (last) instar and pharate adult whiteflies were removed from green bean leaves, staged, placed on filter paper in small Petri dishes containing drops of water, and observed daily for eclosion. For T. vaporariorum reared at 25°C and L:D 16:8, 55 and 80% adult eclosion were observed when whiteflies were removed at stages 4 (0.23-0.26 mm in body depth) and 5 (≥ 0.27 mm in body depth), respectively, so that at least 50% eclosion was only achieved in this species of whitefly when adult eye development had already been initiated (in Stage 4), and 80% eclosion when adult wing development had been initiated (Stage 5). In contrast, 63% of B. tabaci emerged as adults if removed from the leaf at Stage 3 (0.18-0.22 mm in body depth), and 80% emerged if removed at Stage 4/5, stages in which adult formation had not yet been initiated. The mean number of eggs laid by experimental (those removed at Stages 4-5, 6-7 or 8-9) and control (those that remained on the leaf prior to eclosion) whiteflies, and the mean percent hatch of these eggs were not significantly different in experimental and control groups. Stages 7, 8 and 9 are characterized by a light red adult eye, medium red bipartite adult eye and dark red or red-black bipartite adult eye, respectively. Mean adult longevity also was not significantly different between experimental and control groups. However, for all groups of T. vaporariorum, adult female longevity was significantly (at least 2 times) greater than male longevity. Our results identify the critical feeding periods for last instar/pharate adults of two important pest species of whitefly. Since in both species of whitefly the critical feeding period is achieved when weight gain reaches a plateau, it appears that the critical feeding period is more closely correlated with the attainment of a critical weight than with either the time that ecdsyteroid titers first peak or the time when adult development is initiated.

Research paper thumbnail of Role of ecdysteroids in the regulation of sperm release from the testis of the gypsy moth, Lymantria dispar

Journal of Insect Physiology, 1990

Release of mature sperm from the testes of the gypsy moth, Lymantria dispar, into the seminal duc... more Release of mature sperm from the testes of the gypsy moth, Lymantria dispar, into the seminal ducts occurs in a daily rhythmic pattern. The rhythm of sperm release is initiated in developing pharate adults 3-4 days after spermatogenesis and development of the reproductive tract has been completed. At that time a significant decline occurs in the blood titre of RIA-detectable ecdysteroids. Infusion of 20-hydroxyecdysone into male pupae inhibits the release of sperm from the testis in a dose-dependent and age-dependent fashion. The decline in haemolymph ecdysteroid levels seems essential for the initiation of the rhythmic release of sperm from the testis, but does not appear to play a role in determining the phase of this rhythm.

Research paper thumbnail of Prothoracicotropic hormone levels in brains of the European corn borer, Ostrinia nubilalis: Diapause vs the non-diapause state

Journal of Insect Physiology, 1992

Brains from non-diapause-bound, diapause-bound and diapausing European corn borers contain protho... more Brains from non-diapause-bound, diapause-bound and diapausing European corn borers contain prothoracicotropic hormone (PTTH) which stimulates the prothoracic glands of both Lymantriu d&par and Ostrinia nubilalis to produce ecdysone and 3-dehydroecdysone in a dose-dependent manner. At a dose of 0.75 brain equivalents, PTTH activity is highest in non-diapause-bound and diapausing prepupae. Levels are approx. 50% as high in younger 5th instars. In diapausing prepupae, PTTH activity again falls to approx. 50% after 5-8 weeks of refrigeration. Prothoracic glands from diapausing 0. nubilafis prepupae were refractory to stimulation. In uiuo experiments indicate that brains from diapausing prepupae have more moult-stimulating activity than those from non-diapause-bound prepupae. However, this may be due to the presence of factors other than PTTH. Based on gel filtration HPLC, the molecular weight range of the small form of 0. nubilalis PTTH is 1500-3300 Da, somewhat less than the 500&7000 Da peptide reported for other lepidopterans.

Research paper thumbnail of Kopec revisited—Neuroendocrine regulation of metamorphosis in the gypsy moth (Lymantria dispar): Development of a larval in vivo assay for prothoracicotropic hormone

Journal of Insect Physiology, 1992

The role of the brain as a. neuroendocrine regulator of metamorphosis in the gypsy moth, Lymantri... more The role of the brain as a. neuroendocrine regulator of metamorphosis in the gypsy moth, Lymantria dispar L. was originally demonstrated by Kopec more than 70 years ago. We have reexamined this role by determining haemolymph ecdysteroid titres, activity and responsiveness of the prothoracic glands, and growth of female last (i.e. fifth)-instar larvae in relation to secretion of the brain prothoracicotropic hormone (PTTH), the factor known to trigger moulting and metamorphosis in insects. The head critical period for secretion of PTTH in Lymantria reared at 25°C in a 16 h light-8 h dark cycle was shown by neck ligation to occur on day 7-8 of the fifth instar. The critical period occurred shortly after a small peak of haemolymph ecdysteroid that reached 600 pg 20-hydroxyecdysone equivalents/PI, as determined by radioimmunoassay. Feeding was completed by day 7, thus neck ligation did not affect nutrient intake. Animals starved from day 5 onward completed pupation at the same time as non-starved controls and showed normal increases in haemolymph ecdysteroid titres. Animals neck-ligated on day 7 and injected 5 days later with extracts of brain, retrocerebral complex, or brain tissues containing lateral or median neurosecretory cells were stimulated to pupate within 5 days, and brain-extract-injected animals showed an increase in haemolymph ecdysteroid titre of over 4000 pg/pl. Animals neck-ligated earlier had lower haemolymph ecdysteroid titres than day 7, neck-ligated larvae and their prothoracic glands showed lower activity in vitro. Using the in vivo assay, PTTH activity was detected in pre-hatch eggs and in brains taken from day-5 last-instar larvae, day-l pupae and day-l adults. The assay appears specific to tissues from the brain and retrocerebral complex, since no activity was found with extracts of the subesophageal ganglion, fat body or muscle.

Research paper thumbnail of Ecdysteroid titers and developmental expression of ecdysteroid-regulated genes during metamorphosis of the yellow fever mosquito, Aedes aegypti (Diptera: Culicidae)

Journal of Insect Physiology, 2006

Ecdysteroid titers and expression profiles of ecdysone-regulated genes were determined during the... more Ecdysteroid titers and expression profiles of ecdysone-regulated genes were determined during the last instar larval and during the pupal stages of Aedes aegypti (Diptera: Culicidae). Three peaks of ecdysteroids occurring at approximately 24, 30-33 and 45-48 h after ecdysis to the fourth instar larval stage were detected. In the pupa, a large peak of ecdysteroids occurred between 6 and 12 h after ecdysis to the pupal stage. A small rise in ecdysteroids was also detected at the end of the pupal stage. Quantitative reverse transcriptase polymerase chain reaction analyses of the expression of ecdysone receptors and ecdysone-regulated genes showed that the peaks of expression of most of these genes coincided with the rise in ecdysteroid levels during the last larval and pupal stages. In the last larval stage, ecdysteroid titers and mRNA expression profiles of ecdysone-regulated genes are similar to those observed for Drosophila melanogaster. However, in the early pupal stage, both ecdysteroid titers and the expression of ecdysone-regulated genes are somewhat different from those observed in D. melanogaster, probably because the duration of the pupal stage in D. melanogaster is 84 h while in Ae. aeqypti the duration is only 48 h. These data which describe the relationship between ecdysteroid titers and mRNA levels of Ae. aegypti ecdysteroid-regulated genes lay a solid foundation for future studies on the hormonal regulation of development in mosquitoes.

Research paper thumbnail of Ecdysteroid levels/profiles of the parasitoid wasp, Diapetimorpha introita, reared on its host, Spodoptera frugiperda and on an artificial diet

Journal of Insect Physiology, 2000

Diapetimorpha introita is an ichneumonid ectoparasitoid of the fall armyworm, Spodoptera frugiper... more Diapetimorpha introita is an ichneumonid ectoparasitoid of the fall armyworm, Spodoptera frugiperda. Since it has been reported that D. introita wasps reared on an artificial diet exhibit a significantly lower percentage of adult eclosion and fecundity than hostreared wasps, this study was undertaken to elucidate the factors responsible for the reduced viability observed in diet-reared wasps. A system of markers has been devised to track the development (from the initiation of cocooning through adult eclosion) of D. introita. Although wasps reared on artificial diet developed more slowly than did those reared on host pupae, both diet-and hostreared wasps passed through the same stages of development -the eyes enlarged and moved backward, the gut was purged and upon ecdysis the exarate pupa emerged. The thorax was the first to darken, followed by the head and then the abdomen. Pharate pupal formation occurred before gut purge. Two peaks of hemolymph ecdysteroids were observed, one in wasps in which gut purge was almost complete and the second in day-2 exarate pupae. Ecdysone and 20-hydroxyecdysone were the major ecdysteroids present in hemolymph sampled at these times. Small quantities of 20,26-dihydroxyecdysone, polar ecdysteroids and/or possibly 26hydroxyecdysone were also present. In six stages of development, hemolymph ecdysteroid titers were significantly higher in hostreared than in diet-reared wasps (Eye 1, Eye 2, Gut Purge 2, Pharate Pupa, Head/Thorax Dark, and Abdomen Dark). Relatively high percentages of mortality were observed in diet-reared wasps in four of these stages and in two others which occurred in close proximity to one of the stages, the Abdomen Dark stage. Thus, insufficient ecdysteroid in the hemolymph may be responsible, in part, for the relatively high percentage of mortality that occurred in wasps reared on an artificial diet. Published by Elsevier Science Ltd.

Research paper thumbnail of Identification of the molting hormone of the sweet potato (Bemisia tabaci) and greenhouse (Trialeurodes vaporariorum) whitefly

Journal of Insect Physiology, 2005

In order to identify the whitefly molting hormone, whole body extracts of mature 4th instar and n... more In order to identify the whitefly molting hormone, whole body extracts of mature 4th instar and newly formed pharate adult Bemisia tabaci (Biotype B) and Trialeurodes vaporariorum were prepared and subjected to reverse phase high performance liquid chromatography (RPHPLC). Ecdysteroid content of fractions was determined by enzymeimmunoassay (EIA). The only detectable ecdysteroids that were present in significant amounts in whitefly extracts were ecdysone and 20-hydroxyecdysone. The concentrations of 20-hydroxyecdysone in B. tabaci and T. vaporariorum extracts, respectively, were 40 and 15 times greater than the concentrations of ecdysone. The identity of the two ecdysteroids was confirmed by normal phase high performance liquid chromatography (NPHPLC). When ecdysteroid content of RPHPLC fractions was assayed by radioimmunoassay (RIA), small amounts of polar ecdysteroids were also detected indicating that these ecdysteroids have a very low affinity for the antiserum used in the EIA. Ecdysteroid at 10.4 mM administered by feeding stimulated 2nd instar whitefly nymphs to molt. Based on our results, it appears that 20-hydroxyecdysone is the whitefly molting hormone.

Research paper thumbnail of Molting in workers of the Formosan subterranean termite Coptotermes formosanus

Journal of Insect Physiology, 2008

The Formosan subterranean termite, Coptotermes formosanus, with its huge colonies, is a major urb... more The Formosan subterranean termite, Coptotermes formosanus, with its huge colonies, is a major urban pest in several southern states and Hawaii as well as in South Asia. Because of their cryptic nature (underground habitat) and very long life cycle, not much is known about molting in termite workers. In C. formosanus, the workers stop foraging and lose their gut fauna, respectively, approximately 10 and 5 days prior to ecdysis. In any given colony an average of 1.01% (range 0.6-1.8) of the workers were found to molt each day under laboratory conditions. Workers destined to molt become sluggish and their head capsules develop a mottled texture one day prior to ecdysis. Ecdysis was generally accomplished with the assistance of other workers, which also fed on the exuviae. Immediately after molting worker mandibles were light pink in color and became fully melanized approximately two days later. Gut fauna were acquired on the fourth day after molting. Flagellates were transferred as small encysted cells from other workers through proctodeal feeding. Juvenile hormone III titer ranged between 30-41 pg/mg bodyweight in all stages except in workers sampled 6 days prior to ecdysis. In these workers the titer was 80.5 pg/mg. The high juvenile hormones (JH) titer may also be involved in causing defaunation. Ecdysteroid titer increased from 2.1 pg/mg in non-molting workers to 359.5 and 332.4 pg/mg one and two days following defaunation, respectively. There was a second smaller peak two days prior to ecdysis.

Research paper thumbnail of Mode of action of the venom of the ectoparasitic wasp,Euplectrus comstockii, in causing developmental arrest in the European corn borer,Ostrinia nubilalis

Invertebrate Neuroscience, 1997

Research paper thumbnail of Ecdysteroid Regulation of Salivary Gland Degeneration in the Ixodid Tick,Amblyomma hebraeum:A Reconciliation ofin Vivoandin VitroObservations

General and Comparative Endocrinology, 1998

Salivary gland degeneration in the female tick Amblyomma hebraeum Koch is triggered by an ecdyste... more Salivary gland degeneration in the female tick Amblyomma hebraeum Koch is triggered by an ecdysteroid (ES) hormone. Under both in vivo and in vitro conditions, degeneration requires 4 days for completion. In partially fed females that have fed beyond a ''critical weight,'' the commitment period for salivary gland degeneration occurs between 24 and 48 h after removal from the host. Although tissue degeneration begins within 24 h postengorgement, ES titer as measured by radioimmunoassay (RIA) does not rise to threshold levels until 48 h postengorgement. To explain this anomaly we examined two hypotheses: (1) there is an early hormonal signal (e.g., 3-dehydroecdysone; 3DE) that is an ES not detectable by the antibody used in our RIA; and (2) the low hemolymph titer during the first 2 days postengorgement is not an accurate reflection of the ES concentration within the tissue itself. 3-Oxoecdysteroid 3␤-reductase (ketoreductase) was present in salivary glands, but neither ketoreductase nor 3DE was detected in hemolymph. The ES concentration of salivary gland homogenates was similar to that of hemolymph, while that of saliva was undetectable. Together, these results support our second hypothesis that the metabolically active tissue of the salivary gland experiences a suprathreshold concentration of hormone even though the concentration in hemolymph is below threshold levels. 1998 Academic Press Female ticks of the family Ixodidae secrete copious amounts of saliva into the host during a feeding period that can last as long as 2 weeks (reviewed by . Within 4 days after the female detaches from its host, the salivary glands degenerate . Degeneration is characterized by the presence of autophagic vacuoles within the fluid secretory cells and by a loss of Ͼ90% of maximal secretory capability . Although the salivary glands are committed to degenerate once a certain ''critical weight'' (CW; approximately 300 mg in Amblyomma hebraeum; Harris and Kaufman, 1984) has been attained, the process is probably initiated only after detachment from the host . Salivary gland degeneration is under hormonal control. Since both ecdysone (E) and 20-hydroxyecdysone (20E) cause salivary gland degeneration when infused into the tick hemocoel or when glands are exposed to physiological amounts of these ecdysteroids (ES) in vitro , it is probable that degeneration is regulated at least in part by these steroid hormones. An ES receptor has recently been identified in salivary gland homogenates . The epidermis is

Research paper thumbnail of Laboratory Rearing Procedures for Two Lepidopteran Weed Biocontrol Agents

Florida Entomologist, 2006

BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access t... more BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access titles in the biological, ecological, and environmental sciences published by nonprofit societies, associations, museums, institutions, and presses.

Research paper thumbnail of Effects of selected physical and chemical treatments of Colorado potato beetle eggs on host acceptance and development of the parasitic wasp, Edovum puttleri

Entomologia Experimentalis et Applicata, 1999

ABSTRACT

Research paper thumbnail of Disruptive endocrine effects of parasitism by Cotesia congregata in host Manduca sexta larvae

Comparative Biochemistry and Physiology Part B: Biochemistry and Molecular Biology, 2000

Research paper thumbnail of Host‐parasite interactions between whiteflies and their parasitoids

Archives of Insect Biochemistry and Physiology, 2005

There is relatively little information available concerning the physiological and biochemical int... more There is relatively little information available concerning the physiological and biochemical interactions between whiteflies and their parasitoids. In this report, we describe interactions between aphelinid parasitoids and their aleyrodid hosts that we have observed in four host‐parasite systems: Bemisia tabaci/Encarsia formosa, Trialeurodes vaporariorum/E. formosa, B. tabaci/Eretmocerus mundus, and T. lauri/Encarsia scapeata. In the absence of reported polydnavirus and teratocytes, these parasitoids probably inject and/or produce compounds that interfere with the host immune response and also manipulate host development to suit their own needs. In addition, parasitoids must coordinate their own development with that of their host. Although eggs are deposited under all four instars of B. tabaci, Eretmocerus larvae only penetrate 4th instar B. tabaci nymphs. A pre‐penetrating E. mundus first instar was capable of inducing permanent developmental arrest in its host, and upon penetrat...

Research paper thumbnail of Juvenile hormone esterase activity and ecdysteroid titer inHeliothis virescens larvae injected withMicroplitis croceipes teratocytes

Archives of Insect Biochemistry and Physiology, 1992

ABSTRACT Juvenile hormone esterase (JHE) activity in the hemolymph of 5th-instar Heliothis viresc... more ABSTRACT Juvenile hormone esterase (JHE) activity in the hemolymph of 5th-instar Heliothis virescens larvae injected with Microplitis croceipes teratocytes was inversely related to the number of teratocytes injected. JHE activity in the hemolymph of larvae injected with 750 3-day-old teratocytes (the approximate number from one parasitoid embryo) was depressed to less than 5% of those levels found in control larvae. During the latter portion of the digging stage and in the burrowing-digging (BD) stage JHE activity in larvae treated with 350 teratocytes was approximately 40% of control values. However, injection of 180 teratocytes did not significantly affect JHE titers. Two-day-old teratocytes caused the greatest reduction in JHE titer with decreasing effects observed with injections of 3- to 6-day-old teratocytes. Nevertheless, because 2-day-old teratocytes were difficult to separate from host hemocytes, 3-day-old teratocytes were used in most of these studies. Injections of nonparasitized H. virescens hemolymph plasma, Micrococcus luteus bacterial cell walls, washed M. croceipes eggs, or teratocytes from Cotesia congregata did not depress JHE titers. Teratocyte injections also significantly reduced growth of host fat body. Ecdysteroid titers in cell formation, day 2 (CF2) larvae injected as new 5th instars with 350 3-day-old teratocytes failed to increase, as compared to noninjected and saline-injected controls. An injection of 1 μg/larva of 20-hydroxyecdysone at the BD stage permitted normal pupation in 50% of the teratocyte-treated larvae as compared to 0% pupation for teratocyte-treated control larvae not treated with 20-hydroxyecdysone. Teratocytes seem to be responsible for the inhibition of JHE release and thus indirectly impact on ecdysteroid titers. © 1992 Wiley-Liss, Inc.

Research paper thumbnail of Aedes aegypti TMOF modulates ecdysteroid production by prothoracic glands of the gypsy moth,Lymantria dispar

Archives of Insect Biochemistry and Physiology, 2000

Trypsin modulating oostatic factor (TMOF) is a decapeptide that inhibits the biosynthesis of tryp... more Trypsin modulating oostatic factor (TMOF) is a decapeptide that inhibits the biosynthesis of trypsin-like enzymes in the midgut of several insect species and, as such, serves as a dipteran oostatic hormone. In vitro incubation of lepidopteran prothoracic glands with Aedes aegypti TMOF revealed that this decapeptide, in the presence of brain extract, modulates ecdysteroid production. The modulatory effect was highly dependent on both the concentration of TMOF and brain extract. Typically, TMOF was stimulatory in the presence of lower concentrations of Lymantria dispar brain extract (0.01 and 0. 025 brain equivalent), and either neutral or inhibitory at higher concentrations (0.25, 0.5, and 1.0 brain equivalent) of extract. In the presence of European corn borer (Ostrinia nubilalis) brain extract, TMOF also exhibited modulatory effects, effects that again were dependent on the concentrations of both brain extract and TMOF present in the incubation medium. At 1.5 brain equivalents, TMOF was inhibitory at all but the highest concentration tested (5x10(-6) M), at 1.0 brain equivalent, TMOF was stimulatory at 10(-6) M and at 0. 5 brain equivalents, TMOF did not significantly affect PTG synthesis of ecdysteroids. Results suggest the presence of a modulatory peptide(s), which fine tunes the synthesis and release of ecdysteroids by PTGs in accordance with the insect's developmental/physiological requirements.

Research paper thumbnail of Age-specific interaction between the parasitoid, Encarsia formosa and its host, the silverleaf whitefly, Bemisia tabaci (Strain B)

Journal of Insect Science, 2003

The effect of hostage, the instar of Bemisia tabaci (Gennadius) parasitized, on the growth and de... more The effect of hostage, the instar of Bemisia tabaci (Gennadius) parasitized, on the growth and development of Encarsia formosa (Gahan) was studied. E. formosa was able to parasitize and complete its life cycle no matter which instar of B. tabaci (Strain B), [also identified as B. argentifolii (Bellows and Perring)], was provided for oviposition, but parasitoid development was significantly slower when 1st or 2nd instar B. tabaci rather than 3rd or 4th instars were parasitized. Host age influenced the day on which E. formosa nymphs hatching from eggs was first observed. Mean embryonic development was significantly longer when 1st (5.4 days) rather than 2nd, 3rd or 4th instars (4.1, 3.4 and 3.5 days, respectively) were parasitized. The duration of the 1st instar parasitoid and the pupa, but not the 2nd or 3rd instar parasitoid, were also significantly greater when 1st instars were parasitized than when older host instars were parasitized. Interestingly, no matter which instar was parasitized, the parasitoid did not molt to the 3rd instar until the 4th instar host had reached a depth of about 0.23 mm (Stage 4-5) and had initiated the nymphal-adult molt and adult development. Histological studies revealed that whitefly eye and wing structures had either disintegrated or were adult in nature whenever a 3rd instar parasitoid was present. It appears, then, that the molt of the parasitoid to its last instar is associated with the host whitefly's nymphal-adult molt. However, the initiation of the host's final molt, while a prerequisite for the parasitoid's 2nd-3rd instar molt, did not necessarily trigger this molt. In contrast to its significant effect on various aspects of parasitoid development, host instar did not significantly influence the mean size of the parasitoid larva, pupa, or adult. Larval and pupal length and adult head width were similar for all parasitoids, regardless of which host instar was parasitized as was adult longevity. Adult parasitoid emergence was more synchronous when 2nd, 3rd and 4th instars were parasitized than when 1st instars were parasitized. Results are compared with those reported when the greenhouse whitefly, Trialeurodes vaporariorum, was parasitized by E. formosa, and provide possible explanations for why T. vaporariorum is a more suitable host than B. tabaci for E. formosa.

Research paper thumbnail of Host plant pubescence: Effect on silverleaf whitefly, Bemisia argentifolii, fourth instar and pharate adult dimensions and ecdysteroid titer fluctuations

Journal of Insect Science, 2003

BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access t... more BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access titles in the biological, ecological, and environmental sciences published by nonprofit societies, associations, museums, institutions, and presses.

Research paper thumbnail of Host-parasitoid interactions relating to penetration of the whitefly, Eretmocerus mundus

Journal of Insect Science, 2005

It has been reported that the aphelinid wasp Eertmocerus mundus parasitizes all four nymphal inst... more It has been reported that the aphelinid wasp Eertmocerus mundus parasitizes all four nymphal instars of the sweet potato whitefly, Bemisia tabaci (Biotype B), with 3 rd instars being the preferred hosts. The parasitoid lays its egg on the leaf underneath the host nymph. First instars hatch and later penetrate the whitefly. Previous studies have shown that the initiation of parasitoid penetration induces the host to form a cellular capsule around the parasitoid. As described here, females never oviposited once the 4 th instar whitefly nymph had initiated adult development. First instar E. mundus larvae were observed under 2 nd , 3 rd and 4 th instar whitefly nymphs, however, penetration did not occur until the whitefly had reached the 4 th instar. The non-penetrating E. mundus larva almost always induced permanent developmental arrest in its 4 th instar whitefly host and also caused a reduction in whole body host ecdysteroid titers. Therefore, unless there is a peak in molting hormone titer in the area local to penetration, it appears that the induction of capsule formation is not due to an increase in ecdysteroid titer. As the capsule formed around the penetrating parasitoid, host epidermal cells multiplied and became cuboidal and columnar, and relatively thick layers of new cuticle were deposited within the developing capsule, particularly near its ventral opening. The newly formed host cuticle was thinner in the dorsal part of the capsule and appeared to be absent at its apex. These results provide new information regarding the timing and dynamics of parasitoid oviposition and egg hatch as related to larval penetration, parasitoid-induced changes in whitefly development, molting hormone titers and the process of capsule formation.

Research paper thumbnail of Critical periods for the brain and prothoracic glands of 5th instars of the European corn borer, Ostrinia nubilalis hubner

Comparative Biochemistry and Physiology Part A: Physiology, 1982

1. 1. Classical ligation techniques were used to determine the critical periods for the head and ... more 1. 1. Classical ligation techniques were used to determine the critical periods for the head and the prothoracic glands in the larval-pupal molt of the European corn borer. 2. 2. Most larvae reared under LD 16:8 and 30°C released sufficient PTTH between lights on + 13 hr and lights on — 3 hr to stimulate the prothoracic glands to produce ecdysone. 3. 3. Ecdysone was first released just before lights on, with almost all larvae having produced sufficient ecdysone to elicit a molt by lights on + 6 hr. 4. 4. Critical periods for the brain and prothoracic glands of Ostrinia are compared with those of other lepidopterans.

Research paper thumbnail of Critical Feeding Periods for Last Instar Nymphal and Pharate Adults of the Whiteflies,Trialeurodes vaporariorumandBemisia tabaci

Journal of Insect Science, 2007

A critical feeding period is the time after which 50% of a given species of insect can be removed... more A critical feeding period is the time after which 50% of a given species of insect can be removed from its food source and complete development by undergoing adult eclosion. The critical feeding period was determined for the greenhouse white fly, Trialeurodes vaporariorum, and the sweet potato whitefly, Bemisia tabaci (Biotype B) (Homptera/Hemiptera: Aleyrodidae). Fourth (last) instar and pharate adult whiteflies were removed from green bean leaves, staged, placed on filter paper in small Petri dishes containing drops of water, and observed daily for eclosion. For T. vaporariorum reared at 25°C and L:D 16:8, 55 and 80% adult eclosion were observed when whiteflies were removed at stages 4 (0.23-0.26 mm in body depth) and 5 (≥ 0.27 mm in body depth), respectively, so that at least 50% eclosion was only achieved in this species of whitefly when adult eye development had already been initiated (in Stage 4), and 80% eclosion when adult wing development had been initiated (Stage 5). In contrast, 63% of B. tabaci emerged as adults if removed from the leaf at Stage 3 (0.18-0.22 mm in body depth), and 80% emerged if removed at Stage 4/5, stages in which adult formation had not yet been initiated. The mean number of eggs laid by experimental (those removed at Stages 4-5, 6-7 or 8-9) and control (those that remained on the leaf prior to eclosion) whiteflies, and the mean percent hatch of these eggs were not significantly different in experimental and control groups. Stages 7, 8 and 9 are characterized by a light red adult eye, medium red bipartite adult eye and dark red or red-black bipartite adult eye, respectively. Mean adult longevity also was not significantly different between experimental and control groups. However, for all groups of T. vaporariorum, adult female longevity was significantly (at least 2 times) greater than male longevity. Our results identify the critical feeding periods for last instar/pharate adults of two important pest species of whitefly. Since in both species of whitefly the critical feeding period is achieved when weight gain reaches a plateau, it appears that the critical feeding period is more closely correlated with the attainment of a critical weight than with either the time that ecdsyteroid titers first peak or the time when adult development is initiated.

Research paper thumbnail of Role of ecdysteroids in the regulation of sperm release from the testis of the gypsy moth, Lymantria dispar

Journal of Insect Physiology, 1990

Release of mature sperm from the testes of the gypsy moth, Lymantria dispar, into the seminal duc... more Release of mature sperm from the testes of the gypsy moth, Lymantria dispar, into the seminal ducts occurs in a daily rhythmic pattern. The rhythm of sperm release is initiated in developing pharate adults 3-4 days after spermatogenesis and development of the reproductive tract has been completed. At that time a significant decline occurs in the blood titre of RIA-detectable ecdysteroids. Infusion of 20-hydroxyecdysone into male pupae inhibits the release of sperm from the testis in a dose-dependent and age-dependent fashion. The decline in haemolymph ecdysteroid levels seems essential for the initiation of the rhythmic release of sperm from the testis, but does not appear to play a role in determining the phase of this rhythm.

Research paper thumbnail of Prothoracicotropic hormone levels in brains of the European corn borer, Ostrinia nubilalis: Diapause vs the non-diapause state

Journal of Insect Physiology, 1992

Brains from non-diapause-bound, diapause-bound and diapausing European corn borers contain protho... more Brains from non-diapause-bound, diapause-bound and diapausing European corn borers contain prothoracicotropic hormone (PTTH) which stimulates the prothoracic glands of both Lymantriu d&par and Ostrinia nubilalis to produce ecdysone and 3-dehydroecdysone in a dose-dependent manner. At a dose of 0.75 brain equivalents, PTTH activity is highest in non-diapause-bound and diapausing prepupae. Levels are approx. 50% as high in younger 5th instars. In diapausing prepupae, PTTH activity again falls to approx. 50% after 5-8 weeks of refrigeration. Prothoracic glands from diapausing 0. nubilafis prepupae were refractory to stimulation. In uiuo experiments indicate that brains from diapausing prepupae have more moult-stimulating activity than those from non-diapause-bound prepupae. However, this may be due to the presence of factors other than PTTH. Based on gel filtration HPLC, the molecular weight range of the small form of 0. nubilalis PTTH is 1500-3300 Da, somewhat less than the 500&7000 Da peptide reported for other lepidopterans.

Research paper thumbnail of Kopec revisited—Neuroendocrine regulation of metamorphosis in the gypsy moth (Lymantria dispar): Development of a larval in vivo assay for prothoracicotropic hormone

Journal of Insect Physiology, 1992

The role of the brain as a. neuroendocrine regulator of metamorphosis in the gypsy moth, Lymantri... more The role of the brain as a. neuroendocrine regulator of metamorphosis in the gypsy moth, Lymantria dispar L. was originally demonstrated by Kopec more than 70 years ago. We have reexamined this role by determining haemolymph ecdysteroid titres, activity and responsiveness of the prothoracic glands, and growth of female last (i.e. fifth)-instar larvae in relation to secretion of the brain prothoracicotropic hormone (PTTH), the factor known to trigger moulting and metamorphosis in insects. The head critical period for secretion of PTTH in Lymantria reared at 25°C in a 16 h light-8 h dark cycle was shown by neck ligation to occur on day 7-8 of the fifth instar. The critical period occurred shortly after a small peak of haemolymph ecdysteroid that reached 600 pg 20-hydroxyecdysone equivalents/PI, as determined by radioimmunoassay. Feeding was completed by day 7, thus neck ligation did not affect nutrient intake. Animals starved from day 5 onward completed pupation at the same time as non-starved controls and showed normal increases in haemolymph ecdysteroid titres. Animals neck-ligated on day 7 and injected 5 days later with extracts of brain, retrocerebral complex, or brain tissues containing lateral or median neurosecretory cells were stimulated to pupate within 5 days, and brain-extract-injected animals showed an increase in haemolymph ecdysteroid titre of over 4000 pg/pl. Animals neck-ligated earlier had lower haemolymph ecdysteroid titres than day 7, neck-ligated larvae and their prothoracic glands showed lower activity in vitro. Using the in vivo assay, PTTH activity was detected in pre-hatch eggs and in brains taken from day-5 last-instar larvae, day-l pupae and day-l adults. The assay appears specific to tissues from the brain and retrocerebral complex, since no activity was found with extracts of the subesophageal ganglion, fat body or muscle.

Research paper thumbnail of Ecdysteroid titers and developmental expression of ecdysteroid-regulated genes during metamorphosis of the yellow fever mosquito, Aedes aegypti (Diptera: Culicidae)

Journal of Insect Physiology, 2006

Ecdysteroid titers and expression profiles of ecdysone-regulated genes were determined during the... more Ecdysteroid titers and expression profiles of ecdysone-regulated genes were determined during the last instar larval and during the pupal stages of Aedes aegypti (Diptera: Culicidae). Three peaks of ecdysteroids occurring at approximately 24, 30-33 and 45-48 h after ecdysis to the fourth instar larval stage were detected. In the pupa, a large peak of ecdysteroids occurred between 6 and 12 h after ecdysis to the pupal stage. A small rise in ecdysteroids was also detected at the end of the pupal stage. Quantitative reverse transcriptase polymerase chain reaction analyses of the expression of ecdysone receptors and ecdysone-regulated genes showed that the peaks of expression of most of these genes coincided with the rise in ecdysteroid levels during the last larval and pupal stages. In the last larval stage, ecdysteroid titers and mRNA expression profiles of ecdysone-regulated genes are similar to those observed for Drosophila melanogaster. However, in the early pupal stage, both ecdysteroid titers and the expression of ecdysone-regulated genes are somewhat different from those observed in D. melanogaster, probably because the duration of the pupal stage in D. melanogaster is 84 h while in Ae. aeqypti the duration is only 48 h. These data which describe the relationship between ecdysteroid titers and mRNA levels of Ae. aegypti ecdysteroid-regulated genes lay a solid foundation for future studies on the hormonal regulation of development in mosquitoes.

Research paper thumbnail of Ecdysteroid levels/profiles of the parasitoid wasp, Diapetimorpha introita, reared on its host, Spodoptera frugiperda and on an artificial diet

Journal of Insect Physiology, 2000

Diapetimorpha introita is an ichneumonid ectoparasitoid of the fall armyworm, Spodoptera frugiper... more Diapetimorpha introita is an ichneumonid ectoparasitoid of the fall armyworm, Spodoptera frugiperda. Since it has been reported that D. introita wasps reared on an artificial diet exhibit a significantly lower percentage of adult eclosion and fecundity than hostreared wasps, this study was undertaken to elucidate the factors responsible for the reduced viability observed in diet-reared wasps. A system of markers has been devised to track the development (from the initiation of cocooning through adult eclosion) of D. introita. Although wasps reared on artificial diet developed more slowly than did those reared on host pupae, both diet-and hostreared wasps passed through the same stages of development -the eyes enlarged and moved backward, the gut was purged and upon ecdysis the exarate pupa emerged. The thorax was the first to darken, followed by the head and then the abdomen. Pharate pupal formation occurred before gut purge. Two peaks of hemolymph ecdysteroids were observed, one in wasps in which gut purge was almost complete and the second in day-2 exarate pupae. Ecdysone and 20-hydroxyecdysone were the major ecdysteroids present in hemolymph sampled at these times. Small quantities of 20,26-dihydroxyecdysone, polar ecdysteroids and/or possibly 26hydroxyecdysone were also present. In six stages of development, hemolymph ecdysteroid titers were significantly higher in hostreared than in diet-reared wasps (Eye 1, Eye 2, Gut Purge 2, Pharate Pupa, Head/Thorax Dark, and Abdomen Dark). Relatively high percentages of mortality were observed in diet-reared wasps in four of these stages and in two others which occurred in close proximity to one of the stages, the Abdomen Dark stage. Thus, insufficient ecdysteroid in the hemolymph may be responsible, in part, for the relatively high percentage of mortality that occurred in wasps reared on an artificial diet. Published by Elsevier Science Ltd.

Research paper thumbnail of Identification of the molting hormone of the sweet potato (Bemisia tabaci) and greenhouse (Trialeurodes vaporariorum) whitefly

Journal of Insect Physiology, 2005

In order to identify the whitefly molting hormone, whole body extracts of mature 4th instar and n... more In order to identify the whitefly molting hormone, whole body extracts of mature 4th instar and newly formed pharate adult Bemisia tabaci (Biotype B) and Trialeurodes vaporariorum were prepared and subjected to reverse phase high performance liquid chromatography (RPHPLC). Ecdysteroid content of fractions was determined by enzymeimmunoassay (EIA). The only detectable ecdysteroids that were present in significant amounts in whitefly extracts were ecdysone and 20-hydroxyecdysone. The concentrations of 20-hydroxyecdysone in B. tabaci and T. vaporariorum extracts, respectively, were 40 and 15 times greater than the concentrations of ecdysone. The identity of the two ecdysteroids was confirmed by normal phase high performance liquid chromatography (NPHPLC). When ecdysteroid content of RPHPLC fractions was assayed by radioimmunoassay (RIA), small amounts of polar ecdysteroids were also detected indicating that these ecdysteroids have a very low affinity for the antiserum used in the EIA. Ecdysteroid at 10.4 mM administered by feeding stimulated 2nd instar whitefly nymphs to molt. Based on our results, it appears that 20-hydroxyecdysone is the whitefly molting hormone.

Research paper thumbnail of Molting in workers of the Formosan subterranean termite Coptotermes formosanus

Journal of Insect Physiology, 2008

The Formosan subterranean termite, Coptotermes formosanus, with its huge colonies, is a major urb... more The Formosan subterranean termite, Coptotermes formosanus, with its huge colonies, is a major urban pest in several southern states and Hawaii as well as in South Asia. Because of their cryptic nature (underground habitat) and very long life cycle, not much is known about molting in termite workers. In C. formosanus, the workers stop foraging and lose their gut fauna, respectively, approximately 10 and 5 days prior to ecdysis. In any given colony an average of 1.01% (range 0.6-1.8) of the workers were found to molt each day under laboratory conditions. Workers destined to molt become sluggish and their head capsules develop a mottled texture one day prior to ecdysis. Ecdysis was generally accomplished with the assistance of other workers, which also fed on the exuviae. Immediately after molting worker mandibles were light pink in color and became fully melanized approximately two days later. Gut fauna were acquired on the fourth day after molting. Flagellates were transferred as small encysted cells from other workers through proctodeal feeding. Juvenile hormone III titer ranged between 30-41 pg/mg bodyweight in all stages except in workers sampled 6 days prior to ecdysis. In these workers the titer was 80.5 pg/mg. The high juvenile hormones (JH) titer may also be involved in causing defaunation. Ecdysteroid titer increased from 2.1 pg/mg in non-molting workers to 359.5 and 332.4 pg/mg one and two days following defaunation, respectively. There was a second smaller peak two days prior to ecdysis.

Research paper thumbnail of Mode of action of the venom of the ectoparasitic wasp,Euplectrus comstockii, in causing developmental arrest in the European corn borer,Ostrinia nubilalis

Invertebrate Neuroscience, 1997

Research paper thumbnail of Ecdysteroid Regulation of Salivary Gland Degeneration in the Ixodid Tick,Amblyomma hebraeum:A Reconciliation ofin Vivoandin VitroObservations

General and Comparative Endocrinology, 1998

Salivary gland degeneration in the female tick Amblyomma hebraeum Koch is triggered by an ecdyste... more Salivary gland degeneration in the female tick Amblyomma hebraeum Koch is triggered by an ecdysteroid (ES) hormone. Under both in vivo and in vitro conditions, degeneration requires 4 days for completion. In partially fed females that have fed beyond a ''critical weight,'' the commitment period for salivary gland degeneration occurs between 24 and 48 h after removal from the host. Although tissue degeneration begins within 24 h postengorgement, ES titer as measured by radioimmunoassay (RIA) does not rise to threshold levels until 48 h postengorgement. To explain this anomaly we examined two hypotheses: (1) there is an early hormonal signal (e.g., 3-dehydroecdysone; 3DE) that is an ES not detectable by the antibody used in our RIA; and (2) the low hemolymph titer during the first 2 days postengorgement is not an accurate reflection of the ES concentration within the tissue itself. 3-Oxoecdysteroid 3␤-reductase (ketoreductase) was present in salivary glands, but neither ketoreductase nor 3DE was detected in hemolymph. The ES concentration of salivary gland homogenates was similar to that of hemolymph, while that of saliva was undetectable. Together, these results support our second hypothesis that the metabolically active tissue of the salivary gland experiences a suprathreshold concentration of hormone even though the concentration in hemolymph is below threshold levels. 1998 Academic Press Female ticks of the family Ixodidae secrete copious amounts of saliva into the host during a feeding period that can last as long as 2 weeks (reviewed by . Within 4 days after the female detaches from its host, the salivary glands degenerate . Degeneration is characterized by the presence of autophagic vacuoles within the fluid secretory cells and by a loss of Ͼ90% of maximal secretory capability . Although the salivary glands are committed to degenerate once a certain ''critical weight'' (CW; approximately 300 mg in Amblyomma hebraeum; Harris and Kaufman, 1984) has been attained, the process is probably initiated only after detachment from the host . Salivary gland degeneration is under hormonal control. Since both ecdysone (E) and 20-hydroxyecdysone (20E) cause salivary gland degeneration when infused into the tick hemocoel or when glands are exposed to physiological amounts of these ecdysteroids (ES) in vitro , it is probable that degeneration is regulated at least in part by these steroid hormones. An ES receptor has recently been identified in salivary gland homogenates . The epidermis is

Research paper thumbnail of Laboratory Rearing Procedures for Two Lepidopteran Weed Biocontrol Agents

Florida Entomologist, 2006

BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access t... more BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access titles in the biological, ecological, and environmental sciences published by nonprofit societies, associations, museums, institutions, and presses.

Research paper thumbnail of Effects of selected physical and chemical treatments of Colorado potato beetle eggs on host acceptance and development of the parasitic wasp, Edovum puttleri

Entomologia Experimentalis et Applicata, 1999

ABSTRACT

Research paper thumbnail of Disruptive endocrine effects of parasitism by Cotesia congregata in host Manduca sexta larvae

Comparative Biochemistry and Physiology Part B: Biochemistry and Molecular Biology, 2000

Research paper thumbnail of Host‐parasite interactions between whiteflies and their parasitoids

Archives of Insect Biochemistry and Physiology, 2005

There is relatively little information available concerning the physiological and biochemical int... more There is relatively little information available concerning the physiological and biochemical interactions between whiteflies and their parasitoids. In this report, we describe interactions between aphelinid parasitoids and their aleyrodid hosts that we have observed in four host‐parasite systems: Bemisia tabaci/Encarsia formosa, Trialeurodes vaporariorum/E. formosa, B. tabaci/Eretmocerus mundus, and T. lauri/Encarsia scapeata. In the absence of reported polydnavirus and teratocytes, these parasitoids probably inject and/or produce compounds that interfere with the host immune response and also manipulate host development to suit their own needs. In addition, parasitoids must coordinate their own development with that of their host. Although eggs are deposited under all four instars of B. tabaci, Eretmocerus larvae only penetrate 4th instar B. tabaci nymphs. A pre‐penetrating E. mundus first instar was capable of inducing permanent developmental arrest in its host, and upon penetrat...

Research paper thumbnail of Juvenile hormone esterase activity and ecdysteroid titer inHeliothis virescens larvae injected withMicroplitis croceipes teratocytes

Archives of Insect Biochemistry and Physiology, 1992

ABSTRACT Juvenile hormone esterase (JHE) activity in the hemolymph of 5th-instar Heliothis viresc... more ABSTRACT Juvenile hormone esterase (JHE) activity in the hemolymph of 5th-instar Heliothis virescens larvae injected with Microplitis croceipes teratocytes was inversely related to the number of teratocytes injected. JHE activity in the hemolymph of larvae injected with 750 3-day-old teratocytes (the approximate number from one parasitoid embryo) was depressed to less than 5% of those levels found in control larvae. During the latter portion of the digging stage and in the burrowing-digging (BD) stage JHE activity in larvae treated with 350 teratocytes was approximately 40% of control values. However, injection of 180 teratocytes did not significantly affect JHE titers. Two-day-old teratocytes caused the greatest reduction in JHE titer with decreasing effects observed with injections of 3- to 6-day-old teratocytes. Nevertheless, because 2-day-old teratocytes were difficult to separate from host hemocytes, 3-day-old teratocytes were used in most of these studies. Injections of nonparasitized H. virescens hemolymph plasma, Micrococcus luteus bacterial cell walls, washed M. croceipes eggs, or teratocytes from Cotesia congregata did not depress JHE titers. Teratocyte injections also significantly reduced growth of host fat body. Ecdysteroid titers in cell formation, day 2 (CF2) larvae injected as new 5th instars with 350 3-day-old teratocytes failed to increase, as compared to noninjected and saline-injected controls. An injection of 1 μg/larva of 20-hydroxyecdysone at the BD stage permitted normal pupation in 50% of the teratocyte-treated larvae as compared to 0% pupation for teratocyte-treated control larvae not treated with 20-hydroxyecdysone. Teratocytes seem to be responsible for the inhibition of JHE release and thus indirectly impact on ecdysteroid titers. © 1992 Wiley-Liss, Inc.