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Papers by David Rivers

Archives of Insect Biochemistry and Physiology, 2004

The action of venom from the ectoparasitic wasp, Nasonia vitripennis, was monitored by examining ... more The action of venom from the ectoparasitic wasp, Nasonia vitripennis, was monitored by examining alterations in patterned muscular movements characteristic of pupariation and eclosion behavior in the flesh fly, Sarcophaga bullata. Venom injected into larvae prior to pupariation caused a dose-dependent delay in pupariation. Eventually, such larvae did pupariate, but puparia were abnormally formed. Barographic records revealed that all elements of pupariation behavior were present in venom-injected larvae, but pupariation behavior was not well synchronized with tanning, thus implying that the venom caused disruption in the temporal organization of central motor programs. When larvae were ligated and injected with venom posterior to the ligature, no response was evident in the posterior region, suggesting that the venom does not directly stimulate muscles or neuromuscular junctions. Injection of exogenous ecdysteroid into venom-injected larvae restored some elements of pupariation behavior, consistent with ecdysone's role in stimulating the release of anterior retraction factor and puparium tanning factor, two factors that are released from the CNS to regulate pupariation. When the venom was injected into newly emerged imagoes, the duration of extrication behavior was shortened, whereas all phases of post-eclosion behavior were lengthened. These observations imply that the venom affects CNS centers that regulate the muscular systems engaged in extrication and post-eclosion behavior. Arch. Insect Biochem. Physiol. 57: 78-91, 2004. Abbreviations used: CNS = central nervous system; EtOH = ethanol; 20E = 20-hydroxyecdysone; LC = lethal concentration; LT = lethal time; VRE = venom reservoir equivalent.

Entomologia Experimentalis et Applicata, 1995

The gregarious, ectoparasitoid Nasonia vitripennis (Walker) (Hymenoptera: Pteromalidae) was offer... more The gregarious, ectoparasitoid Nasonia vitripennis (Walker) (Hymenoptera: Pteromalidae) was offered pupae representing seven fly species, but only members of two families (Sarcophagidae and Muscidae) were parasitized. Host acceptance as an oviposition site did not imply host suitability for parasitoid growth: N. vitripennis produced fewer progeny, a higher proportion of males, required a longer development time, and produced smaller adult wasps on Musca domestica L. (Diptera: Muscidae) than on the three sarcophagid species tested [Sarcophaga bullata Parker, S. crassipalpis Macquart, and Peckia abnormis (Enderlein) (Diptera: Sarcophagidae)]. The physiological and nutritional status of a preferred host, S. bullata, influenced oviposition behavior and development of N. vitripennis. Progeny allocation and sex ratio, which were regulated by the female parasitoid during oviposition, differed on living and dead nondiapausing hosts and on diapausing pupae. Differences in the host's nutritional condition was reflected in changes of the wasp's development time and adult body size. Envenomation was essential for successful development of the parasitoid on nondiapausing hosts, but venom injection by N. vitripennis did not increase the suitability of diapausing or dead pupae. The results suggest that wasp development is enhanced by changes induced in the host by parasitism.

Journal of insect …, 2006

Nondiapausing larvae of the flesh fly, Sarcophaga bullata, responded to several forms of short-te... more Nondiapausing larvae of the flesh fly, Sarcophaga bullata, responded to several forms of short-term environmental stress (low temperature, anoxia and desiccation) by accumulating glycerol. Elevation of this polyol, regardless of the type of stress that induced accumulation, conferred cold resistance: larvae with high glycerol levels were 3-4 times more tolerant of a 2h exposure to -10 degrees C than unstressed larvae. Protection against low temperature injury, as well as dehydration, was also attained by injection of exogenous glycerol into third instar larvae. This artificially induced cold hardiness was only temporary: when glycerol-injected larvae were exposed to -10 degrees C immediately after injection, survival was high, but none survived if they were injected and then held at 25 degrees C for 2 days before the -10 degrees C exposure. Larvae ligated behind the brain immediately after low temperature exposure failed to accumulate glycerol, but glycerol did accumulate in larvae ligated 6-24h after cold treatment, thus implying a critical role for the brain in initiating glycerol production. Interestingly, a much shorter exposure (2h) to low temperature was sufficient to reduce the maximum rate of water loss. Collectively, these observations suggest that multiple pathways may be exploited in response to stress: one pathway is most likely associated with rapid cold hardening (RCH) which generates immediate protection, and a second pathway remains activated for a longer period to enhance the initial protection afforded by glycerol.

The mode of action of venom from the endoparasitic wasp, Pimpla turionellae, was studied using in... more The mode of action of venom from the endoparasitic wasp, Pimpla turionellae, was studied using in vitro assays and fluorescent microscopy. Crude venom was found to be cytotoxic to an embryonic cell line (BTI-TN-5B1-4) derived from the cabbage looper, Trichoplusia ni. Susceptible cells displayed progressive morphological changes, such as retraction of cytoplasmic extensions, followed byrounding, swelling, and eventual vacuolization of the cytoplasm, all within 6 h of venom treatment. Cell death, however, did not occur for an additional 6-10 h at 27oC. Pre-treatment of cell monolayers with the osmotic protectants raffinose and sucrose afforded limited protection from the effects of venom: the presence of either saccharide yielded a time and dose-dependent delay in the induction of cell rounding and swelling. The protection was not permanent as all pre-treated cells eventually died by 24-36 h following incubation with crude venom. Venom-induced changes in cell morphology were preceded ...

Encyclopedia of Entomology, 2008

ACS Symposium Series, 1990

ABSTRACT The specificity of Bacillus thuringiensis activity resides largely with the insecticidal... more ABSTRACT The specificity of Bacillus thuringiensis activity resides largely with the insecticidal crystal proteins. The "specificity domain" of the toxin moiety has recently been identified and is proposed as the receptor binding domain. The bacterial spore and other factors may play a role in insecticide specificity, especially for less susceptible insects. Insect susceptibility is dependent on gut pH, proteases, the presence and type of receptor (toxin-binding) protein, and on membrane interactions with the cytolytic domains of the toxins. The implications for industrial standardization of B. thuringiensis products is that assay systems must account for each of the bacterial components which play a role in insecticidal activity.

The Journal of biological chemistry, Jan 25, 1991

Insecticidal crystal proteins (delta-endotoxins), CryIA(a) and CryIA(c), from Bacillus thuringien... more Insecticidal crystal proteins (delta-endotoxins), CryIA(a) and CryIA(c), from Bacillus thuringiensis are 82% homologous. Despite this homology, CryIA(c) was determined to have 10-fold more insecticidal activity toward Heliothis virescens and Trichoplusia ni than CryIA(a). Reciprocal recombinations between these two genes were performed by the homolog-scanning technique. The resultant mutants had different segments of their primary sequences exchanged. Bioassays with toxin proteins from these mutants revealed that amino acids 335-450 on CryIA(c) are associated with the activity against T. ni, whereas amino acids 335-615 on the same toxin are required to exchange full H. virescens specificity. One chimeric protein toxin, involving residues 450-612 from CryIA(c), demonstrated 30 times more activity against H. virescens than the native parental toxin, indicating that this region plays an important role in H. virescens specificity. The structural integrity of mutant toxin proteins was as...

Journal of Invertebrate Pathology, 2002

Journal of Invertebrate Pathology, 1991

Annals of the …, 1998

Abstract: Envenomation by the ectoparasitic wasps Nasonia vitripennis (Walker), Muscidifurax zara... more Abstract: Envenomation by the ectoparasitic wasps Nasonia vitripennis (Walker), Muscidifurax zaraptor Kogan & Legner, and Trichomalopsis near americana (Hymenoptera: Pteromalidae) caused rapid death (within 24 h) or a developmental arrest in the fly host ...

New developments in cell apoptosis research, 2007

ABSTRACT Cell death, specifically apoptosis, is a feature of host-parasitoid relationships involv... more ABSTRACT Cell death, specifically apoptosis, is a feature of host-parasitoid relationships involving parasitic wasps. Though there are numerous examples of endosymbiotic virus-induced (e.g., polydnaviruses) and venom-mediated apoptosis in host hemocytes, there is very little evidence for this form of cell death being triggered in other host tissues. Is this due to specificity in tissue responsiveness? In terms of timing of events during parasitism (i.e., at the initial stages of parasitism), this is a likely scenario. But throughout the duration of the association between the parasitoid and host, several developmental and physiological changes in host tissues may be regulated by apoptotic signals. There simply is very little evidence to draw any conclusions. Somewhat surprisingly, in most instances when apoptosis has been identified in host tissue (hemocytes), investigations of the pathways involved or specific intracellular changes have apparently not been conducted. Consequently, apoptosis is known to be induced by polydnaviruses, but what relationships exist between this form of cell death and those triggered by wasp venoms are unclear, nor have any attempts been made to compare mechanisms of oncosis evoked by these viruses and parasitoid venoms. What follows is an attempt to show homology in the modes of death evoked by pathogenic insect viruses, endosymbiotic viruses that reside within endoparasitic wasps, and venoms produced by ectoparasitic wasps. As will be discussed, oncosis and apoptosis are intimately linked by common signal transduction pathways and mitochondria. The focus of this paper is to attempt to provide evidence, admittedly at times circumstantial, and speculation on the possible linkage between the modes of action of ectoparasitic wasp venoms and insect viruses.

Archives of Insect Biochemistry and Physiology, 2006

Venom from the endoparasitic wasp Pimpla turionellae L. (Hymenoptera: Ichneumonidae) was found to... more Venom from the endoparasitic wasp Pimpla turionellae L. (Hymenoptera: Ichneumonidae) was found to contain a complex mixture of biogenic amines, noradrenalin, phospholipase B, and several proteins and peptides. The amount of noradrenalin and serotonin was found to be highest in venom from newly emerged wasps and decreased with age. Histamine was detected in minute amounts in comparison to the other venom components, and declined with increasing age of the parasitoids. Total peptides and proteins detected by reversed-phase HPLC increased with host age. Old-aged (30-33 days after emergence) wasps contained 2-fold more phospholipase B than young (&amp;amp;amp;amp;amp;lt;10 days [d] old) or medium-aged (10-22-d-old) females. Increases in phospholipase B alone, however, did not account for all changes in total venom protein because by 40 days after emergence, the levels of this enzyme began to decline while the amount of total protein was higher than in younger wasps. For all venom components detected, the amount present in the venom sharply decreased following host exposure. This was presumed to be the result of venom depletion associated with envenomation. Consistent with this view were the modest increases in venom components in wasps displaying a decreased rate of parasitization. When adult females were offered honey alone or in combination with feeding on hosts, no significant changes in venom composition were observed, with the exception of noradrenalin, which was found to be 5 times higher in concentration in wasps fed honey only. These results suggest that wasp age and incidence of parasitism are more important features influencing the composition of venom than the diet of adult females.