Dan Johnson | Cal Southern Univerisity (original) (raw)

Papers by Dan Johnson

Canadian Entomologist, 1996

Physiological Entomology, 1997

Abstract. .We restrained forty-nine nymphal migratory grasshoppers (Melanoplus sanguinipes) in a ... more Abstract. .We restrained forty-nine nymphal migratory grasshoppers (Melanoplus sanguinipes) in a series of orientations to the sun and measured rate of temperature change due to radiation intercepted, compensating for temperature loss by convection and greybody reradiation. Direct solar radiation affected body temperature significantly, but diffuse radiation did not. The coefficient of direct solar heating (Hdir), varied from 0.603 to 0.690 depending on how radiation interception was estimated, and on whether insect size was expressed as mass or as a function of length. H is the rate of temperature change as a proportion of the maximum rate assuming complete conversion of all incident radiation to heat. None of the Hdir estimates was significantly different from visible-spectrum absorbance to (0.722), suggesting that the latter is a reasonable approximation of HdirIn simulations, equilibrium body temperature elevation decreased with body size where energy influx was expressed as the amount intercepted (W), but increased with body size when expressed as insolation as (W m-2) because at a specified insolation, the amount of energy intercepted increases with body size. Expressing energy influx as the amount intercepted reveals the underlying biophysical mechanisms which determine body temperature.This paper presents a model of body temperature elevation in which fundamental physical processes are assembled to provide good estimates. This basis in physics implies that the model can can be applied with confidence to conditions other than those in which it was derived.

Canadian Entomologist, 1998

Page 1. The Canadian Entomologist Vol. 130 Ottawa, Canada SeptemberIOctober 1998 No. 5 ENVIRONMEN... more Page 1. The Canadian Entomologist Vol. 130 Ottawa, Canada SeptemberIOctober 1998 No. 5 ENVIRONMENTAL, PHYSICAL, AND BEHAVIOURAL DETERMINANTS OF BODY TEMPERATURE IN GRASSHOPPER NYMPHS (ORTHOPTERA: ACRIDIDAE) DEREK J. LACTIN ...

Journal of Thermal Biology, 1996

l. Body temperatures (Tb) of Melunoplus sanguinipes F. nymphs were measured in temperature gradie... more l. Body temperatures (Tb) of Melunoplus sanguinipes F. nymphs were measured in temperature gradients established using incandescent light bulbs. 2. Relative frequency distributions of possible Tb were estimated by linking equations describing the effects of distance from the light bulb and orientation to it. 3. The distribution of Tb was significantly different from that expected if insects positioned themselves randomly, and 35 2 Tb 5 43'C occurred more frequently than expected; this is conclusive evidence for behavioural thermoregulation. 4. The modal Tb. 40°C. approximated the temperatures for maximum rates of feeding (38.6 C) and development (42.2'C); at 40 C, both rates occur at > 95% of their maximum rate. Crown copyright 'Q 1996 Published by Elsevier Science Ltd.

Biological Control, 1996

The influence of behavioral thermoregulation by grasshoppers (Melanoplus sanguinipes) on mycosis ... more The influence of behavioral thermoregulation by grasshoppers (Melanoplus sanguinipes) on mycosis caused by Beauveria bassiana was investigated in controlled environments. The cardinal temperature for B. bassiana conidial germination and hyphal development was approximately 35°C. A low prevalence of mycosis (I7%) was observed in inoculated nymphs exposed to a continuous temperature of 35 and 40°C, whereas continuous exposure to 30°C did not have a significant effect on disease development. Daily exposures to 35 and 40°C for 1 and 6 h, respectively, decreased mycosis in nymphs. In both environments, a strong correlation (r H 0.95) was observed between hyphal growth on potato dextrose agar and final mycosis. Although high temperatures delayed conidial germination, only conidia exposed to continuous 35 or to 40°C for more than 8 h exhibited reduced germination after 24 h. The effects of temperature on conidial germination were poorly correlated with disease, and when nymphs were exposed to 35°C for 24 h, less mycosis was observed only in grasshoppers exposed between 1 and 2 days postinoculation. The thoracic temperature of nymphs permitted to bask adjacent to a heat source ranged from 38 to 42°C. In nymphs basking for 1 h per day, 46% less mycosis was observed, decreasing to 98% less disease in nymphs allowed to bask for 6 h or greater per day. On a heat gradient, a higher prevalence of B. bassiana-infected nymphs selected hotter positions than noninfected nymphs, suggesting a ''behavioral fever'' response to infection. This study indicates that high temperature and thermoregulation can adversely affect B. bassiana mycosis of grasshoppers and may explain the poor efficacy of this entomopathogen observed in some field experiments. r

Botany-botanique, 1995

Fungi are among the most important microbial pathogens of grasshoppers with potential for develop... more Fungi are among the most important microbial pathogens of grasshoppers with potential for development as biological control agents. Unlike most other insect pathogens that must be ingested to initiate disease, fungi generally invade insects via the external cuticle. The most common fungi that are pathogenic to grasshoppers are Beauveria bassiana, Metarhiziwn anisopliae, Metarhizium flavoviride, Sorosporella sp., and fungi in the E~itomophaga grylli complex. A review of the latest information on the development of these fungi as microbial control agents of grasshoppers is presented. Species in the E. grylli complex are being used in classical biocontrol. This has resulted in controversy as there are indigenous nonpest grasshopper species that may be affected through introduction of the nonindigenous fungal strains. Beauveria bassiana and M. flavoviride are being developed for inundative control. These fungi can be mass produced and applied with equipment used for conventional pesticides. Conidia are applied either at ultralow volume in oil, as oil emulsions, or as bran-bait formulations. Field trials in Africa and North America have demonstrated significant grasshopper reductions. Improvements in formulation and inoculum targeting may further improve their efficacy.

Journal of Invertebrate Pathology, 1995

Journal of Invertebrate Pathology, 1998

The effect of conidial concentration, soil texture, and soil sterilization on the efficacy of Bea... more The effect of conidial concentration, soil texture, and soil sterilization on the efficacy of Beauveria bassiana against ovipositing grasshoppers (Melanoplus sanguinipes) was investigated in a controlled environment. In the first experiment, mortality of female grasshoppers ovipositing into a sterile loamy-sand soil containing conidia of B. bassiana was measured. The prevalence of mortality increased as the concentration of conidia in soil increased, and a median lethal concentration of 10 4 colony-forming units (CFU) per gram of soil (dry weight) was observed. Conidia (10 2.9 to 10 3 CFU per abdomen) were recovered from the abdomens of grasshoppers ovipositing into sand containing 10 5.5 and 10 6 conidia per gram. Similar numbers of eggs were laid among treatments during the first oviposition period (1 to 7 days), but an effect of conidial concentration on eggs laid was observed during the second oviposition period (8 to 14 days). This was attributed to reduction in female numbers and not to reduction in fecundity independent of mortality. In a second experiment, grasshoppers oviposited into soils of three different textures (loamy-sand, sandy-loam, or clay-loam) that were amended with 10 5 B. bassiana conidia per gram and possessed either a viable or heat-killed microflora. There was no effect of soil texture on mortality of ovipositing grasshoppers, on the number of eggs laid, on positioning of egg pods in the soil profile, or on numbers of B. bassiana CFU recovered from female abdomens. However, a higher prevalence of mortality was observed for females ovipositing into the sterilized than nonsterilized sandyloam and clay-loam soils. Substantial populations of fungi and bacteria were recovered from nonsterilized soils. The predominant fungi isolated from these soils were members of the genera Chrysosporium, Fusarium, Gliocladium, Penicillium, Rhizopus, and Trichoderma, whereas Bacillus, Paenibacillus, and Pseudomonas species were the most commonly isolated bacteria. This study demonstrates that ovipositing grasshoppers are susceptible to relatively low densities of conidia in soils of varying textures, but the soil microflora may have an adverse affect on the efficacy of B. bassiana in field soils.

Biocontrol Science and Technology, 1996

Biocontrol Science and Technology, 1993

Conidia of the Hyphomycete fungus Beauveria bassiana (Bals.) were applied in an attempt to reduce... more Conidia of the Hyphomycete fungus Beauveria bassiana (Bals.) were applied in an attempt to reduce field populations of grasshoppers, primarily the migratory grasshopper Melanoplus sanguinipes (Fabricius). Dry spores were applied with wheat bran carrier to three fallow fields at a rate of 2.0 × 1013 spores ha−1 in 10 kg bait ha−1. Examination of culture plates that had been placed in the field to capture spores and of bran carrier with scanning electron microscopy indicated that a substantial portion of the B. bassiana colony—forming units (spores and clumps of spores) did not adhere to the bran and were applied in the field as free particles. Grasshoppers collected from the treated plots at intervals after application were assayed for infection by B. bassiana. The observed rate of mycosis in the treated populations was 70% of those collected after 2 days, declining to 41% by 13 days and 5% by 19 days after application. Analysis of reductions in population density gave results in agreement with the infection data. Treated populations declined 60% and 33% by 9 and 15 days after application respectively. The reductions were significant on both post—treatment sampling dates (p < 0.05) and the three replicated fields gave comparable results. This is the first field demonstration of effectiveness of this fungus as a microbial control agent of grasshoppers.

Biological Control, 1997

The influences of temperature on the mortality of grasshoppers (Melanoplus sanguinipes) inoculate... more The influences of temperature on the mortality of grasshoppers (Melanoplus sanguinipes) inoculated with the entomopathogenic fungi, Beauveria bassiana and Metarhizium flavoviride, alone and in combination was investigated. Basking by grasshoppers had less influence on the prevalence and timing of mortality in nymphs treated with M. flavoviride than with B. bassiana. In B. bassiana-treated nymphs allowed to bask for only 1 h/day, 44% less mortality was observed, decreasing to 98% less death in nymphs basking for H4 h/day. In contrast, only a slight decrease in mortality (13 to 23%) was observed in M. flavoviride-treated nymphs permitted to bask for 4 to 6 h/day. For both fungi, more mortality was observed in nymphs exposed to 35 than to 40°C for various durations per day. However, exposure to high temperatures had a greater inhibitory effect on B. bassiana than M. flavoviride. The efficacy of both entomopathogens, alone and in combination, was determined in simulated cool and hot fluctuating temperature environments and at a constant 25°C. The former two environments were derived from weather data on two different days at Lethbridge in July and were adjusted to simulate grasshopper thermoregulation during daylight periods (0600 to 2200 h). At 25°C, there was no difference between treatments in the prevalence of mortality. In the hot temperature environment, less mortality was observed for B. bassiana (3%) than for M. flavoviride (52%). Conversely, in the cool temperature environment, less mortality was observed for M. flavoviride (46%) than for B. bassiana (100%). Application of both pathogens simultaneously resulted in a final prevalence of mortality that was greater than that for M. flavoviride in the hot temperature environment and equal to that for B. bassiana in the cool temperature environment. The application of B. bassiana and M. flavoviride in combination may be a way to overcome some of the constraints of temperature on entomopathogenic Hyphomycetes against grasshoppers, especially where temperatures fluctuate or are high for a significant period of time. r 1997 Academic Press

Geophysical Research Letters, 2005

1] Regional network data reveal deep non-volcanic tremor occurs in five independent sections alon... more 1] Regional network data reveal deep non-volcanic tremor occurs in five independent sections along the U.S. section of the Cascadia subduction zone with different recurrence intervals. Sizeable tremor episodes occur during periods with no measurable geodetic deformation as well as coincident with episodic slow slip events, and the displacement amplitudes of the tremor with and without geodetic deformation are similar. The tremor depths cover a wide range that does not coincide directly with the subducting slab interface. The tremor can migrate bidirectionally from the point of initiation, and more than one spatially distinct tremor source can be active at a given time.