Influence of Thermal Ecology on the Mycosis of a Rangeland Grasshopper

Abstract

The clearwinged grasshopper, Camnula pellucida, exploits incident solar radiation to raise internal body temperatures above ambient levels. Under adequate temperature and light conditions, grasshopper body temperatures may exceed air temperatures by 10°—15°C with both nymphs and adults preferring to thermoregulate near 40°C, their optimal temperature for development. Comparison of age—specific phenology data collected from field sites with projections from computer simulation studies on grasshopper development, indicated that incident solar radiation can highly accelerate maturation of grasshoppers. Also, prolonged exposure to temperatures above 35°C is beneficialto grasshoppers, as it is detrimental to the fungal pathogen Entomophaga grylli (US pathotype I), which is a major cause of natural mortality in many species. E. grylli protoplasts grew little or not at all if incubated at a constant 35°C in tissue culture medium. Studies, conducted in vivo at constant temperatures, verified that E. grylli has an upper thermal limit of survival and development near 35°C. IN nature, however, these organisms are exposed to fluctuating temperatures. Further in vitro studies revealed that protoplast survival and development were significantly affected by incubation at 40°C for as little as 2 h per day and almost totally inhibited by 40°C for 8 h each day. In vivo incubation studies also showed an increase in the incubation period and a decline in the proportion of grasshoppers dying of E. grylli mycosis with increased daily exposure to 40°C. Infected grasshoppers were also held at 25°—30°C and allowed to range freely between shaded and lighted areas, so body temperatures could be raised through normal basking activity. Compared to a control group held in diffuse light, E. grylli mycosis was almost totally eliminated from the basking grasshoppers. The few individuals treated with solar radiation that died from E. grylli infection survived significantly longer then infected individuals not exposed to the solar simulator. Computer simulations using field—collected temperature, moisture, and solar radiation data revealed that behaviorally regulated thermal effects on E. grylli survival and development could limit disease development in some locations and seasons. Although it is unclear that the behavioral trait of basking is an adaptive response to selection pressures caused either by the pathogen or by other selective factors, it is clear that thermoregulatory behavior provides survival advantages to C. pellucida. In addition to their specific biological significance, these results demonstrate that behavioral exploitation of a physical resource in the environment can be used to profoundly alter biological relationships between species in this case, allowing one organism to eliminate an antagonist by causing its mortality.

Thermoregulatory behaviour affects prevalence of chytrid fungal infection in a wild population of Panamanian golden frogs

“…This is especially true for ectotherms where ambient conditions constrain the physiological temperatures of both host and pathogen (Carruthers et al 1992;Blanford & Thomas 1999Jackson & Tinsley 2002;Blanford et al 2003;Klass et al 2007;Laine 2008;Lazarro et al 2008). Several experimental studies have now demonstrated an effect of temperature on the susceptibility and behaviour of ectotherm hosts and/or the virulence of their pathogens (e.g.…”

“…Several experimental studies have now demonstrated an effect of temperature on the susceptibility and behaviour of ectotherm hosts and/or the virulence of their pathogens (e.g. Carruthers et al 1992;Blanford & Thomas 1999;Ferguson & Read 2002;Jackson & Tinsley 2002;Wilson et al 2002;Yourth et al 2002;Woodhams et al 2003Woodhams et al , 2008Lazarro et al 2008). However, the functional mechanisms underlying these effects and their potential to affect the outcomes of infections under natural conditions are not well understood (Carey et al 1999;Jackson & Tinsley 2002).…”

Effects of Lecanicillium longisporum infection on the behaviour of the green peach aphid Myzus persicae

“…Not all pathogen-induced ''behaviours'' are detrimental to the host. In particular, high body temperatures generated by behavioural fever prevent pathogen growth in flies (Watson et al, 1993), grasshoppers (Carruthers et al, 1992) and locusts (Blanford et al, 1998) infected with fungi.…”

Thermoregulation in four species of British grasshoppers (Orthoptera: Acrididae)

“…Kemp (1986) argued that there was no a priori reason for supposing a linear relationship between body temperature and ambient, and, furthermore, the relationship often proved non-linear over the full range of ambient temperatures. These objections have been overcome by fitting a non-linear Functional Ecology 1997 11, [705][706][707][708][709][710][711][712][713] regression curve, often incorporating solar radiation intensity into the model (Kemp 1986;Carruthers, Larkin & Firstencel 1992).…”