Behavioural fever in the Senegalese grasshopper, Oedaleus senegalensis, and its implications for biological control using pathogens

Abstract

1. Thermoregulatory behaviour of the Senegalese grasshopper, Oedaleus senegalensis (Krauss), was investigated in the field following a spray application of an oil‐based formulation of Metarhizium flavoviride Gams and Rozsypal in Niger, West Africa. 2. Measurements of environmental temperature, wind speed and solar radiation were made in conjunction with measurements of internal body temperatures of grasshoppers from a control (unsprayed) and treated plot using microthermocouples and hand‐held thermometers. Grasshoppers were monitored for 4 days from the third day after application. 3. Oedaleus senegalensis utilized a range of thermoregulatory behaviours to maximize body temperatures during periods of low insolation and ambient temperature, and to minimize excessive heat loading during the hottest periods. Preferred body temperature of uninfected grasshoppers was 39 °C, with a range from 24 °C in the early morning to a high of 46 °C during periods of high insolation and ambient temperature. 4. Infected grasshoppers altered their thermoregulatory behaviour and showed a behavioural fever response to the pathogen. Preferred body temperatures of infected individuals were raised to a new set point of ≈ 42 °C. This is believed to be the first evidence for a behavioural fever in response to a microbial infection for any natural population. In the present study, its effects appeared to provide little therapeutic advantage to hosts infected following application. Preliminary evidence from other studies, however, indicates that modifications to host thermoregulation could be a significant constraint to the pathogen and may limit its impact under certain conditions.

The effects of temperature on host–pathogen interactions in D. melanogaster: Who benefits?

“…Elliot, Thomas, and Blanford, among others, discovered that when locusts were infected with a pathogenic fungus, placing them at warmer temperatures prolonged their survival. In fact, when given the choice, the infected locusts relocate themselves to warmer areas of their environment (Blanford et al, 1998;Elliot et al, 2002;Thomas and Blanford, 2003). Similar affects of temperature on fungal infections have also been seen in grasshoppers (Inglis et al, 1996(Inglis et al, , 1997 and houseflies (Watson et al, 1993).…”

“…But the situation may be more complex. The efficacy of an insect's immune system may depend in part on temperature-dependent physiological changes in the host (Blanford et al, 1998;Elliot et al, 2002;Thomas and Blanford, 2003). There are myriad changes in metabolism, the nervous and endocrine systems, behavior, and the like, that occur in insects as their temperature increases (Neven, 2000).…”

Thermal and physical stresses induce a short-term immune priming effect in Galleria mellonella larvae

“…Traniello et al (2002) demonstrated that naïve termites reared alongside termites previously exposed to Metarhizium anisopliae can improve the subsequent resistance of the naïve termites to the fungal pathogen. A potential role for 'behavioural fever', where insects alter their temperature through thermoregulatory behaviour, leading to an increased ability to withstand infection has been suggested (Watson et al, 1993;Blanford et al, 1998;Elliot et al, 2002).…”

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

“…Previous, laboratory-based, behavioural fever studies (e.g. Kluger 1977;Louis et al 1986;Blanford et al 1998;Cabanac & Cabanac 2004) have not monitored the infection status of individuals along with their body temperatures, and therefore, were unable to investigate whether or for how long body temperatures remained elevated once the infection was gone.…”