Dose-dependent behavioural fever responses in desert locusts challenged with the entomopathogenic fungus Metarhizium acridum

Abstract

Behavioural fever is a common response to immune challenge in ectotherms and confers survival benefits. However, costs accrue rapidly as body temperature rises. Thus, the magnitude of adaptive fever responses might reflect the balance of costs and benefits. We investigated behavioural fever in desert locusts, Schistocerca gregaria, infected with the entomopathogenic fungus Metarhizium acridum. We first tracked the time course of behavioural fever in infected locusts, demonstrating that body temperatures rose on the day following inoculation (day 1), and reached peak intensity on the day after that (day 2). Subsequently, the magnitude of fever responses varied during a day, and locusts tended to exhibit high-intensity fever responses in the mornings when basking was first possible. We speculate that this may have resulted from increased fungal load caused by unimpeded growth overnight when locusts could not fever. We next inoculated locusts with different M. acridum doses ranging from 0 to ca. 75,000 conidia. The magnitude of their behavioural fever responses on day 2 post-inoculation was positively related to fungal dose. Thus, we demonstrate dose-dependency in the behavioural fever responses of desert locusts and suggest that this may reflect the adaptive deployment of behavioural fever to minimize costs relative to benefits.

Research Progress on Phytopathogenic Fungi and Their Role as Biocontrol Agents

“…Today, the development and application of pathogenic microorganisms that affect locusts is becoming increasingly important. Pathogenic fungi of locusts are mainly distributed in the subclasses Zygomycetes and Deuteromycetes (Clancy et al, 2018). At present, the locust-toxic pathogenic fungi used in artificial propagation mainly include Metarhizium anisopliae, Beauveria bassiana, and Metarhizium anisopliae, although Entomophaga grylli and Fusarium verticillioides are also used (Tralamazza et al, 2019).…”

“…The most studied and applied of these is the E. grylli complex, which includes at least four pathogenic fungi: E. calopteni, E. macleodii, E. praxibuli, and E. asiatica. Metarhizium acridum, which specializes in parasitizing locusts, secretes a series of proteins, including proteases, chitinases, and cytochrome P450 (Zhao et al, 2014;Clancy et al, 2018). These proteins enhance the ability of M. acridum to adapt to different conditions (Moisan et al, 2019).…”

Combining Transcriptomics and Proteomics Reveals Potential Post-transcriptional Control of Gene Expression After Light Exposure in Metarhizium acridum

“…Insect behavior control by M. acridum has never been observed, but the strong accumulation of a sphingomyelinase containing an export signal peptide could indicate it has a role in insect killing as observed for Bacillus cereus (Doll et al 2013). The accumulation of the enzyme in response to light is in accordance with the host lifestyle, as locusts are known to engage in behavioral fever by basking in the sun, a phenomenon beginning on day 1 post-infection (Clancy et al 2018).…”

Subtilisin-like Pr1 proteases marking the evolution of pathogenicity in a wide-spectrum insect-pathogenic fungus

“…Third, fungal responses to various stress cues encountered during infection and after entry into host hemocoel are critical for successful infection and host mummification [30]. Encountered stress cues include high osmolarity in trehalose-concentrated host hemolymph, oxidative stress of reactive oxygen species generated from host immunity defense, and behavioral fever (elevated temperature) of early infected host [30,45,46]. For this reason, we assayed cellular responses to two osmotic agents (NaCl and sorbitol), two oxidants (menadione and H 2 O 2 ) and three cell wall stressors (Congo red, calcofluor white, and SDS) during colony growth on CDA.…”