Abstract
Entomopathogenic fungi can cause substantial mortality in harmful insects. Before killing the insect, these pathogens start by negatively affecting the biological parameters of the host. Prior to our study, the information about how fungal exposure affects the biological parameters of the stable fly, Stomoxys calcitrans was still elusive. Therefore, we aimed to assess the infection of S. calcitrans with some Metarhizium anisopliae strains, and their impact on feeding, fecundity, fertility and other life-history traits of this fly. Among the 11 M. anisopliae strains screened, we identified ICIPE 30 as the most virulent strain against S. calcitrans. We observed that the infectivity of this strain was sex and age-dependent. Infected male S. calcitrans died earlier than their counterpart females. Older infected S. calcitrans died faster than infected young ones. Also, male and female S. calcitrans successfully transmitted ICIPE 30 conidia to their mates. We demonstrated that infection by ICIPE 30 extended the feeding time of S. calcitrans and consequently reduced the feeding probability of the fly and the amount of blood taken. Using a dual test oviposition bioassay, we determined that uninfected gravid female S. calcitrans avoided laying eggs on substrates amended with ICIPE 30 conidia. We showed that these conidia could lower the hatchability of the eggs deposited by gravid females. Using, a no-choice test, we showed that gravid female S. calcitrans infected with ICIPE 30 laid fewer eggs than uninfected females and those eggs hatched less. Using 11 strains of M. anisopliae and four high concentrations of ICIPE 30 conidia, we verified that S. calcitrans larvae were not susceptible to fungal infection. Further, we showed that though these larvae were tolerant to fungal infection, there was a significant effect on their fitness, with contaminated larvae having a small bodyweight coupled with longer developmental time as compared to uncontaminated larvae. Our study provides detailed information on how fungal infection affects the biology of S. calcitrans and the potential of using M. anisopliae ICIPE 30 as a biopesticide to reduce the fly population. Such knowledge can assist in developing fungal-based control strategies against this harmful fly.
Highlights
Metarhizium anisopliae (Hypocreales: Clavicipitaceae) is a ubiquitous entomopathogenic fungus infecting a wide range of insect hosts and used for biological control (Brunner-Mendoza et al, 2019)
Of all the S. calcitrans individuals infected with 11 strains of M. anisopliae, only those infected with the strain ICIPE 30 had simultaneously, lower median lethal time (Figure 1C) and lower proportion of alive individuals (20%) at the end of our experiment (Figure 1D)
At the end of our experiment, the proportion of alive S. calcitrans infected with the strain ICIPE 7 was similar to that of S. calcitrans infected with the strain ICIPE 30 (Figure 1D), the strain ICIPE 7 took the longest time (>5 days) to kill half individuals of S. calcitrans as compared to the strain ICIPE 30 (
Summary
Metarhizium anisopliae (Hypocreales: Clavicipitaceae) is a ubiquitous entomopathogenic fungus infecting a wide range of insect hosts and used for biological control (Brunner-Mendoza et al, 2019). Its mode of action involves attachment to the host’s cuticle, germination, epicuticle penetration and dissemination inside the insect body as hyphae (Ortiz-Urquiza and Keyhani, 2013) This infection mechanism is facilitated by a group of enzymes including hydrolases, proteases, chitinases and lipases (Brunner-Mendoza et al, 2019). When proliferating inside insect tissues, blastospores produce toxic molecules (e.g., destruxins) that induce pathogenesis, paralysis, cellular alterations and dysfunction of the middle intestine, malpighian tubules, and muscle tissues (Samuels et al, 1988). These cascades of events provoke insect death 3–7 days after infection (Mondal et al, 2016). Before the death occurs, several pre-lethal reactions including the reduction in development, feeding propensity, and reproduction can be observed in infected insects
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