Seasonal patterns of persistence and infectivity of Metarhizium anisopliae var. acridum in grasshopper cadavers in the Sahel

Abstract

Field‐based experiments were conducted to evaluate the fate and infectivity of the entomopathogenic fungus Metarhizium anisopliae var. acridum (Deuteromycotina: Hyphomycetes) in grasshopper cadavers in the Sahel. Unlike uninfected cadavers, which were rapidly scavenged, those infected with the fungus persisted in the environment for a number of weeks. The environmental factor most associated with cadaver disappearance was rainfall. The high environmental humidity associated with rainfall was also required for sporulation of the fungus on host cadavers, although the likelihood of sporulation differed between microsites. Characteristics of the infection profile from infective cadavers were investigated by the sequential exposure of uninfected hosts to sporulating cadavers in field cages. This experiment revealed that cadavers remained infective for > 30 days, with the net infectivity changing through time. The most likely explanation for these changes is climatic influences on both the fungus and host. High humidity was not required for infection. A measurement of the transmission coefficient between healthy hosts and sporulating cadavers in the field was obtained at a realistic density of infectious cadavers. This revealed a figure of 0.45 m2 day−1. Overall, these experiments show that following host death, M. anisopliae var. acridum can be persistent in the environment, sporulate on host cadavers and reinfect new hosts at a realistically low field density, although at least in arid or semi‐arid areas, rainfall may be critical to the horizontal transmission of this pathogen.

Pathogen avoidance and prey discrimination in ants

“…Our results are in line with Marikovsky's field study showing that Formica rufa ants never feed on sporulating nestmates infected by Tarichium fungi [44]. Such an avoidance behaviour may explain why sporulating insects seem to remain in the environment for weeks while uninfected decaying prey are quickly eaten by a wide range of scavengers like birds or other invertebrates [45]. Put together, these results suggest that sporulating corpses are unattractive and even repellent to scavenging ants that refrain from retrieving such food items.…”

Laboratory and field studies for the control of Chagas disease vectors using the fungus Metarhizium anisopliae

“…Luz et al (1999 also found that infected dead T. sordida and T. infestans disappeared due to the activity of ants and other animals. Arthurs et al (2001) noticed that uninfected grasshopper cadavers in the Niger Republic were rapidly scavenged largely by ground-dwelling ants and beetles, but those infected with the fungus persisted in the environment for a number of weeks, which was not found in our experiments.…”

Variability in conidial thermotolerance of Metarhizium anisopliae isolates from different geographic origins

“…M. anisopliae conidia are primarily found in the top 1-5 cm of soil (Hu and St. Leger, 2002;Vänninen et al, 2000). Soil temperatures of up to 65°C have been reported during the rainy season in the Niger Republic, West Africa (Arthurs et al, 2001). We observed that soil surfaces subjected to full sunlight reached 60°C in irrigatedcorn Welds in Logan, UT USA (41°N) in mid-July at 5:00 pm (daylight saving time).…”