The effect of ergosterol on the allogrooming behavior of termites in response to the entomopathogenic fungus Metarhizium anisopliae

Abstract

Termites have physiological and behavioral immunities that make them highly resistant to pathogen infections, which complicates biocontrol efforts. However, the stimuli that trigger the pathogen-avoidance behaviors of termites are still unclear. Our study shows that workers of Coptotermes formosanus exposed to the conidia of Metarhizium anisopliae exhibited a significantly higher frequency and longer duration of allogrooming behaviors compared with untreated termites. Volatile compounds in the cuticle of control termites and termites previously exposed to a suspension of M. anisopliae conidia were analyzed and compared using a gas chromatography-mass spectrometer (GC-MS). Our results showed that the amount of ergosterol differed between the fungus-exposed and control termites. Choice tests showed that termites significantly preferred to stay on filter paper treated with ergosterol (0.05, 0.1, or 1.0 mg/mL) compared with control filter paper. In addition, termites exposed to ergosterol followed by M. anisopliae conidia were allogroomed at a significantly higher frequency and for a longer duration than termites exposed to alcohol (the solvent used with the ergosterol in the ergosterol trials) alone followed by M. anisopliae conidia. These results showed that ergosterol may enhance the allogrooming behavior of termites in the presence of entomopathogenic fungi.

Keywords: allogrooming behavior; entomopathogenic fungus; ergosterol; recognition; social immunity; termite.

Fig. 1

Termite (Coptotermes formosanus) mortality at different concentrations of Metarhizium anisopliae. The day of intersection of each colored line and the black line represents the LT50 of termites in each treatment.

Fig. 2

Frequency and duration (mean ± SE) of termite (Coptotermes formosanus) allogrooming behavior at 2 concentrations of Metarhizium anisopliae. Different capital letters indicate significant differences between the 2 concentrations in the same group of groomed termites. Different lowercase letters indicate significant differences among 3 groups of groomed termites at the same concentration (Tukey's honestly significant difference [HSD] test, P < 0.05).

Fig. 3

Gas chromatogram of volatiles from the Metarhizium anisopliae‐exposed termites (Coptotermes formosanus). MA: 1 × 10⁸ conidia/mL M. anisopliae‐treated workers; Tween: 0.1% Tween 80‐treated workers; blank: untreated workers; the red circle shows the significantly different volatile (ergosterol).

Fig. 4

Aggregation preference of termites (Coptotermes formosanus) under different ergosterol treatments. Dots represent raw data; deeper colors reflect overlapping data.

Fig. 5

Frequency and duration (mean ± SE) of termite (Coptotermes formosanus) allogrooming behavior under different ergosterol treatments. CK: untreated worker; A + T: alcohol + 0.1% Tween 80 treated worker; A + M: alcohol + Metarhizium anisopliae conidia treated worker; E + M: ergosterol + M. anisopliae conidia treated worker. Different capital letters above the bars indicate significant differences between the treatment groups (Tukey's honestly significant difference [HSD] test, P < 0.05).