Effect of Metarhizium anisopliae on the fertility and fecundity of two species of fruit flies and horizontal transmission of mycotic infection

Abstract

In Mauritius, the peach fruit fly, Bactrocera zonata Saunders (Diptera: Tephritidae), and the melon fly, Bactrocera cucurbitae (Coquillett), are the major pest of fruits and vegetables, respectively. Fruit growers make use of broad-spectrum insecticides to protect their crops from fruit fly attack. This method of fruit fly control is hazardous to the environment and is a threat to beneficial insects. The entomopathogenic fungus, Metarhizium anisopliae (Metchnikoff) Sorokin (Hypocreales: Clavicipitaceae), which was isolated from the soils of Mauritius, was used to investigate whether fungus-treated adult fruit flies could transfer conidia to non-treated flies during mating, and whether fungal infection could have an effect on mating behavior, fecundity, and fertility of the two female fruit fly species. When treated male flies were maintained together with non-treated female flies, they were able to transmit infection to untreated females, resulting in high mortalities. Similarly, fungus-infected female flies mixed with untreated males also transmitted infections to males, also resulting in high mortalities. Infection by M. anisopliae also resulted in the reduction of the number of eggs produced by females of B. cucurbitae. The results suggest that M. anisopliae may have potential for use in integrated control programs of B. zonata and B. cucurbitae using the sterile insect technique in Mauritius.

Keywords: biological control; entomopathogenic fungus; mating behavior.

Figure 1.

Mean mortality (±SEM) of Bactrocera zonata due to horizontal transmission of Metarhizium anisopliae from one treated fly (donor) to three uninfected flies (recipients) of the opposite sex at 1, 2, 3, 4, and 5 days postexposure to the donor fly. Each day on the x-axis represents different batches of successively introduced flies, and each column represents mean mortality of three flies exposed to one donor fly. Treatment female donor (unshaded bars): histograms with the same small letter are not significantly different (ANOVA and Tukey’s test, P < 0.019). Treatment male donor (shaded bars): histograms with the same capital letter are not significantly different (ANOVA and Tukey’s test, P < 0.001). High quality figures are available online.

Figure 2.

Mean mortality (±SEM) of Bactrocera cucurbitae due to horizontal transmission of Metarhizium anisopliae from one treated fly (donor) to three uninfected flies (recipients) of the opposite sex at 1, 2, 3, 4, and 5 days postexposure to the donor fly. Each day on the x-axis represents different batches of successively introduced flies and each column represents mean mortality of three flies exposed to one donor fly. Treatment female donor (unshaded bars): histograms with the same small letter are not significantly different (ANOVA and Tukey’s test, P < 0.005). Treatment male donor (shaded bars): histograms with the same capital letter are not significantly different (ANOVA and Tukey’s test, P < 0.015). High quality figures are available online.

Figure 3.

Mean number of eggs/female/day (±SEM) of Bactrocera cucurbitae (N = 10) for a period of seven days after exposure to Metarhizium anisopliae. Histograms with the same letter are not significantly different (ANOVA and Tukey’s test, P < 0.0001). High quality figures are available online.