Horizontal Transmission of Metarhizium anisopliae in Fruit Flies and Effect of Fungal Infection on Egg Laying and Fertility.

Fly-to-fly transmission of conidia of the entomopathogenic fungus Metarhizium anisopliae and the effect of fungal infection on the reproductive potential of females surviving infection were investigated in three fruit fly species, Ceratitis cosyra, C. fasciventris, and C. capitata. The number of conidia picked up by a single fruit fly was determined in C. cosyra. The initial uptake (Day 0) of conidia by a single fly was approx. 1.1 × 10⁶ conidia after exposure to the treated substrate. However, the number of conidia dropped from 7.2 × 10⁵ to 4.1 × 10⁵ conidia after 2 and 8 h post-exposure, respectively. The number of conidia picked up by a single fungus-treated fly ("donor") varied between 3.8 × 10⁵ and 1.0 × 10⁶ in the three fruit fly species, resulting in 100% mortality 5-6 days post-exposure. When fungus-free flies of both sexes ("recipient" flies) were allowed to mate with "donor" flies, the number of conidia picked up by a single fly varied between 1.0 × 10⁵ and 2.5 × 10⁵, resulting in a mortality of 83-100% in C. capitata, 72-85% in C. cosyra and 71-93% in C. fasciventris 10-15 days post-inoculation. There was an effect of fungal infection on female egg laying in the three species of fruit flies as control flies laid more eggs than fungus-treated females. The percentage reduction in fecundity in flies infected with M. anisopliae was 82, 73 and 37% in C. capitata, C. fasciventris and C. cosyra, respectively. The results are discussed with regard to application in autodissemination techniques.