Pre-mortality effects of Zoophthora radicans infection in the diamondback moth

Larval food consumption and weight gain were not affected by Z. radicans until the third day after infection, one day prior to death from mycosis. No food was eaten on the day on which larvae died. Overall, infected larvae ate 45% less leaf tissue than uninfected larvae. Of the leaf tissue consumed by infected larvae, 87.5% was eaten on the first two days after infection and after this time infected larvae gained little weight. The efficiency with which ingested food was converted into body weight did not change as infection progressed. Infected female moths laid significantly fewer eggs than control moths. This difference was not only due to differential mortality between the infected and control treatments as egg production by infected females, prior to death (day 4 after infection), was significantly less than that of control females during the same period. Holding females for 24 h after eclosion (to allow further egg maturation), prior to infection, did not result in greater overall egg production when compared with moths infected on the day of eclosion. In olfactometer studies, Z. radicans infection in male moths did not affect the response to synthetic sex pheromone until the third day after inoculation when no individuals responded to pheromone. The response of Z. radicans infected male moths to mechanical stimulation was not affected until the third day after inoculation when infected individuals moved significantly shorter distances than controls. The number of infected female moths exposing their sex pheromone glands was significantly reduced by the third day after inoculation when compared with uninfected controls. Sex pheromone gland exposure by females and the number of male moths exhibiting wing fanning behaviour in response was positively correlated, indicating that gland exposure was an accurate method for assessing pheromone production.