Seasonal changes in infestation level of sugarcane by the pink borer, Sesamia inferens (Lepidoptera : Noctuidae), in relation to a parasitoid, Cotesia flavipes (Hymenoptera : Braconidae), on Okinawa Island

Abstract

Infestation of sugarcane by the pink borer, Sesamia inferens (Walker) (Lepidoptera : Noctuidae), parasitism of the pink borer by Cotesia flavipes (Cameron) (Hymenoptera : Braconidae) and host-parasitoid relationships were examined on Okinawa Island over a period of 4 years. Bimonthly surveys indicated that infestation by the pink borer had two peaks, one in April/May (20.5 to 29.3%) and the other, in August (22.2 to 29.5%), whereas parasitism of the pink borer had only one peak in August (61.2 to 80.1%). The density of C. flavipes at time t depended most strongly on the density of the pink borer at time t (r=0.77 to 0.84), whereas, the density of the pink borer depended most strongly on the density of C. flavipes at time t-3, i.e., 1.5 months earlier (r= -0.29 to -0.44). It was notable that the mean number of parasitoids that emerged from a single host varied seasonally, being smallest in February (17.6 to 26.8) and largest in August (48.8 to 59.2). A positive correlation between the mean number of emerged parasitoids and the mean temperature in each month (r=0.87) suggested that the number of eggs oviposited by a female per host was influenced by temperature.