Interaction of maize weevil (Coleoptera: Curculionidae) and parasitoid Anisopteromalus calandrae (Hymenoptera: Pteromalidae) in a small bulk of stored corn

Monthly samples of a stored-corn ecosystem in southeastern Georgia were used to examine interaction between the maize weevil, Sitophilus zeamais Motschulsky, and its parasitoid, Anisopteromalus calandrae (Howard). Counts of adults were made when the samples were taken. Counts were made again after the samples had been held at 30 degrees C and 60% RH for 1 wk and for 3 wk. Host and parasitoid develop within grain kernels; at any time, their numbers can be divided into interstitial and intrakernel populations. Interstitial populations, estimated by the first count, consisted of adults that were in the interstices of the grain mass when a sample was taken. In these populations, numerical response of the parasitoid to host density was clear and indicated a degree of natural control. The intrakernel populations, estimated by counts 2 and 3 combined, included immature stages and adults that had not yet emerged from grain kernels at the time of sampling. Analysis of these populations showed that the rate of parasitism responded to changes in host density, but lagged behind. This delayed density-dependence allowed enough fluctuation in the weevil population for significant damage to occur during periods of peak population density. Nevertheless, A. calandrae may be an effective biological control agent if it is introduced in sufficient numbers early in the storage period to suppress the initial buildup of weevil populations. For long storage periods, additional introductions would be required to prevent weevil populations from rebounding once the parasite population declined.