Effects of the Milling Degree of Rice and Storage Volume on the Interaction Between Plodia interpunctella (Lepidoptera: Pyralidae) and Its Parasitoid Bracon hebetor (Hymenoptera: Braconidae)

The ability of Bracon hebetor Say, a larval parasitoid of certain stored product moths, to suppress a Plodia interpunctella (Hlibner) population was studied in differing rice products. The larvae of P. interpunctella gathered on the topmost layer of the experiment cages filled with rice product (less than 3 cm in depth), and were rarely observed in deeper depths (deeper than 3 cm). Without P. interpunctella, B. he-etor did not show a preference for any of the three types of milled rice products used. In rice flour, the searching behavior of B. hebetor for P. interpunctella was limited, apparently due to the thick webbing pro-uced by the moth larvae. B. hebetor suppressed P. interpunctella population successfully in cracked rice kernels, but failed to suppress the moth population in rice flour. In whole rice kernels, B. hebetor suppressed the moth population only when the volume of rice in the cage was large enough to support a high population density of P. interpunctella (2.4 kg/cage). Success and failure of B. hebetor to suppress the moth population in the three different rice products are discussed in relation to the larval webbing and intraspecific com-etition of P. interpunctella larvae.