Effects of Wheat Cultivar and Temperature on Suppression of Rhyzopertha dominica (Coleoptera: Bostrichidae) by the Parasitoid Theocolax elegans (Hymenoptera: Pteromalidae)

A laboratory study was conducted to examine the role of two temperatures, five divergent wheat cultivars, and the pteromalid parasitoid Theocolax elegans (Westwood) on progeny production by the lesser grain borer, Rhyzopertha dominica (F.). Adult T. elegans were introduced into half of the jars while host and parasitoid progeny were allowed to develop through the first generation. Adult R. dominica and parasitoid progeny were collected and quantitatively analyzed to assess efficacy of the parasitoid at suppressing R. dominica progeny. Wheat cultivars strongly influenced the quantity of lesser grain borer progeny in jars without parasitoids (Coker, Wakefield, 2163 > Munich > Wawawai). Results show that when R. dominica reproduced at lower densities, the parasitoid suppressed the host equally well at each temperature. However, when the host reproduced at greater densities, the parasitoid showed increased suppression at the lower temperature compared with that at the upper temperature. More parasitoids per available host always emerged at the lower temperature. Analysis of interactions among the three trophic levels indicated that the wheat cultivar, the first trophic level, did not significantly influence the reproductive capacity of the parasitoid, the third trophic level. This study showed that decreased grain temperature enhanced biological control in stored wheat when beetle densities were high.