SEX-RATIO AND SEXUAL DIMORPHISM IN WESTERN CORN-ROOTWORM (COLEOPTERA,CHRYSOMELIDAE) ADULTS ON YELLOW STICKY TRAPS IN CORN

Field studies were conducted in 1993 to investigate a possible sexual dimorphism in the elytra coloration pattern of western corn rootworm, Diabrotica virgifera virgifera LeConte, adults, and to compare the sex ratio of adults captured on 2 types (Olson and Pherocon AM) of commer cial yellow sticky traps with those obtained by aspiration. Striped an d solid variations in elytra pattern were found in both sexes. Of the western corn rootworm adults that exhibited the solid elytra pattern, >99% captured on yellow sticky traps and 97% collected by aspiration w ere male. In contrast, of those adults which exhibited the striped ely tra pattern, 79% captured on yellow sticky traps and 42% collected by aspiration were male. Sex ratio of adults varied significantly over ti me and among sampling methods. Sticky traps captured a significantly g reater proportion of males compared with aspiration. No significant di fference in sex ratio was found between the 2 types of sticky traps; h owever, the Olson trap captured significantly more corn rootworm adult s overall than the modified Pherocon AM trap.