Fitness of Diabrotica barberi, Diabrotica longicornis, and Their Hybrids (Coleoptera: Chrysomelidae)

Diabrotica barberi Smith & Lawrence, the northern corn rootworm, and Diabrotica longicornis (Say) (Coleoptera: Chrysomelidae), are currently recognized as closely related chrysomelid species. Hybridization has been proposed to occur between them, although the viability of hybrids has never been tested. The objective of this study was to assess life-history parameters of D. barberi,D. longicornis, and their hybrids under laboratory conditions to examine the potential for Þeld hybridization. D. barberi and D. longicornis were collected in allopatry and were used to create lab colonies. Parental species were crossed to obtain F1 hybrids, F2 hybrids, and backcrosses to either parental species. Various life-history traits, which may contribute to overall Þtness, were measured, and population growth rates were calculated for all crosses. D. barberi had greater reproductive potential thanD. longicornis, butD. longicornis individuals lived longer thanD. barberi individuals. In other traits, the two parental species were similar. The Þtness of hybrids of aD. longicornis female and D. barberi male, as estimated by reproduction, survival, developmental time, longevity, and head capsule width, was similar to that of the parental species. Hybrids of a D. barberi female and D. longicornis male demonstrated consistently poor egg viability, low survival, and shortened adult life span. The cause of the hybrid unidirectionality is unknown, but these data collectively suggest that hybrids of a D. longicornis female and D. barberi male and F2 backcrosses with parentals could potentially be as viable as either parental species and contribute to population growth under Þeld conditions.