Host-race formation remains controversial as a source of herbivorous insect diversity, and examples of host races are still fairly scarce. In this study, analysis of five enzyme loci in the ostensibly generalist tumbling flower beetle Mordellistena convicta (Coleoptera: Mordellidae) revealed hidden host-plant and plant-organ related genetic differentiation. Mordellistena convicta turned out to be a complex of cryptomorphic species, each with fewer hosts than the nominal species. These cryptic species, in turn, were divided into taxa that showed host-race characteristics: samples from different host plants and organs exhibited (1) genetic indications of partial reproductive isolation, (2) differences in size and emergence timing that suggested divergent host-related selection, and (3) among-host selective differences in mortality from parasitoids. Host-race formation in M. convicta, which has a somewhat different life history from the well-studied host races, enlarges the group of insects considered likely to undergo this process. The widespread sympatry of the M. convicta species complex, along with its spectrum of host-correlated genetic differentiation, suggests that these host specialist taxa developed in sympatry.

Host-race formation remains controversial as a source of herbivorous insect diversity, and examples of host races are still fairly scarce. In this study, analysis of five enzyme loci in the ostensibly generalist tumbling flower beetle Mordellistena convicta (Coleoptera: Mordellidae) revealed hidden host-plant and plant-organ related genetic differentiation. Mordellistena convicta turned out to be a complex of cryptomorphic species, each with fewer hosts than the nominal species. These cryptic species, in turn, were divided into taxa that showed host-race characteristics: samples from different host plants and organs exhibited (1) genetic indications of partial reproductive isolation, (2) differences in size and emergence timing that suggested divergent host-related selection, and (3) among-host selective differences in mortality from parasitoids. Host-race formation in M. convicta, which has a somewhat different life history from the well-studied host races, enlarges the group of insects considered likely to undergo this process. The widespread sympatry of the M. convicta species complex, along with its spectrum of host-correlated genetic differentiation, suggests that these host specialist taxa developed in sympatry.

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Field observations at three locations in the Texas High Plains were used to develop and validate a degree-day phenology model to predict the onset and proportional emergence of adult Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae) adults. Climatic data from the Texas High Plains Potential Evapotranspiration network were used with records of cumulative proportional adult emergence to determine the functional lower developmental temperature, optimum starting date, and the sum of degree-days for phenological events from onset to 99% adult emergence. The model base temperature, 10 degrees C (50 degrees F), corresponds closely to known physiological lower limits for development. The model uses a modified Gompertz equation, y = 96.5 x exp (-(exp(6.0 - 0.00404 x (x - 4.0), where x is cumulative heat (degree-days), to predict y, cumulative proportional emergence expressed as a percentage. The model starts degree-day accumulation on the date of corn, Zea mays L., emergence, and predictions correspond closely to corn phenological stages from tasseling to black layer development. Validation shows the model predicts cumulative proportional adult emergence within a satisfactory interval of 4.5 d. The model is flexible enough to accommodate early planting, late emergence, and the effects of drought and heat stress. The model provides corn producers ample lead time to anticipate and implement adult control practices.

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