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Seasonal adaptations to daylength often limit the effective range of insects used in biological control of weeds. The leaf beetle Diorhabda carinulata (Desbrochers) was introduced into North America from Fukang, China (latitude 44° N) to control saltcedars (Tamarix spp.), but failed to establish south of 38° N latitude because of a mismatched critical daylength response for diapause induction. The daylength response caused beetles to enter diapause too early in the season to survive the duration of winter at southern latitudes. Using climate chambers, we characterized the critical daylength response for diapause induction (CDL) in three ecotypes of Diorhabda beetles originating from 36, 38, and 43° N latitudes in Eurasia. In a field experiment, the timing of reproductive diapause and voltinism were compared among ecotypes by rearing the insects on plants in the field. CDL declined with latitude of origin among Diorhabda ecotypes. Moreover, CDL in southern (<39° N latitude) ecotypes was shortened by more than an hour when the insects were reared under a fluctuating 35-15°C thermoperiod than at a constant 25°C. In the northern ( >42° N latitude ) ecotypes, however, CDL was relatively insensitive to temperature. The southern ecotypes produced up to four generations when reared on plants in the field at sites south of 38° N, whereas northern ecotypes produced only one or two generations. The study reveals latitudinal variation in how Diorhabda ecotypes respond to daylength for diapause induction and how these responses affect insect voltinism across the introduced range. [ABSTRACT FROM AUTHOR]

Coccinellids are important natural enemies of aphid pests in wheat, Triticum aestivun em Thell, in the Great Plains of the United States.Coccinellid community development in wheat fields is unpredictable; therefore, precise, efficient sampling methods for coccinellids are needed for use in integrated pest management research and decision making. Our objectives were to compare removal sampling with quadrat sampling for estimating population density of adult and larval coccinellids in winter wheat, and to determine if timed count sampling and sweepnet sampling were useful for estimating adult and larval coccinellid densities. Removal sampling accurately estimated population densityfor adults of most species but consistently underestimated larval density. Timed count samples and sweepnet samples were significantly correlated with absolute density of both larval and adult coccinellids.Regression models were developed to convert estimates of relative toestimates of absolute population density. Depending on sampling method and life stage, models included the number of tillers per 0.3 m, wheat plant growth stage, plant height, and the number of aphids per tiller as variables; R{sup}2{end} values ranged from 0.89 to 0.93. Sweepnet sampling was more precise per unit of effort than timed count, quadrat, or removal sampling for estimating adult coccinellid density. Removal sampling (removing all coccinellids seen during 2 successive 15-min searches from each of 9 plots (25 m{sup}2{end}) was the least efficient method. [ABSTRACT FROM AUTHOR]