Hesperus Adults Research Articles

State‐dependent sampling bias in insects: implications for monitoring western tarnished plant bugs

AbstractInsect populations vary in the proportion of individuals exhibiting a particular ‘state’ (e.g., developmental stage, sex, egg load, or nutritional status). Because an insect's developmental state often determines both its size and its behavior, it is likely that this will also affect the probability of being sampled. We propose that a comprehensive approach to pest management must consider the interaction between the structure of a pest population (i.e., the relative number of individuals in each state) and any state‐dependent sampling bias. To illustrate the usefulness of this method we sampled populations of the western tarnished pest bug, Lygus hesperus Knight (Heteroptera: Miridae), in cotton fields. Our sampling technique utilized large cages to measure the absolute densities of each L. hesperus stage and adult sex within a population. This technique allowed us to document a wide range of absolute stage structures and sex ratios across 10 L. hesperus populations in California. Using a combination of cage samples and sweep net samples, we quantified the state‐dependent sampling bias by calculating the efficiency of sweep sampling as a function of L. hesperus developmental stage and sex. We found that the efficiency of sweep nets increased steadily with each successive developmental stage (i.e., nymphal instar) of L. hesperus. We also found that sweep nets are slightly more efficient in capturing male vs. female L. hesperus adults. Since other studies have documented that the stage and sex of L. hesperus can affect feeding impact on cotton flower buds, our results suggest that accurate predictions of Lygus damage will need to incorporate stage and sex‐dependent sampling biases.

The effects of mullein plants (Verbascum thapsus) on the population dynamics of Dicyphus hesperus (Heteroptera: Miridae) in tomato greenhouses

The response of Dicyphus hesperus Knight (Heteroptera: Miridae) to whitefly populations in tomato greenhouses was measured in the presence and absence of mullein ( Verbascum thapsus L.) as an alternative host plant. The dynamics of the D. hesperus population on tomato ( Lycopersicon esculentum Mill.) and on mullein plants were followed through an entire growing season. In houses with mullein plants, more predators occurred on mullein when whitefly density was low on tomato. A mark-release-recapture experiment where rabbit IgG was used as an external marker showed that D. hesperus adults moved from mullein plants to tomato plants. D. hesperus was always more abundant in houses with mullein than in the houses with tomato plants alone. Movements between tomato and mullein plants are discussed as a strategy to optimize predator foraging. The use of mullein as an alternative host plant may contribute to the establishment of D. hesperus and help to preserve the predator population when prey on tomato crops is scarce.

Potential Use of Dicyphus hesperus Knight (Heteroptera: Miridae) for Biological Control of Pests of Greenhouse Tomatoes

The potential of Dicyphus hesperus Knight as a predator of greenhouse whitefly, Trialeurodes vaporariorum (Westwood), and two-spotted spider mites, Tetranychus urticae Koch, was assessed in the laboratory and in a tomato greenhouse. D. hesperus adults fed readily upon both pest species in the laboratory, and nymphs completed development from egg to adult on either whitefly or mites. Whitefly, however, were a superior food for growth and development of D. hesperus compared to mites. Development time was shorter and resulting adult body size was larger for nymphs reared on whitefly compared to those reared on mites. In a greenhouse release, adults oriented to and oviposited on whitefly-infested sentinel plants but did not orient to mite-infested sentinel plants. D. hesperus adults oviposited on greenhouse tomatoes and their progeny completed development in a greenhouse in which both whitefly and mites were present. The results are discussed as they relate to the use of D. hesperus for biological control of pests of greenhouse vegetables.

Evaluation of Diel Variation of Sweepnet Effectiveness in Lentils for Sampling Lygus hesperus (Heteroptera: Miridae)

Relative effects of the abiotic environment and time of sampling on population estimates of Lygus hesperus Knight in lentils were determined during 2 years. Sweepnet samples were taken randomly at two locations in two fields every hour for 72 consecutive hours. Light, temperature, relative humidity, and wind velocity were the abiotic factors studied. Number of L. hesperus adults collected by sweepnet in lentils and the abiotic factors monitored in 1983 or early season 1984 were not correlated. There is no predictable optimum time within a 24-h cycle for sweepnet sampling of adults early in the season. Optimum sampling time for lygus bug nymphs late in the season was late afternoon. Lygus bug nymphs collected by sweepnet were correlated with relative humidity, temperature, and light in both years.