Within-Plant and Within-Field Distribution Patterns of Asian Bean Thrips and Melon Thrips in Snap Bean

SIMPLE SUMMARY: Melon thrips and Asian bean thrips are the major insect pests of beans, inflicting economic losses on bean growers. Thrips infestations impose direct damage by feeding on leaves, flowers and fruits and indirect damage by transmitting viral diseases. Bean growers control thrips pests by spraying conventional insecticides without having basic information about their behavior and biology. This kind of nonjudicial use of insecticides causes the deterioration of the control program by enhancing pest populations. The present study was conducted in six bean fields with variable environmental conditions. Asian bean thrips occur mostly on flowers, and melon thrips are found on host foliage. Management decisions should be implemented based on evaluating population density in flowers and leaves. The distributions of Asian bean thrips, melon thrips and their larvae were mostly aggregated. However, to determine their population density, the number of samples should be collected at a 0.10 or 0.20 precision level based on a predetermined density of 5–10 adults per five-leaf sample. This is a cost-effective and accurate sampling method. ABSTRACT: Asian bean thrips, Megalurothrips usitatus Bagnall, are a serious pest of vegetable crops, especially leguminous crops, across the Asian continent. In Florida, it is a new invasive pest of snap beans. In 2019, it was recorded for the first time in the United States in snap bean (Phaseolus vulgaris) fields. Another thrips species, melon thrips, Thrips palmi Karny, is also a serious pest that affects several vegetable crops. Within-plant and within-field distribution patterns of M. usitatus and T. palmi were determined in snap bean fields in southern Florida. The highest number of both thrips species (Asian bean thrips and melon thrips) in snap beans were in flowers, followed by leaves and pods. Both adults and immatures of these thrips exhibited regular to clumped distribution patterns in bean fields. Several statistical indices showed agreement in the distribution patterns of Asian bean thrips, melon thrips, and larvae, irrespective of sampling units and plot size, in three years of study. In most instances, the distribution of Asian bean thrips and melon thrips was aggregated. This study assessed the optimum sample size to accurately determine the population density of these thrips for management purposes. The results from this study will be useful for implementing targeted management programs against thrips pests, thereby reducing labor costs and time. This information will also help reduce agrochemical use.