To sweep or to vacuum: a comparison of lygus bug (Lygus hersperus Knight) populations in two varieties of dry beans

Lygus bugs, Lygus hesperus Knight, are a problem for the production of dry beans. Their feeding directly kills the flowers and damages the seeds. Two baby lima bean varieties with differing canopy covers were sampled for Lygus bugs and natural enemies in the summer of 2010 to compare population structures and evaluate the efficacy of net sweeps. Bush beans are upright and allow for more sunlight penetration to the soil while Vine bean varieties form a mesh-like cover which is hypothesized to provide more protection from high daily summer temperatures and predators. It also prevents a net to effectively penetrate, which may affect what insects are sampled. Four blocks with two 80 meter length rows of each variety were sampled with sweep nets every 1-2 weeks. An insect vacuum was used to detect any sampling bias in sweeping an open canopy against a closed canopy. Lygus bugs adults were counted and differentiated by sex. Nymphs were differentiated by instar level. First and second instar lygus bugs were counted under one group. The natural enemies of interest were assassin bugs, damsel bugs, minute pirate bugs, big eyed bugs, lacewings, ladybird beetles, hoverflies and spiders. Preliminary data suggests the following: bush beans were the more preferred variety, time of sampling did not affect composition of insects caught, and that the bias in sampling method observed in the previous year between vacuum and net sweeps was not observed to the extent it was observed in the previous year.