The biology of the bean thrips

Abstract

Hercothrips fasciatus was first collected in Yuba, California, in 1894. Its primary injury is the extraction of fluids from the host plants which results in desiccation. The favorite hosts are the prickly lettuce, Lactuca scariola, beans, cotton and pears. Winter is passed in the adult stage on the under side of leaves of green plants. Reproduction is both bisexual and parthenogenetic; sex ratio of [female][female] to [male][male] is about 2:1. About the last of March the overwintering adults migrate to prickly lettuce, sow-thistle, etc., where 2 generations are passed. About the last of June, crops become infested. The eggs are inserted in the plant tissue; the larva has 2 stages and pupates in the soil. There is a short prepupal stage in which the wing stubs are visible. In the prepupal and pupal stages the insect is mobile but takes no food. Mature adults emerge from the soil. The hosts are reached by short flights. In summer, the egg stage is about 7 days, the larval stages together about 10 days, and the pupal stages about 5 days. The pre-oviposition period is 3-4 days. The natural mortality of the immature stages is about 60%. The only internal insect parasite is Thripoctenus russelli; the chief predator Orius insidiosus var. tristicolor. The adults are active at 50[degree]-117[degree] F (opt. 75[degree]-90[degree]F). The rate of development increases with an increase in temp. The relative humidity range of adult activity is wide (opt. somewhat less than 40%). Both pupa and adult are comparatively susceptible to drowning. || ABSTRACT AUTHORS: Auth. summ