EVects of diVerent Beauveria bassiana isolates on Weld populations of Lygus lineolaris in pigweed (Amaranthus spp.)

The tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), is a pest of various fruit, vegetable, Wber, and seed crops; including cotton. Lygus spp. populations often build on alternate host plants before moving to cotton, and in the midsouthern U.S. wild host plants, such as pigweed (Amaranthus spp.), play a major role in L. lineolaris population development. Three isolates of the entomopathogenic fungus Beauveria bassiana (Balsamo) were evaluated for L. lineolaris control in redroot pigweed (Amaranthus retroXexus L.): one from L. lineolaris in Mississippi (TPB3); one from Lygus hesperus (Knight) in California (WTPB2); and one commercial isolate from Mycotrol® (GHA). Fungal applications resulted in moderate to high mycosis in adults (33 to 80%) and moderate mycosis in nymphs (36 to 53%) that were collected from Weld plots at 2 days post-treatment and incubated under laboratory conditions. Although TPB3 was previously found to be more pathogenic in laboratory bioassays, there was not a consistent separation of this isolate from the other two isolates in Weld trials. Where diVerences in adult mycosis or mortality were observed, TPB3 was the most pathogenic. However, in one Weld trial 7 day mortality for nymphs treated with GHA was higher than those treated with TPB3 or WTPB2. Infection rates at 2, 7, and 14 days posttreatment from caged and non-caged adults suggested that movement of adults among plots occurred, which could have masked some treatment eVects. Fungal treatments did not signiWcantly reduce populations relative to controls. This may have been caused by delayed mortality rates under Weld conditions and/or diYculties with estimating population change under Weld conditions characteristic of wild host plant populations (e.g., heterogeneous populations, adult movement, and small plot size). Further work evaluating time–dose–mortality over dynamic temperatures, spring and fall Weld trials on this and other wild hosts, and improved methods for estimating populations on wild hosts are needed. Published by Elsevier Inc.