Journal of Invertebrate Pathology 90 (2005) 10–23 www.elsevier.com/locate/yjipa 0022-2011/$ - see front matter. Published by Elsevier Inc. doi:10.1016/j.jip.2005.07.003 Acquisition of lethal doses of Beauveria bassiana conidia by western Xower thrips, Frankliniella occidentalis, exposed to foliar spray residues of formulated and unformulated conidia  Todd A. Ugine a,¤ , Stephen P. Wraight b , John P. Sanderson a a Department of Entomology, Comstock Hall, Cornell University, Ithaca, NY 14853, USA b USDA-ARS Plant Protection Research Unit, Ithaca, NY 14853, USA Received 22 December 2004; accepted 5 July 2005 Available online 13 September 2005 Abstract Secondary acquisition of Beauveria bassiana conidia was recorded on the whole bodies and selected body parts of second-instar nymphs and adult female western Xower thrips exposed to foliar spray residues of three diVerently formulated conidial preparations, for 24 h. Conidia were formulated in emulsiWable oil or with clay (wettable powder), or were essentially unformulated conidia (tech- nical grade powder suspended in water with a surfactant). Formulation had no signiWcant eVect on dose acquisition and no eVect on virulence of acquired conidia. The mean nymphal LC 50 /LD 50 was 116 conidia/mm 2 and 52 conidia/insect, respectively; the values for adults were 19 conidia/mm 2 and 5 conidia/insect. Greatest numbers of conidia were recorded on the legs and abdomens of nymphs and on the legs, wings, and thoraces of adults. As would be expected, numbers of conidia acquired increased with residue concentra- tion (application rate). However, an inverse relationship was noted between acquisition rate (conidia acquired/total conidia applied) and residue concentration. The mechanism underlying this response was not determined. However, there was no indication that any body parts (e.g., tarsi) became saturated with spores, which suggests that either the thrips were repelled by the conidial residues or that as the concentrations of conidia on the substrate increased, conidia somehow became more diYcult to acquire. Slopes of the LC probit regressions were lower than those of the LD regressions (mean 1.14 vs 1.78), suggesting that the low slopes often obtained in fungal pathogen assays could be partly an artifact of unequal rates of dose acquisition at low vs high application rates. Published by Elsevier Inc. Keywords: Western Xower thrips; Frankliniella occidentalis; Beauveria bassiana; Bioassay; Formulations; Foliar spray residues; Secondary pick-up 1. Introduction The western Xower thrips, Frankliniella occidentalis (Pergande), causes substantial economic losses to green- house crops throughout the world. The losses are generally attributed to leaf, Xower, and fruit deformation, and fruit/ Xower abortion caused by thrips feeding damage, plant death, or unsaleability due to infection with thrips- transmitted tospovirus. The ability of western Xower thrips to develop resistance to chemical insecticides (Brødsgaard, 1994; Immaraju et al., 1992; Zhao et al., 1994) has led to the investigation of a variety of biolog- ical agents with thrips-control potential in greenhouse crops. These agents include the entomopathogenic fun- gus Beauveria bassiana (Balsamo) Vuillemin, (Brown- bridge et al., 2000; Murphy et al., 1998; Vestergaard et al., 1999).  This paper reports the results of research only. Mention of a pro- prietary product does not constitute an endorsement or recommenda- tion by the USDA. * Corresponding author. E-mail addresses: tau2@cornell.edu (T.A. Ugine), spw4@cornell.edu (S.P. Wraight), jps3@cornell.edu (J.P. Sanderson).