Premortality Effects of Zoophthora radicans Infection in Plutella xylostella Michael J. Furlong, Judith K. Pell, and G. V. P. Reddy 1 Department of Entomology and Nematology, IACR–Rothamsted, Harpenden, Hertfordshire AL5 2JQ, United Kingdom Received September 10, 1996; accepted May 14, 1997 The effect of Zoophthora radicans infection on food consumption and utilization by Plutella xylostella lar- vae and oviposition by adults was investigated. Larval food consumption and weight gain were not affected by Z. radicans until the third day after infection, 1 day prior to death from mycosis. No food was eaten on the day on which larvae died. Overall, infected larvae ate 44% less leaf tissue than control larvae. Of the leaf tissue consumed by infected larvae 87.5% was eaten on the first 2 days after infection and after this time infected larvae gained little weight. The efficiency with which ingested food was converted into body weight did not change as infection progressed. In- fected female moths laid significantly fewer eggs than control moths. This difference was not only due to differential mortality between the infected and control treatments as the egg production by infected females, until the point of death (Day 4 after infection), was significantly less than that of control females over the same period. Incubating females for 24 hr after eclo- sion (to allow further egg maturation), prior to infec- tion, did not result in greater overall egg production when compared with moths infected on the day of eclosion. The possible causes for these reductions in larval feeding and adult oviposition rates are discussed.  1997 Academic Press Key Words: Zoophthora radicans; Plutella xylostella; feeding rate; weight gain; food conversion efficiency; oviposition rate. INTRODUCTION The diamondback moth, Plutella xylostella (Lepidop- tera: Yponomeutidae) is a universally distributed pest of cruciferous crops (Talekar and Shelton, 1993). The moth is a particularly severe pest in Southeast Asia (Talekar, 1992) where, in certain regions, the rapid development of resistance to all major classes of insecti- cide has rendered it a problem unmanageable by conven- tional insecticide use (Syed, 1992; Iqbal et al., 1996). Biological control strategies utilizing larval parasi- toids have met with some success (Lim, 1986; Sastrosis- wojo and Sastrodihardjo, 1986; Ooi, 1992; Talekar et al., 1992). More recently, the naturally occurring, envi- ronmentally safe, fungal entomopathogen Zoophthora radicans (Zygomycetes: Entomophthorales) has been developed as a biological control agent (Furlong et al., 1995; Furlong and Pell, 1996; Pell et al., 1993a). The slow mode of action of fungal entomopathogens has led to criticism of their use for insect pest control. However, Hajek (1989), Tyrrell (1990), and Mohamed et al. (1985) have all demonstrated reduced feeding in lepidopteran larvae infected with entomophthoralean fungi. Infec- tions of hyphomycetous fungi either have little effect on host food consumption (Thorvilson et al., 1985; Lord et al., 1987) or they reduce the quantity of food consumed as infection develops (Mohamed et al., 1982; Moore et al., 1992). Wang and Knudsen (1993) demonstrated that Beauveria bassiana (Balsamo) Vuillemin (Hypho- mycetes) infection did not reduce the intrinsic fecun- dity of Diuraphis noxia (Homoptera: Aphididae) Kurdyumov, whereas Fargues et al. (1991) demon- strated that sublethal B. bassiana infection in Leptino- tarsa decemlineata Say (Coleoptera: Chrysomelidae) larvae reduced the fecundity of subsequent adults. Zoophthora radicans kills infected P. xylostella lar- vae and adults within 3–4 days of infection (Pell et al., 1993b; Furlong et al., 1995). This paper describes the effect of infection on the feeding rate and weight gain of larvae and on the oviposition rate of female moths. MATERIALS AND METHODS Insects Plutella xylostella larvae were obtained from a labo- ratory culture which has been maintained at IACR– Rothamsted for over 5 years. The culture was main- tained on Chinese cabbage plants, Brassica chinensis var. pekinensis cv. Tip Top, in a constant environment room at 23  2°C and a 12:12-hr light:dark photope- riod. 1 Present address: University of Agricultural Sciences–Dharwad, Agricultural Research Station, Hagari–583 138, Bellary District, Karnataka, India. JOURNAL OF INVERTEBRATE PATHOLOGY 70, 214–220 (1997) ARTICLE NO. IN974690 214 0022-2011/97 $25.00 Copyright  1997 by Academic Press All rights of reproduction in any form reserved.