INVASION EFFICIENCY AS A MEASURE OF EFFICACY OF THE ENTOMOGENOUS NEMATODE STEINERNEMA-CARPOCAPSAE (RHABDITIDA, STEINERNEMATIDAE)

Potential of entoniogenous nematodes for biological control generally is assessed by host mortality; nematode efficacy often is estimated by LC50. Nematode invasion efficiency (i.e., the percentage of the' infe ctive-stage juveniles that invade and establish in the host) has been proposed as an alternative to LC50, as a measure of nematode efficacy. The relationship between these two measurements of nematode efficacy was explored in studies with Mexican and All strains of Steinernema ca rpocapsae (Weiser) tested against last instars of three lepidopteran s pecies: Agrotis ipsilon (Hufnagel), Spodopterafrugiperda (J.E. Smith), and Galleria mellonella (L.). Estimates of LC50 ranged from 4 to 91 i nfective-stage juveniles (infectives) per host. Invasion efficiency (p ercentage invading) ranged from 11 to 31% among the six host-nematode combinations when concentrations of 10 to 100 infectives per host larv a were tested and ranged from 1 to 28% when single infectives were tes ted against individual larvae in one-on-one bioassays. We observed no obvious host- or nematode strain-related patterns in invasion efficien cy and no correlation between LC50 estimate and invasion efficiency. W e recommend that determinations of percentage host mortality and nemat ode invasion efficiency be done simultaneously for assessments of nema tode efficacy.