RELEASE DENSITY, EFFICIENCY AND DISAPPEARANCE OF TRICHOGRAMMA-NUBILALE FOR CONTROL OF EUROPEAN CORN-BORER

We evaluated how many Trichogramma nubilale should be released at a single location to control Ostrinia nubilalis in sweet corn. Six 8.6 x 16 m plots received 18.4 to 2 090 females T. nubilale/SAI when plants were in the mid to late whorl stage, where SAI, surface area index, is the plant surface area/m2. To evaluate the potential control by our releases, we exposed laboratory-reared O. nubilalis egg masses to the released parasitoids at 4 times after the release. When an egg mass was parasitized by T. nubilale, 75.7 % of the eggs in the egg mass were parasitized. We developed an equation to estimate the percent of egg masses that a single female was expected to parasitize in a day (efficiency of parasitism) and female disappearance (death and dispersal) rates, if both were constant during our experiment. The exponential disappearance rate was - 0.52 +/- 0.03 day-1, which implied that 40 % of the remaining females disappeared per day. The efficiency of parasitism was 0.050 % parasitism/female/SAI/day, which implied that at least 351,000 females/ha would be needed to achieve 90 % parasitism. Clearly, for T. nubilale to be a successful biological control agent, efficiency of parasitism must be increased and disappearance rates must be reduced.