EVALUATION OF AN OVIPOSITION TRAP FOR MONITORING EGG POPULATIONS OF DIABROTICA SPP (COLEOPTERA, CHRYSOMELIDAE) IN-FIELD CORN

Traps consisting of open, cylindrical tins containing moistened clay a ggregates were evaluated as field oviposition sites for corn rootworm, Diabrotica spp. Six trap features were investigated: clay aggregate s ize, water saturation level, trap opening, trap cover, trap volume, an d trap position relative to corn plants. More eggs were recovered in t raps containing clay aggregates ranging from 0.5 to 3.5 mm diameter co mpared with aggregates from 2.5 to 8.0 mm diameter. Saturation of the trap to 2.5 cm from the opening resulted in greater egg recovery compa red with traps saturated to 6.0 cm from the opening. Covering the expo sed surface of the trap with a metal ring and/or a corn leaf increased egg recovery in the field. Oviposition traps were placed in four comm ercial corn fields in 1990 and three in 1991 to monitor egg population s. Egg recovery from traps and estimates of the absolute egg populatio n in the soil were compared with densities of adult corn rootworm to p redict larval damage on roots of corn planted the next year. Ln five f ields, adult populations were above the current economic threshold of one beetle per plant. However, economic damage to roots occurred only in the field in which the most eggs were recovered from traps (226.6 e ggs per trap) and soil samples (30.2 eggs per litre). Mean egg recover y per trap per field was correlated with mean damage ratings from untr eated corn.