D. DZOIC
Ministry of Agriculture and Forestry, 10000 Zagreb, Croatia
M. IVEZIC, E. RASPUDIC, M. BRMEZ
Univ. of J.J. Strossmayer, Fac. of Agriculture in Osijek, 31000 Osijek, Croatia

A new insect pest was identified in 1995 in Croatia - the western corn rootworm (Diabrotica virgifera virgifera LeConte). The first objective of this research was to determine the population density of all stages, except eggs in commercial corn fields. The second objective was to investigate the efficacy of three organophosphate insecticides on larvae.  The experiment was conducted in 1999 and 2000 in Gunja, Croatia (44^o87’N, 18^o94’ E). Treatments were corn hybrids (OSSK 444, OSSK 552, Florencia,) and three soil insecticides (terbufos, chlorpyriphos-ethyl, chlormephos) applied at planting. Results showed the highest number of larvae per plant (0.70) in the untreated plot of OSSK 552. In 1999, significant differences in larval numbers occurred between hybrids, but not between the insecticides. In 2000, larval numbers only differed statistically between the insecticide treatments. The highest beetles population counted per plant was 0.55 in 2000. This population level is very close to economic threshold of 0.70 beetles per plant. Significant differences in beetle numbers per plant between hybrids were only detected in 2000. Pheromone traps containing the lure, , caught significantly more beetles than the Multigard^® yellow sticky-trap. Terbufos was the only soil insecticide providing a significant yield advantage to the hybrids, but only in 2000. Based on the current value of corn and cost of insecticide, terbufos is the only soil insecticide that would be cost-effective for growers. These studies should be conducted with other insecticides, and growers should avoid planting corn after corn in their fields.