Temporal distribution of Chaetocnema pulicaria (Coleoptera: Chrysomelidae) populations in Iowa

In 1999 and 2000, yellow sticky cards and sweep net samples were used to document the occurrence of an overwintering adult generation of Chaetocnema pulicaria Melsheimer, corn flea beetle, followed by two distinct populations peaks during the growing season in Iowa. Emergence of the overwintering adult generation started in mid-April and continued until early June in both years, with populations as high as 45 +/- 7.9 per 10 sweeps. Periods that ranged from 14 to 32 d were observed in 1999 and 2000 when C. pulicaria was not found following the overwintering generation. The first summer peak of C. pulicaria was observed between the end of June into the middle of July, with the highest observed peak at 16.70 +/- 1.42 C. pulicaria per 10 sweeps in cornfields, The second summer peak of C. pulicaria was observed between the middle into early September, with populations as high as 27.80 +/- 2.76 C. pulicaria per 10 sweeps. During the growing season. more C, pulcaria a were caught on yellow sticky cards originating from soybean borders than from grass borders. There were significantly greater numbers of C. pulicaria on yellow sticky cards located in grass borders adjacent to cornfields at the end of the growing season, compared with yellow sticky cards located within cornfields, indicating the movement of C. pulicaria from the cornfield back into the grass borders at the end of the growing season. In 2000, from August to the end of the corn growing season, significantly more C. pulicaria were found in grass borders than in the cornfields. Based on this new quantitative information, planting time could be altered to avoid the emergence of the overwintering generation of C. pulicaria. In addition, knowledge concerning the seasonalities of the first and second population peaks of C. pulicaria during the corn growing season could be used to recommend optimal timing for foliar-applied insecticide applications. This new knowledge concerning the seasonal dynamics of C. pulicaria will help to improve management recommendations for Stewart's disease of corn, caused by the bacterium Pantoea stewartii, and that is vectored by C. pulicaria.