SOYBEAN MATURITY GROUP AND INCIDENCE OF VELVETBEAN CATERPILLARS (LEPIDOPTERA, NOCTUIDAE) AND MEXICAN BEAN BEETLES (COLEOPTERA, COCCINELLIDAE)

Five soybean varieties from maturity groups IV-VIII were routinely mon itored in the 1993 and 1994 growing seasons to examine the effect of p lant maturity on the seasonal abundance of velvetbean caterpillars, An ticarsia gemmatalis Hubner, and Mexican bean beetles, Epilachna varive stis Mulsant. Differences were detected in the population density of p est populations, percentage of defoliation, and yield. The early matur ing varieties (groups IV and V) had lower mean infestations, although the peak A. gemmatalis populations occurred in all varieties at the sa me time in Georgia. During the population peak in mid-September, the g roup IV-V varieties were already maturing and no longer attractive to the damaging population densities of 30-60 A. gemmatalis per 25 sweeps that were present oil the group VI-VIII varieties. Similar trends wer e noted for E. varivestis populations. Population peaks occurred in al l varieties in mid-September, with highest densities in the group VIII variety and much lower populations in all the earlier-maturing variet ies. Plots treated with diflubenzuron at 0.28 kg (AI)/ha in mid-August had lower insect populations and percentage defoliation and higher yi elds than corresponding untreated plots for all varieties except the g roup IV variety, in which no differences were detected because of low insect populations. Significant linear regressions were obtained betwe en peak d. gemmatalis population densities and percentage defoliation for all 5 maturity group soybeans. Significant linear regressions also were obtained between population peaks and yield reductions for the g roup V-VIII varieties. The economic injury levels (EIL) for A. gemmata lis were lower for the group IV and. V entries (25-30 per 25 sweeps) t han for the group VI-VIII entries (35-40 per 25 sweeps). Thus, it appe ars that a standard EIL for A. gemmatalis cannot be established across all maturity group soybeans in the southern region. The soybean matur ity group affected the density of both the A. gemmatalis and E. varive stis population peaks, but the timing of these peaks was similar acros s all varieties. The group IV and V varieties can be planted to escape high populations of these pests and resultant plant injury, and these varieties had yields comparable to the later maturing entries.