SOYBEAN PUBESCENCE AND ITS INFLUENCE ON LARVAL DEVELOPMENT AND OVIPOSITION PREFERENCE OF LEPIDOPTEROUS INSECTS

Lepidopterous insects often cause serious economic damage to soybean, Glycine max (L.) Merr. One possible source of resistance to these pests is plant pubescence. To determine the effects of pubescence on the larval stages of corn earworm (CEW), Helicoverpa zea (Boddie), velvetbean caterpillar (VBC), Anticarsia gemmatalis Hubner, and soybean looper (SBL), Pseudoplusia includens (Walker), they were reared on foliage of 'Tracy-M' lines isogenic for dense, normal, or glabrous pubescence. In addition, SBL was reared on foliage of 'Davis' lines isogenic for the same characters. To determine the effect of pubescence on oviposition preference and on subsequent larval defoliation levels, SBL and VBC imagoes were allowed to oviposit, under free choice conditions, on Tracy-M lines isogenic for dense, normal, and glabrous pubescence type. In all instances, larval growth and development were significantly (P less-than-or-equal-to 0.05) reduced and oviposition preference was significantly increased by the presence of plant pubescence. Corn earworm larvae were more affected by pubescence than SBL or VBC larvae, as exhibited by a greater increase in larval development time and a greater decrease in pupal weight when reared on normal and dense isolines. No differences were noted in VBC and SBL growth and development on normal vs. dense isolines. In one environment, SBL deposited significantly more eggs on dense plants than on normal plants. Larval populations of both SBL and VBC produced a significantly higher level of defoliation on normal and dense isolines than on the glabrous isoline. These results show that pubescence of soybean, when compared with plants without pubescence, functions as a resistance mechanism to the larval stage of lepidopterous defoliators but enhances adult oviposition. Under free-choice conditions, the level of increased larval damage due to the superior food substrate of glabrous plants is more than offset by the reduction in oviposition on these plants.