Effects of Resistant Sorghum Hybrids on Sorghum Midge (Diptera: Cecidomyiidae) Biology

Abstract

Fewer ovipositing female sorghum midges, Contarinia sorghicola (Coquillett), were found on flowering panicles of two resistant grain sorghum hybrids, ATx2755 x RTx2767 and ATx2761 x RTx2767, than on susceptible hybrids, ATx2752 x RTx430 and ATx3042 x RTx2737, on a few occasions during the 1981 growing season. However, these differences in adult abundance occurred erratically and did not follow any apparant pattern. It was doubtful that the resistance of these hybrids could be attributed to an effect on the number of ovipositing midges. Determination of the number of progeny produced per female that oviposited in panicle spikelets of susceptible and resistant hybrids was complicated by competition between midges at high population densities. An interference index was used to compensate for this competition. Midges infesting resistant hybrids produced 50 to 60% fewer progeny per female than midges infesting susceptible hybrids, regardless of midge density. This percentage of reduction became ineffectual in preventing economic damage to resistant hybrids as midge densities reached high levels. There was a slight, but nonsignificant, increase in the developmental time of midges infesting resistant sorghum hybrids. These results suggest that the effects of midge resistant sorghums would be cumulative in reducing midge density through time.