Relationship of sorghum midge, Contarinia sorghicola (Coquillett), density and damage to resistant and susceptible sorghum hybrids

Abstract

Three methods were used in 1980 and 1981 to investigate the relationship between adult soghum midge, Contrainia sorghicola (Coquilllett) (Diptera: Cecidomyiidae), density levels and yield loss in susceptible (S) and resistant (R) sorghum hybrids: 1) The Natural Infestation Method involved counting the number of ovipositing midges present on flowering panicles and relating this density to resulting damage. 2) The Cage Infestation Method utilized infestation of caged sorghum panicles with fixed numbers of female midges and quantification of resulting damage. 3) The Stepwise Model Method consisted of the identification and quantification of the steps leading from midge infestation to yield loss. Hybrids used were ATx2752 x RTx430 (S), Atx2755 x RTx2767 (R), and ATx2761 x RTx2767 (R). The Natural Infestation and Stepwise Model methods gave similar results: 36-51 spikelets destroyed per ovipostiting midge on the susceptible and 9-13 on the resistant hybrids. The Cage Infestation technique resulted in significantly lower numbers of spikelets destroyed per midge: 10-22 spikelets of the susceptible and 4-6 of the resistant hybrids. Oviposition best fit the Poisson with zeroes over six other discrete frequency distributions. Quantity of oviposition at constant temperatures in environmental chambers fit a model based on absolute reaction-rate theory. However, this could not be verified in the field due to lack of sufficient differences in temperature. After the midge reached the adult stage, additional eggs did not mature in its ovaries. Weight of undamaged sorghum kernels was inversely related to percentage of destroyed spikelets in the susceptible hybrid. Results for this characteristic varied in the resistant hybrids. Five percent of the sorghum midge eggs were laid in pedicellated spikelets, and they apparently developed in adult midges with the same relative frequency as eggs laid in sessile spikelets...