Predicting Sorghum Midge (Diptera: Cecidomyiidae) Generations and Abundance

Abstract

A total of 39,687 assessments of abundance of ovipositing sorghum midge, Contarinia sorghicola (Coquillett), and sorghum, Sorghum bicolor (L.) Moench, spikelets in flower were used to evaluate, refine, and validate a sorghum midge population dynamics simulation model. Number of spikelets per panicle was related positively to panicle length, with 42% of the variability in the number of spikelets attributable to length. Uniformly growing fields of sorghum were in flower ≤13d. Most spikelets (388.2) per panicle were in flower the seventh day after flowering began in a field. The refined model was used to predict accurately time of sorghum midge emergence in all (mean R2 = 0.83) but one field (R2 = 0.59). However, predictions of sorghum midge abundance varied in accuracy (observed/predicted range of sorghum midges = 0.77-1.21). Predicted time of development of the F1 to F5 generations of sorghum midges ranged from 21.0 to 15.8 d. Abundance of ovipositing sorghum midges increased 2.5-, 3.7-, 24.6-, and 12.6-fold between the P-F1, F1-F2 F2-F3, and F3-F4 generations, respectively, and then declined. Abundance was greatest (22.7 sorghum midges per panicle) in the F4 generation. The economic-threshold level was exceeded during the last days of the F3 generation.