PREDICTING SORGHUM MIDGE (DIPTERA, CECIDOMYIIDAE) GENERATIONS AND ABUNDANCE

A total of 39,687 assessments of abundance of ovipositing sorghum midg e, Contarinia sorghicola (Coquillett), and sorghum, Sorghum bicolor (L .) Moench, spikelets in flower were used to evaluate, refine, and vali date a sorghum midge population dynamics simulation model. Number of s pikelets 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 less-than-or-equa l-to 13 d. Most spikelets (388.2) per panicle were in flower the seven th 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 mid ges = 0.77-1.21). Predicted time of development of the F1 to F5 genera tions of sorghum midges ranged from 21.0 to 15.8 d. Abundance of ovipo siting sorghum midges increased 2.5-, 3.7-, 24.6-, and 12.6-fold betwe en the P-F1, F1-F2, F2-F3, and F3-F4 generations, respectively, and th en 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.