| Abstract: | Data on the population dynamics of the sorghum midge, Contarinia sorghicola (Coquillett), in relation to the anthesis of sorghum, Sorghum bicolor (L.) Moench, were used to validate and refine a model to simulate sorghum midge development. Greater understanding of, and ability to predict, sorghum midge population dynamics in relation to the development and location of sorghum would improve sorghum midge management capabilities. Sorghum hybrid and length of panicle accounted for 47.8% of the variability in the number of spikelets per panicle. Longer panicles bore more spikelets. An individual sorghum panicle required 8 d to complete anthesis. Most spikelets were vulnerable to sorghum midge oviposition on days 3-4 of anthesis. Most spikelets in a field were in anthesis on days 7 and 8. A model to simulate sorghum midge population dynamics was formulated by combining a temperature-dependent poikilotherm development model, a temperature-independent distribution of sorghum midge development times, a distribution of abundance of sorghum spikelets in anthesis in a field, and assessments of daily abundance of ovipositing sorghum midges. The model was used to accurately predict sorghum midge emergence and occurrence of generations. Sorghum midge generation time ranged from 15.8-20.5 d. Abundance increased from no, or few, ovipositing sorghum midges in May to a maximum in mid-July. The static economic-threshold density of one ovipositing sorghum midge per panicle in anthesis was estimated to be exceeded on 27 July, during the last days of the season's third generation of sorghum midges. Wind was the primary determinant of the direction and probably distance of dispersal of sorghum midges. The prevailing direction of morning winds in the Brazos River Bottom shifted from south southeast in May to south southwest in August. Most sorghum midges trapped during late-July and August dispersed toward the northeast, but some dispersed against the prevailing wind direction and toward nearby sorghum. Sorghum midges were trapped >400 m from where they had emerged. The maximum altitude that sorghum midges traversed in passively dispersing between sorghum fields was not determined. |
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