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Sudan Journal of Agricultural Research

Effect of ecological factors on sorghum midge, Stenodiplosis sorghicola (Coq.), (Diptera: Cecidomyiidae) population

Fadlelmula, A.A., Mohammed, A.E., and  Khafagi, R.M.

Abstract

“Um Binein 7” (a susceptible variety to sorghum midge) was used to monitor the midge Stenodiplosis sorghicola and the associated biotic and abiotic factors. It was sown under supplementary irrigation during January 2004 to December 2006 at 10 day intervals to provide a continuous flowering. The biotic factors monitored were the panicle inhabiting phytophagous insects, (head bugs, head worms and bees) and the natural enemies (Predators) while the aboitic factors were temperature, relative humidity and rainfall. At 50% flowering, data on midge and the associated insects were monitored daily between 9.00 – 10.00 am, while for temperature and relative humidity a thermograph on daily basis was used to record data and the amount of rainfall was measured by a rain gauge. Supportive laboratory studies were carried to determine the starting and the termination of the diapause larval period through dissection of infested spikelets using a binocular. Threshed, shuttered and infested panicles were stored to record the time for adult emergence using a fine mesh trap. In the field, the appearance of adult sorghum midge was governed by a drop in temperature (27 0C) and an increase in relative humidity (> 60%). A rainfall period of 5-7 weeks was needed prior to the appearance of an adult midge and the peak of adult counts was attained 15 weeks later. The incidence of the associated insects was low. The laboratory studies revealed that the increase in temperature (> 34 0C) and the drop in relative humidity (< 34%) triggered midge larvae to enter into a diapause. The larval diapause was terminated 20 weeks later, when the temperature dropped (< 30 0C) and the relative humidity increased (> 60%). Adult’s emergence from diapaused larvae was recorded two weeks after the larval diapause termination. The temperature was (<28 0C) and the relative humidity was (>75%) and a rainfall periodicity of 4-5 weeks was needed prior to adult emergence.

Sudan Journal of Agricultural Research Vol. 15(2010) PP. 49-60