Ecological studies and control measures of the sorghum midge, Stenodiplosis (=Contarinia) sorghicola (Coq.), (CECIDOMYIIDAE: DIPTERA)in rainfed sorghum

Surveys on distribution of sorghum midge at the rainfed areas of Gedarif, Blue Nile and Sinnar states were carried out during the seasons 2004/05 and 2005/06. In each state, 10 - 20 sites have been selected and surveyed for midge incidence. The co-ordinates Latitude, Longitude and Altitude of each site were marked using the device Global Positioning System (GPS). Results indicated that, the sorghum midge was observed in all areas (sites) in the three states. The incidence of the midge infestation varies between states and even within sites of the same state. The midge damage ranged between 10 - 45 %, 25 - 60% and 5 - 65% at Blue Nile, Gedarif and Sinnar sites respectively. Sudan grass (Adar) was observed in all sites that have been surveyed. In Gedarif, Adar was observed in most sites especially in the southern areas. The effects of temperature, relative humidity, rainfall, associated insects and a natural enemy on midge density experiment was executed at Damazin Research Farm under rainfall conditions. Supplementary irrigation was used to support the crop during the dry season. Data on temperature, relative humidity, rainfall, the numbers of sorghum midge adults, associated insects and natural enemies were recorded throughout the experimental period. Observations on the commencement and the termination of the diapausing larvae and the commencement of the adults emergence were studied. Information on the abundance of sorghum midge adults during the day hours from 6.00 a.m to 18.00 p.m were recorded. The sorghum midge adults were not observed during the period from January to May when the temperature ranged between 27 _ 34 deg C, the relative humidity between 19 - 46% and amount of rainfall ranged between 72 - 86 mm. Emergence of the first midge adults occurred during the 4th week of June to the 2nd week of July (temperature ranged between 27 _ 29 deg C, relative humidity ranged between 65-75% and total amount of rain received before adults emergence between 126 - 163 mm). The peak of midge incidence was observed during the period from the 3rd week of October to 2nd week of November, when the relative humidity ranged between 60 - 80%, the cumulative rainfall was 680 mm and the temperature ranged between 28 _ 31 deg C. Sorghum midge larvae entered diapause during the period from the 4th week of December to the 2nd week of January when the temperature is high ( 34 deg C, relative humidity is low ( 34% i.e. no rains) and the absence of the flowering sorghum panicles. The termination of larval diapausing was observed between the 4th week of May to the 2nd week of June and the commencement of adult emergence was observed between the 2nd week of June to the 1st week of July, (temperature ranged between 26-31 deg C, R.H was 60% and rainfall started 2 - 4 weeks before adults emergence). Population of natural enemies (NE) and associated insects was very low, (ranged between 1 - 4 Individuals/5 panicles for season 2004/05 for both NE and associated insects; 1 - 16 individuals and 1 - 5 individuals/5 panicles for season 2005/06, respectively). Sorghum midge density was higher during the day hours, i.e. between 9.00 - 11.00 a.m., and was very low during the mid day, i.e. between 13.00- 15.00 p.m. Screening for resistance to sorghum midge trial was conducted at Damazin Research Farm, during the rainy seasons 2004/05 and 2005/06. Forty - two sorghum entries including released and local varieties and landraces were planted on August 12 and August 21 season 2004/05, on August 21 and August 31 season 2005/06. Data collected were midge damage rating (MDR), percent yield loss (%YL) and adult midge density. Morphological characters as plant height, days to 50% flowering, panicle type, panicle length, duration of flowering period, and glumes coverage were considered. Results indicate that, entries Wad Ahmed, Dabar 1.1, Gadam EIHamam and Elnar Walaat showed midge damage rating 2.4, yield loss 20%, glume coverage 20% and panicle types of compact and semi-compact, while entries Korab, GadambeIIia Bloom, Bosho, Agbad, Beid Eltimsah, Y urowash, Elgabali, Baladi Malawan and Amanni showed high susceptibility to sorghum midge, ( midge damage rating 8.6, yield loss 80%, glume coverage 60%) and panicle type is loose. The predators Orius, Orius insidiosus ( flower bug) and the spiders are the most important and abundant predators of the sorghum midge. The parasitoids incidence was very low during October, after which the density starts to increase. The peak parasitoids incidence was during November, and decreased very sharp from December onwards. Three hymenopterous parasitoids were collected during this study. One was been identified by Dr. Musa A. Ahmed (ARC Taxonomist) as Aprostocetus sp (Crawford), (Hymenoptera: Eulophidae) and the other two species are unidentified and were sent to National History Museum in UK for further identification