INCIDENCE OF CEREAL APHIDS AND SEASONAL ABUNDANCE OF THEIR PARASITOIDS IN WHEAT FIELDS IN SOHAG (UPPER EGYPT)

Field experiments were conducted at Shandaweel Agric. Res. Station, Sohag, A.R.C. Incidence of cereal aphids and their associated parasitoids on wheat variety Sakha 93 were studied during two successive seasons of 2003/2004 and 2004/2005. Results indicated that wheat plants were infested by 4 cereal aphids as the oat aphid, Rhopalosiphum padi (L.), the greenbug, Schizaphis graminum (Rond.), the corn leaf aphid, Rhopalosiphum maidis (Fitch) and the english grain aphid, Sitobion avenae (F.).
R. padi was the most dominant cereal aphids followed by S. graminum, R. maidis and S. avenae during 2004 and 2005 seasons. The cereal aphids started to appear on January 20th and 25th during 2004 and 2005 seasons, respectively, and their population increased to the maximum level on March 16th and 22nd during 2004 and 2005 seasons. The population then decreased to reach its lowest level on April 6th and 3rd during 2004 and 2005 seasons, respectively, till they vanished completely from wheat plants on April 13th and 10th during 2004 and 2005 seasons, respectively. Five species of aphid parasitoids were identified during the two seasons. Recorded parasitoids were Diaretiella rape (M’Intosh), Praon spp. (Mackauer), Aphidius colemani (Viereck), Aphidius matricariae (Haliday) and Trioxys spp. The first and second parasitoid were the most dominant, however, A. colemani, A. matricariae and Trioxys spp were the least dominant parasitoids. The high percentage of parasitism was noticed in March for the all parasitoids, whereas, the lowest percentage of parasitism was observed in February during both seasons. Regarding seasonal abundance to these parasitoids. D. rape  and P. necans were occurred from the first of February to the end of third week of March during both seasons. A. matricariae was observed from 10 to 15th February to the end of third week of March during two years. However,  A. colemani was noticed from 10-22 February till the third week of March during both seasons. Trioxys spp was distributed with very few numbers from the end of first week of March till the end of this month.
Statistical analysis of multiple regression indicated that parasitoids and plant age, in 2004 season, and parasitoids, maximum temperature and then the age of the plant, in 2005 season played the most important role in controlling cereal aphid populations in wheat fields.