Host selection behavior of diaeretiella rapae mclntosh [hymenoptera: braconidae] attacking cereal aphids in Upper Egypt

The present investigation was carried out in Assiut Governorate to study the relative abundance of cereal aphid parasitoids and evaluate the host selection and host-instar preference of Schizaphis graminum [Rondani] and Rhopalosiphum padi L. by the braconid parasitoid, Diaeretielia rapae Mclntosh during 2015 wheat growing season

The obtained results revealed that the dominance percentages of the primary parasitoids were so high and presented by 81.53% of the total caught parasitoids* However, the secondary parasitoids showed low dominance percentages and presented by 18.47%

The parasitoids, D. rapae and Alloxysta australiae [Ashmead] revealed the highest dominance percentage and presented by 76.38 and 47.93% of the total collected primary and secondary parasitoids, respectively

The aphid, S. graminum appeared as more relatively preferred for. rapae than K. padi species

The development of D. rapae was found to be possible in any instar of 5. graminum and R. padi

The second and third instars of S. graminum presented the optimal response for D. rapae growth and survival, while the third and fourth instars of R. padi presented the optimal response for parasitization by the same parasitoid species

The averages of the development times from oviposition until the appearance of the mummified aphid were 7.68 and 8.01 days for S. graminum and R. padL respectively. Offspring production per female was high in the adult stage than others. Nymphs parasitized and mummified by D. rapae during the first and second instars may be reach to maturity but not produce any progeny

Resistance of some soybean varieties to bemisia tabaci [genn.] [homoptera: aleyrodidae] and thrips tabaci L. [thysanoptera: thirpdae] in Assiut

The present investigations were conducted at the Experimental Farm of the Agriculture Research Station, Arab-El-Awamer [Abnoub district], Assiut Governorate during 2013 and 2014 soybean growing seasons. The obtained results showed that the populations of T. tabaci and B. tabaci started in a few numbers on all soybean varieties during the first week of July in 2013 and 2014 seasons. The peak populations of these pests occurred during August and/or during September and ranged from 1 to 3 peaks for T. tabaci and from 1 to 2 peaks for B. tabaci according to each variety. Results also indicated that there were highly significant differences in susceptibility between the soybean varieties [F = 7.72 and 18.84 > 0.01] and between seasons [F10.44 and 4.27 > 0.01] for T. tabaci and B. tabaci populations, respectively. The combined effect of the weekly mean of maximum and minimum temperature, average relative humidity and predator populations was responsible for 81.80 % and 87.10 % of the changes in the populations of T. tabaci and B. tabaci during the two seasons of study. Concerning the resistant status of the tested soybean varieties to the whitefly and the cotton thrips, the results showed different susceptibility degrees to these pests. The cultivars H 117, G 22 C 111 and H 32, G 22, C 111 appeared as susceptible [S] to the cotton thrips and the whitefly infestations, respectively. Meanwhile, the cultivars H 117, H 30, Clark and H 117, H 127, H 30 Clark appeared as low susceptible [LR] to the aforementioned pests infestations, respectively

Hymenopterous parasitoids associated with cereal aphids in wheat fields at Assiut

The present study was carried out in Assiut area to investigate the relationship between cereal aphids and their associated parasitoids on wheat plants during two successive seasons, 2011 and 2012. The results indicated that of 48,000 mummified aphids collected from wheat plants in two seasons, 89.69% adult parasitoids were emerged. Ten parasitoid species belonging to five families of order hymenoptera were identified. The primary parasitoid species were recorded, Aphidius colemani Vereck, A. matricariae Haliday, Diaeretiella rapae [Mclntosh], ffptiedrus plagjfator[Ness], Praon necans Mackauer and Trioxyssy., in addition the secondary parasitoids were, AUoxysta Australia [AsbmQandA], Dendrocerus carpenter [Cuitis], Chalclds sp.,and Aphidencyrtus sp. Data show that, Diaeretiella rapae was the most dominant and abundant primary parasitoid species represented 87.99% and 64.35% during 2011 and 2012 seasons, respectively. In spite of aphids, five aphid species namely, Scbhaphis grawinumfiwfaw, Rbopaloslphum pad! L, R. maldls [Fitch.], Sitobion avenae [Fab.] and Metopolophium dlrbodum [Walker] were found attacking wheat plants in Assiut region. Rbopaloslpbum padl and Schizaphls gramlnum were the most dominant and abundant cereal aphids on wheat plants represented [55.55 and 54.41%] and [40.68 and 43.11%] in both two species during 2011 and 2012 seasons, respectively. The maximum population level of cereal aphids was recorded during the 1[st] wk of March [529.0 and 729.0] during the two seasons, respectively. The parasitoids appeared early in the season in relatively low population density but its population fluctuated in high density during the 2nd wk of March [408.0 and 335.6] in 2011 and 2012 seasons, respectively, coincided with the collapse of aphids from wheat field. This work indicated that wheat fields are rich in aphid parasitoid species which of course play a significant role in suppressing aphid infestations