The field trials were conducted at the experimental farm of the Faculty of
Agriculture, Mansoura University, Egypt during the two successive seasons, 2001 and
2002 to investigate the relative susceptibility of three soybean varieties to infestation
with the soybean stem. fly, Melanagromyza cunctans Meigen and to study the
population density of this insect pest together with the role of its associated
paraaitoids. -The effect of 'certain weather conditions on its abundance was also
determined. Certain biological and life' table characteristics of M. cunctans under
laboratory conditions were investigated.Giza 35 and Giza 21 varieties were less susceptible to infestation with M. cunctans than Giza 82.· Me/anagromyza cunctans larvae and pupae had three peaks by dissecting .the soybean stems of all varieties. The abundance of the adults by a sweeping-net indicated that the insect showed two peaks on Giza 82. Moreover, three peaks on Giza 35 and Giza 21 were recorded during 2001 season, whereas, in the second season of 2002, four peaks occurred on Giza 82 and Giza 35. Meanwhile, on Giza 21, the adult stage had three peaks. Three endoparasitoid species were associated with M. cunctans pupae. They were Eurytoma sp., Cryptoprymna sp., and Halticoptera sp. During 2001 season, Eurytoma sp. occurred in a relatively short period from July 19 to September 15 and the highest percentage of 75.0% parasitism was recorded during the fourth week of August on Giza 35. Meanwhile, in the second season (2002), the highest percentage of parasitism was 50.0% in the first week of August on Giza 82. In both seasons of 2001 and 2002, Cryptoprymna sp. prevailed in the period from the third week of June to the end of experiment in the second week of
September. The percentage of parasitism varied from 14.0 to 60.0%, 25.0 to 66.0%,
and 20.0 to 75.0% on Giza 82, Giza 35 and Giza 21, respectively in the first season.
The parasitoid had four peaks on Giza 82 variety, and five peaks on Giza 21 and Giza
35. In the second season, the percentage of parasitism ranged from 14.0 to 75.0%,
25.0 to 60.0%, and 9.0 to 80.0% on. Giza 82, Giza 35 and Giza 21, successively. The percentage of parasitism by Halticoptera sp. in the first season varied from
14.0 to 50.0% on Giza 82,16.0 to 40.0% on Giza 35, and 17.0 to 40.0% on Giza 21.
The parasitoid showed two peaks on the three tested varieties. In the second season,
the percentage of parasitism ranged from 14.0 to 60.0%, 14.0 to 33.0%, and 9.0 to
40.0% on Giza 82 and Giza 35 and Giza 21, respectively. The parasitoid had two
peaks on Giza 82 and Giza 21. While, it had three peaks on Giza 35.The average duration from egg to adult was 18.5 days. The total mortalitypercentage of immature stages reached 44.1%. The longevity of female and malewere 15.75 and 9.7 days. The average number of eggs laid per female was 121.0. inaddition, certain life table parameters were determined.