Population trend of canola aphid, Lipaphis erysimi (Kalt.) (Homoptera: Aphididae) and its associated natural enemies in different Brassica lines along with the effect of gamma radiation on their population

Studies regarding the determination of population trend of Lipaphis erysimi (Kalt.) and its associated natural enemies in different Brassica lines along with the effect of gamma radiation on their population were conducted at Agricultural Research Farm, Malakandher, Khyber Pakhtunkhwa Agricultural University, Peshawar during spring 2007. Three different Brassica lines F6B3, F6B6 and F6B7 were used, which were replicated four times in Randomized Complete Block Design. The data revealed that aphid infestation invariably started in all three varieties during last week of February 2007 (1st observation). The peak population of 4.39 aphids per leaf was recorded during 2nd week of March and lowest population of 1.02 aphids per leaf was recorded during 5th week of March. The species of lady bird beetle (Coccinella septempunctata) and syrphid fly (Syrphus balteatus) first appeared on 24th February with a mean number of 0.40 lady bird beetle per leaf and 0.87 syrphid fly per leaf, respectively. At the time when aphid population started to increase the peak population of C. septempunctata (0.70 lady bird beetle per leaf) and S. balteatus (1.04 syrphid fly per leaf) was recorded on the 2nd week of March. Chrysoperla carnea appeared in the 1st week of March and their peak population was recorded during the 3rd week of March with mean population of 1.46 C. carnea per leaf. Among all the Brassica lines, F6B7 showed comparatively more resistance as compared to F6B3 and F6B6. F6B3 showed least resistance against L. erysimi, which was found to be the most susceptible cultivar. F6B7 was also found superior in terms of natural enemies. Maximum number of all natural enemies was recorded on this variety followed by F6B6. Lowest number of natural enemies was recorded in F6B3. No significant effect was recorded for the effect of gamma radiation on the population of aphids, natural enemies and on the varieties.