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Keywords: Applied Sciences
Agriculture & related technologies
Plants injuries, diseases& pests
Insect culture
Issue Date: 2010
Abstract: The biology and population ecology of B. tabaci under field and laboratory conditions were determined in different agro-zones of Sindh province of Pakistan during 2000-2005. The investigations on the biology of the whitefly on musk melon and cucumber in laboratory conditions (30.8±2.13 0 C) revealed that the egg to adult longevity was higher (27.96±2.60 ♀ and 23.63±1.33 ♂ ) days on cucumber than musk melon (29.56±2.59 ♀ and 25.06±1.12 ♂ ) days. However, the fly laid more eggs on musk melon (88.00±7.96). The result of biology under temperature regimes 10, 15,20,25,30 and 35 0 C showed that the highest fecundity and development was recorded at 30 0 C and adult lived longer at 10 0 C whereas at 35 0 C no hatching of the eggs was recorded. Under field conditions, lesser fecundity and more hatching was recorded at 23.31±2.79 0 C than 31.57±4.25 0 C. Investigations on starvation capacity of 1 st instar crawlers indicated that 100% mortality was recorded with in 4.5 hours on dry blotting paper and no mortality was observed on wet blotting paper plus melon leaves. However, the LT 50s differences between moistened blotting paper and green leaf treatments were not significant at 95% confidence limits. Studies on distribution of immature stages on melon leaf showed that the proximal leaf sectors had significantly (P<0.01) more egg-density whereas distal sectors had more nymphal density. The investigations on effect of melon leaf maturity on nymphal mortality revealed that the fly laid more eggs on 3 rd node leaf and maximum nymphal survival percentages (97.65% of 1 st plus 2 nd instars) and (94.69% of 3 rd plus 4 th instars) were recorded on 4 th node leaf, respectively. Maximum adult emergence (95.03%) was recorded on 4 th leaf node. The highest mortality rates (0.102) in eggs, (0.088) in 1 st plus 2 nd instar nymphs on 3 rd node leaf and (0.088) in 3 rd plus 4 th instar nymphs were recorded on 4 th node leaf, respectively. The k-values 0.042, 0.064 and 0.908 were recorded for nymphs of 3 rd , 4 th and 5 th node leaves, respectively. The 3-year life table studies indicated that more than 20% mortality occurred in egg and 1 st instar nymphs and less than 20% was recorded in 2 nd , 3 rd , and 4 th instar nymphs, respectively. Similarly, maximum mean mortality percent (48.30±5.36) in all life stages was brought by the activities of predators followed by EMDFM (13.02±2.26), temperature (12.15±7.91), HFDH (8.30±1.60), parasitism (6.14±1.26), NTDH (3.89±1.20), fungal attack (1.10±0.50), abnormal adults (0.69±0.36) and wind plus rain (0.66±0.62), respectively. Seasonal abundance of parasitoids at Dadu , Tandojam and Thatta revealed that Aphelinid parasitoids, two species of genus Encarsia and three species of Eretmocerus were found parasitizing the nymphs of the whitefly at all agro-zones with parasitoid: whitefly ratios (1.7.93), (1:8.25) and (1:18.33) in spring and in summer as (1:8.26), (1:9.71) and (1:24.41) at Dadu, Thatta and Tandojam, respectively. Studies on sampling and distribution of the whitefly adults revealed that cylindrical shaped yellow sticky trap captured significantly (P<0.01) maximum (22.87 ± 2.69) flies followed by flat and round shape; cylindrical trap at 6  above the ground level caught maximum (14.37 ± 2.02) flies. The highest population (6.56 ± 1.34) per leaf of B. tabaci was recorded on the 2 nd -node leaves. More activity (6.56 ± 1.34 flies per leaf) was xixrecorded at 8.00 a.m. than (4.03 ± 0.83) at 12.00 noon. Studies on preferential distribution on cucurbit and non-cucurbit crops indicated that the population of B. tabaci was significantly (P<0.01) more on cucurbit crops than on the non-cucurbit crops except brinjal. The whitefly population was positively correlated (r=0.66) with the pH of the crops. The results on seasonal population variation of B. tabaci in different agro-zones of Sindh during 2000-2001revealed that musk melon, cucumber and Indian squash retained the highest population of the fly at Thatta in spring and summer followed by Badin, Dadu, Sakrand and Tandojam. Studies further showed that mixed and continuous cropping system favored the activities of the whitefly. It is concluded that musk melon and cucumber equally favored the development of B. tabaci. Temperature at 30 o C enhanced rate of development, starved 1 st instar crawler lived for 5 hours on dry blotting paper, more eggs were laid on proximal leaf sector and maximum nymphs were found on distal sector, maximum k-value was recorded on 5 th node leaves, maximum mortality (dx) was recorded in egg and 1 st inster nymph and the most effective mortality factors (dxf) were predation followed by EMDFM and temperature, higher ratio of parasitoids: whitefly were observed at Dadu and Thatta in spring, cylindrical shaped trap mounted at 6" above ground level gave more catches and the highest adult population of B. tabaci was recorded on the 2nd- node leaves at 8.00 a.m., cucurbit crops and brinjal were preferred hosts and the seasonal population due to mixed and continuous cropping was recorded more in spring and summer seasons than autumn in Thatta followed by Badin, Dadu, Tandojam and Sakrand.
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