Seasonal abundance of parasitoids on whitefly Bemisia tabaci in melon crops at three different locations of Sindh, Pakistan

Seasonal abundance of Bemisia tabaci parasitoids was assessed on melon leaves at different locations of Sindh, Pakistan, i.e. Dadu, Tandojam and Thatta, in the spring and summer 2006. Two species of parasitoids belonging to genus Encarsia and three species of Eretmocerus (Aphelinidae) were found in melon fields. The overall mean number, 126.66 +/- 8.47 per leaf of whitefly in spring and 137.12 +/- 7.93 in summer with mean number of parasitoids 15.88 +/- 1.32 and 16.16 +/- 3.11 was recorded at Dadu, respectively. Similarly, mean number of the whitey 114.74 +/- 5.87 and 128.42 +/- 7.98 with 6.26 +/- 0.95 and 5.26 +/- 0.80 parasitoids was recorded in spring and summer seasons at Tandojam, respectively. At Thatta, the mean numbers 137.2 +/- 8.46 and 161.9 +/- 7.61 of the whitetly were recorded in spring and summer seasons with 16.6 +/- 0.93 and 16.66 +/- 2.09 parasitoids, respectively. The overall parasitism percentages were 11.74 +/- 2.22, 4.27 +/- 0.86 and 10.41 +/- 1.37 in spring and 12.7 +/- 11.08, 5.48 +/- 0.81 and 12.11 +/- 0.07 in summer at Dadu, Tandojam and Thatta, respectively. The whitefly/parasitoids ratios, 1:7.93, 1:18.33 and 1:8.26 in spring and 1:8.26, 1:24.41 and 1:9.71 in summer were recorded at Dadu, Tandojam and Thatta, respectively. Regression analyses showed that parasitoid population was positively correlated with whitefly population at all the zones in summer season and negatively correlated in spring season only at Tandojam and Thatta. Positive correlation was observed between parasitoid populations and temperature in all the zones in both the season except spring season at Dadu. In response to the relative humidity (RH), the population of parasitoids behaved differently. At Dadu, it was negative with RH in summer, at Thatta in spring and Tandojam in both the seasons. Analysis of variance showed a highly significant difference between zones and seasons (p<0.01). The population of parasitoids was highly significant (p<0.01) between zones. However, it was non-significant between seasons. DMR test showed nonsignificant difference in parasitoid populations at Thatta and Dadu.