Journal of Agricultural Science and Sustainable Production (Feb 2013)
Relationship Between Parasitism Rates in Egg Traps and Natural egg Populations of Sunn-pest Eurygaster Integriceps Put
Abstract
Some researchers have been used sunn-pest egg traps for estimating parasitism rates or population changes of its egg parasitoids (belonging to Scelionidae and Encyrtidae). However, quantitative relationships of these data to absolute field counts have not been studied. It is felt so a need for standardizing this method. In this study, it was attempted to discover role of height as well as egg density per trap in catching parasitoids. For this purpose, a factorial experiment at a RCBD basis was run in five blocks with three levels of height (20, 40, and 70cm) and three levels of density (1, 2, and 4 clutches of eggs) in a field in Sharifabad, Varamin. Two observations for each treatment were included in each block. Experiment was repeated in two sequential weeks. Thus a series of egg-traps were placed each time, based on map of design and removed one week later. First trapping was carried out at April 24th and later one at May 1st. Rate of parasitism by Trissolcus vassilievi and T.grandis as well as overall parasitism were compared. In the first trapping, neither height nor density made an effect on parasitism. In second trapping however, it was observed a significant difference in %parasitism by T.grandis between traps placed at 20 and 70 cm, as 10.8% of first one vs. 34.4% of second one was attacked by this species. On the other hand a highly significant difference also was recorded between densities 1, and 2 egg masses, as 12.9 and 37.9% of respected densities was attacked by T.vassilievi. No significant difference was seen in overall parasitism in second time of trapping. Total rate of parasitism was 11.5 and ≈ 50% in two times of trapping respectively. It seems that there was a tendency toward top of wheat plants in T.grandis and in an opposite direction in T.vassilievi. This may be one of the components that separates two species niche and makes their co-existence possible. Significant biases were observed in traps both in parasitism percentage and natural combination of wasps.
