The Impact of the Host Plant on the Functional Response Parameters of Diaeretiella rapae (Maclntosh) to Different Densities of Myzus persicae (Sulzer) (Homoptera: Aphididae).

The functional responses of Diaeretiella rapae (Maclntosh) across various host densities of the 2nd instar nymphs of Myzus persicae (Sulzer) were evaluated on three host plants (cowpea, cucumber, and tomato). Experimental results exhibited that the parasitiod attack significantly more individuals of M. persicae on cowpea than other host plants. The percentage of hosts subjected to parasitism by D. rapae decreased as the density of the hosts increased. The functional response of D. rapae on the 2nd instar nymph of M. persicae corresponded to a type II model on all host plants. The specific type of functional response for D.rapae did not alter with changing host plants. The attack rate (a) and handling time (Th) coefficients varied across different host plants. The values obtained for attack rates and handling time differ depending on the type of plant host. D. rapae showed the lowest instantaneous attack rate and the longest handling time on cucumber. Estimated attacking rate values(a) for D. rapae against M. persicae were 0.259, 0.312 and 0.456 on cucumber, cowpea, and tomato, respectively. The shortest handling time was found for cowpea (0.624 h), followed by that for tomato (0.7104) and cucumber (0.7152 h). In all examined host plants, D. rapae exhibited an inverse density-dependent mortality pattern as host density increase. This finding may be regarded as a promising biological control agent for the management of M. persicae. Therefore, introducing parasitoids at the onset of the growing season when host populations are low could enhance the effectiveness of pest management strategies.