Landscape context does not constrain biological control of Phenacoccus manihoti in intensified cassava systems of southern Vietnam

In this study, we contrasted temporal population fluctuations of P. manihoti, A. lopezi, and associated hyperparasitoids within low- and high-diversity landscapes in Tay Ninh (Vietnam). Across years and landscape types we found 24.8 ± 17.7% (mean ± SD) plants infected with P. manihoti and on average 5.6 ± 5.3 mealybugs per cassava tip. High parasitism levels were attained across both years, with season-long averages of 49.9-52.1% in either low- or high-diversity settings. Hyperparasitism levels were on average 2.8 ± 5.4%, and a total of three hyperparasitoid species were recorded. Cassava age was a significant predictor of P. manihoti incidence, abundance, parasitism rate and hyperparasitism rate. Landscape type significantly affected P. manihoti incidence and hyperparasitism rate (at particular ages), but not P. manihoti abundance or parasitism rate. At the scale of individual cassava tips and entire fields, A. lopezi expressed a strong density-dependent response to P. manihoti during the early season. This work constitutes the first, comprehensive assessment of A. lopezi establishment, parasitism rates, and parasitoid x host dynamics from a key cassava-growing region in SE Asia. Our study underlines how this exotic parasitic wasp effectively suppresses a globally-important insect pest in its newly invaded range, thus providing cost-free, environmentally-sound and lasting control across the developing-world tropics.
Source: Biological Control - Category: Biology Source Type: research