Differences in dispersal abilities between parasitoid species sharing a host may result in asynchronous colonization of host patches and periods of time (delays) when hosts are exploited in the absence of potential competitors. Previous field cage studies showed Eretmocerus mundus Mercet and Encarsia pergandiella Howard were able to coexist for the duration of a field season when released simultaneously and at the same rate on whitefly-infested cotton plants, and interspecific competition did not influence their ability to suppress their host. The objectives of this study were to investigate the effects of time delay and initial population density on the population dynamics of En. pergandiella and Er. mundus and their abilities to suppress Bemisia argentifolii Bellows and Perring. Field cages enclosing cotton plants were inoculated with whitefly adults and treated by releasing Er. mundus and En. pergandiella either in sequence (one before the other), at two release rates (1× or 3×), and both in sequence and at two release rates. The sequence of release alone did not affect parasitoid population dynamics. However, when released at two rates, or in sequence and at two rates, the density of En. pergandiella was higher at the high rate and when released first. Results suggest that early colonization of host patches is favorable to En. pergandiella without a negative impact on host suppression. Results provide insight to explain the observed patterns of establishment and population dynamics of Aphelinid parasitoids assemblages in agroecosystems.
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