Seasonal abundance of aphid hyperparasitoids in organic greenhouse crops in The Netherlands
Abstract: In this study we present the results of a survey on hyperparasitoid incidence in parasitized aphids among 10 organic growers of sweet pepper on different locations in The Netherlands. Monitoring took place during an entire growing season, from January till November. Parasitized aphids (mummies) were collected from the crop and from banker plants. The parasitoids and hyperparasitoids that emerged from the collected mummies were morphologically identified in the laboratory and the percentage of hyperparasitism was determined per sampling date. The most abundant hyperparasitoid species was Dendrocerus aphidum Rondani. The number of greenhouses infected with this species soon increased from 5 in February to 10 in April and the hyperparasitoids remained present till the end of the cropping season in November. The presence of these hyperparasitoids early in the season indicates that they probably overwinter in the greenhouses. Rates of hyperparasitism caused by this species increased in most greenhouses to 100 % in April-May. The second most abundant species was Asaphes suspensus Walker. The first infected greenhouses appeared in May and the relative abundance of this species increased after summer. In most cases the rates of hyperparasitism caused by this species remained low. The species Phaenoglyphis villosa (Hartig) was only found occasionally. Possible strategies to minimize risks of hyperparasitism are further discussed.