Abstract
AbstractGreenhouse crops are thought to be simplified ecosystems because they often consist of monocultures that are relatively isolated from their environment. However, insect pests are still able to colonize these protected crops, which threaten their yields. Similarly, natural enemies of pests may be able to colonize greenhouses, providing a form of natural biological pest control. Protected strawberry crops are grown in several types of greenhouses that vary in their degree of openness. Crops often suffer from aphid outbreaks, which can be partly controlled by insect parasitoids immigrating from the surrounding environment. We investigated variations over space and time in both the aphid and parasitoid community diversity and species assemblages associated with protected strawberry crops. We sampled aphids and parasitoids in five regions of France in the spring and summer of two successive years. Despite the relative isolation of these protected crops, we identified a high aphid species richness in them, even at the greenhouse scale. Aphid community composition varied with spatial and temporal factors, but the species assemblages present were mostly determined by local factors. Parasitoid communities were mostly similar among the studied regions, but varied between seasons, with this temporal variation being related to changes in aphid species composition. The study of trophic interactions occurring between aphids and parasitoids allowed the most prevalent and efficient parasitoid species to be identified. The structures of food webs strongly varied in time and space, compromising any prediction of “natural” biological control. We also highlighted ecological factors that can disrupt aphid biological control, such as the occurrence of hyperparasitism or the possibility of apparent mutualism between aphid species. Finally, we showed that the degree of openness of greenhouses influenced both the aphid communities and the hyperparasitism rates in them. These results provide valuable information to improve aphid biological control in protected crops.
Highlights
In agriculture, crops can be cultivated in greenhouses to optimize growing conditions and provide plant protection
Thirteen aphid species were identified, and the majority of aphids belonged to five species: Acyrthosiphon malvae (Mosley; 22.7%), Rhodobium porosum (Sanderson; 16.7%), Macrosiphum euphorbiae (Thomas; 22.8%), Chaetosiphon fragaefolii (Cockerell; 17%), and Aphis gossypii Glover (11.2%)
The aphids we found in strawberry crops, especially M. euphorbiae and A. malvae, can be parasitized by a large range of parasitoid species (Stary 1966, Stary et al 1971, Michelena Saval and Moscardo 1987, Kavallieratos et al 2004, Stary 2006)
Summary
Crops can be cultivated in greenhouses to optimize growing conditions and provide plant protection. Greenhouse crops are often monocultures and held in closed systems, which prevents entry of crop pests from the local environment, and restricts colonization by these pests’ primary natural enemies (Perdikis et al 2011). While it has been suggested that greenhouses are simplified ecosystems, they are still subject to unpredictable species colonization events that may generate complex ecological systems with high variation in species richness, community assemblages, and trophic network. Such ecological variations limit the ability of producers to predict both pest pressure on their crops and pest regulation by natural enemies
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