Abstract
Natural enemies have been shown to be effective agents for controlling insect pests in crops. However, it remains unclear how different natural enemy guilds contribute to the regulation of pests and how this might be modulated by landscape context. In a field exclusion experiment in oilseed rape (OSR), we found that parasitoids and ground-dwelling predators acted in a complementary way to suppress pollen beetles, suggesting that pest control by multiple enemies attacking a pest during different periods of its occurrence in the field improves biological control efficacy. The density of pollen beetle significantly decreased with an increased proportion of non-crop habitats in the landscape. Parasitism had a strong effect on pollen beetle numbers in landscapes with a low or intermediate proportion of non-crop habitats, but not in complex landscapes. Our results underline the importance of different natural enemy guilds to pest regulation in crops, and demonstrate how biological control can be strengthened by complementarity among natural enemies. The optimization of natural pest control by adoption of specific management practices at local and landscape scales, such as establishing non-crop areas, low-impact tillage, and temporal crop rotation, could significantly reduce dependence on pesticides and foster yield stability through ecological intensification in agriculture.
Highlights
Numerous pests attack crops causing large economic damage without efficient conventional or biological control[1]
Our study explored the combined effect of parasitoids and ground-dwelling predators on the biological control of pollen beetles in oilseed rape fields (OSR)
Combining an exclusion experiment with pollen beetle sampling over two life stages allowed us to directly assess the importance to pest control of two different natural enemy guilds and the surrounding landscape
Summary
Numerous pests attack crops causing large economic damage without efficient conventional or biological control[1]. Parasitoids and predators can attack a pest during different periods of its occurrence in the field[14], resulting in stronger pest suppression than a single-enemy species[15] This additive effect may be diminished by antagonistic interactions between natural enemies such as intraguild predation[16]. Ground-dwelling predators may exert a considerable pollen beetle mortality in OSR27, 28 as they attack mature larvae when they drop to the soil to pupate, but their actual predation rates have not been assessed In this context, OSR provides an interesting experimental case to better comprehend the strength of pest control exerted by different natural enemies acting on different periods of the pest occurrence in the field. We aimed (i) to quantify the individual and combined effects of ground-dwelling predators and parasitoids on controlling pollen beetle densities in OSR, and (ii) to assess whether biological control efficacy is affected by the surrounding landscape
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