Is leaf pruning the key factor to successful biological control of aphids in sweet pepper?

BACKGROUND Aphids (Hemiptera: Aphididae) are a problematic pest in global sweet pepper cultivation. Control of aphids often relies on insecticides, leading to widespread resistance. Biological control of aphids is mainly based on releasing specialist natural enemies, but they often fail to control outbreaks. Macrolophus pygmaeus Rambur (Hemiptera: Miridae) is a zoophytophagous generalist which attacks several sweet pepper pests, including aphids. Previous research showed that M. pygmaeus is capable of strongly reducing aphid populations in sweet pepper, but complete control was seldom achieved. Sweet pepper plants continue to grow during the season, reaching > 3 m high in Belgian and Dutch greenhouses. Dense foliage and large vertical distance from the flowers to the lower leaves impede the search efficiency of the predator. Leaf pruning may improve aphid predation by M. pygmaeus by increasing the probability of encountering prey. RESULTS Four and five treatments (foliage range: 100 cm to full length) respectively were tested in a semi-commercial sweet pepper greenhouse in 2017 and 2018. Aphid populations in pruned treatments grew more slowly than in the control and M. pygmaeus was eventually able to control aphids in all pruned treatments in 2018. There was no difference in aphid control between the pruned treatments. Sweet pepper production was lower in the treatments with the shortest foliage lengths. CONCLUSION Leaf pruning up to 160 or 190 cm foliage length improves aphid control by M. pygmaeus in sweet pepper without affecting production. (c) 2019 Society of Chemical Industry