Background: The cotton aphid, Aphis gossypii Glover (Hemiptera: Aphididae) is an important pest of cotton and horticultural crops globally. In China, smallholder farmers regularly intercrop cotton with garlic or onion. Aside from higher farm-level revenue, cotton intercrops are typified by lower Aphis gossypii abundance than monocrops. So far, the mechanistic basis of this lowered pest pressure has not been empirically assessed.
Results: Field trials showed that Aphis gossypii abundance is lower and (relative) abundance of aphid predators higher in early-season cotton intercrops than in monocrops. Cage trials and Y-tube olfactometer tests further indicated that garlic and onion volatiles repel Aphis gossypii alates. Electrophysiological bioassays and gas chromatography-mass spectrometry (GC-MS) identified two physiologically active volatiles, that is, diallyl disulfide and propyl disulfide from garlic and onion respectively. Next, behavioral tests confirmed that both sulfur compounds exert a repellent effect on alate Aphis gossypii.
Conclusion: Garlic and onion volatiles interfere with Aphis gossypii settling, but do not affect its main (ladybird) predators. Meanwhile, early-season cotton/onion intercrops bear higher numbers of Aphis gossypii predators and fewer aphids. By thus unveiling the ecological underpinnings of aphid biological control in diversified cropping systems, our work advances non-chemical management of a globally-important crop pest. © 2023 Society of Chemical Industry.
Keywords: biological control; cotton aphid; crop diversification; farming system redesign; intercropping; repellent effect.
© 2023 Society of Chemical Industry.