Predation Risk Effects of Lady Beetle Menochilus sexmaculatus (Fabricius) on the Melon Aphid, Aphis gossypii Glover

Simple SummaryBiological control is an important method for pest management. Natural enemies not only prey on pests directly but also release predation risk cues to pests, causing physiological and behavioral changes in them, reducing their fitness, and ultimately leading to a decrease in their population.Aphis gossypiiis an important insect pest of melon and many other crops worldwide. This study examined the predation risk effects ofMenochilus sexmaculatus, which is abundant in agricultural areas of southern China, onA. gossypii. The results showed that the presence ofM. sexmaculatussignificantly altered the host preference of the aphids. The longevity of the aphids was shortened, and the reproductive period and offspring production were decreased significantly after exposure toM. sexmaculatusfor 24 h. The enzyme activities of SOD and CAT were increased, and the content of MDA in aphids also showed an increase under the predation risk ofM. sexmaculatus. Through a combined GC-MS and behavioral response experiment, the results showed that alkane compounds may mediate the predation risk. The results will offer an alternative strategy for utilizing these alkanes as repellents to manage aphids.AbstractPredation risk posed by natural enemies can alter pest performance. In our previous study, we foundMenochilus sexmaculatusprovides risk cues to melon aphids, resulting in increased numbers of winged aphids. However, the effects of predation risk on multiple traits including behavior, physiology, growth rate, and reproductive capacity of pests are not clear. This study examined the effects of predation risk on host preference, the activities of two important defense enzymes (CAT and SOD), longevity, and offspring production. The Y-tube trial results showed that the risk ofM. sexmaculatussignificantly altered the host preference of the aphids, leading to avoidance behavior. When exposed toM. sexmaculatusfor a long period (24 h), the reproductive period and offspring production were significantly decreased, and adult longevity was significantly shortened. The defense enzyme activities of SOD and CAT, as well as the MDA content (which is considered a marker of oxidative stress and cellular damage) in the aphids, significantly increased underM. sexmaculatusrisk. The compounds ofM. sexmaculatusextracted with n-hexane and volatile compounds collected with HS-SPME were analyzed by GC-MS, and when combined with the behavior response experiment, the results showed that the alkane compoundsn-henicosane,n-docosane,n-tricosane,n-pentacosane, andn-hentriacontane may contribute to the impact of predation risk. The results will be helpful in the comprehensive evaluation of the ability of lady beetles to affect the aphid population, and provide new ideas for using these compounds in aphid control.Keywords:Menochilus sexmaculatus;Aphis gossypii;predation risk;host preference;defense enzyme activities;fitness