Abstract
As part of my research on the mass production and augmentative release of ladybirds, I reviewed the primary research literature to test the prediction that ladybirds are effective aphid predators in greenhouses. Aphid population reduction exceeded 50% in most studies and ladybird release rates usually did not correlate with aphid reduction. The ratio of aphid reduction/release rate was slightly less for larvae than adults in some studies, suggesting that larvae were less effective (than adults) in suppressing aphids. Some adult releases were inside cages, thereby limiting adult dispersion from plants. Overall, the ratio of aphid reduction/release rate was greatest for ladybird adults of the normal strain (several species combined), but least for adults of a flightless Harmonia axyridis strain. The combined action of ladybirds and hymenopteran parasitoids could have a net positive effect on aphid population suppression and, consequently, on host (crop) plants. However, ladybird encounters with aphid-tending or foraging ants must be reduced. Deploying ladybirds to help manage aphids in greenhouses and similar protective structures is encouraged.
Highlights
Culturing plants in greenhouses, glasshouses, or hothouses has existed in Europe and Asia since the early 19th century, with expansion into North America and other regions of the world in recent years [1,2,3]
C. sativus glandular trichomes did not negatively affect predation capacity maculata DeGeer did not remain on potted cucumber Cucumis sativus L. plants long enough to of 2nd instar larvae of of other ladybirds, aphid suchA.asgossypii
At a release density of 10 larvae (2nd instars) per replicate pot, with approximately 1000 M. persicae per pot, the density of aphids was reduced by 97%, 98%, and 99% in seven days, due to predation by C. maculata, A. bipunctata, and
Summary
Glasshouses, or hothouses has existed in Europe and Asia since the early 19th century, with expansion into North America and other regions of the world in recent years [1,2,3]. We consider the ladybird beetle’s ability to cause rapid declines in aphid population density (and thereby diverting aphid outbreaks), via repeated ladybird releases or increasing the ladybird release rate, to be an alternative gauge of effectiveness [38,39] in greenhouses and glasshouses. Biotic factors including host plant defenses, ladybird life stage at release, interactions with other predators, aphid parasitoids, and ants could limit ladybird effectiveness. Prior research conducted primarily in the laboratory and in open field settings suggests that host plant defenses could have negative or neutral effects on aphids as well as ladybirds [41]. To compare ladybird efficacy across studies listed, I used the Pearson Product t-test compared the ratio of aphid population reduction/release rate between larvae and adults.
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