Possibly the biological pest control agent by excellence, ladybugs have become a staple in the market of insects used to combat plagues, especially for their role in the control of aphids. But ladybugs, the members of the insect family Coccinellidae, can feed on a wide range of plagues that go from caterpillars and beetle larvae (genus Coleomegilla of ladybugs) to mites (genus Stethorus) and whiteflies, thrips, mealy bugs and psyllids. About 90% of the species of this family are beneficial to crops, with the remaining 10% being either neutral or, very rarely, damaging under some circumstances. All of these damaging ladybugs are known to belong to the same subfamily, Epilachninae, however, and so when the ladybugs are used as a biological agent of pest control the species to be released are carefully selected to be entirely carnivorous or almost entirely carnivorous, to make sure that they do not harm the crops that they are supposed to protect.
Two ladybugs: Henosepilachna guttatopustulata (left), a common pest of solanaceous plants, and Coccinella septempunctata (right), a major agent of biological pest control. The ladybugs like the left one comprise less than 10% of all the species of this family.
Since ladybug are predatory both as larvae and as adults, and since some species have adult individuals that overwinter before the first frosts and reemerge on the following spring, the number of damaging insects that one of these can eat is astounding: up to five thousand aphids alone per ladybug. If a thousand lacewings could eat 300,000 of those over a few weeks, ladybugs can eat up to 5,000,000 (yes, that's five million aphids!) over the course of one or two years. This can effectively solve plague problems over the whole growing season, rather than during the limited time in which other agents of biological pest control are in their larvary stage. This also highlights the importance of implementing a conservative model of pest control species introduction, in which the insects are not merely released by the thousands each year, but actually stimulated to establish and reproduce in cropland areas. Since one single ladybug can lay over 300 eggs during her life, establishing a permanent population of ladybugs can really pay up over time.
The life stages of ladybugs. They are highly predatory in both the larval and adult stages.
Common name(s): Ladybugs, ladybeetles, ladybirds.
Often-used species: Depends on the region, native or long-established species are almost always used.
Type of predator: Depends on the species, some are generalist and some are far more specialized.
Potential damaging effects: None registered from any species outside the Epilachninae subfamily.
Interesting literature on its usage: A general overview of these insects (2014), a general review of their usage against soft-bodied insects (2017), a review of the use of exotic species, with an interesting subsection discussing the importance of biodiversity in the landscape to ensure their establishment and efficacy (2020), a review of their use against aphids in particular (2015).