We are seeing a lot of these odd, yet very common, insects in grapes and strawberries during our scouting and research, and I got some questions about what they were. These are lady beetle larvae (Fig. 1) and pupae (Fig. 2) or coccinelle in French. Lady beetles have a complete metamorphosis as they are beetles (Coleoptera) in the family Coccinelidae and the different life stages take very different and unusual shapes (Fig. 3) that can make it hard to connect the immature stages to the adult lady beetles.
There are many different species of ladybug with nearly 6000 species worldwide and almost 500 species in North America. Most of the species are native to North America but some have been either accidentally or intentionally introduced (see below). Lady beetles are beneficial insects that feed on other insects. They prey as larvae and adults on soft-body phytophagous insects (insects that feed on plants) such as aphids, whiteflies, and scale insects that are most often considered pests. During its development, a single lady beetle larva can consume hundreds of preys, thus providing natural biological control of some of our common pests. It is therefore important to preserve these insects in agroecosystems by reducing pesticide use and choosing pesticides that are less toxic to pollinators and beneficial insects. For more information on how to select less toxic pesticides, please see this Oregon State publication or download the app “Reduce bee poisoning from pesticides”.
In some cases, lady beetles can become pests and in fruit that would be the case of the multicolored Asian lady beetle (MALB; Harmonia axyridis; Fig. 4). This species is native to Asia and was introduced repeatedly both accidentally and intentionally for the control of pecan aphids. While MALBs are beneficial when feeding on insect pests earlier in the season, they can become problematic around grape harvest when feeding on grape clusters. They will mainly aggregate where diseases, birds, or other insects have already opened up the berries. They do not cause significant feeding damage, but when accidentally harvested with the grapes, they can taint and spoil an entire batch of wine, possibly causing significant economic loss. When harvested with the clusters, MALBs will emit a bitter chemical compound as a defense mechanism and this compound, 2-isopropyl-3-methoxypyrazine, will affect the taste of the resulting wine if more than one MALB is found in 1 Kg of grapes. To learn more about MALB, please view this previous article. MALBs can also become a nuisance pest when they congregate on and inside homes and other buildings in search of overwintering sites. For more information on what to do to prevent MALBs from entering your home, please visit this article.
Happy growing season!This article was posted in Insects and tagged Christelle Guédot, Grapes, insects, lady beetle, ladybug, multicolored Asian lady beetle, Strawberries.