To keep in the spirit of Halloween, I wanted to talk about a beneficial insect with orange and black coloration. The first to come to mind is the multi-colored Asian lady beetle, Harmonia axyridis. Both the coloration and the timing (now) that they move into homes and other structures have also earned this beetle the name “Halloween beetle”.
The multi-colored Asian lady beetle is the most common lady beetle I observe in managed and natural ornamental environments. The multi-colored Asian lady beetle is native to eastern Asia and was brought to the U.S. in 1916 to control aphids in food crops. At first, they did not establish well. Around 1988, an established population was found in a natural habitat. Since then, they have adapted very well and are now found throughout the U.S.
Adults of are highly variable in color and spot pattern. Their body color ranges from a pale orange to bright red, both with and without spots, and if there are spots their number can vary. One diagnostic feature for all multicolored Asian lady beetles is a dark patch in the shape of an “M” just behind the head on the pronotum. The juvenile stages or larvae are mostly black but with two lateral orange stripes on the middle segments of their abdomen. These larvae resemble tiny, short-snouted alligators with long legs. The larvae take a week or two to develop and then transform into pupae. Within a few days, the adults will emerge from the pupal skin and resume their hunt for aphids or other prey items.
Multi-colored Asian lady beetle adults are generalist predators that have been reported to consume more than 250 aphids each day and the larvae may eat more than 1,500 during their development. Multi-colored Asian lady beetles also will consume scales, a diversity of beetles and caterpillars. They are also omnivorous and feed on nectar and pollen from plants. They are highly beneficial when it comes to reducing populations of aphids. If you don’t spray your roses (or other aphid infested plants) with pesticides, these predators really can do their job well and suppress a pest population.
Not all good beetles are good all the time. In the fall months, as the weather cools, hundreds to thousands of multi-colored Asian lady beetles begin moving indoors to hunker down for the winter. At this time, multicolored Asian lady beetles are referred to as nuisance pests. In addition to their high numbers in buildings, they also produce a defensive compound that has a bad odor which makes them a little nastier when disturbed indoors. The best method to control multi-colored Asian lady beetle as nuisance pests is to prevent them from getting in the first place. Anything that can seal openings in homes will help in their control.
By Paula Shrewsbury, Ph.D., Associate Professor and Extension Specialist, University of Maryland, Department of Entomology. This article was published originally in the University of Maryland TPM/IPM Weekly Report, October 5, 2018.