A few weeks ago we visited pesky stink bugs and ladybeetles as they attempted to escape the confines of our homes (What comes in must go out). Last week we watched contented flocks of aphids sipping sap from small spireas and roses. As the ladies imbibed, they excreted copious amounts of sweet sticky liquid called honeydew from their derrières. The odors emanating from aphid-ridden plants provide airborne signals to many kinds of aphid hunters. Sugary solutions like honeydew are a food for lady beetles and when present on a plant, beetles tend to hang around and search for aphids. Three weeks ago when I visited the spirea garden almost every stem on each shrub as cloaked in hordes of aphids. This week on my return to the garden nary an aphid was to be found.
Each beetle can lay hundreds of eggs each year of their lives.
This week on my return to the garden nary an aphid was to be found. Hungry larvae of Harmonia axyridis and several other species of lady beetles roamed the bushes feasting on the tiny sap-suckers. Without much stealth or finesse, beetle larvae captured aphids in their jaws and proceeded to munch their hapless prey. Small aphids disappeared in just a minute or two, but large, plump aphids required several minutes to eat. A period of rest often followed before the hunt for aphids resumed. When aphids were not present beetles turned their attention and appetites to each other. A single larva of the multicolored Asian lady beetle may devour 1,200 aphids during the course of development. After forming a pupa on a leaf or stem, the adult beetle emerges in about a week. Adult beetles are also aphid-eating machines and may consume more than 250 aphids daily. Each female beetle may live more than one year and produce more than 700 eggs in a season. This ability to produce so many young with the potential for eating so many aphids makes the multicolored Asian lady beetle one of the premier biological control agents in our gardens. They provide excellent control of aphids in crops like pecans in southern states. In addition to eating enormous quantities of aphids, they devour other pests including adelgids, scale insects, and psyllids. Multicolored Asian lady beetles are exotic insects and not native to the United States. As early as 1916, scientists deliberately attempted to introduce Harmonia axyridis into the United States from their aboriginal home in Asia. We are not exactly sure how or when this lady beetle arrived, but by the mid-1980s, it was firmly entrenched in the southern United States. By 1993, Harmonia occurred in several Mid-Atlantic States, including Maryland. Today Harmonia ranges from Florida to Washington State. Reports abound of people being “bitten” by lady beetles and I confess that I have gotten a small nip every now and then. The “bite” was something less than that of a Doberman and more like a tickle. No break in the skin is a “no foul” in my book. Handling lady beetles can result in the release of a smelly, bitter, secretion that may leave a faint yellow stain on your skin, wall, or curtain. This neat trick is reflex bleeding and it is their way of delivering a nasty surprise to a would-be predator or bug geek. All is not sweetness and light with these exotic aphid eaters. As we know, these ladies can be a nuisance when they invade our homes in the autumn (Ladybug, ladybug, fly away home). Many folks are concerned that this very successful lady beetle may be displacing some species of native lady beetles here in the United States and abroad. However, for the time being, these ladies provide great service in my garden and I welcome them each spring.
References
The interesting articles “Overwintering, phenology and fecundity of Harmonia axyridis in comparison with native Coccinellidae species in Italy” by Bazzocchi, Lanzoni, Accinelli and Burgio and “Measuring and modeling the dispersal of Coccinella septempunctata (Coleoptera: Coccinellidae) in alfalfa fields by Werf, Evans, and Powell served as a references for this Bug of the Week. For more information on multicolored Asian lady beetles, please visit the following web sites.
http://www.nysaes.cornell.edu/ent/biocontrol/predators/harmonia.html
http://ohioline.osu.edu/hse-fact/1030.html
http://www.ars.usda.gov/is/AR/archive/mar95/001030.beetlemagstory.htm