The cool wet weather seems to have created the perfect conditions for producing record numbers of aphids on many flowering trees and shrubs. In the last episode of Bug of the Week, we learned the plight of rose aphids under attack from the strange larvae of flower flies. These legless maggots stalk, capture, and suck the life from their hapless aphid victims. However, aphid peril does not end here. Other hunters are afoot.
This week on one small rose bush, I discovered roughly a dozen larvae of the multicolored Asian lady beetle and several other species of lady beetles feasting on a serious infestation of rose aphids. Alligator-like larvae roamed quickly over the leaves and stems searching for tasty aphids. Without much stealth or finesse, 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. A single larva of the multicolored Asian lady beetle may devour 1,200 aphids during the course of development. After forming a pupa on the surface of the plant, the adult beetle emerges in about a week. Adult beetles are also aphid-eating machines and may consume more than 250 aphids daily.
Small orange eggs indicate that lady beetle larvae will soon be at work hunting aphids.
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 most effective 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 an exotic insect 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 “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. All is not sweetness and light with these exotic aphid eaters. Many folks are concerned that this very successful lady beetle may be displacing some species of our native lady beetles. In addition, there is that somewhat disconcerting behaviors of entering homes with the approach of winter (see Ladybug, ladybug, flyaway home). Overall, these ladies provide great service in my garden and I welcome them each spring.
References
The interesting article “Overwintering, phenology and fecundity of Harmonia axyridis in comparison with native Coccinellidae species in Italy” by Bazzocchi, Alberto Lanzoni, Gianumberto Accinelli and Giovanni Burgio served as a reference 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