Article

29 October 2004

Asian lady beetles: Do they or don't they?

Richard Haynes

Photos and sketches by the author.

Figure 1. Multicolored Asian lady beetles (Harmonia axyridis).

You bet they pinch!

Sitting in my office-laboratory last spring, I felt what seemed like a pinprick. Brushing at the spot, I saw a little yellowish beetle fly away.

The “attack” was not personal. No skin was broken, though the place smarted for a while. This beetle was probably hunting for moisture after hibernating in the ceiling. It and its relatives were just beginning to stir, and, as the day warmed, a small army of the tiny animals rained down from between the ceiling tiles. The vacuum was busy that day.

My visitors were Harmonia axyridis, Japanese beetles. Sometimes they are called Halloween ladybugs, because they are often seen during this season.

The U.S. Department of Agriculture (USDA) originally introduced these beetles from Japan in 1916 as a biological control agent, but they failed to become established. The USDA tried again in the 1960s. But not until the late 1980s did H. axyridis settle in the South. By what means remains unknown. By the mid-1990s, it had spread far beyond southern state borders.

This aphid-eating beetle is now prevalent across most of the U.S. In some locations it may be replacing certain of the native species. In time, the indigenous beetles will likely adapt to this Asian import, and a more balanced H. axyridis population will result.

Figure 2. The “M” on the pronotum.

Figure 3. Pincher jaw (circled) of lady beetle

The multicolored Asian lady beetle (the entomologically preferred name) was not the first of its kind brought to the U.S. as a biological control agent. That honor belongs to the Australian lady beetle, or vedalia beetle, Rodolia cardenalis (Muls.) that was shipped from Australia to California in 1888. There it successfully attacked the cottony-cushion scale insect that was destroying citrus tree twigs and leaves, along with the citrus industry.

The multicolored Asian beetle (Family Coccinellidae) can have many more colors and spots than lady beetles native to the U.S. Adults range from pale mustard yellow to bright red-orange. Sometimes they are black. They can have from zero to 10 black spots each on elytra (wing cover). A distinguishing feature is the spotted black “M” (or “W”) on the yellow pronotum (head shield) as shown in Fig. 2).

Figure 4. Multicolored Asian Beetle eggs on the underside of a northern red oak leaf Quercus rubra L.

Figure 5. Larva sketch made from an earlier field drawing.

This oval shaped, 6 mm x 5 mm beetle is highly beneficial to all growers, for it has a huge appetite for aphids, scales and many types of harmful plant lice. The literature reports that an adult beetle is capable of consuming up to 250 aphids per day. Each larva can devour up to 1,200 aphids during its 12 to 14 day span, during which four molts occur, the larva growing larger each time.

Figure 6. Lady bird pupa. Notice beginnings of “M” on the nascent pronotum. From a field sketch.

After the final molt, the larva enters an immobile pupal form that typically lasts 5 to 6 days. The pupae can be found on leaves of a variety of ornamental, orchard and forest trees and shrubs.

The life cycle from spring egg hatch to adult requires about a month. Many adult beetles will then live up to two or more years.

In early fall, Asian lady beetles aggregate in large numbers and fly to sunny surfaces. Light colored buildings and walls in full sun are prime attractants. They often become overwintering pests, entering buildings through any crevice and crack they find. Inside, they cluster together within wall spaces, in the voids around windows and doors, or in dropped ceilings.

Lack of prey and cold breezes trigger the hibernation impulse. Geographically, the response occurs around October in northern areas and November to January in southern regions. H. axyridis often returns to the same over-wintering location year after year.

While overwintering, H. axyridis does not do any of the following: (a) lay eggs; (b) cause destruction to its surroundings (unless, of course, it is squashed); (c) reproduce; (d) carry disease; (e) sting.

Figire 7. Underside showing four of the six leg openings.

Figure 8. Underside of lady beetle. Arrows point to the four leg openings into the body.

Even though these beetles are valuable predators, they can be real nuisances. Warm days may find many of them crawling down walls, across ceilings or flying from draperies to counters. Some people may be frightened, and the basic response is to rid the house of them. However, it does no good to flail around, beat or swat at the little creatures.

To smash one is a serious mistake! Destruction of a beetle results in a very foul odor and an ugly, yellow-orange stain that can be difficult to remove, particularly from fabric.

Like many of its kin, H. axydridis “bleeds” from around its leg openings and other body areas if disturbed or frightened. This viscous orangey fluid, which has an offensive odor, is its response to stress or predators.

How best to remove them? Unlimber the vacuum cleaner and suction them into its bag. Then seal the bag and discard into an outdoor trash receptacle.

How does one permanently remove them? Don't ask. They've been living overhead in my place four years now.