Lady Beetles

Lady beetles (coccinellids) are important predators of aphids worldwide. They are most successful in warm weather (temperature is the main limiting factor to voracity), and are probably most effective when acting in conjunction with other aphid predators. Adults (Plate 153) are fairly resistant to starvation. At times of low prey availability, beetles can switch to other food such as pollen (this ability is more pronounced in some species than others). The eyesight of lady beetles is poor and beetles have to almost touch aphids in order to detect them. Once an aphid is found and consumed, however, the beetle intensively searches the immediate area. In addition, lady beetles respond positively to light and negatively to gravity and intensify search behavior when aphid honeydew is encountered. Since aphids are congregated in colonies in the upper parts of the canopy, this search pattern tends to bring predators in contact with prey. Not all aphids encountered are eaten; however, disturbance by lady beetles may make aphids more vulnerable to attack by other predators. Eggs are bright orange ovals laid on end in groups. Larvae (Plate 154) are multi-colored, often mostly blue with red or orange markings. Pupae may be found on leaves, attached by the narrow posterior end. Adults are usually red or orange with black spots, or black with red spots. There is some variation in spot patterns within species. When larvae hatch from eggs they begin to feed on nearby unhatched eggs and other small larvae. There are usually four instars. The voracity of small larvae is relatively low. First and second instar larvae kill 2-20 aphids per day. Third and fourth instars feed on more aphids, with fourth instars consuming as many or more aphids than second and third instars combined (also more than adults). It is therefore important to have coccinellids completing development in the orchard.

In one Ontario peach orchard study, the twospotted lady beetle, Adalia bipunctata (L.), was found to comprise 54% of all adult coccinellids, 69% of all larvae, but 100% of all fourth instars. Therefore it is one of a small number of lady beetle species to complete development in orchards; this phenomenon has been noted by European researchers as well. This species is only moderately cannibalistic, larvae are gregarious, and there is a low level dispersion of eggs by the female. The twospotted lady beetle is less likely than other coccinellids to leave the trees before the aphids have been controlled. Females possess high fecundity, averaging 30 eggs per batch. These traits combine to produce high predatory efficiency on apple aphid. The twospotted lady beetle overwinters as adults in small aggregations, averaging about 3 beetles per cluster, in tree crevices, house walls, etc. Beetles prefer south-facing walls or crevices. In spring and early summer this species prefers fruit trees; after aphids decline in midsummer, adults spread out to herbaceous hosts as well. The twospotted lady beetle is reddish with a black spot in the middle of each elytron (wing cover). The color pattern is highly variable in Europe, but not in North America. Adults have an oval shape, with the head often hidden past the eyes. The lateral edge of the pronotum (shield between the head and wings) is white. Adults are 14/100 - 1/5 inch (3.5-5.2 mm) long, and 1/10 - 16/100 inch (2.8-4.0 mm) wide.

Other common species in our area include the ninespotted lady beetle, Coccinella novemnotata Herbst; this species is apparently being displaced by an introduced European species, the sevenspotted lady beetle, C. septempunctata (L.). The European species is a valuable orchard predator in Europe; its effect in North American orchards remains to be seen. The former species possesses nine spots on the elytra (four on each elytron with a spot shared near the base of the wings); the latter species has seven spots (three on each elytron with a shared spot). The ninespotted lady beetle is 18/100 - 3/10 inch (4.7-7.0 mm) long, with a rounder shape. There is white on the edge of the pronotum and a pale band between the eyes. This species has a round shape. The head, like that of the twospotted lady beetle, is largely hidden by the pronotum. The head of the sevenspotted lady beetle is black with two separated white spots. Coleomegilla maculata (DeGeer) is a smaller, narrower lady beetle [4.2-16/100 - 1/4 inch (6.6 mm) long and 1/10 - 15/100 inch (2.8-3.8 mm) wide], with six black spots on each elytron (against a pink to red background). This species is highly polyphagous; in fact it is mainly a pollen feeder, although it will take insect prey (mites are a good food source). The convergent lady beetle, Hippodamia convergens Guerin, is a common coccinellid in our area, but prefers field crops and low-growing vegetation. Its head is visible from above. The adult length is 16/100 - 29/100 inch (4.2-7.3 mm) long and 1/10 - 1/5 inch (2.5-4.9 mm) wide. It has two white lines on the pronotum converging toward the rear.

For the last several years, the multicolored Asian lady beetle (see fact sheet) has become the most common coccinellid in our orchards and vineyards. Both adults and larvae may be quite common. This species forages in a wider range of niches than other lady beetles, so could attack a wider range of hosts.  There is substantial variability in the degree of development of spots and intensity of red color. A distinguishing mark is a W- or M-shaped pattern on the pronotum, immediately behind the head. There has been recent interest in trapping to reduce numbers invading houses.  There has been concern over its potential to damage fruit crops, as shown in a Michigan State University link.

Most of the above from a chapter in the Mid-Atlantic Orchard Monitoring Guide, entitled Aphid Predators,
by D. G. Pfeiffer and H. W. Hogmire
E-mail to: Douglas G. Pfeiffer