Download Convergent Lady Beetles

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The Convergent Lady Beetle
Introduction
Throughout the world the lady beetle has been a symbol of good luck.
American pioneers believed that it was good luck to have the lady beetle
hibernate inside their log cabins. The Swedish believe that the number of
spots on a lady beetle is an omen prophetic of the coming harvest—fewer
than seven spots predict a good harvest, while more than seven foretell
famine. Some Greeks believe that finding a lady beetle inside the house
predicts the birth of a son; killing the beetle results in the child being born a
girl. In Yugoslavia, the beetle is the bearer of good news. Other mystical
properties associated with these insects include warning of danger and
forecasting of weather. To some, the beetle is also a love oracle and a
bringer of new clothes. The truth about lady beetles is that, while they
cannot predict the future, they do bring “good luck” to man in the sense that
they feed on a number of insect pests injurious to crops.
The Coccinellidae
The common names lady beetle, ladybird beetle, ladybird, and ladybug
actually refer not to one, but to several species of beetles in the family
Coccinellidae (from Gk kokklvos, meaning scarlet and referring to the color of
the adults of some species). The Coccinellidae is a large family containing
about 3000 species. Some coccinellids are serious crop pests (e.g., EpiIachna
varivestis, the Mexican bean beetle); however, most are predacious and are
considered quite beneficial. The vedalia lady beetle, Rodolia cardinalis, is a
famous example of the successful use of an insect to biologically control an
insect pest. This predator is credited with saving the citrus industry in
California by controlling the cottony cushion scale.
Morphology
Like many beetles, the lady beetle has hard wing covers known as elytra.
The elytra are actually the first pair of wings which have been modified in
form and function so they no longer resemble wings. The elytra’s function is
no doubt to protect the soft abdomen and underlying second pair of wings.
While in some species (e.g., lady beetle) the elytra can be lifted and used as
airfoils in flight, in many species the elytra are fused into one piece. Such
beetles cannot fly, but probably are better protected.
As is typical of Coleoptera, the mouthparts of the lady beetle are of the
chewing type. The heavy mandibles are well constructed for grasping, killing,
and chewing prey. The majority of lady beetles feed on soft-bodied insects,
particularly aphids and coccids.
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Life Cycle
The convergent lady beetle (H. convergens) is primarily an aphid predator and
has been a popular biological control for aphids since 1912. Its popularity has
no doubt been due (at least partially) to the ease of collecting and storing this
species.
The life span of H. convergens is one year. Eggs, which are laid in the spring,
develop into darkish gray larvae with orange spots. These soft-bodied, carrotshaped, spiny larvae appear quite unlike the round, hard-bodied adults, yet
both have a voracious appetite for aphids. It has been claimed that the
convergent lady beetle is capable of eating more than 50 aphids a day when
actively feeding.
The pupae of H. convergens, as is typical of coccinellids in general, do not
spin cocoons, but are naked. They attach themselves to a leaf by cementing
the tip of the abdomen to the leaf. When disturbed, the pupae have the habit
of lifting the body to a vertical position, then dropping back down again. This
behavior may have a protective function by discouraging predation or
parasitism of the exposed pupae.
During the first week in June, new adult beetles appear. They are active
crawlers and fliers and can disperse nearly 5 miles in as little as 3 days.
Throughout the spring and autumn, adults are abundant in the fields.
However, as winter approaches they migrate to the mountains where they
congregate in large numbers prior to winter hibernation. For example, in the
Sierra Nevada Mountains of California, literally thousands of adult beetles
assemble before moving off to hibernate under nearby leaf litter and stones.
It is from these aggregations that the beetles can be easily collected.
For about 9 months while in the mountains, the adults do not feed but live
off stored fat. The ability to undergo long periods of fasting under cool
temperatures has allowed man to conveniently store H. convergens under
refrigeration (5–8ºC) for months. The beetles that Carolina Biological supplies
can be satisfactorily held in the refrigerator until spring, when they should be
released in the garden. Providing a vial of water and a vial of sugar water,
each with a cotton wick, may help the survival of the beetles during
refrigeration. Beetles received after the last frost but before June should be
released immediately and not stored in the refrigerator. At this time they
have used up their stores of fat and need to begin actively feeding.
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Further Reading
DeBach, Paul, “Biological Control by Natural Enemies”, Cambridge University
Press, London, 1974.
Essig, E. D., “College Entomology”, Macmillan Company, New York,1954.
To order call:
1-800-334-5551 (US and Canada)
336-584-0381 (International)
For technical help call:
1-800-227-1150
Carolina Biological Supply Company
2700 York Road, Burlington, North Carolina 27215
CB130519806