Spot Distribution on Ladybug Elytra

Ladybugs beetles, also called ladybirds or lady beetles, are found all over the world, in the United States alone, there are about 4-5,000 species found. The best known and most common American ladybugs is found from southern Canada to South America, and they are called convergent lady beetle. Convergent lady beetles are sold commercially for aphid control. Ladybugs are small, domed, shiny, oval-shaped winged insects, and they are usually red or yellow with black spots or black with red or yellow spots. North American ladybugs have a range of colors from pale yellow-orange to bright red-orange with or without black spots on the wing cover. Ladybugs are slightly elongated in shape and its length can range from 4-7 mm. The primary purpose of the ladybug’s bright colors is to serve as a warning to its predators. The most common species is the two-spotted ladybug.

The ladybugs have a three-body part that consists of a head, thorax, and an abdomen. The head is small and concealed. It includes a mouth, compound eyes, and antennae. The thorax has a pronotum with grayish spots on it. The pronotum of the ladybug is often confused with the head. The abdomen holds the excretory, reproductive, and digestive system of the insect. The wings of the ladybug are covered by elytra, which are modified wings.

Common name	Scientific name
Convergent lady beetle	Hippodamia convergens Guerin
Fifteen-spotted lady beetle	Anatis labiculata
Nine-spotted lady beetle	Hippodamia sinuata Muls.
Spotted lady beetle	Coleomegilla maculata
Twicestabbed lady beetle	Chilocorus stigma
Two-spotted lady beetle	Adalia bipunctata
Red lady beetle	Cycloneda munda
Seven-spotted lady beetle	Coccinella septempunctata
Asian lady beetle	Harmonia axyridis

The ladybug’s life cycle depends on the temperature, humidity, and food supply. The average life cycle (from egg to adult) requires three to four weeks. If the temperature is cooler, the life cycle can last up to six weeks. In the spring, after a long hibernation, the ladybugs find food, mate, and the females lay fifty to three hundred eggs in an aphid colony. The eggs, usually bright yellow and laid in clusters of about twenty on the undersides of the leaves, hatch in three to five days. The larva that hatches from the egg is small, elongated, flattened and has three pairs of legs. The matured larva is mostly black to dark bluish-gray, with a prominent bright yellow-orange patch on the sides of abdominal segments. When the larvae mature, they attach themselves to a plant leaf or stem, and their skins splits open, exposing the pupa. The pupa is about the size of an adult ladybug, but it is wrapped up to protect the ladybug while it is undergoing metamorphosis. An adult ladybug emerges in several days (usually seven to ten days) depending on the temperature. Development from egg to adult may take only two to three weeks depending on the location of the eggs, availability of prey, and the time of year.

Ladybugs are predators of aphids and other soft scales insects, such as mealybugs, mites (which are garden pests), and other insects that are harmful to plants. Ladybug larvae can eat up to twenty-five aphids a day, and an adult ladybug can eat up to fifty aphids. Three hundred aphids are eaten by adult ladybugs before it lays eggs. In the ladybug’s lifetime, five thousand aphids are eaten. Ladybugs have poor eyesight, and they have to almost touch the aphids in order to detect them. Once they detect aphids, they are immediately consumed. The ladybugs respond positively to light and negatively to gravity and intensify search behavior when aphids are encountered. Adult ladybugs are fairly resistant to starvation.

Ladybugs aggregate from few to several hundred to hibernate in autumn. They may aggregate in at the base of a tree, along a fence row, under a fallen tree, or under a rock. They are sometimes found under leaves where they are protected from the cold winter temperatures. Some congregate in and around buildings to keep warm.

In October, one hundred and forty-four ladybugs were collected from the Brown Library at Bellarmine University where they were found congregating by the windows in the southwest stairwell. We counted the number of spots found on both left and right elytra of the ladybugs, and determined whether or not there was a correlation between the spots on the elytra.

Number of Spots	Left	Right
0	18	15
1	6	7
2	3	5
3	8	8
4	7	9
5	9	6
6	12	12
7	14	15
8	24	24
9	42	44

Chi-square results show that the fit is good, meaning that there is a similarity between the left and right elytra spots. By comparing the numbers of the correlation coefficient, 0.969, it is evident that the number of spots on the left elytra is almost always the same as the number of spots on the right elytra. Observation of the graph shows that less constancy of the wing spots increases as the number of spots decreases. This could be due to the inconsistent fading of the spots on the ladybugs as they age. Other factors that effected the constancy of the numbers are the possibility of several species being included in our count. However, many had the same pattern of nine and nine, which is the spot pattern of the Asian Multicolored Lady beetle, that has been proven to be more aggressive in their hibernation indoors. Because the ladybug beetles were found inside the Brown Library, it makes sense that most of them would be this species.

Beers, E.H., Brunner, J.F., Willett, M.J., and Warner, G.M. (1993) "Orchard Pest