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LADYBIRD BEETLES

Dr. E. F. Legner, University of California, Riverside

(Contacts)

Ladybird beetles are part of a large cosmopolitan insect family, the Coccinellidae, with ca. 252 genera and 3,312

species known as of 1995. They occur in large numbers in most regions, and are the most often encountered of

all predaceous Coleoptera. Important morphological characters of these "ladybird beetles" include a short clavate

antenna; head recessed into prothorax; prothorax conspicuously narrower than elytral bases; tarsal formula 4-4-4,

with the 3rd segment reduced; legs short and stout. The body is usually subhemispherical, the dorsum highly

convex, the venter nearly flat; dorsum smooth. Their color varies from red or orange to black.

Coccinellids are primarily predaceous as larvae and adults, but some species are phytophagous on green plants,

others feeding on fungal spores. In the subfamily Epilachninae, mostly in genus Epilachna, there are several

phytophagous species that cause serious injury to legumes, potato and other crops. Species in the tribe

Psylloborini are fungus-feeders, and one species is coprophagous. Some species live in ant nests, and many feed

voraciously on aphids, mites, scale insects and whiteflies and at times on thrips and other insects. Adults usually

feed on the same prey species as the larvae. The entomophagous species are mainly predaceous on Coccidae,

Aphididae and Aleyrodidae. Several species of Aiolacaria and Neoharmonia are effective predators on all immature stages of some chrysomelids, while

other genera and species favor mites and Chermidae (Clausen 1940/1962). Coccinellidae are important to biological control, and many species have been

successfully imported for the control of pest insects.

Among aphid and scale feeding species, there is frequently a pronounced tendency to vary their diet, so that many will be found at times to feed on

immatures of Hemiptera, Lepidoptera, etc. Some have been known to feed extensively at nectar glands of plants on sap, pollen, fungi, honeydew, etc.

(Watson & Thompson 1933). This is especially obvious during times of normal food scarcity and seems to be a general habit among coccinellids.

Chilomenes vicina Muls. feeds extensively on eggs and young larvae of cotton worm, Prodenia litura F. in Egypt during times of aphid scarcity (Bishara 1

934). Neocalvia anastomozans Crotch consistently preys on the larvae of fungus-feeding Psyllobora, also a coccinellid (Camargo 1937). Both larvae and

adults of Hippodamia tridecimpunctata L. in Japan feed on eggs and young larvae of the rice beetle, Lema oryzae Kuway during June and July, when the

preferred aphid hosts are scarce. This coccinellid is rated as one of the most important natural enemies of that beetle (Kuwayama cited by Clausen, 1940).

The ability to change diet is advantageous because it maintains the species during host scarcity. A definite tendency toward cannibalism in both larval and

adult coccinellids serves the same purpose. Schilder & Schilder (1928) and Balduf (1935) provided early but still valid information on the food habits of

Coccinellidae.

Effective use has been made of Coccinellidae in biological control, both classical and augmentative. The most noteworthy

example is the Australian vedalia beetle, Rodolia cardinalis Muls., to control the cottony-cushion scale, Icerya purchasi

Mask. and other related species in many worldwide areas (see separate discussion under CASE HISTORIES).

Cryptolaemus montrouzieri Muls., an Australian predator of mealybugs, has been effective in reducing heavy infestations

in a number of areas. Because of its size, it seems not too well adapted to prey on sugarcane mealybugs or other of similar

habit which are protected by leaf sheaths. Cryptognatha noidiceps Mshll., from Trinidad and tropical America, was

responsible for most of the complete control of the coconut scale, Aspidiotus destructor Sign. in Fiji. An undetermined

species closely related to Cryptognatha, was imported to Cuba from Malaya in 1930 and was able to control heavy

infestations of the citrus blackfly, Aleurocanthus woglumi Ashby, in just a few months. Azya trinitatis Mshll. was the

most effective of a series of species introduced for the control of Aspidiotus destructor in Puerto Rico (Clausen 1940/1962).

For diaspine scale insect control, coccinellids seem limited by certain physical characteristics of the scale covering.

Species which have been completely or partially control all had a relatively thin and readily penetrated covering. Those scales with very thick and tough

overings, such as Chionaspis, Prontaspis and Lepidosaphes, are relatively free from attack. Coccinellid species that are very polyphagous among the light

scale covering attack group, have been found unable even to complete development when limited to hosts having a heavy covering (Clausen 1940).

Generally, not much effect has been recorded against aphids. However, Flint et al. (1995) report that releases of the convergent lady beetle, Hippodamia

convergens Guerin-Meneville, which are collected in mountain aggregations in California, significantly reduced melon aphid numbers on potted

chrysanthemum and rose plants outdoors. Release rates were quite high, ranging from 34-60 adult lady beetles per potted shrub. This lady beetle is the

least expensive and most widely released aphid predator in the United States. It is unusual because a large portion of its California population migrates

to the mountain ranges when aphid populations in the Central Valley decrease during summer (Flint et al. 1995). The beetles spend the winter in massive

mountain aggregations, taking in water but consuming no aphids. They then fly back to the valley in March when temperatures are warmer. This habit

allows collectors to harvest and package large numbers of the beetles for sale in nurseries and through garden supply catalogs, etc.

Entomophagous Coccinellidae are usually thought of as being wholly predaceous, but certain species are specialized to the extent that they may develop

as solitary external parasitoids. This is found in some species that attack hosts much larger than themselves. Novius limbatus Mats., which attacks all

stages of the very large Drosicha corpulenta Kuw. in Japan, is only a fraction of the size of the adult coccid female. There are times when the egg was laid

under the scale and the resulting larva retained its feeding position on the body venter of a single host until mature and ready to pupate (Clausen 1940/1962).

How effective a coccinellid is in reducing the host population is related to the relationship of the larva to its host. The closer it approaches the habits of a

parasitoid the more effective it is in biological control. Because of this quality, Rodolia is able to bring its host to low densities where it is held permanently.

The egg is laid on the adult Icerya female or on the egg mass, and there is enough food material in the egg output of the one female to carry the larva to maturity.

Therefore, the larva is spared the need to search for food, and the species is able to maintain itself in an exceedingly low host population density. The same

condition operates in species which are effective against diaspine Coccidae and Aleyrodidae, although in modified form. These hosts even when relatively

scarce, are gregarious and thus reduce considerably the necessity of searching for food. The adult beetle is an active flier and finds the food on which its

progeny are to develop prior to oviposition (Clausen 1940/1962).

Aphid-feeding species such as Hippodamia convergens Guer., which also those which attack solitary Coccidae, often find difficulty in locating enough hosts

in a low population to carry them to maturity. They are often effective in reducing heavy infestations, but usually only after crop injury has occurred, and

their value is thus reduced. This may be overcome by spraying the environment with sugar substances that simulate a high host density (see work by

Hagen et al. in section on Manipulation).

There are certain specific adaptations in host relationships that are of interest. Newly hatched larvae of Cryptognatha nodiceps under the covering of mature

Aspidiotus scale usually find a number of eggs which have not be consumed by the parent beetle, and these provide its first nourishment. Following emergence

from under the scale covering, it feeds mostly on 2nd instar larvae, while following the first molt, attack is extended to any stage of either sex of the host (Taylor

1935). Young larvae of Scymnus sieverini Weise feed principally on young scales of diaspine Coccidae, but the nearly full grown larvae prefer eggs. Rhizobius

ventralis Er. larvae, which hatch from eggs laid underneath ovipositing Saissetia females may feed either on the eggs or on the female scale, but those which are

free on the foliage attack only young scales (Clausen 1940/1962).

Adult coccinellids usually attack the same host species that serve as food for the larvae, even though a different stage may be favored. They chew their prey

vigorously and devour all but the harder portions of the body, whereas the larvae usually bite out a hole in the body wall and suck out the fluid contents. In

some cases a marked degree of pre-oral digestion occurs, in which the fluid contents are sucked out and repeatedly pumped back into the prey, thus effecting

a rapid and thorough mixing with the digestive juices (Clausen 1940/1962).

The amount of food consumed is proportional to the predator's size. Clausen (1916) provided feeding records of a number of California coccinellids, which

indicate that the 4th instar larvae of species of average size, such as H. convergens, consume ca. 50 aphids per day and that adult females, if ovipositing, have

very nearly the same capacity. The giant Caria dilatata F. larva of China consumes 400-500 bamboo aphids daily. Bishara (1934) studying Chilomenes vicina

Muls, normally an aphid feeder, found it to destroy up to 22 eggs or 12-15 young larvae of Prodenia litura F. daily during times of aphid scarcity. This same

rate was recorded for Coccinella undecimpunctata L.

Oviposition.-- The kind of host insect attack determines the manner and place of oviposition. Most species that feed on aphids, such as H. convergens lay

their eggs in compact clusters of 10-50, the spindle-shaped eggs standing vertically on the leaf or bark surface. However, Synoncha grandis Thbg. spaces the eggs

at intervals of several millimeters. When attacking aphids on pine and bamboo, Caria dilatata F. places the eggs in two rows, averaging a total of 28 in each group.

When these are placed on pine needles, a mucilaginous ring is formed about the needle a few mm. below the mass of eggs (Liu 1933). This is though to provide a

degree of protection from predators. Coccinellids that feed on red mites and some of the species that attack diaspine scales lay their eggs singly or in small clusters,

and horizontally, in the vicinity of the hosts. However, the latter more often place them singly beneath empty scale coverings, the ovipositor being inserted

beneath the margin, through a feeding hole that was made by the female, or sometimes through a parasitoid emergence hole. This kind of behavior is frequent

among those species attacking scales that have a soft covering such as Aspidiotus destructor and related species. Species of genera Chilocorus, Scymnus,

Cryptognatha, Pentilia and Rhizobius usually oviposit in this manner. Several species that attack Aleyrodidae consistently lay the eggs singly or in pairs

within the pupal cases from which the whiteflies have emerged. In attacking lecaniine Coccidae such as Saissetia oleae Bern., that have a large egg chamber

under the female's body, Rhizobius ventralis and others insert their eggs under the living host adult. The mealybug predators usually lay their eggs abundantly

over the hosts, directly on the dorsum of the female scale or in one of the grooves on the surface of the egg sac (Clausen 1940/1962).

Reproduction.-- Reproductive capacity is usually relatively high, with 1,550 eggs secured by E. K. Carnes (cited by Clausen, 1940) from a female H.

convergens during slightly more than 2 months. Swezey (1905) secured a max. of 944 from Callineda testudinaria Muls. It may be concluded that the aphid

feeding species of genera Coccinella, Callineda, Leis and Hippodamia lay the greatest number of eggs, which ranges from 500-1,000. Those which attack

diaspine Coccidae, Aleyrodidae and red mites produce much less. The oviposition period is quite long, usually exceeding one month. In some cases it has

extended over 3-4 months, but this is usually associated with lower temperatures and food scarcity. Oviposition rate is governed by the same factors, seldom

exceeding 10-12 per day over an extended period even in the most prolific species (Clausen 1940/1962).

Mating usually occurs within 1-2 days after emergence, and fertile eggs are laid 7-10 days later. Older females that have had sufficient time for egg formation

before mating will produce fertile eggs in a much shorter period of time, however. Virgin females of several species have been observed to lay a much smaller

total number of eggs than mated females. However, unfertilized do not hatch, as they do in Hymenoptera. In many cases only a single mating is necessary

to ensure fertilization of eggs deposited during the female's entire lifetime (Clausen 1940/1962)

Developmental Stages.--Eggs of larger aphid feeding coccinellids are uniformly spindle-shaped and yellow or orange-yellow. Species attacking diaspine

Coccidae, Aleyrodidae and red mites have eggs with their poles much more broadly rounded. They may be yellow, white or greenish-yellow, with the chorion

often bearing minute reticulate markings. Eggs of Cryptolaemus montrouzieri are amber in color, those of Rodolia cardinalis are distinctly orange. There

is a noticeable darkening of the eggs as they incubate. Just prior to hatching, the egg becomes almost black in species that have dark colored larvae, while

in others it becomes grayish. Egg color is influenced to a considerable extent by the color of the host insects on which female beetles feed.

Larvae of larger aphid feeding coccinellids, such as Coccinella and Hippodamia, have variable color markings and bear a number of relatively short setae on

their segments. This is also true of many species that attack Coccidae. In Chilocorus and related species, the larvae may bear large, branched fleshy

processes on each segment. Others are white, with delicate setae. Many species of Hyperaspis, Scymnus, Cryptolaemus, etc. bear a heavy covering of

white waxy material, which may be in the form of granules, slender threads, tufts or plates, depending on the species. These are produced as a glandular

secretion. There seems to be a tendency among the species attacking mealybugs and other hosts having a waxy covering to bear a similar covering

themselves. This is the result of feeding on hosts with a high wax content rather than as an adaptation for protection. However, some species developing

on diaspine Coccidae have this heavy waxy covering while others on the same host do not (Clausen 1940/1962). Early work on the morphology and

classification of coccinellid larvae may be found in Böving (1917) and Gage (1920).

Coccinellids usually have 4 larval instars, with exceptions being Pseudonycha japonica Kuris, which Iwata (1932) found to have 5, and Hyperaspis

lateralis Muls. in which the autumn generation has only 3 larval instars contrasted to the normal 4 of the spring generation (McKenzie 1932).

They usually pupate in situ on the foliage or bark at the point where they had fed. However, Cryptolaemus montrouzieri frequently descend the tree

trunk and pupates in masses in sheltered places thereon or in trash on the ground surface. Chilocorus similis and Chilocorus spp. and Cryptognatha

assemble for pupation in large aggregations on the twigs, the lower sides of main branches and the trunk (Clausen 1940/1962). When ready to pupate,

the mature larva fastens the caudal tip of the body securely to the substrate by means of a mucilaginous secretion. Aphid-feeding species generally

cast the final larval exuviae almost completely, and it remains only as a collar or ring about the abdomen base. Rodolia, Cryptolaemus and some species

of Curinus and Scymnus just effect a median split of the exuviae over the anterior body portion (Clausen 1940/1962).

Some Examples of Ladybird Beetles

Key References: