Left: Lebia grandis feeding on Colorado potato beetle eggs. D.N.Ferro
Right: Ground beetle larva. E. Memmler

By Eric Wellington Riddick USDA, ARS, Biological Control and Mass Rearing Research Unit
P. O. Box 5367, Mississippi State, MS 39762.

Lebia grandis
(Coleoptera: Carabidae)

Lebia grandis  belongs to a large family of beetles containing approximately 40,000 species. The cosmopolitan genus Lebia contains approximately 450 species that are distributed primarily in the tropics. Forty-eight species occur in North America north of Mexico. The life history is known for less than 10 of the North American species. The adults are predators and first instar larvae are parasitoids of chrysomelid beetles.

Appearance

Lebia  beetles are usually colorful as adults and range in size from 2.5 to 14 mm in length, depending on the species. Lebia grandis is the largest species in the genus in North America. Its body length ranges from 8.5 to 10.5 mm. Its head is usually pale (with a reddish tinge) as are its mouthparts, antennae, and thorax. Its abdomen is mostly black with a metallic blue, purple, or sometimes greenish luster to the elytra (wing covers). Its legs are entirely pale with a reddish tinge.

Lebia grandis first instar larvae are pale to tan in coloration, heavily sclerotized (hardened), with well developed appendages, mouthparts and antennae, as is typical for carabid larvae. The body length ranges from 3 to 4 mm and the width is approximately 0.5 mm. The second instar larvae undergo a gradual degeneration of appendages, develop a distended body with much reduced sclerotization (a simple form of hypermetamorphosis), eventually bearing little resemblance to the first instars.

Habitat

Lebia grandis is distributed in the eastern to mid-eastern United States and into adjacent Canada. It has been found inhabiting arable land and its vicinity. It has been found on cultivated potato (Solanum tuberosum) and on horsenettle (Solanum carolinense) on arable land and neighboring open fields. Adults have also been observed on goldenrod (Solidago spp.).

Pests Attacked

Lebia grandis is an indigenous natural enemy of the Colorado potato beetle, Leptinotarsa decemlineata. In fields of cultivated potato, adults are specialist predators of all immature stages of L. decemlineata. However, note that in no-choice feeding trials in the laboratory, L. grandis adults devoured the larvae of the asparagus beetle (Crioceris asparagi). [Neither adults nor larvae of C. asparagi are known to feed on potato plants.] L. grandis larvae are specialist ectoparasitoids of L. decemlineata mature larvae and pupae in the soil.

Lebia grandis has not been found in association with L. decemlineata on its ancestral host plant (Solanum rostratum) in central Mexico. It is conceivable that L. grandis was historically a specialist enemy of the closely related Leptinotarsa juncta on horsenettle in the southeastern United States.

Life Cycle

Adults are diurnal under ideal conditions of high humidity and high temperature in late spring and summer in Maryland, USA. They have been seen on the upper-most foliage of potato plants feeding on the larvae of the Colorado potato beetle in Maryland. Adults are also nocturnal and have been captured in pitfall traps placed within plant rows during the growing season.

Adults emerge in late May to early June in Maryland, several weeks after the spring emergence of Colorado potato beetles. This ensures that prey (eggs and first to second instar larvae of L. decemlineata) are available for L. grandis adults, especially females, to feed on. It also provides adequate time for females to mate, then oviposit into soil near the base of the potato plants. Eggs are deposited singly into sandy soil. An adhesive substance (a possible secretion from the female's accessary glands) covers each egg as it is laid, causing each to adhere to sand granules and become difficult to detect. A single female L. grandis can lay as many as 1300 eggs in its lifetime.

As first instar L. grandis emerge from the egg stage (within 2 weeks), they are very sensitive to dryness, but fairly-well resistant to drowning. They readily search in the soil for L. decemlineata larvae about to pupate. First instars might follow an odor trail left behind by the L. decemlineata mature larvae, which burrow into the soil just prior to constructing their pupation chambers. In order to insure successful parasitism, L. grandis first instars must locate the L. decemlineata larvae before they seal their pupation cells. Apparently, L. grandis have a difficult time penetrating the sealed cells.

Once locating the host, the first instar larva attaches to the integument (skin) of the host with its mandibles and begins feeding. After molting, the second instar L. grandis larva does not resume feeding. Metamorphosis to the pupal stage occurs soon thereafter, without any period of diapause. At 25°C, the adult emerges from the soil within 3 weeks from when it began feeding on its host. Two generations of L. grandis are probably produced each year in many populations in the southeastern United States. Adults overwinter beneath the soil surface in or near potato fields.

Effectiveness

L. grandis have been considered by some to be the most promising indigenous enemy of L. decemlineata in North America. No large scale field studies have been conducted to date. Under field conditions, L. grandis could be an effective predator/parasitoid of L. decemlineata on normal potato, when used in combination with other control strategies.

Foliar applications of Bt are probably compatible with the action of L. grandis. However, natural densities of L. grandis will not be great enough to effect control of this pest. Thus, augmenting the populations by releasing mass reared adults is one potential method for maximizing the effectiveness of this enemy of L. decemlineata. However, previous rearing experiments have resulted in only limited success in mass-producing L. grandis.

Conservation

In fields of normal (non-genetically engineered or transgenic) potato, the judicious use of pesticides will help conserve carabid populations. Timing of pesticide applications prior to spring emergence of adults would also help reduce unintentional killing of these natural enemies.

The growing of transgenic potatoes (containing the delta endotoxin derived from the bacterium, Bacillus thuringiensis ssp. tenebrionis) that confer resistance to attacks from adults and larvae of the Colorado potato beetle presents a unique challenge to the conservation of L. grandis. In pure stands of transgenic potato, L. grandis adults will not persist due to the low availability of prey to feed on. This problem is magnified due to the fact that L. grandis larvae will not have its hosts, L. decemlineata mature larvae and pupae.

Pesticide Susceptibility

As far as known, Lebia grandis adults and larvae can be killed by organophosphate, carbamate, or pyrethroid insecticides when contacting residues on the ground or foliage of potato plants. However, spray formulations of Bt are probably much less harmful.

Commercial Availability

Not available commercially at this time.

References

Bousquet, Y. and A. Larochelle. 1993. Catalogue of the Geadephaga (Coleoptera: Trachypachidae, Rhysodidae, Carabidae including Cicindelini) of America north of Mexico. Mem. Entomol. Soc. Canada, 167.

Capogreco, J.V. 1989. Immature Lebia viridis Say (Coleoptera: Carabidae): bionomics, descriptions, and comparisons to other Lebia species. Coleopts. Bull. 43: 183-194.

Chaboussou, F. 1939. Contribution à l'étude biologique de Lebia grandis Hentz, prédateur américain du Doryphore. Ann. Épiphyt. Phytogén. (N.S.) 5: 387-433.

Groden, E. 1989. Natural mortality of the Colorado potato beetle, Leptinotarsa decemlineata (Say). Ph.D. dissertation, Michigan State University, East Lansing.

Hemenway, R., and W.H. Whitcomb. 1967. Ground beetles of the genus Lebia Latrielle in Arkansas (Coleoptera: Carabidae): ecology and geographical distribution. Proc. Ark. Acad. Sci. 21: 15-20.

Jacques, R.L., Jr. 1988. The potato beetles: the genus Leptinotarsa in North America (Coleoptera: Chrysomelidae). Flora and Fauna Handbook 3. E. J. Brill, New York.

Lindroth, C.H. 1969. The ground beetles (Carabidae, excl. Cicindelinae) of Canada and Alaska. Part 6. Opuscula Entomol. Suppl. 34: 945-1192.

Logan, P.A., T.H. Casagrande, T. H. Hsiao, and F. A. Drummond. 1987. Collections of natural enemies of Leptinotarsa decemlineata (Coleoptera: Chrysomelidae) in Mexico, 1980-1985. Entomophaga 32: 249-254.

Madge, R.B. 1967. A revision of the genus Lebia Latreille in America north of Mexico (Coleoptera: Carabidae). Quaest. Entomol. 3:139-242.

Mena-Covarrubias, J., F.A. Drummond, and D.L Haynes. 1996. Population dynamics of the Colorado potato beetle (Coleoptera: Chrysomelidae) on horsenettle in Michigan. Environ. Entomol. 25: 68-77.

Riddick, E.W., G. Dively, and P. Barbosa. 1998. Effect of a seed-mix deployment of Cry3A-transgenic and nontransgenic potato on the abundance of Lebia grandis (Coleoptera: Carabidae) and Coleomegilla maculata (Coleoptera: Coccinellidae). Ann. Entomol. Soc. Am. 91: 647-653.

Riddick, E. W. Unpublished data.

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