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Lebia grandis
(Coleoptera: Carabidae)

By Donald C. Weber, Invasive Insect Biocontrol and Behavior Laboratory, USDA-ARS, Beltsville, MD 200705, and Eric W. Riddick National Biological Control Laboratory, USDA-ARS, Stoneville, MS 38776

Lebia grandis belongs to a large family of beetles containing approximately 40,000 species. The cosmopolitan genus Lebia contains approximately 450 species. Forty-eight species occur in North America north of Mexico. The life history is known for only two of the North American species. The adults are predators, as with many carabid beetles, but larvae are ectoparasitoids of pupae or prepupae (mature larvae) of chrysomelid beetles.

Appearance

Lebia  beetles are 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, 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. 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-western United States and into adjacent Canada. It has been found inhabiting agricultural lands and their surroundings. It has been found on cultivated potato (Solanum tuberosum) and on horsenettle (Solanum carolinense) on arable land and neighboring open fields. Adults also occur on goldenrod (Solidago spp.).

Pests Attacked

Lebia grandis is an indigenous natural enemy of the Colorado potato beetle, Leptinotarsa decemlineata, and the false potato beetle, Leptinotarsa juncta, which is an occasional pest of eggplant. In fields of cultivated potato and eggplant, adults are specialist predators of all immature stages of Colorado potato beetle. In no-choice feeding trials in the laboratory, L. grandis adults consumed the larvae of the asparagus beetle (Crioceris asparagi), and also the three-lined potato beetle (Lema trilinea) but this has never been observed in the field. L. grandis larvae are specialist ectoparasitoids of Colorado potato beetle and false potato beetle prepupae (mature larvae) and pupae in the soil.

Lebia grandis has not been found in association with Colorado potato beetle on this pest’s ancestral host plant (Solanum rostratum) in central Mexico. Because it was described from North Carolina in 1830, it is clear that L. grandis was historically a specialist enemy of the closely related false potato beetle on horsenettle in the southeastern United States, before the Colorado potato beetle adapted to potato and spread into the eastern US. Subsequently, L. grandis adopted the Colorado potato beetle as a new and more abundant host, and is now found as far north as Michigan and southern Maine, north of the range of false potato beetle.

Life Cycle

Adults are primarily nocturnal, but may also be seen during the day under ideal conditions of high humidity and high temperature in late spring and summer in Maryland, USA. Unusual for a temperate-zone carabid beetle, they are adapted to foraging on foliage, as opposed to running along the soil surface.

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 early instar larvae of Colorado potato beetle) 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 (possibly a secretion from the female's accessory 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 several days), they are very sensitive to dryness, but fairly-well resistant to wet conditions. They readily search in the soil for Colorado potato beetle larvae about to pupate. First instars may follow an odor trail left behind by the Colorado potato beetle mature larvae, which burrow into the soil to pupate. How quickly the larvae must find it host, in order to insure successful parasitism, may depend on soil conditions which allow the host to seal its pupal cells.

Once locating the host, the first instar larva attaches to the integument (skin) of the host with its mandibles and begins feeding, all of which takes place during several days of the first larval stadium, killing the host. 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 in 28 days from when it began feeding on its host; below this temperature emergence decreases, and at 17°C, only 2.5% of adults emerged after a mean of 73 days. No adults developed above a constant temperature of 33°C, for which the mean developmental time was 19 days. 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 Colorado potato beetle in North America. No large scale field studies have been conducted to date. However, cage studies support its ability to reduce pest numbers. Under field conditions, L. grandis could be an effective predator/parasitoid of Colorado potato beetle on potato or eggplant, when used in combination with other control strategies.

Foliar applications of Bacillus thuringiensis tenebrionis are 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 populations by releasing mass reared adults is one potential method for maximizing the effectiveness of this enemy of Colorado potato beetle. However, rearing experiments have resulted in only limited success in mass-producing L. grandis.

Conservation

In fields of normal (non-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.

In transgenic potatoes (containing the delta endotoxin derived from the bacterium, Bacillus thuringiensis ssp. tenebrionis) L. grandis adults will not persist due to the low availability of prey to feed on and larval hosts to parasitize.

Presence of L. juncta as alternative prey and hosts, either on horsenettle or eggplant (both are hosts of both species), will tend to conserve L. grandis populations in the absence or scarcity of Colorado potato beetle.

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 Bacillus thuringiensis tenebrionis (Btt or Bt San Diego) are not harmful.

Commercial Availability

Lebia grandis is 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. Memoires of the Entomological Society of Canada, 167.

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

Chaboussou, F. 1939. Contribution à l'étude biologique de Lebia grandis Hentz, prédateur américain du Doryphore. Annales des Épiphyties et de Phytogénetique (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. Proceedings of the Arkansas Academy of Sciences 21: 15-20.

Hentz, N.M. 1830. Description of eleven new species of North American insects. Transactions of the American Philosophical Society 3: 253-258.

Lindroth, C.H. 1969. The ground beetles (Carabidae, excl. Cicindelinae) of Canada and Alaska. Part 6. Opuscula Entomologica Supplementum (Lund) 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). Quaestiones Entomologicae 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. Environmental Entomology 25: 68-77.

Riddick, E. W., and P. Barbosa. 2000. Cry3A-intoxicated Leptinotarsa decemlineata (Say) are palatable prey for Lebia grandis Hentz. Journal of Entomological Science 35: 342-346.

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). Annals of the Entomological Society of America 91: 647-653.

Szendrei, Z., and D.C. Weber. 2009. Response of predators to habitat manipulation in potato fields. Biological Control 50: 123–128.

Szendrei, Z., M.H. Greenstone, M.E. Payton, and D.C. Weber. 2010. Molecular gut-content analysis of a predator assemblage reveals the effect of habitat manipulation on biological control in the field. Basic and Applied Ecology 11: 153-161.

Weber, D.C., D.R. Rowley, M.H. Greenstone, and M.M. Athanas. 2006. Prey preference and host suitability of the predatory and parasitoid carabid beetle, Lebia grandis, for several species of Leptinotarsa beetles. Journal of Insect Science 6:09, available online: http://insectscience.org/6.09 .

Weber, D.C., R.S. Pfannenstiel, and J.G. Lundgren. 2008. Diel predation pattern assessment and exploitation of sentinel prey: New interpretations of community and individual behaviors. Pp. 485-494 in Proceedings of the Third International Symposium on Biological Control of Arthropods, Christchurch, New Zealand, 8-13 February 2009, edited by Peter G. Mason, David R. Gillespie & Charles Vincent. USDA Forest Service Publication FHTET-2008-06, Morgantown, WV, USA.

Weber, D.C., P. Saska, and C.S. Chaboo. 2008. “Carabid beetles as Parasitoids” in Encyclopedia of Entomology, edited by John L. Capinera (2nd edition), Kluwer, Vol. 2, pp. 35-37.

Weber, D.C. Unpublished data.

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