The Carolina horsenettle is a weed found in field crops, grass pastures, and hay fields. This weed is in the Solanaceae family, which includes tomato, pepper, and potato. The larvae of the false potato beetle (Leptinotarsa juncta) are known to feed on this weed (Figure 1). Last week, many Carolina horsenettle plants were observed in a forage field at the University of Kentucky Research and Education Center at Princeton, KY. The proportion of plants being attacked by the false potato beetle was low (9%) and the number of larvae per plant varied from 1 to 8.
How to avoid confusing these potato beetles
It is not hard to guess that the false potato beetle received its name due to its resemblance to the Colorado potato beetle (Leptinotarsa decemlineata), but only the latter is considered a major pest of cultivated solanaceous crops (see more details here). However, differences in larvae and adult insect appearances, along with host range, can be helpful in correctly identifying these two similar insects.
Larvae
The larvae of these two beetle species are hump-backed and can be misidentified. Nonetheless, larvae of the false potato beetle is paler compared with larvae of Colorado potato beetle. In addition, the false potato beetle larvae have a single row of black dots along the sides of their bodies, whereas the Colorado potato beetle has two rows of black dots (Figure 2).
Adults
The adults of both beetle species display very similar color patterns, shape, and size; thus, they can easily be mistaken for each other (Figures 3). However, the easiest way to identify both species is by looking at the five black lines along each of the hard wings (elytra), counting from the middle to the edge. The 3rd and 4th black lines on the false potato beetle merge at the tip of the wing, whereas on the Colorado potato beetle, these two bands are not merged (Figure 4). Also, the field characteristic to separate the adults is whether the third light-colored stripe is white (Colorado potato beetle) or orange (false potato beetle). Moreover, the punctures along the wings can be useful to identify these beetles: punctures are aligned on the false potato beetle and scattered on the Colorado potato beetle.
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Host preferences
The Colorado potato beetle is a severe pest of potato, but also feeds on tomatoes and eggplants. Colorado potato beetle has a worldwide distribution, and growers may be concerned with false potato beetles attacking their crops. However, these two species have some differences regarding their host plant preferences. The false potato beetle is usually found feeding exclusively on horsenettle (Solanum carolinense), black nightshade (Solanum nigrum), and ground cherry (Physalis spp.). Although it can feed on potatoes, it cannot complete its life cycle on this host. Also, the false potato beetle can be a significant pest of eggplant in Kentucky.
More information
- Jackes, R. L. 2000. Colorado Potato Beetle & False Potato Beetle. University of Florida. link
- Colorado Potato Beetle Management (ENTFACT-312)
By Armando Falcon-Brindis, Entomology Research Associate, Raul T. Villanueva, Entomology Extension Specialist, and Avery Ritchey, Entomology Summer Intern
Kentucky Pest News 