The insect commonly known as the “potato bug” is the Colorado Potato Beetle (Leptinotarsa decemlineata), a major defoliating pest of potatoes and other nightshade plants. Both the striped adult beetles and the reddish, humpbacked larvae feed voraciously on foliage, which can destroy a crop if left unchecked. The species is notorious for developing resistance, having evolved resistance to over 50 different insecticides since the mid-20th century. This widespread resistance has led growers to focus on integrated pest management, making the use of the beetle’s natural enemies an important control strategy.
Insect Predators of the Potato Beetle
Ground beetles, particularly species like Lebia grandis, are effective predators of the Colorado Potato Beetle’s eggs and larvae. They often hunt nocturnally on the soil surface and climb plants to feed. The larvae of L. grandis are unusual, as they are parasitoids that seek out and consume the beetle’s pupae buried in the soil.
Other insect allies include predatory stink bugs, such as the Spined Soldier Bug (Podisus maculiventris). This bug uses its piercing mouthpart to inject enzymes and consume the body fluids of the soft-bodied larvae. Certain lady beetles, including the Twelve-spotted Lady Beetle and the Seven-Spotted Lady Beetle, are effective generalist predators. They primarily target the bright yellow-orange egg clusters and the earliest larval stages of the pest.
Larger Animals that Consume Potato Bugs
Larger animals consume potato beetles, but often with less reliability than insects due to the pest’s defensive characteristics. The Colorado Potato Beetle contains toxic alkaloids called leptines, which serve as a chemical defense mechanism. This toxicity makes the beetle distasteful or harmful to many predators.
Certain domestic fowl, such as guinea fowl and some breeds of chickens, can be trained to forage for the beetles without damaging the potato plants. Guinea fowl are particularly effective, consuming both adults and larvae directly from the foliage. In the wild, amphibians like toads, along with bird species such as starlings and crows, may also consume the beetles or their larvae.
Parasites and Pathogens as Biological Controls
One specific non-predatory control is the parasitic wasp Edovum puttleri. This parasitoid lays its eggs inside the eggs of the potato beetle. The developing wasp larva then consumes the beetle embryo, preventing it from hatching.
Microbial agents, specifically the bacterium Bacillus thuringiensis subspecies tenebrionis (Bt-t), are a commercially available and highly effective option. When consumed by the beetle larvae, the bacterium releases a protein toxin that destroys the lining of the larval gut, leading to paralysis and death. Bt-t is most effective against the young larval stages and does not harm beneficial insects or vertebrates.
Encouraging Natural Enemies in the Garden
Integrating natural controls requires modifying the garden environment to support beneficial organisms. Reducing or eliminating broad-spectrum insecticides is fundamental, as these chemicals kill natural predators and parasites along with the pest. Providing habitat for ground beetles and other soil-dwelling predators can be achieved by applying a thick layer of organic mulch between potato rows.
Planting beneficial insectary plants is another strategy, as they provide nectar and pollen for adult predators and parasitic wasps. Plants like dill, fennel, and sweet alyssum attract Spined Soldier Bugs and various lady beetles, sustaining their populations. Targeted application of biopesticides like Bt-t should be timed to coincide with the hatching of the first and second larval instars, maximizing efficacy.