The potato psyllid, Bactericera cockerelli, is a destructive insect pest that affects several important vegetable crops. Known also as the tomato psyllid, this small insect is a concern for commercial agriculture and home gardens. Its ability to damage plants directly through feeding is compounded by its role as a carrier for a plant disease, making its presence in crops problematic.
Identification and Life Cycle
Adult potato psyllids are tiny insects, measuring only 2-3 millimeters long, and resemble miniature cicadas. They possess clear wings held in a roof-like position over their dark-colored bodies, which often feature a distinct white band on the abdomen. When disturbed, these adults exhibit a characteristic jumping or hopping motion before taking flight. Their small size and quick movement can make them difficult to spot without careful inspection.
The potato psyllid life cycle consists of three stages: egg, nymph, and adult. Females lay hundreds of eggs on short stalks along the edges or undersides of leaves. These minuscule eggs are initially white or light yellow, darkening to an orange-yellow color as they mature. Hatching occurs within one to two weeks, depending on the temperature.
Upon hatching, the psyllid enters its nymphal stage. The nymphs are flat, oval, and greenish-yellow, resembling scale insects, and are largely immobile on the undersides of leaves to feed. Nymphs progress through five developmental stages, known as instars, over about three weeks before emerging as winged adults. In warm weather, the entire life cycle from egg to adult can be completed in as little as a month, allowing for multiple generations within a single growing season.
Host Plants and Direct Feeding Damage
The potato psyllid primarily feeds on plants in the nightshade family, Solanaceae. This group includes crops such as potatoes, tomatoes, peppers, and eggplants. The insect uses its piercing-sucking mouthparts to penetrate the plant’s phloem tissue and extract sap. Both adult and nymphal stages feed on the plant, but the nymphs are responsible for the most significant direct damage.
This feeding activity introduces toxins from the psyllid’s saliva into the plant, leading to a physiological disorder known as “psyllid yellows.” Symptoms include the yellowing or purpling of leaves, particularly in the upper portions of the plant. Affected leaves may also curl upwards and appear stunted.
The overall growth of the plant can be inhibited, resulting in a bushy or “rosetted” appearance. In potatoes, this direct feeding damage also affects tuber development, causing them to be small and misshapen, which reduces the marketable yield. If psyllid populations are controlled early, plants can sometimes recover from the effects of psyllid yellows.
Zebra Chip Disease Transmission
The most significant threat from Bactericera cockerelli is its ability to transmit the bacterium Candidatus Liberibacter solanacearum (Lso). This bacterium is the causal agent of Zebra Chip disease. The potato psyllid acts as a vector, acquiring the bacterium by feeding on an infected plant and transmitting it to healthy plants. An adult psyllid that acquires the pathogen remains a carrier for life and can pass the bacterium to its offspring.
In potato plants, the bacterium affects the phloem tissue, disrupting the transport of sugars and starches. This leads to foliar symptoms such as yellowing, leaf curling, and stunted growth, which can appear similar to psyllid yellows. The most definitive symptoms, however, are found within the potato tubers themselves. When infected tubers are sliced, they exhibit dark lines, flecks, and streaks in the internal tissue.
These internal markings become more pronounced and turn dark brown or black when the potatoes are fried, creating a striped pattern that gives the disease its name. This discoloration makes the potatoes unmarketable for producing potato chips and french fries, leading to entire crops being rejected. The disease also impacts fresh market potatoes and can cause infected seed tubers to fail to sprout or produce only weak plants. In other host plants like tomatoes, Lso infection can manifest as blotchy leaves and reduced fruit production.
Management and Control Strategies
Cultural control practices are the first line of defense to prevent both direct feeding damage and the spread of Zebra Chip. This includes sourcing certified pest-free transplants and seed potatoes to avoid introducing the pest. Removing weed hosts, such as field bindweed and other nightshade plants, can eliminate alternative breeding sites. Maintaining plant health through proper irrigation and fertilization also helps plants better withstand pest pressure.
Biological control can play a supporting role in managing psyllid numbers. Natural predators like ladybugs, lacewings, and some predatory mites feed on psyllid nymphs and eggs. However, in agricultural settings, the populations of these beneficial insects are often not high enough for complete control. In some regions, the introduction of specific parasitoid wasps, such as Tamarixia triozae, is being explored as a more targeted biological control method.
Chemical control is a common strategy for managing potato psyllids, particularly in commercial production. A variety of insecticides are labeled for use against psyllids on vegetable crops. For safety and effectiveness, all label directions, including application rates and timing, must be followed. The rotation of insecticides with different modes of action is also recommended to help prevent the development of insecticide resistance.