Over the last few years, we’ve heard of 2 or 3 unusual cases of high tunnel tomato producers losing entire crops of their tomatoes, with plants suddenly looking brown and covered in leaf mines/tunnels (Figure 1). After collecting specimens, we’ve confirmed the very hungry and tiny culprit is the caterpillar of the tomato pinworm (Keiferia lycopersicella). The adult stage of this insect is a tiny (~1/4-inch long), drab-colored moth that can be easy to miss, and the caterpillars can be devastating to your crop if they are not detected and managed early.
Figure 1. Symptoms of tomatoes with severe tomato pinworm infestation.
What is the biology and life cycle of the pest? This insect is typically found in Mexico, California, and Texas, where temperatures are warmer year round; however, tomato pinworm is increasingly reported from greenhouses in colder regions, including Delaware, Missouri, Pennsylvania, and Virginia. There is also evidence that tomato fields that are near greenhouses may also become infested. Fortunately for us, this insect does not survive the winter in colder regions like ours because it does not diapause (period of suspended development when insects are inactive), so it relies on a food source year round to sustain development and survival.
The tomato pinworm attacks plants in the Solanaceae (nightshade family); preferring tomato, but some varieties of eggplant and potato may be attacked as well. There are also several weedy plants in the nightshade family that are suitable hosts for the tomato pinworm, including Carolina horsenettle, a common invasive weed in Indiana. This insect can complete its life cycle in as little as 28 days and as many as 67 days. As with many insects, development occurs more rapidly in warmer temperatures than cooler temperatures. The eggs are quite small and laid alone or in groups of three, so they are challenging to spot. Young caterpillars are also small and feed within leaves, creating blotch-like leaf mines (Figure 2). Older caterpillars are easily visible to the naked eye and tie or fold leaves to feed inside (Figure 3). Mature caterpillars drop to the ground and pupate in a loose case of soil particles they build around themselves. The tiny adult moths emerge 2-4 weeks later. There may be as many as 8 generations of this pest each year and importantly generations overlap with each other, leading to infestations growing and reaching damaging levels quickly.
Figure 2. Signs and symptoms of tomato pinworm damage on tomato leaves. Note presence of blotch-like leaf mines, caterpillar frass (poo), and both young and old caterpillars on the same leaf (designated by arrows).
Figure 3. A tomato leaf with edges that have been folded/tied by mature tomato pinworm caterpillars.
What are the symptoms of damage? Small, blotch-like mines on the leaves (caused be the youngest, smallest caterpillars) and leaves that are tied with silk or folded over (caused by older, larger caterpillars). Mature caterpillars may also enter stems or fruits, leaving behind “pin-sized” holes in the latter (Figure 4). Feeding injury to the stems and fruits can lead to secondary infection by plant pathogens, leading to fruit rot and even plant death. Needless to say, this insect is an important one to be on the lookout for!
Figure 4. A tomato with characteristic “pin-sized” holes and frass (poo) caused by tomato pinworm feeding.
What are critical management steps?
- Sanitation is key!! Tomato pinworm infestations are often the result of accidental movement of the pest via shipments of infested fruit, seedlings, creates, or picking containers. Although this insect is not known to survive the winter in field-grown tomatoes in our region, protected environments may extend the activity of this insect.
- For producers growing in greenhouses or high tunnels, it is extremely important to inspect transplants for eggs, caterpillars, or signs of leaf mining as soon as they are received. Continue inspecting transplants throughout the season as they are received, and be vigilant about removing and destroying plant debris that accumulates during and after each tomato crop. Carrying out these critical management steps will help eliminate any life stages (eggs, young caterpillars, or pupae on the soil surface) that may survive unnoticed to infest the next crop.
- Insecticides are effective against this pest; however, they are most effective against the smaller, youngest caterpillars, so it is critical to scout and detect early (and regularly!) to detect infestations before they gain a foothold. Please take care to read insecticides labels carefully to ensure that any insecticide you plan to apply is labelled for use in greenhouse and high tunnel settings. Systemic products that circulate throughout plant tissues, such as coragen (active ingredient: chlorantraniliprole) are most likely to be effective against tomato pinworm caterpillars, because they spend most of their time in protected locations: young larvae feed within leaf mines and older larvae feed within tied or folded leaves. It will be difficult to reach and manage caterpillars feeding in these locations with contact insecticides. Refer to the Midwest Vegetable Production Guide for Commercial Growers, or contact your local university extension specialist for information about current, crop-specific insect pest management recommendations.
- If you are concerned about an insect that you suspect is tomato pinworm, please contact the Purdue Plant and Pest Diagnostic Laboratory and submit a picture or sample of the insect and affected plant parts! They will work with specialists to confirm the identity of the insect!
We hope you’ve had a successful growing season and look forward to sharing important insect pest/activity updates with you next year!