Thrips, aphids, planthoppers, leafhoppers, and whiteflies are common pests of specialty crops that are often misidentified. Whether it’s tomatoes or squash, it’s important to know the differences between these insects and what it means to see them on or around your crops. Below, we provide some information and diagnostic tips to identify each of these groups of pests.
Thrips, order Thysanoptera, are tiny insects with slim feathery wings, large dark eyes, and slender bodies. Fun fact, you NEVER have one thrip, it’s one thrips. What can I say, Entomologists are goofy. Often residing in the flowers of common fruit and vegetable crops. Thrips can vary in color, though yellow and black are the most common varieties. Their wings are one of their most recognizable traits— about the length of the insect’s abdomen and covered in a hair-like fringe. Most thrips are small and can be anywhere from 0.5 – 4 mm in length and can be observed with the naked eye for those with strong vision. Thrips have rasping mouthparts that puncture the leaves of plants. They don’t create holes in the plants but rather windows of damage resulting from them feeding by scrapping the layers of leaf tissue. These windows of damage are often surrounded by tiny black dots that are the thrips frass (poop). Typically, thrips’ damage is cosmetic, meaning it can cause some visible damage to the plant or fruit. High populations on vulnerable seedlings can lead to stunted or deformed growth. Aside from cosmetic injury, a major problem with thrips is that they can spread diseases such as Tomato Spotted Wilt Virus (TSMV) or Iris Yellow Spot Virus (IYSV), which can lead to lasting growth problems on targeted plants and unmarketable fruit. The important thing to know about thrips, when it comes to management, is that they spend a portion of their lifecycle in the soil. This results in the need to apply a product to the soil to attack this stage (entomopathogenic nematodes or soil-dwelling beetle and mite predators) or reapply foliar treatments every 5-7 days until the population is under control. The best way to monitor this pest is to hold a piece of paper parallel to the ground and tap the plant material above. The thrips will be dislodged, land on the paper, and are easy to identify by the wiggle motion they use to move around.
Figure 1. Thrips damage on tomato (Photo by Samantha Willden)
Figure 2. Thrips on onion (Photo by Samantha Willden).
Figure 3. Black flower thrips (Photo by John Obermeyer).
Figure 4. Thrips damage and fecal spots on onion (Photo by John Obermeyer).
Aphids, order Hemiptera, family Aphididae, are small, round plant pests. A variety of different colors, including green, yellow, orange, black, purple, pink, and brown, aphids are a very common pest on most crops and can cause extreme damage depending on the species and density on the plant. These insects can be identified in several ways: their pear-shaped bodies, long thin antenna, and their two tailpipes located on the latter end of their abdomen. Most aphids reside on the undersides of leaves, particularly mature ones. Green aphids can often be harder to spot because they can blend into the background. Aphids can be anywhere from 2 – 4 mm long and sometimes have wings, allowing them to travel from plant to plant. In vegetable systems, aphids do not lay eggs. They give live birth to clones, and the young (nymphs) look just like the adults, but only smaller. Aphids are piercing/sucking pests that use a straw-like mouth to tap directly into the phloem of the plant and feed on the sugary plant juices. When populations are high, aphid waste (called honeydew) can drop onto leaves or fruits, rendering them sticky and sometimes infested with sooty mold. This damage can be washed off but will require extra labor. Some aphid species can also spread disease. For example, the potato aphid (Macrosiphum euphorbiae) can vector Potato Virus Y (PVY) which can affect tomatoes, eggplants, and potatoes. Identifying aphid species can be difficult and will require a microscope or hand lens. See this guide for assistance in identifying aphids: https://aphidnet.org. In most situations the species does not matter when it comes to management, however if using parasitoids then proper selection depends on the aphid species (or more importantly, size). In general, management interventions should occur if the aphid populations are increasing on plants. Flag initial infestations and monitor them at least twice weekly to see if they spread.
Figure 5. Melon aphids on cucumber leaf (photo by Samantha Willden).
Figure 6. Honeydew residue and sooty mold on tomato (Photo by Samantha Willden).
Figure 7. Pink and green potato aphid adults, nymphs and shed skin (exuvia) (Photo by John Obermeyer).
Leafhoppers, order Hemiptera, family Cicadellidae, are tiny, often green, insects with an affinity for hopping from leaf to leaf. Though there is quite a bit of diversity in terms of color, size, and patterning, leafhoppers do have a similar shape and some features that allow them to be easily identified. Typically, leafhoppers can be anywhere from 2 – 33 mm in length (larger than both aphids and thrips), and rather slender. Their body is triangular. They have large eyes on either side of their head and apparent spines on their middle and back legs. They jump and move quickly off the plant when disturbed. Their coloration allows them to blend into crops, making them hard to spot. Other colors include yellow, brown, red and black, blue, teal, and orange. Like aphids and thrips, leafhoppers have straw-like mouthparts and feed on plants’ leaves and stems. One of the most common species is the potato leafhopper—about 3 mm in size, bright green, slender, and spikey. Feeding damage by leafhoppers causes yellowing tips of leaves as well as sections of leaves drying out and flaking off. This damage is often called “hopperburn”. This can then lead to stunted growth and potential death of the plant.
Figure 8. Adult Potato leafhopper (Photo by John Obermeyer).
Figure 9. Hopperburn on alfalfa (Photo by John Obermeyer).
Whiteflies, order Hemiptera, family Aleyrodidae, are tiny insects with opaque, round, white wings. Less than 3 mm in size, greenhouse whiteflies, a common species in Indiana, have slight triangle-shaped wings when held together, often yellow heads and medium-length antennae. Whiteflies are one of the leading vectors of plant viruses, however, the major diseases they spread such as Tomato Chlorosis Virus (ToCV) and Tomato Infectious Chlorosis Virus (TICV), are not prominent in Indiana. In the absence of plant viruses, their feeding can cause wilting, yellowing, and stunted growth. In addition to that, their excrement is like aphids in that it can support the growth of sooty mold on your crops. An abundance of whiteflies can lead to lower fruit production and sometimes plant death.
A common misconception is that aphid exuvia (the skin they shed as they grow, which are tiny, white, shed skins, are often misidentified as whiteflies. When comparing an aphid molt to a whitefly, some key characteristics to look for are 1) size and shape, 2) color, and 3) sturdiness. Whiteflies have large wings in comparison to their bodies and round heads. Aphid molts are very skinny, have no wings or wing-like appendages, and have no discernable heads. Coloration is the largest commonality, as both are similar shades of white, however, many species of whiteflies have pale yellow heads which is not a feature that aphid molts have. Lastly, aphid molts are very flimsy, and can often be blown away with the tiniest gust of wind. Even though whiteflies are still incredibly small and dainty, they maintain a level of sturdiness that aphid molts do not have.
Figure 10. Whiteflies on tomato leaf (Photo by Samantha Willden).
Figure 11. Dead whitefly on tomato leaf (Photo by John Obermeyer).
Figure 12. Whiteflies on tomato (left), aphid molts on tomato (right) (left photo by Samantha Willden, right photo by John Obermeyer).
When managing pests on specialty crops, knowledge of insect identification can be helpful in determining how to react to a pest. It is important to have a correct identification, especially if you are interested in using biological control. If you are unsure, send a sample (specimen or image) to the Plant and Pest Diagnostic Lab. When looking for insecticide recommendations, visit the Midwest Vegetable Production Guide.