Mostly misidentified insect and mite pests within the greenhouse


Proper identification of insect and mite pests and the plant damage they cause are an important part of plant protection and pest control. Some of the most misidentified insect and mite pests in the greenhouse are mistaken for each other because of similarities in the pest’s appearance or the damage they cause. Here are some of the main culprits.

First, let’s discuss the damage. Because two spider mites (Tetranychus urticae), western flower thrips (Frankliniella occidentalis), and cicadas all have piercing mouthpieces, the damage they cause may appear similar, if not identical.

Two spotted spider mites use their stiletto-like mouthpieces to pierce individual plant cells and feed on them, causing damage to the spongy mesophyll, palisade parenchyma, and chloroplasts. Symptoms of feeding damage include leaves that are bleached and covered in small silver-gray to yellow spots (Figure 1). In addition, the upper surface of the leaf becomes blotchy. Leaves that are heavily infested with spider mites have webbing on the underside along the midrib, and skins (cast) are present (Figure 2). The leaves become bronzed, turn brown, and eventually fall off the plants.

Western flower thrips feed on the mesophyll and epidermal cells of the leaf tissue with a single stylet in their mouth that pierces plant cells. They then insert a series of paired stilettos that tear and damage the cell tissue, allowing western flowering thrips to absorb cellular fluids. Feeding symptoms include a silvery leaf (Figure 3), leaf scars, distorted growth, sunken tissues on the underside of the leaves, and deformed flowers. Black droppings (“thrips poop”) can be found on the underside of the leaves (Figure 4).

Figure 2 – with molting skins and webbing on the underside of the leaf, especially in the case of severe infestation

Western flowering thrips: The upper leaf surface appears silvery (Figure 3) with sunken tissues on the undersides of the leaves.

Black fecal deposits (“thrips poop”) may be present on the undersides of the leaves in the sunken tissue (Figure 4).

eafhoppers: Nymphs and nymph moults are present on the undersides of the leaves, but no fecal deposits (Figure 5).

Mushroom mosquito (left) and bank fly (right) adult on yellow sticky card

Cicadas are another insect pest that can cause plant damage, much like two-spot spider mites and western flower thrips. Leafhoppers feed on the vascular tissue of plants, including phloem (food-conducting tissue) and xylem (water-conducting tissue). Feeding them will cause leaves to appear speckled or bleached. On the underside of the leaf there are nymphs and skins or cast skins of the nymphs (Figure 5). In addition, there are no straps or black feces (“thrips poop”) on the underside of the leaves.

Although plant damage may appear a bit similar on the three pests, you can use a 10x or 16x hand lens and look for the real culprit on the underside of the leaf.

Let us now consider pests with a similar appearance. Although adult fungus mosquitoes and riparian flies may look the same when they are flying around or being present on plants, they look very different.

Adults with fungus gnats (Bradysia spp.) Are winged, about 3 to 4 mm long, with long legs and antennae that resemble a mosquito. In addition, each front axle has a “y-shape”.

Coastal adults (Scatella spp.), On the other hand, resemble a housefly, Musca domestica, except that they are smaller, 3.1 mm long, black, with short legs and antennae. In addition, each front axle has at least five light spots.

For comparison, Figure 6 shows an adult mushroom mosquito and a bank fly trapped on a yellow sticky card.

Still at a loss?
If you still need verification of the proper identification of two-spot spider mites, western flower thrips, cicadas, fungus flies, or bank flies, you can submit specimens or specimens (preferred preferred) to an extender or independent plant diagnostic clinic. Below is a list of educational materials that will help you identify all of the major insect and mite pests that are found in greenhouse production systems:

  • Identification of insects and related pests of horticultural plants (Lindquist, RK and RA Cloyd). 2005.
  • Plant protection: control of greenhouse insects and mite pests (Cloyd, R. A). 2007.
  • Pest Control (Cloyd, R. A). 2016.
  • Integrated pest management for floriculture and tree nurseries (Tricity, SH). 2001.
  • Perennial pests and diseases: the biological approach (Gill, S., RA Cloyd, JR Baker, DL Clement, and E. Dutky). 2006.

Raymond A. Cloyd is Professor and Extension Specialist in Horticultural Entomology / Plant Protection in the Department of Entomology at Kansas State University. He can be reached at 785-532-4750 or