First identified in 2008 as a potential pest of soybeans in the United States, trochanter mealybugs (Pseudococcus sp.) have a wide variety of hosts, including corn, sorghum and alfalfa. While their role as a pest of soybean is still not fully understood, it appears that this mealybug has the potential to be a problem in alfalfa and multiple infestations have been reported in southwest Kansas this season.
Trochanter mealybugs are small (~2mm) unarmored, scale insects. They are flattened, whitish, and wax-covered and feed on plant roots removing fluids from the plant with piercing-sucking mouthparts. Due to their small size and life history, they often go undetected. The motionless mealybugs you see with a dense wax coating are all females; large egg sacs are produced under the wax when mature. The eggs hatch and the immature “crawlers” are how the mealybugs disperse between plants. This stage is difficult to control because they can hide in extremely tight spaces. Males, who do not feed, will often go unnoticed as they are smaller, winged and look nothing like the females.
Mealybugs are also moved readily in irrigation water as the waxy covering on their bodies helps them survive being submerged. These insects tend to move the greatest distances with the help of ants. In fact, increased ant activity in infested fields is often noticed before mealybugs are discovered. The ants are tending the mealybugs to eat the honeydew the bugs excrete and in turn the ants protect them from predators.
Plants infested with these mealybugs typically look like they have a potassium deficiency with yellowed leaf margins, stunted growth, and parts of a field may fail to adequately green up. If fields display these symptoms and they cannot be explained by other factors, plants should be dug up and roots examined for the presence of these insects. Again, the presence of ants may be a clue and often small, sunken trails on the soil surface can be found that ants are using to move mealybugs around the field in.
There are no thresholds or control measures for this pest, and it is important to note that their waxy covering would make mealybugs very hard to control with contact insecticides, even when feeding in exposed locations. Crop rotation may help, but this pest can survive on several crop and weed species. Attempts to control the ants in a field would not eliminate the mealybug population.
The distribution of these mealybugs in Kansas alfalfa is not well understood. If you do find trochanter mealybugs in your fields, please do not hesitate to contact your local extension agent. To see pictures of this pest in Kansas alfalfa fields, simply type mealybugs in alfalfa, ksu into your internet browser box.
Information provided by Anthony Zukoff, Extension Entomologist in Garden City.
Stacy Campbell is a Crop Production Extension agent in the Cottonwood District (which includes Barton and Ellis counties) for K-State Research and Extension. You can contact him by e-mail at [email protected] or by calling 785-628-9430.