Lethal and Sub-Lethal Effects of Insecticides on the Pink Hibiscus Mealybug, Maconellicoccus hirsutus (Hemiptera: Pseudococcidae)

The pink hibiscus mealybug, Maconellicoccus hirsutus (Green) (Hemiptera: Pseudococcidae) is a pest of many plants, and a new problem on dates in California. The effects of seven insecticides and water on different life stages of this mealybug were studied to identify the best material for control. Water did not have any significant effect on mealybugs, but the insecticide treatments significantly affected all life stages tested. The egg hatch rate ranged from 28.5% to 17.2% for spirotetramat, bifenthrin, flupyradifurone, fenpropathrin, and buprofezin treatments, and was lower for sulfoxaflor (2.8%) and acetamiprid (0.1%). Despite high survival of neonate crawlers in the non-treated control and water treatments, 53.1% and 34.6% survived in the spirotetramat and buprofezin treatments, respectively; survival was zero in the other treatments. Spirotetramat and buprofezin caused very low mortality of nymphs in the first day post-treatment, but mortality significantly increased over time and reached 42.8% and 50.6% by day 6, respectively. The other treatments were highly toxic to the nymphs (79.4-99.4% on day 6). Insecticides also had a significant effect on the feeding ability of nymphs. By day 6 after treatment, 73.9% to 100% of nymphs treated with different insecticides stopped feeding although they were still alive. Insecticides showed no effect on the mortality of adult females, but the percentages of ovipositing females were significantly reduced (51.1% to 10.6%) in all insecticide treatments, except buprofezin, which was not statistically different from water and the non-treated control. In the process of our studies, we identified abnormalities in the appearance of eggs from females treated with various insecticides, and these aberrant eggs are described.