Integrating Chemical and Biological Approaches Toward Managing Armored and Soft Scale Insects

Carlos Roberto Quesada Machigua, Purdue University

Abstract

Scale insects are among the most important pests that attack landscape ornamentals, greenhouse plants, forest and urban trees. Armored scales (Diaspididae) are characterized by the waxy covers over their bodies. In contrast, soft scales (Coccidae) lack these covers and are known for honeydew production. Some armored and soft scales are semelparous and lay all their eggs over a course of days. Other species are iteroparous, laying their eggs over the course of several weeks. I studied how differences between armored and soft scales and egg laying strategies could alter efficacy of selected insecticides using scale species. Pine needle scale (Chionaspis pinifoliae) and calico scale (Eulecanium cerasorum) represented iteroparous armored and soft scales, whereas and oleander scale (Aspidiotus nerii) and striped pine scale (Toumeyella pini) represented semelparous species. Efficacy of selected insecticides and their impacts on natural enemies (bifenthrin, chlorantraniliprole, dinotefuran, horticultural oil, imidacloprid, insecticidal soap, pyriproxyfen, spiromesifen, spirotetramat) were evaluated. Finally, I examined susceptibility of two predators, green lacewings (Chrysoperla rufilabris) and the beetle Rhyzobius lophanthae to insecticide residues on oleander scale. Both species of armored scale were susceptible to all insecticides tested when applied to crawler stage. In contrast, bifenthrin and pyriproxyfen were the only insecticides that killed soft scale insects. Also, egg laying strategies altered the efficacy of insecticides. Semelparous scales were more susceptible to single applications of insecticides than those that were iteroparous. Field and laboratory experiments indicated that reduced risk insecticides had a lower impact on natural enemies than broad-spectrum insecticides. Under field conditions, populations of natural enemies were most likely to be reduced when insecticides were applied just as their seasonal abundance began to increase. Rhyzobius lophanthae larvae were more susceptible to pesticide residues than green lacewings. I hypothesize that this was because the chewing habit of lady beetle larvae exposed them to more pesticide residues than the sucking habit of lacewing larvae. Overall, residues of foliar application of systemic insecticides caused higher mortality on R. lophanthae larvae than residues of soil applications. Even though soil applications systemic insecticides were less acutely toxic, they had sub-lethal effects on R. lophanthae larvae.

Degree

Ph.D.

Advisors

Sadof, Purdue University.

Subject Area

Entomology

COinS