Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/10/2002
Publication Date: 8/1/2002
Interpretive Summary: Aphids can be serious foliage-feeding pests of pecan. We tested a kaolin based particle film, as an alternative to chemical insecticides, against th black pecan aphid in the laboratory to understand how particle film affects this pest species. Applications of this kaolin-based product coats leaves with a white particle film. We found that fewer aphids selected leaves treated with particle than leaves not treated with particle film and hypothesized that visual cues (used by aphids to detect potential hosts) fr treated leaves were inappropriate. Under orchard conditions, aphids genera occur on the lower surfaces of pecan leaves. When adults move to new leave they typically alight on the upper leaf surface and then move to the lower leaf surface. However, in this study, when aphids did move to treated foli or were directly placed onto the upper leaf surface of treated foliage, the percentage of aphids that remained on the upper leaf surface was higher tha athe percentage that remained on the upper leaf surface of control leaves. Microscope observations revealed that body parts became coated with particl film thus inhibiting aphid movement. Even if aphids disperse to leaves treated with particle film, physical properties of the particle film may re the aphids. Since particle film is coverage dependent, sessile pests such aphids may exploit a non-uniform coating. In addition, mortality of aphids treated leaves was greater than on control leaves thus leading to decreased production of progeny by aphids on treated leaves. Light reflectance by treated foliage was increased and absorptance decreased compared with contr foliage whereas transmittance of light through control and particle film treated leaves was similar.
Technical Abstract: Three species of aphids attack pecan, Carya illinoensis (Wang.) K. Koch, and cause economic damage. We tested a kaolin-based particle film against one of these aphid species, black pecan aphid (Melanocallis caryaefoliae [Davis]). Effect of particle film on host selection, adult mortality, and production of nymphs by M. caryaefoliae was tested on seedling pecans in the laboratory. Fewer M. caryaefoliae adults selected treated foliage compared with untreated foliage. A higher percentage of adults that did select treated foliage were recovered from upper leaf surfaces compared with the percentage of adults recovered from upper leaf surfaces of untreated leaves. Observations with a microscope revealed an accumulation of particle film on aphid body parts, especially on tarsi, and strongly suggests that aphid mobility was restricted. Adult mortality was higher on treated foliage and led to an overall decrease in production of nymphs on those seedlings. In addition, we measured spectral properties of treated seedling pecan foliage. Light reflectance by treated foliage was increased and absorptance decreased compared with control foliage whereas transmittance of light through control and particle film-treated leaves was similar.