The Susceptibility of Life History Stages of the Pear Psylla to Oil Treatment1

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Abstract
Oils in the viscosity range of 30 to 405 sec (SUS at 100°F) were evaluated for effectiveness by direct contact and residually against life history stages of the pear psylla, Psylla pyricola Förster. Adults and nymphs are killed by direct contact with oil emulsions well below the standard concentrations employed in practice. The residue causes a striking reduction in oviposition for an extended period after treatment. This effect ends as green tissue becomes exposed for feeding and oviposition. Mortality of adults caged on treated branches is higher than among adults on untreated branches. Newly hatched nymphs exposed to oil residue on bark may be killed. The egg is unaffected by direct treatment with concentrations of 20% oil or higher. Control under field conditions is likely due chiefly to kill of adults by direct treatment. Under field conditions an oil with a viscosity of 60 sec was as effective as those up to 405 sec. Possibilities for more effective use of highly refined, light oils are discussed.

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