Relationship of frankliniella occidental (Thysanoptera: Thripidae) population density and feeding injury to the frequency of insecticide applications to gloxinia

Abstract

Abamectin, chlorpyrifos, and cyfluthrin applied at 5, 10, or 15 d intervals reduced feeding injury to gloxinia (Sinningia speciosa Benth & Hook) flower from western flower thrips, Frankliniella occidentalis (Pergande). Less than 9 mm2 of feeding injury per flower sample was found on flowers from all insecticide treatments compared with 74 mm2 on control flowers. Five- and 10-d intervals between applications of abamectin and chlorpyrifos and 5-d intervals between applications of cyfluthrin held thrips flower injury to a tolerable level. For abamectin and cyfluthrin, the number of thrips per flower and the amount of thrips injury to flowers decreased as the length of time between applications decreased. The frequency of chlorpyrifos application did not correlate well with thrips populations. The amount of flower injury attributable to insecticide phytotoxicity increased as the interval between application decreased (r2 = 0.79-0.86), and approached unacceptable levels (>4.0% of petal tissue necrotic) at 10-d intervals for chlorpyrifos, and at 5-day intervals for abamectin, cyfluthrin, and chlorpyrifos.

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