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Pear Psylla Nymph Bioassay

by Louis Nottingham and Betsy Beers, June 1, 2017

Fig 1. 5th instar nymph
Fig 1. 5th instar pear psylla nymph

Introduction

A laboratory bioassay was conducted to test the toxicity of various insecticides/miticides to pear psylla nymphs (Fig. 1). Nexter (pyridaben), Vendex (fenbutanin-oxide), Nealta (cyflumetofen), FujiMite (fenpyroximate), and Bexar (tolfenpyrad), were chosen due to their similar modes of action: disrupting mitochondrial function. Bexar (tolfenpyrad) is still undergoing registration for pears. This assay is a part of a series involving Bexar which will help determine its most apt placement in future pear IPM programs, if approved. Actara (thiamethoxam) was included for comparison to a common product used in late spring and early summer.

Methods

Leaves with heavy pear psylla nymph infestations were gathered from potted plants in the greenhouse at WSU-TFREC, and sprayed in the lab with the products listed in Table 1. There were 5 replicated of each treatment. Percent mortality of 4th and 5th instars, combined, was analyzed.nymph bioassay table 1

Results

Bexar was the most toxic product to pear psylla nymphs. Of the registered products, Actara 25 WG and Nexter 75 WP were the most toxic (killing ca 60% of nymphs), while FujiMite SC and Vendex 50 WP were marginally toxic (killing 25 and 10% of nymphs, respectively), and Nealta showed no toxicity (killed 0 nymphs). No phytotoxicity by any treatment was observed.

Fig 2. Pear psylla 4th and 5th instars nymph % mortality from various insecticides. 24 and 48 hr mortality were analyzed separately. Bars not sharing a common letter are statistically different.
Fig 2. Pear psylla 4th and 5th instars nymph % mortality from various insecticides. 24 and 48 hr mortality were analyzed separately. Bars not sharing a common letter are statistically different.
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