Effects of temperature on acaricidal and insecticidal activities of the benzoylureas flucycloxuron and diflubenzuron
1991
Grosscurt, A.C. | Wixley, R.A.J.
Effects of temperature on the activity of flucycloxuron on larval stages of Panonychus ulmi (Koch), based on LC₅₀ values, were highly significant (P < 0.001) with temperature coefficients of −1.7 in both the ranges of 15° to 25 °C and 20° to 30 °C. The slopes of probit regression lines at 15° and 20 °C were significantly steeper than those at 25° and 30 °C. As a consequence the temperature coefficients based on LC₉₀ values were −4.4 and −2.2, for the 2 temperature ranges. The ovicidal activity of flucycloxuron on P. ulmi was low and was only statistically detectable at 20 °C (LC₉₀ of 84 mg a.i./l). In studies with larvae of Aedes aegypti (Linnaeus), Leptinotarsa decemlineata (Say), Plutella xylostella (Linnaeus), Spodoptera exigua (Hübner) and Spodoptera littoralis (Boisduval) probit regression lines were parallel over temperature. The activity of flucycloxuron on these five insect species was not affected by temperature. Based on LC₅₀ values, diflubenzuron showed positive temperature coefficients on P. xylostella of +2.1 at 15° to 25 °C and +2.5 at 20° to 30 °C. For S. littoralis the temperature coefficient was positive (+2.4) at 15° to 25 °C but negative (−1.9) at the 20° to 30 °C range. Temperature coefficients of diflubenzuron were neutral for A. aegypti, L. decemlineata and S. exigua. In the design and analysis of these studies special allowance was made for date effects and variation in natural mortality over temperature.
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