Fate of Pyriproxyfen in Soils and Plants

Abstract

Since the 1990s, the insect growth regulator pyriproxyfen has been widely used worldwide as a larvicide in vector control and in agriculture to fight a very large number of pests. Due to its widespread use it is of first importance to know how pyriproxyfen behaves in the terrestrial ecosystems. This was the goal of this work to establish the fate profile of pyriproxyfen in soils and plants. Thus, in soil, pyriproxyfen photodegrades slowly but its aerobic degradation is fast. The insecticide presents a high tendency to adsorb onto soils and it is not subject to leaching into groundwater. On the contrary its two main metabolites (4′-OH-Pyr and PYPAC) show a different fate in soil. When sprayed to plants, pyriproxyfen behaves as a translaminar insecticide. Its half-life in plants ranges from less than one week to about three weeks. The review ends by showing how the fate profile of pyriproxyfen in soils and plants influences the adverse effects of the molecule on non-target organisms.

Efficacy of biorational insecticides against Bemisia tabaci (Genn.) and their selectivity for its parasitoid Encarsia formosa Gahan on Bt cotton

“…are responsible for the degradation and dissipation of agrochemicals (insecticides, fertilizers etc.) after their spray on plants 4 , 57 . It has been documented that a steady increase in temperature (beyond 30 °C) and a decrease in relative humidity (below 70%) result in the gradual degradation of residues of IGRs, reduction in their half-life, and resultantly reduction in their efficacy 4 , 57 , 58 .…”

“…after their spray on plants 4 , 57 . It has been documented that a steady increase in temperature (beyond 30 °C) and a decrease in relative humidity (below 70%) result in the gradual degradation of residues of IGRs, reduction in their half-life, and resultantly reduction in their efficacy 4 , 57 , 58 . A variation in the toxicity/performance of tested biorationals (five IGRs and two plant-extracts) in present laboratory and field studies may be attributed to differences in experimental conditions experienced by the target insect ( B. tabaci ) and biorational molecules in the laboratory (30 ± 2 °C, 65 ± 5% RH) and field (> 40 °C and relative humidity fluctuating between 50 and 70% in cotton crop).…”

“…The tested IGRs are recommended against insect pests on crops where these IGRs absorb into and form a reservoir of their toxic residues within the leaf-tissues (local-systemic/translaminar action). This type of absorption of IGRs residues increases with post-application interval and hence minimizes their residual toxicity on the treated leaf-surface 4 , 57 . Such types of post-application behavior of IGRs molecules ensure a gradual increase in toxicity against sucking pests like whiteflies (but not longer than 1–2 weeks) and a steady decrease in contact toxicity against predators, parasitoids 57 and other non-target arthropod fauna 4 .…”

“…Biological behavior and response of biocontrol agents toward their host/prey under insecticides’ stress is also influenced by several environmental factors (humidity, temperature, rainfall, wind-speed, etc.) which are responsible for the post-application degradation and dissipation of insecticides 4 , 57 . The results reviewed in some research reports show that a steady increase in temperature (beyond 30 °C) and decrease in relative humidity (below 70%) cause gradual degradation of IGRs’ residues on plants or in other media, reduction in their half-life and resultantly reduction in their toxicity against parasitoids/predators and its host/prey 4 , 57 , 58 .…”

“…It has been reported that a biorational tool is effective on some crops, but not on others because of the variation in several factors [like plant-species (crop types), plant development-stages, physiochemical properties of chemicals, formulation of chemicals, application methods and climatic conditions (humidity, temperature, rainfall, wind-speed, etc.)] which are responsible for the degradation and dissipation of biorational insecticides after their spray on plants 4 , 57 . For example, foliar application of ASSAIL (acetamiprid) 20% SL) @ 300 mL/ha demonstrated a significant variation in B. tabaci population reduction on five cotton varieties including super-98 (65% reduction), BH-163 (98% reduction), VH-159 (73% reduction), NIAB-884 (83% reduction) and NIAB-101 (68% reduction) at 72 h post-application interval 9 .…”