The effects of reduced dose and strip-spraying of aphicides on aphids and their predators and parasitoids in winter wheat fields
The effects of reduced dose and strip-spraying of aphicides on aphids and their predators and parasitoids in winter wheat fields
An attempt was made to describe and quantify the effects of reduced dose application and strip-spraying of summer aphicides on the grain aphid, Sitobion avenae F. and its associated natural enemies. Changes in the ratio of natural enemies to the target pest within half and full dose treated areas were evaluated and an increase in the ratio was observed within the half dose treatment only although both doses of the insecticides tested substantially decreased the pest population. Strip-applications were conducted to test the hypothesis that `leaving unsprayed areas within sprayed fields could enhance natural enemy migration into the untreated areas and thereby facilitate their survival and propagation leading to further suppression of the target pest'. The validity of this hypothesis was demonstrated to a certain extent through a relatively higher number of predators trapped in the unsprayed strips compared with the sprayed areas. Detailed studies were also carried out by employing barriered exclusion methods to measure the rate at which a ground active polyphagous predator distributed itself between treated and untreated areas. For this, marked Pterostichus melanarius, Ill. were introduced into partially treated barriered areas and their distribution was assessed from pitfall trap catches. Higher numbers were recaptured in untreated areas than in treated parts. Residual toxicity of lower doses of dimethoate to Coccinella 7-punctata L. was assessed under field conditions. Mortality was higher and persisted longer with full dose than with lower doses. A laboratory investigation was also conducted to evaluate the effects of reduced doses of pirimicarb, dimethoate and demeton-S-methyl on Bembidion lampros Herbst. and S.avenae. B.lampros. There was a clear dose-response relationship for B.lampros with a significant proportion surviving at lower doses, whereas, aphid numbers were significantly reduced (P< 0.05) with all doses in comparison with control. Loss and damage models were employed to estimate and forecast profit margins for reduced dose and strip-spraying. At low aphid populations, low grain value and high cost of control, reduced dose applications and strip-spraying were found to be economic in comparison with full doses and whole-plot spraying.
University of Southampton
1989
Taye-Belayneh, Yeneneh
(1989)
The effects of reduced dose and strip-spraying of aphicides on aphids and their predators and parasitoids in winter wheat fields.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
An attempt was made to describe and quantify the effects of reduced dose application and strip-spraying of summer aphicides on the grain aphid, Sitobion avenae F. and its associated natural enemies. Changes in the ratio of natural enemies to the target pest within half and full dose treated areas were evaluated and an increase in the ratio was observed within the half dose treatment only although both doses of the insecticides tested substantially decreased the pest population. Strip-applications were conducted to test the hypothesis that `leaving unsprayed areas within sprayed fields could enhance natural enemy migration into the untreated areas and thereby facilitate their survival and propagation leading to further suppression of the target pest'. The validity of this hypothesis was demonstrated to a certain extent through a relatively higher number of predators trapped in the unsprayed strips compared with the sprayed areas. Detailed studies were also carried out by employing barriered exclusion methods to measure the rate at which a ground active polyphagous predator distributed itself between treated and untreated areas. For this, marked Pterostichus melanarius, Ill. were introduced into partially treated barriered areas and their distribution was assessed from pitfall trap catches. Higher numbers were recaptured in untreated areas than in treated parts. Residual toxicity of lower doses of dimethoate to Coccinella 7-punctata L. was assessed under field conditions. Mortality was higher and persisted longer with full dose than with lower doses. A laboratory investigation was also conducted to evaluate the effects of reduced doses of pirimicarb, dimethoate and demeton-S-methyl on Bembidion lampros Herbst. and S.avenae. B.lampros. There was a clear dose-response relationship for B.lampros with a significant proportion surviving at lower doses, whereas, aphid numbers were significantly reduced (P< 0.05) with all doses in comparison with control. Loss and damage models were employed to estimate and forecast profit margins for reduced dose and strip-spraying. At low aphid populations, low grain value and high cost of control, reduced dose applications and strip-spraying were found to be economic in comparison with full doses and whole-plot spraying.
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Published date: 1989
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Local EPrints ID: 462650
URI: http://eprints.soton.ac.uk/id/eprint/462650
PURE UUID: 9fc969d0-a92d-48cc-8e7f-6436e08f4e21
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Date deposited: 04 Jul 2022 19:36
Last modified: 04 Jul 2022 19:36
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Author:
Yeneneh Taye-Belayneh
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