Bulletin of Entomological Research (1996) 86, 559-566

M.R. McNeill, L.M. Hunt and R.B. Chapman (1996)
Field application and effects of chlorpyrifos residues on Sitona discoideus (Coleoptera: Curculionidae) adults and implications for biological control by Microctonus aethiopoides (Hymenoptera: Braconidae)
Bulletin of Entomological Research 86 (5), 559-566
Abstract: Chlorpyrifos was applied to field lucerne at a rate (0.3 kg/ha) recommended to control the weevil Sitona discoideus Gyllenhal. The fate of the weevil population and that of the immature stages of its parasitoid Microctonus aethiopoides Loan were examined by field sampling. A single application of chlorpyrifos reduced the weevil population by 96.2% 14 days after application. There was no significant decline in the control population between sampling intervals nor a change in the parasitism levels. However, in the insecticide-treated plots c. 88% of survivors (n=8) were parasitized. The effects of chlorpyrifos residues at 0.3 and 1.0 kg/ha were also examined. At the lower rate, residues produced c. 40-60% weevil mortality for up to 15 days after application although a significant decline in activity only occurred between days 1 and 3. At 1.0 kg/ha, the activity decay curve was much slower with no significant decline in weevil mortality for the, first 15 days of the experiment. Weevil gender was shown to be a significant factor influencing mortality. Mortality of unparasitized weevils was also significantly greater than for parasitized hosts while the stage of parasitoid development had a significant effect on mortality. Where parasitoid development was sufficiently advanced, late-instar larva emerged and successfully pupated from cadavers up to 18 h following host mortality. The consequences of applying insecticide to control S. discoideus as they relate to the parasitoid and the success of biological control are discussed.
(The abstract is excluded from the Creative Commons licence and has been copied with permission by the publisher.)
Link to article at publishers website
Database assignments for author(s): Mark R. McNeill

Research topic(s) for pests/diseases/weeds:
control - general
health/environmental effects of pesticides
Research topic(s) for beneficials or antagonists:
resistance to pesticides

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Pest and/or beneficial records:

Beneficial	Pest/Disease/Weed	Crop/Product	Country	Quarant.
	Sitona discoideus	Alfalfa/lucerne (Medicago sativa)	New Zealand
Microctonus aethiopoides (parasitoid)	Sitona discoideus	Alfalfa/lucerne (Medicago sativa)	New Zealand