|Abstract or Summary
- The feasibility of managing codling moth, Cydia pomonella (L.), with mixtures
of Bacillus thuringiensis-based microbial and selected chemical insecticides was
studied under laboratory and field conditions. Joint actions (synergism, additivity and
antagonism) of these mixtures were determined for both egg and larval stages. Higher
rates of microbial control agents (MCAs), Dipel® 2X and MVP®, combined with low
to medium rates of chemical insecticides gave additive or synergistic egg and/or larval
mortality. Esfenvalerate and permethrin synergised the effect of these MCAs, whereas
carbaryl, azinphosmethyl, phosmet and diflubenzuron had an additive effects. For all
chemical insecticides, often the interactions were better with Dipel than MVP.
Generally, egg exposure to low rates of the chemical insecticides alone or in
combination with MCAs, caused the larvae hatching from these eggs to be more
susceptible to insecticides-MCA mixtures. Most mixtures produced better results when
treated at the blackhead stage of egg development.
Adult and larval exposure to sublethal rates of azinphosmethyl, phosmet,
carbaryl, esfenvalerate and permethrin manifested short- and long-term effects. Adult
exposure caused deleterious effects on the survival and oviposition, and the larval
exposures affected survival and pupal formation. Carbaryl, esfenvalerate and
permethrin affected the pupal survival and subsequent eclosion of adults. Only esfenvalerate and permethrin significantly extended the larval period and reduced pupal weight and subsequent egg deposition. The deleterious sublethal effects of pyrethroids observed in the present study may provide added control of codling moth in the field. Diflubenzuron and MCAs had neither adulticidal activity nor long-term effects on codling moth biology.
Results of field efficacy tests indicate that utilization of mixtures of Dipel with low rates of pyrethroids (0.1-0.2X) or diflubenzuron (0.25-0.50X) in the codling moth management is possible and indeed might be beneficial. Dipel-diflubenzuron mixtures were only suitable when applied 3 times/generation. These mixtures were environmentally safe and did not cause any outbreak of phytophagous mites. Standard application rate (2 times/generation) and timing were found to be appropriate for Dipel-pyrethroid (esfenvalerate and permethrin) mixtures. These pyrethroids at all test rates (0.1-1.0X), applied alone or mixed with MCAs, were toxic to predatory phytoseiids, thus caused an outbreak of European red mite and yellow spider mites particularly at higher rates. However, mixtures of Dipel and 0.1X of esfenvalerate/permethrin were less disruptive than corresponding 0.2-1.0X standard rate. These mixtures were selective to most predatory insects, spiders and Zetzellia malt. Hence, use of these mixtures instead of full rate of pyrethroids may improve the prospects of biological control of insect and mite pests in apple orchards.