Pesticide Resistance in codling moths
Codling
moth larvae damage fruit directly making it a pest that can be tolerated at
only very low levels. For seven decades, chemical measures have been the mainstay
of codling moth control, but insecticide use is beginning to fail on a worldwide
scale due to evolution of pesticide-resistant strains. It seems that no matter
which pesticide is used it is only a matter of time before the moth evolves
resistance.
Development of resistance to lead arsenate and DDT in codling moth resulted in a shift to organophosphate insecticides. Codling moth control with organophosphates has formed the basis for management systems in apple over the past 25 years. The argument has been made that organophosphate use should be maintained as long as possible as these products provide control of key pests while allowing survival of some natural enemies of secondary pests, particularly in apple orchards. However, detection of organophosphate resistance in codling moth threatens the future of these systems. Resistance, while not widespread, is well established in a number of pear orchards.
Pear production provides a sobering glimpse of what might lie ahead for pest control programs in apple given the development of organophosphate resistance in codling moth. Recurring resistance by pear psylla has lead to the use of a series of insecticides with different modes of action. The result has been an unstable management system, outbreaks of secondary pests, resistance problems, and high pest control costs.
Resistance
in codling moth has been identified and yet remains localized. Historical data
exist on resistance and codling moth population levels in several locations.
There are regional and crop-influenced differences in resistance levels that
provide an opportunity for identifying factors which influence the evolution
of resistance. Simple and rapid techniques are available for monitoring levels
of resistance. It is suggested that alternative control tactics such as mating
disruption may be used before resistance in codling moth is widespread and before
tactics detrimental to existing programs have been widely adopted.
Selective Chemical Insecticides
Among insecticides generally used for codling moth control, there are none with enough selectivity and effectiveness to be useful for integrated control programs. During the 1980's, the agricultural chemical industry made a substantial effort to develop selective insecticides for codling moth control. Development efforts focused on insect growth regulators such as the chitin-synthesis inhibitors and juvenile hormone mimics. Research trials and limited grower use have shown that diflubenzuron, a chitin-synthesis inhibitor, provides adequate codling moth control on apple and pears without disrupting biological control of other pests.
Fenoxycarb, a juvenile hormone mimic, is effective against codling moth, leafrollers, and leafminer and is selective and has a long residual activity. A new group of chemicals referred to as ecdysone-agonists, are highly specific. Tebufenozide have shown promise on laboratory and field tests against codling moth, leafrollers, and possibly leafminer. These are much more selective than conventional insecticides and have few, if any, detrimental impacts on natural enemies of pests found in western apple orchards.
Petroleum oils have historically been used as pesticides in pome fruits. These products have become highly refined and pure, reducing some of the phytoxicity concerns associated with former products. The use of summer mineral oil applications to control codling moth has been shown to have promise on pear and research on its utility on apple is currently being examined. In pear, summer oils have provided suppression of spider mites in addition to codling moth, but the impact on other non-target organisms is not fully known.
Insecticidal soaps have been tested for efficacy against several pests of pome fruits with varying results. While some products have demonstrated an ability to suppress pest species, e.g. white apple leafhopper, concerns about phytotoxicity have limited their adoption as selective controls. Soaps are not known to have any efficacy against codling moth eggs or larvae.