Research on Oriental Fruit Moth Pesticide Resistance

One of the key contributions to Ontario fruit production from the labs of Dr. Dave Pree and colleagues at Agriculture and Agri-Food Canada (AAFC) in Vineland was determining the levels of pesticide resistance of Oriental fruit moth (OFM) and helping to develop IPM strategies for the pest when widespread resistance developed in the early 1990's. A paper in the Journal of the Entomological Society of Ontario (Vol. 136, 2005) by Dr. Pree, Karen Whitty, Mitch Pogoda and Lori Bittner updates the status of OFM resistance in Ontario.

The comprehensive article covers a lot of territory in both field and laboratory research conducted in 2003 and 2004. A few highlights from the paper:

• Organophosphate (OP) resistance by OFM is still present at the Jordan Research Farm at varying levels (about a third of the population resistant in generation 1 up to a high of 75% in generation 2 or 3)
  
• Over 50% resistance to OP's by OFM from Norfolk apple orchards
  
• OP resistance is also present in Essex peach orchards at lower levels
  
• No determination if resistance levels represent fluctuations or trends
  
• Generally low levels of pyrethroid resistance, despite frequent use of pyrethroids in peach production (more on this below)
  
• Intrepid (methoxyfenozide), an insect growth regulator which is not yet registered for peach in Ontario, is most effective for control of first generation OFM (later generations are not usually as synchronous (individuals at same stage of development) as the first generation)
  
• No resistance detected to Assail (acetamiprid) - a neonicotinoid also not yet registered for OFM on peach - which provided good field control

Despite the findings of low levels of pyrethroid resistance, Pree et al. (2005) expressed the same concern about over-reliance on pyrethroids for OFM management that Dr. Pree and co-authors expressed in a 1998 paper. So far, pyrethroid resistance for OFM has not become a major problem in peach production but growers should continue to follow a rotational strategy to help lessen the risk.

Phytophagous mite flare-ups can also occur with consistent pyrethroid use and high levels of peach silver mite noted by Pree et al. in 2003 at some sites may have been caused by frequent pyrethroid use. A few peach silver mite outbreaks in 2006 may have occurred for the same reason. In general though, both tolerance of certain levels of infestation and spring oil sprays (an important IPM approach) have contributed to minimal mite outbreaks. Monitoring is the key to ensuring that mite populations do not get out of control, and that is true whether using a program of pyrethroids or with any of the newer contact materials (such as neonicotinoids).

The final statements in the Pree et al. 2005 paper are important:

• There is also an alternative control program (Trimble et al. 2001) that involves the integration of insecticides for the first generation with mating disruption for later generations. That program would likely provide the best long-term resistance management strategy for Oriental fruit moth on peach in Ontario."

I would go one step further than Pree et al. and say that a season-long mating disruption program would provide the ultimate resistance management strategy. The tools for that strategy are already available, they merely wait to be used.

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