Insecticide-resistance monitoring in Ontario codling moth: 2nd year study plan

A codling moth (CM) insecticide-resistance survey initiated in southwestern Ontario apple orchards last summer will be continued in 2009.Orchards in Essex/Kent and Norfolk/Elgincounties will again be surveyed.

Testing will be conducted by trapping male CM during their June and August flight periods using pheromone lure-containing traps. Live moths will then be tested for their level of tolerance to either a dose of the active ingredient in the organophosphate (OP) insecticide, Guthion, or the neonicotinoid insecticide, Calypso. The dose is based on the concentration of each insecticide that causes greater than 90-95% mortality with an insecticide-susceptible CM strain. A control dose for these trials will be a dose of the solvent (acetone) used to dissolve the active ingredient. Mortality of the moths is assessed after 2 days.

In 2008, increased tolerance to OP and neonicotinoid insecticides was observed with the previously described tests. The tolerance of CM to Guthion was highest in Norfolk County moths collected during the first flight in June. In 3 of 5 orchards the Guthion dose caused less than 10% mortality within 2 days, whereas insecticide-susceptible lab CM and abandoned orchard-collected CM had greater than 90% mortality. Calypso was also less effective against the Norfolk moths collected in June. In 4 out of 5 orchards the mortality was less than 35%.

In contrast, Essex County collected moths from 6 orchards were more susceptible to Guthion (32 to 57% mortality), but the range of response to Calypso was the same as that observed in Norfolk County CM populations (14 to 31% mortality).

Fall 2008 collections of the over-wintering stage of CM found very few at all Norfolk/Elgin and Essex County orchards where surveys had been conducted, except for the abandoned orchard in Kent County. This may be good news for those growers as one may expect low numbers of moths within the orchards in the spring. Two factors may have been responsible for reducing the CM over-wintering population: the use of new insecticide classes (Assail, Delegate and Altacor) by the majority of growers and the cool, wet weather conditions during the spring and summer.

In summer 2009, male and female moths from orchards where high insecticide-tolerance is observed will be collected with live traps in order to start a colony for continued testing in the lab. These are considered to be necessary follow-up studies to confirm the level of tolerance observed with the adults and to test for cross-resistance to newly registered products. Currently, populations of CM collected from orchards outside of Ontario (Quebec and Michigan) are being tested in the laboratory using the larval or neonate stage.