Susceptibility of leafrollers (Lepidoptera: Tortricidae) from organic and conventional orchards to azinphosmethyl, spinosad, and Bacillus thuringiensis

Resistance Affects the Field Performance of Insecticides Used for Control of Choristoneura rosaceana in Michigan Apples and Cherries

Simple Summary

In the years that Choristoneura rosaceana was first viewed as a primary pest in fruit orchards, it was routinely targeted with insecticides within integrated pest management (IPM) programs. However, the development of resistance against a number of insecticides in C. rosaceana field populations has limited the efficacy of these control programs. One critical component in C. rosaceana management is to test whether the detected resistance levels resulted in a practical resistance, i.e., a “lack of control under field conditions” or not. Therefore, this study aimed to identify the field performance in apple and cherry orchards of different insecticides against resistant C. rosaceana field populations using field-based residual bioassays and residue analysis. Compounds demonstrating low levels of field-evolved resistance in C. rosaceana populations from apple and cherry orchards did not result in practical resistance in the field-based trial (i.e., lack of control under field conditions). However, compounds with high levels of resistance of C. rosaceana resulted in practical resistance in both resistant populations. Only chlorantraniliprole and indoxacarb showed long-lasting residues with measurable leaf residues over all post-application intervals while the leaf residues of the other compounds had largely degraded within the first 7 days. These findings can help fruit growers make adjustments to spray/re-application intervals and optimally utilize important chemical tools in their integrated pest management programs.

Abstract

Field-based residual bioassays and residue analysis were conducted to assess the field performance and toxicity longevity of different insecticides that had previously been associated with resistance of Choristoneura rosaceana populations collected from apple and cherry orchards. In this study, 12–24 h-old larvae of apple and cherry populations were exposed to apple and cherry leaf samples, respectively, at post-application intervals and a susceptible population served as a reference of each. In the apple and cherry trials, the order of residual longevity of insecticides that effectively controlled the tested populations was as follows: bifenthrin and spinetoram (apple: 14, cherry 21-day post-application), phosmet (apple: 7, cherry 14-day post-application), chlorantraniliprole (apple: 7-day post-application), and indoxacarb and emamectin benzoate (apple: 1, cherry 7-day post-application). Compared to the susceptible population, the resistant populations resulted in a measurable loss of field performance, or “practical resistance”, for the insecticides emamectin benzoate (at 7-day post-application), chlorantraniliprole (at 21-day post-application), and indoxacarb (at all post-application intervals) in the apple trials, while in cherry trial just indoxacarb at 7-day post-application showed a reduced efficacy. In terms of long-lasting residues, only chlorantraniliprole and indoxacarb maintained measurable leaf residues over all post-application intervals while the leaf residues of the other compounds had largely degraded within the first 7 days. These findings can help fruit growers make adjustments to their spray/re-application intervals and optimally utilize important chemical tools in their integrated pest management programs.

Choristoneura rosaceana (Lepidoptera: Tortricidae) Resistance to Insecticides in Michigan Apple and Cherry Orchards

Field populations of Obliquebanded leafroller, Choristoneura rosaceana (Harris), collected from one commercial apple and one commercial cherry orchard in Kent and Newaygo Counties in western Michigan, respectively. A baseline toxicity study of eight insecticides including phosmet, bifenthrin, methomyl, indoxacarb, chlorantraniliprole, spinetoram, emamectin benzoate, and novaluron was conducted on 12- to 24-h-old larvae of the C. rosaceana field populations and compared with a susceptible strain. The resistance levels were low (<10-fold) in all cases except for indoxacarb (>10-fold) in both populations. The cherry population showed levels of resistance to spinetoram, bifenthrin, emamectin benzoate, and indoxacarb with 4.1-, 4.9-, 5.8-, and 21-fold resistance, respectively. The apple population showed levels of resistance to spinetoram, chlorantraniliprole, phosmet, bifenthrin, emamectin benzoate, and indoxacarb with 4.3-, 4.7-, 5-, 5-, 6.3-, and 620.4-fold resistance, respectively. Generally, the apple population showed lower resistance levels to more compounds than the cherry population. Resistance to these insecticides should be monitored periodically for further changes. This represents the first documented case of insecticide resistance for C. rosaceana collected from a cherry orchard in Michigan. A statewide survey of more commercial orchards would help determine the extent of insecticide resistance across Michigan's five tree fruit production regions.

Cross-resistance between azinphos-methyl and acetamiprid in populations of codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae), from Washington State

BACKGROUND

Codling moth, Cydia pomonella (L.), has been intensely managed with the organophosphate insecticide azinphos-methyl for 50 years, and populations have developed resistance. New management programs have been developed and implemented that rely more heavily on other classes of insecticides. A prerequisite for developing effective resistance management strategies for these compounds is to establish their current levels of effectiveness. Adult and neonate larval assays were conducted to assess the response of field-collected codling moth populations from apple in Washington State.

RESULTS

Male codling moth populations exhibited a range of responses to a discriminating concentration of azinphos-methyl in a survey of 20 populations. Populations from certified organic orchards were more susceptible than those from conventional orchards. Mean fecundity was inversely related to azinphos-methyl tolerance. Male responses to azinphos-methyl and acetamiprid varied significantly among populations and were correlated. The residual effectiveness of field applications of both insecticides varied significantly against neonate larvae. Neonate bioassays with insecticide-dipped fruit found significant differences among populations with azinphos-methyl, acetamiprid, methoxyfenozide and spinosad, but not with esfenvalerate.

CONCLUSION

These results support a concern that alternation of insecticides with different modes of action may not be a sufficient strategy to avoid the evolution of broad-spectrum insecticide resistance by codling moth.

Resistance to spinosad in the western flower thrips, Frankliniella occidentalis (Pergande), in greenhouses of south-eastern Spain

Susceptibility to spinosad of western flower thrips (WFT), Frankliniella occidentalis (Pergande), from south-eastern Spain was determined. LC(50) values of the field populations without previous exposure to spinosad collected in Murcia in 2001 and 2002 ranged from 0.005 to 0.077 mg L(-1). The populations collected in Almeria in 2003 in greenhouses were resistant to spinosad (LC(50) > 54 mg L(-1)) compared with the authors' highly susceptible laboratory strain. The highly sensitive laboratory strain leads to very high resistance ratios for the field populations (>13 500), but these ratios do not necessarily mean resistance problems and control failures (spinosad field rate 90-120 mg L(-1)). The populations collected in Murcia from some greenhouses in 2004 were also resistant to spinosad (RF > 3682). Spinosad overuse, with more than ten applications per crop, produced these resistant populations in some greenhouses. Spinosad showed no cross-resistance to acrinathrin, formetanate or methiocarb in laboratory strains selected for resistance towards each insecticide. Correlation analysis indicated no cross-resistance among spinosad and the other three insecticides in 13 field populations and in nine laboratory strains. The synergists piperonyl butoxide (PBO), S,S,S-tributyl phosphorotrithioate (DEF) and diethyl maleate (DEM) did not enhance the toxicity of spinosad to the resistant strains, indicating that metabolic-mediated detoxification was not responsible for the spinosad resistance. These findings suggest that rotation with spinosad may be an effective resistance management strategy.