Effects of field applied residues and length of exposure to tebufenozide on the obliquebanded leafroller (Lepidoptera: Tortricidae)

Studies were conducted with the obliquebanded leafroller, Choristoneura rosaceana (Harris), and tebufenozide to determine the influence of various factors on the efficacy of this insecticide under field conditions. Larvae were exposed to apple foliage collected from commercial orchards at different intervals after insecticide applications. Mortality of neonates on actively growing (terminal) and mature (spur) foliage 10 d after an airblast sprayer application of tebufenozide was 0 and 35-74%, respectively. Feeding by larvae was also assessed on collected foliage. There was significantly less feeding on tebufenozide-treated foliage than chlorpyrifos- and nontreated foliage (P < 0.05). In the second study, to determine the efficacy of tebufenozide in the absence of larval movement to terminals with sublethal residues, terminal foliage with obliquebanded leafroller larvae was collected from two commercial orchards 24 h after an airblast sprayer application of tebufenozide. After larvae were confined on this terminal foliage in the laboratory for 10 d, mortality was >90%. In the third study, to examine the effects of obliquebanded leafroller movement to foliage with sublethal residues, we designed a laboratory bioassay in which larvae were exposed to foliage treated with tebufenozide and transferred to untreated foliage after various exposure intervals. The higher the concentration of tebufenozide, the less exposure time was necessary to cause high levels of mortality of neonates. The terminal feeding behavior ofobliquebanded leafroller larvae, low residues on terminal foliage before the end of the typical 2-wk spray interval, and the length of exposure necessary for high levels of mortality may decrease the effectiveness of tebufenozide for obliquebanded leafroller control.     

Parasitism of obliquebanded leafroller (Lepidoptera: Tortricidae) in commercially managed Michigan apple orchards

The obliquebanded leafroller, Choristoneura rosaceana (Harris), is one of the major arthropod pests of apple in the United States. In 1999 and 2000, a survey of the obliquebanded leafroller parasitoid complex in commercially managed apple orchards in Michigan's two largest fruit production regions was conducted to determine the species present and their importance to obliquebanded leafroller population management. In total, 8,961 obliquebanded leafroller larvae were collected of which 2,174 were parasitized. Parasitism increased from the overwintering generation to the summer generation for both regions and both years. In 1999, 11% of the 1,126 overwintering obliquebanded leafrollers collected were parasitized, whereas 28% of the 3,669 summer generation were parasitized. In 2000, 8% of the 489 overwintering obliquebanded leafrollers collected were parasitized, whereas 26% of the 3,677 summer generation obliquebanded leafrollers collected were parasitized. In total, 20 species of hymenopteran and dipteran parasitoids from seven families were recovered from obliquebanded leafroller larvae over the course of the study. The most abundant hymenopteran parasitoids were Bassus dimidiator Nees (Braconidae) comprising 48% of the total parasitoids, followed by Colpoclypeus florus (Walker) (Eulophidae) (8% of the total) and Macrocentrus linearis (Nees) (Braconidae) (2% of the total). Dipteran parasitoids (Tachinidae) accounted for 36% of the parasitism and were largely comprised of Nilea erecta (Coquillett) (5%) and Actia interrupta Curran (13%). These collections represent new host records for B. dimidiator, Bassus annulipes (Cresson) Hyphantrophaga blanda (Osten Sacken), and Compsilura concinnata (Meigen). The parasitoid C. florus is also reported from Michigan for the first time.     

Baseline monitoring of codling moth (Lepidoptera: Tortricidae) larval response to benzoylhydrazine insecticides

A diet-incorporation larval bioassay was developed to measure the response of codling moth, Cydia pomonella (L.), to the benzoylhydrazine insecticides tebufenozide and methoxyfenozide. The bioassay tested neonates and third, fourth, and fifth instars from a laboratory colony and neonates and fourth instars from a pooled population collected from five certified-organic apple orchards. Bioassays were scored after 6 and 14 d. No differences between the laboratory and field population were found for either insecticide. Significant differences were found in the response of third and fifth instars between the 6 and 14 d bioassays, primarily due to a high proportion of moribund larvae in the shorter assay. Larval age had a significant effect in bioassays and was more pronounced in 6- versus 14-d tests. Fifth instars were significantly less susceptible to both insecticides than other stages, while responses of third and fourth instars were similar. The response of neonates was significantly different from third and fourth instars to tebufenozide but not with methoxyfenozide in the 14-d test. Field bioassays excluded the use of fifth instars and were scored after 14 d. LC50s estimated for 18 field-collected populations varied five- and ninefold for tebufenozide and methoxyfenozide, respectively. The responses of all but six field-collected populations were significantly different from the laboratory strain. Five of these six populations were collected from orchards with no history of organophosphate insecticide use. The LC50 for methoxyfenozide of one field-collected population reared in the laboratory for three generations declined fourfold, but was still significantly different from the laboratory population. These data suggest that transforming current codling moth management programs in Washington from a reliance on organophosphate insecticides to benzoylhydrazines may be difficult.     

Host plant exploitation within a population of a generalist herbivore, Choristoneura rosaceana

Feeding performance of larvae of the obliquebanded leafroller, Choristoneura rosaceana (Harris), was estimated on apple and three alternative hosts in the Okanagan Valley. The obliquebanded leafroller is native to the study area and apple was introduced in the valley at the beginning of the century. Components of insect fitness were measured to help formulate predictions about the evolution of host preference in this generalist herbivore. In the summer, females attained a higher pupal weight on apple than on trembling aspen, wild rose and snowberry. Males performed best on apple and trembling aspen. In the field, females arising from caterpillars fed on apple leaves had a 26% greater mean fecundity than if fed on alternative hosts. The diet also affected development time; females initiated pupation later on trembling aspen than on the other hosts. Finally, no differences were found in larval survival nor in the proportion of larvae diapausing when fed on different hosts. These components of fitness indicate apple as the most suitable host in the summer.In the fall, diet influenced larval propensity to initiate diapause in the second or third instar, the time elapsed from hatching to diapause initiation and the weight of the instars initiating diapause. However, no difference in overwintering survival among larvae fed on different hosts was detected. The rank order of water and nitrogen contents of leaves of the host plants did not match the rank order of larval feeding performance in either season. A high suitability of apple and its abundance in the Okanagan valley are factors that would favor the evolution of an increased utilization of this host by the obliquebanded leafroller.     

Strategy for orchard use of Bacillus thuringiensis while minimizing impact on Choristoneura rosaceana parasitoids

Trials were conducted to study how spring Bacillus thuringiensis Berliner subsp. kurstaki treatments on apple may be timed to maximize the survival of parasitoids of the obliquebanded leafroller, Choristoneura rosaceana (Harris) (Lepidoptera: Tortricidae), found in the southern interior of British Columbia, Canada. Orchard collections verified that second through fourth instar obliquebanded leafrollers were found in varying proportions from pink through the petal fall stage of apple development when spring B. thuringiensis treatments are applied vs. lepidopteran pests. Laboratory‐reared second through fourth instar obliquebanded leafrollers, unparasitized and parasitized by one of three native parasitoid species, were fed untreated apple leaves or leaves treated with B. thuringiensis. The highest mortality of unparasitized obliquebanded leafrollers occurred when fourth instars were exposed to B. thuringiensis‐treated leaves; B. thuringiensis‐induced mortality in the unparasitized second and third instars was less than 50%. The consumption of B. thuringiensis‐treated leaves by host larvae significantly increased the percentage of dead host larvae in all parasitized and unparasitized treatments. However, because of the low susceptibility of this leafroller species to B. thuringiensis, relatively high numbers (38–43%) of three obliquebanded leafroller parasitoid species were able to survive the consumption of B. thuringiensis by second and third instar host larvae. Fourth instar obliquebanded leafrollers were found at the full bloom and petal fall stage of apple development in the orchard, at which time B. thuringiensis treatments are recommended for optimal leafroller control. The highest parasitoid mortality due to host mortality was recorded in Apophua simplicipes Cresson (Hymenoptera: Ichneumonidae) and Macrocentrus linearis (Nees) (Hymenoptera: Braconidae), when the hosts were treated as fourth instars. Both of these parasitoids emerge from fifth and sixth instar obliquebanded leafrollers. Bacillus thuringiensis did not have as negative an impact on Apanteles polychrosidis Viereck (Hymenoptera: Braconidae), which emerges when the host is in the fourth instar. When leafroller mortality and parasitism were combined, the B. thuringiensis treatment did not significantly increase host elimination above that of parasitism alone, except for larvae parasitized by A. simplicipes that were in the fourth instar. The consumption of B. thuringiensis by unparasitized larvae was shown to slow larval development.     

Instar-specific phenology of Pandemis pyrusana and Choristoneura rosaceana (Lepidoptera: Tortricidae) in Washington apple orchards

Head capsule width was used to determine the instar specific phenology of the leafroller Pandemis pyrusana Kearfott and the obliquebanded leafroller, Choristoneura rosaceana (Harris) (Lepidoptera: Tortricidae), attacking apple in Washington state during 2001-2003. In total, 7012 P. pyrusana and 6122 obliquebanded leafroller larvae were measured from apple orchards from mid-March to mid-September. Degree-day accumulations from each site were paired with the head capsule data to determine the periods during which different instars were present in the field. The implications of this work for pest management and biological control of leafrollers is discussed.     

Comparison of efficacy of programs using insecticide and insecticide plus mating disruption for controlling the obliquebanded leafroller in apple (Lepidoptera: Tortricidae)

The relative efficacy of an insecticide program and an insecticide plus mating disruption program using a sprayable pheromone formulation or a hand-applied pheromone dispenser was compared for control of the obliquebanded leafroller, Choristoneura rosaceana (Harris) at three commercial apple farms in a production area along the north shore of Lake Ontario, Canada, during 2000, 2001, and 2002. The average rate of disruption ranged from 50 to 80% in blocks of orchard treated with sprayable pheromone and from 84 to 98% in blocks treated with the hand-applied dispenser. The average proportion of shoots with larval feeding injury ranged from 0.002 to 0.09, 0.001 to 0.09, and 0.005 to 0.13 in the insecticide, insecticide plus sprayable pheromone, and insecticide plus hand-applied dispenser treatments, respectively, during the 3-yr study. The percentage of fruit with damage caused by spring, summer and overwintering larvae ranged from 0.03 to 0.06, 0.01 to 0.02, and 0.01 to 0.03 in the insecticide, insecticide plus sprayable pheromone, and insecticide plus hand-applied dispenser treatments, respectively. The addition of sex pheromone-mediated mating disruption to a conventional, insecticide-based program did not provide additional control of C. rosaceana feeding injury to shoots or fruit. The possible reasons for the failure of mating disruption to provide additional control are discussed.     

Sublethal effects of chronic exposure to tebufenozide on the development, survival, and reproduction of the tufted apple bud moth (Lepidoptera: Tortricidae)

The lethal and sublethal effects of tebufenozide on the survival, development, and reproduction of a field strain of tufted apple bud moth, Platynota idaeusalis (Walker) (Lepidoptera: Tortricidae), were assessed by feeding first and third instars tebufenozide-treated diet until pupation. Larval mortality was 27.4 and 44.7% at 0.1 and 0.2 ppm for first instars and 21.9 and 57.8% at 0.2 and 0.4 ppm for third instars, respectively. Treated larvae exhibited higher pupal mortalities, lower pupal weights, and generally more deformed adults than untreated larvae. Larval development was not affected by tebufenozide when neonates were exposed, but development was accelerated slightly at 0.4 ppm for both males and females when third instars were exposed. All treatments produced sex ratios biased toward males. When paired with either treated or untreated males, females resulting from neonates treated at 0.2 ppm and from third instars treated at both 0.2 and 0.4 ppm laid from 37 to 65% fewer eggs. A reduction in fertility was only found when third instars were treated at the higher 0.4 ppm rate. These results suggest that tebufenozide can exhibit a significant effect on the population dynamics of the tufted apple bud moth.     

Synergism of tebufenozide in resistant and susceptible strains of obliquebanded leafroller (Lepidoptera: Tortricidae) and resistance to new insecticides

Cross-resistance of the obliquebanded leafroller, Choristoneura rosaceana (Harris), to tebufenozide was reported from laboratory studies before it had been used in commercial orchards in New York State. Bioassays with obliquebanded leafroller larvae from tebufenozide and organophosphate susceptible and resistant colonies were conducted with chlorfenapyr, emamectin benzoate, fenoxycarb, fipronil, spinosad, and tebufenozide to determine if cross-resistance was present before these new insecticides were introduced into commercial orchards. Resistance ratios ranged from 1.1 to 3.2 for all insecticides except tebufenozide (12.8). Significant differences between susceptible and resistant colonies were found with emamectin benzoate, fenoxycarb, and fipronil. The effect of the metabolic synergists piperonyl butoxide (PBO) and diethyl maleate (DEM) on tebufenozide toxicity was examined to determine mechanisms for obliquebanded leafroller resistance to tebufenozide and potential mechanisms for other new insecticides. At a concentration of 20 ppm, PBO and DEM significantly synergized the toxicity of tebufenozide in resistant and susceptible colonies (three- to fourfold). Obliquebanded leafrollers may be resistant to new insecticides with distinct modes of action even if these compounds have not been previously used in commercial orchards.     

Characterisation of Cydia pomonella granulovirus from codling moths in a laboratory colony and in orchards of British Columbia*

Sequence analyses indicate that a granulovirus isolated from a laboratory colony of codling moth in British Columbia, Canada is identical or very similar to the Mexican isolate of Cydia pomonella granulovirus (CpGV-M). In addition to codling moth, the vims was found to cause mortality of secondary leafroller pests of North American orchards, including the fruit tree leafroller and the obliquebanded leafroller. A survey in apple growing regions of British Columbia indicates that 23% of the wild population of codling moth larvae carry CpGV.     

The effect of the granulovirus (PapyGV) on larval mortality and feeding behaviour of the Pandemis leafroller,Pandemis pyrusana (Lepidoptera: Tortricidae)

An indigenous betabaculovirus (PapyGV) of the Pandemis leafroller, Pandemis pyrusana (Kearfott), was studied in the laboratory and greenhouse to determine how the virus affected leafroller mortality and foliar damage. Probability of mortality increased with virus concentration as observed after 7 and 10 days of feeding on virus treated diet in neonates and second instar larvae. LC₅₀ estimates for neonates at 7 and 10 days was 2743 and 389 occlusion bodies (OBs)/mm². For second instars, LC₅₀ was 139,487 and 813 OBs/mm² at 7 and 10 days. There was no biologically significant mortality response to increasing virus concentrations by fourth instar larvae; however, when fourth instar larvae were infected with virus on diet and then fed apple leaves, the leaf area consumed declined up to 50% with higher virus concentrations. In a greenhouse study, neonate larvae that fed on seedlings treated with water showed >90% survival and 80% pupation rate of larvae after being transferred to diet. In contrast, larvae that fed on apple seedlings sprayed with 3×10⁶ OBs/ml showed poor survival when transferred to diet after acquiring the virus and failed to reach the pupal stage. This virus shows promise for population regulation and can produce reduction in feeding damage.     

Susceptibility of Diatraea saccharalis (Lepidoptera: Crambidae) to tebufenozide.

Dosage-mortality baselines were determined for first and newly molted third instars of the sugarcane borer, Diatraea saccharalis (F.), with tebufenozide incorporated into an artificial diet. Using death as an endpoint for these assays, LC50 and LC90 values were estimated to be 0.17 and 0.41 ppm for the first and 0.87 and 3.67 ppm for third instars, respectively. Developmental effects also were observed and were defined to include mortality as well as physical impairment and retarded or prolonged development with absence of feeding. Concentrations causing developmental effects in treated larvae (EC50 and EC90) were 5.8- and 3.8-fold lower than the LC50 and LC90, respectively. The critical time of exposure to tebufenozide was determined for developmentally synchronous third instars to be less than 12 h postecdysis. Mortality through adult emergence significantly decreased from 92% (treatment at 0 h postecdysis) to 30% (treatment at 12 h postecdysis), when exposed to tebufenozide at the EC50. For surviving larvae, length of development time until pupation was significantly increased and female pupal weight significantly decreased when larvae were treated at 0 h postecdysis into the third instar. In addition, to modifying the traditional ways of assessing mortality 0-3 d postapplication, this study points out the value of using other approaches to pesticide assessment, especially where insect growth regulators are involved.     

Resistance and cross-resistance to four insecticides in populations of obliquebanded leafroller (Lepidoptera: Tortricidae)

Populations of obliquebanded leafroller, Choristoneura rosaceana (Harris), were collected from organic and conventionally managed orchards located in the Okanagan and Similkameen Valleys of British Columbia Neonate F1 progeny were assayed for resistance to azinphosmethyl, tebufenozide, methoxyfenozide, and indoxacarb using a leaf disk bioassay. Significant differences in resistance levels among populations were observed for all four insecticides. Insects collected from organic sites were more susceptible to all insecticides than were insects collected from conventional sites. Resistance to the benzoylhydrazine insect growth regulators tebufenozide and methoxyfenozide was highly correlated with resistance to azinphosmethyl across populations, indicating cross-resistance between these compounds. The highest levels of resistance were observed with indoxacarb, but resistance levels to indoxacarb did not correlate with those for azinphosmethyl. Dose-response regression lines for tebufenozide were parallel across populations, suggesting that the resistance mechanism(s) were quantitatively, but not qualitatively, different. Cross-resistance between azinphosmethyl and benzoylhydrazine insecticides indicates that a resistance management strategy for obliquebanded leafroller involving the rotation of these materials is not likely to be successful.     

Effect of kaolin on fitness and behavior of Choristoneura rosaceana (Lepidoptera: Tortricidae) larvae

The mechanisms by which kaolin, a clay particle film formulation, affects the fitness and behavior of larvae of obliquebanded leafroller, Choristoneura rosaceana (Harris), were investigated. Feeding experiments tested kaolin as a physical barrier versus a physiological toxin for larvae that consumed kaolin applied either to apple (Malus spp.) leaves or mixed in artificial diet. Behavioral experiments tested the effects of kaolin applied to apple leaves on neonate dispersal and leaf rolling by third and fourth instars. When larvae fed on apple leaves sprayed with kaolin, mortality and time to pupation of larvae increased significantly, whereas pupal mass significantly decreased. When larvae consumed kaolin mixed into an artificial diet, however, the effects on mortality, pupation time, and pupal mass were negligible. There may be minor physiological effects from consumption because male time to pupation was delayed for larvae fed diets containing the highest concentration of kaolin. In behavioral experiments, neonate larvae dispersed more quickly off plants covered with kaolin than control plants, and kaolin delayed the construction of leaf shelters by third and fourth instars. We showed that the effects of kaolin on C. rosaceana larvae are primarily physical, causing changes in dispersal and rolling behaviors and as a physical barrier to feeding.     

Tebufenozide targeted against codling moth (Lepidoptera: Tortricidae) adults, eggs, and larvae

The effectiveness of tebufenozide applied against the adult, egg, and larvae of codling moth, Cydia pomonella (L.), was evaluated. Significant reductions in fecundity and egg hatch occurred after 1-h and 24-h exposures of females and 24-h exposures of males-only to residues in plastic plates. A significant reduction in egg hatch was also found after a 1-h exposure of males. The ovicidal effects of tebufenozide in field trials did not significantly differ for eggs laid on residues or treated topically. Corrected egg mortality exceeded 95% for cohorts laid <130 degree-days after sprays were applied. Fecundity and egg hatch were measured after either a 24-h exposure of moths or a 10-d exposure of moths and eggs on apple trees. Significant reductions in both fecundity and fertility occurred compared with an untreated control up to 7 d in the 24-h assays and accounted for 60-70% fewer larvae produced per mated female. The mean numbers of larvae produced per mated female after the 10-d exposure were reduced 100-75% in assays started on day 0-21 after the spray application compared with the untreated control. Fecundity was significantly reduced for 7 d and egg hatch was reduced for the entire 21-d test period in these trials. Residues had a 14-d half-life on apple foliage. Residues applied to foliage or to foliage and fruit did not significantly increase the proportion of uninjured fruit compared with the untreated control in bioassays where neonates were placed on foliage 10 cm from fruit. However, the proportion of injured fruits with shallow stings versus deep entries was higher on the treated versus the untreated plants. Field applications of tebufenozide reduced fruit injury >90% when applied early during emergence. Plots treated after the beginning of egg hatch had a larger proportion of injured fruits with shallow larval feeding.     

Comparison of delayed female mating on reproductive biology of codling moth and obliquebanded leafroller

Delay of mating was examined as a possible mechanism for population decreases associated with mating disruption for codling moth, Cydia pomonella L., and obliquebanded leafroller, Choristoneura rosaceana (Harris) (Lepidoptera: Tortricidae). We examined the effect of delaying female mating 0, 2, 4, or 6 d while holding male age constant on life table parameters of both species. We found that increasing delays in mating were accompanied by two responses: (1) an increase in the percentage of sterile pairs and (2) a reduction in net reproductive rate and population growth unrelated to sterility. On a percentage basis, obliquebanded leafroller population growth was more strongly affected than codling moth. However, the net fertility rate of obliquebanded leafroller was nearly eight-fold higher than that of codling moth, so that obliquebanded leafroller females that experienced a 4-d delay in mating had nearly the same reproductive rate as codling moth females that experienced no delay. Leslie matrix simulations using life tables with field-based adult longevity estimates showed that codling moth females experiencing >2-d delay in mating resulted in decreases in population density or extinction within two generations. In contrast, obliquebanded leafroller females delayed <6 d showed rapid population growth that decreased as female age at mating increased; only the 6-d delay treatment resulted in decreased population levels. Our results indicate that obliquebanded leafroller females must on average experience a much longer delay in mating to significantly reduce population growth compared with codling moth females, suggesting that delay of mating likely plays a greater role in codling moth mating disruption than for obliquebanded leafroller.     

Comparative activity of baculoviruses against the codling moth Cydia pomonella and three other tortricid pests of tree fruit

The granulovirus of Cydia pomonella (L.) (CpGV) offers potential for selective control of codling moth. Two major limitations of CpGV are its narrow host range and lack of persistence in the orchard agroecosystem. The nucleopolyhedroviruses of the alfalfa looper Autographa californica (Speyer) (AcMNPV) and those of the celery looper Anagrapha falcifera (Kirby) (AfMNPV) have broad host ranges. Comparative assays of CpGV, AcMNPV, and AfMNPV against codling moth neonate larvae revealed a 54-93-fold greater susceptibility of codling moth to the granulovirus than to the two nucleopolyhedroviruses based on the LC(50) values for each virus. The LC(50)s for CpGV, AfMNPV, and AcMNPV were 32.7 capsules/mm(2), 1.77 x 10(3) occlusion bodies (OBs)/mm(2), and 3.05 x 10(3)OBs/mm(2), respectively. The LT(50) determined for AfMNPV using an approximate LC(95) of the virus against neonate larvae was 3.6 days. Histological examination of tissues in moribund codling moth larvae that had been treated with AfMNPV revealed the presence of nonoccluded and unenveloped virus rods in midgut tissue. Neither OBs nor signs of infection were detected in other tissues. The activity of AfMNPV was also evaluated in three other tortricid apple pests (obliquebanded leafroller, Choristoneura rosaceana (Harris); Pandemis leafroller, Pandemis pyrusana Kearfott; and the oriental fruit moth, Grapholitha molesta (Busck)). Codling and Oriental fruit moths were significantly more susceptible to AfMNPV than were the two leafroller species.     

Fecundity and fertility reductions in adult leafrollers exposed to surfaces treated with the ecdysteroid agonists tebufenozide and methoxyfenozide

The effects on the fecundity and fertility of redbanded leafroller, Argyrotaenia velutinana (Walker), and obliquebanded leafroller,Choristoneura rosaceana (Harris), exposed as adults to surfaces treated with the ecdysone agonists tebufenozide (RH-5992) and methoxyfenozide (RH-2485) were examined. The first part of the study consisted of recently emerged moths being exposed to treated surfaces continuously throughout their lives (including mating and oviposition). Continuous exposure to tebufenozide- or methoxyfenozide-treated surfaces significantly reduced the mean number of eggs laid and the percent of eggs that hatched in both species. The second part of the study involved exposure of recently emerged virgin moths (by sex) to treated surfaces for 24 h, after which, the exposed moths were paired with a nontreated partner to mate and oviposit on nontreated surfaces. In this experiment, for A. velutinana, significant reductions in fecundity occurred only when the female was exposed to methoxyfenozide-treated surfaces. Significant reductions in A. velutinana egg fertility occurred with both male and female exposure in the methoxyfenozide treatments and only female exposure in the tebufenozide treatments. For C. rosaceana, significant reductions in fecundity occurred with both male and female exposure in the tebufenozide and methoxyfenozide treatments. Significant reductions in C. rosaceana egg fertility occurred with both male and female exposure in the tebufenozide treatments and only with female exposure in the methoxyfenozide treatments.     

Evaluation of border sprays for managing the codling moth (Tortricidae: Lepidoptera) and the apple maggot (Tephritidae: Diptera) in Ontario apple orchards

The efficacy of two insecticide control programs for managing the codling moth, Cydia pomonella (L.), and the apple maggot, Rhagoletis pomonella (Walsh), were compared in the Georgian Bay, London, Niagara, and Quinte apple production areas of Ontario during 1995, 1996, and 1997. In the border spray program, an initial cover spray of organophosphorus insecticide was applied to eradicate codling moths that may have colonized a test plot during the previous growing season. Subsequent sprays were applied only to a four-tree-wide zone (approximately 20 wide) around the perimeter of the plot to control immigrating codling moths or apple maggots. In the cover spray program, all sprays of organophosphorus insecticide were applied to the entire plot. Apple maggot injury was significantly greater in border spray program plots than in cover spray program plots only during 1995 in the London production area. There was no significant difference in codling moth injury between border spray and cover spray plots in the four production areas during the three-year study. The elimination of cover sprays from border spray plots during July and August may have left the apple crop more susceptible to damage by second generation larvae of the obliquebanded leafroller, Choristoneura rosaceana (Harris), in the London production area during 1995. There was a trend of increasing codling moth injury from 1995 to 1997 in two border spray plots, and apple maggot injury was detected in these plots during the third year of the study.     

Early detection of resistance to tebufenozide in field populations of Cydia pomonella L.: methods and mechanisms

Abstract: Four populations of codling moth Cydia pomonella L. were collected as overwintering larvae from apple orchards with different pesticide pressure (S. Michele, Roncafort, Revò and Vervò) in the Trento province (northern Italy). Mortality rate caused by a predetermined discriminating concentration of tebufenozide topically applied on overwintering larvae was evaluated. Neonate F1 progeny of the same populations were assayed for susceptibility to tebufenozide by feeding them on thinning apples treated with an appropriate discriminating dose of the insecticide. The activities of the main enzyme systems involved in the detoxification of insecticides were also evaluated in each population and related to their susceptibility to tebufenozide. The topical test detected a significant loss in susceptibility to tebufenozide in two populations, S. Michele and Roncafort, while all the overwintering larvae collected in the orchards of Revò and Vervò died when treated topically with the discriminating concentration. The apple‐dipping test performed on the neonate larvae showed a highly significant reduction in the susceptibility of the two populations of S. Michele and Roncafort. A less significant reduction in mortality rate was found in the Revò population; however, no statistical difference was found between the Vervò population and the susceptible reference. None of the four field populations significantly differed from the susceptible strain for Glutathione‐S‐transferase and esterase activity. A significantly higher frequency of individuals of the S. Michele and Roncafort populations exhibited a higher mixed function oxidase activity than the susceptible strain. The small resistance ratio values found for the two populations together with the low frequency of individuals exibiting enhanced enzymatic activity, reveals that the selection process was still at the early stage. Because of its efficiency in early detection of resistance to tebufenozide, topical application on diapausing larvae can thus be considered an appropriate, simple and robust tool for implementing resistance monitoring programmes for tebufenozide.