Pheromone inhibitors for Pandemis pyrusana males ( Lepidoptera : Tortricidae )

A grease matrix was loaded with pheromone components for Pandemis pyrusana and Choristoneura rosaceana (Lepidoptera: Tortricidae), two synchronic and sympatric species affecting apple orchards in Washington, USA. The chemicals used were a 5-blend of cis-11tetradecenyl-acetate (Z11-14Ac), trans-11-tetradecenyl-acetate, cis-11tetradecenyl-1-ol, cis-11-tetradecanal, and cis-9-tetradecenyl-acetate (Z9-14Ac) (90.05:1.89:1.42:0.95:5.69 ratio), or a 2-blend of Z11-14Ac and Z9-14Ac (94:6 ratio). Experiments to test each blend separately in a wind tunnel (at 0.16% and 16% pheromone), or in field trials (1.6% and 16%), indicated that significantly more P. pyrusana males responded to the higher concentration within any blend, and that a source containing the 5-pheromone blend caused significant reduction in attractiveness to this species. Source contact was signif icantly reduced within the P. pyrusana male behavioral sequence. This is the first report for P. pyrusana pheromone inhibitor, but further research is needed to identify whether one or more specific components elicit this response. The inhibitory effect observed probably helps to avoid interspecific matings in nature, and might be useful to develop some strategies against this pest, but it impedes to developing an attracticide formulation targeting simultaneously P. pyrusana and any other sympatric and synchronic species using these chemicals (as C. rosaceana) within their pheromone blends. Additional key words: attracticides, Choristoneura rosaceana, pest control, pheromone components.

possibility of controlling simultaneously two or more pests by mixing their respective pheromones into an attracticide formulation might be economical, and serve to manage several target species at the same time.However, their suitability depends on possible interactions between pheromone components of the target species, e.g.modification of ideal ratios or the presence of inhibitors within the formulation.Several tortricid species use the same pheromone components to attract conspecific males, e.g.cis-11-tetradecenyl-acetate is the main component present in closely similar ratio for Pandemis pyrusana Kearfott and Choristoneura rosaceana (Harris) (Lepidoptera: Tortricidae) (Arn, 1991), two synchronic and sympatric apple (Malus domestica Borkh.)pests in Washington State, USA (Curkovic, 2004).Some compounds added to a species' sex pheromone blend can cause cessation of attraction in conspecific male.In general, compounds leading to this type of response have been called pheromone inhibitors (Witzgall and Priesner, 1991).However, the word antagonist is also used (Renou and Guerrero, 2000) when these components belong to the sex pheromone blends of sympatric species (Fadamiro et al., 1999), playing a role in preventing costly reproductive mistakes (Gemeno et al., 2006).The objective of this research was to test responses from P. pyrusana males to sources containing different concentrations of both, a blend including all pheromone components for P. pyrusana and C. rosaceana together, vs. the P. pyrusana blend alone, in order to evaluate the feasibility to developing an attracticide targeting sympatric species that share pheromone components.Pandemis pyrusana insects were obtained from colonies maintained at the Washington State University Tree Fruit Research and Extension Center (TFREC-WSU), Wenatchee, WA, USA.Colonies were maintained in growth chambers at 23 ± 2°C, 40-50% HR, and 16:8 h photoperiod.Insect management was as described by Curkovic (2004).
A wind tunnel, similar to that described by Cardé and Hagaman (1979), was built at the TFREC-WSU in an environmentally controlled room set at 25 ± 2°C.The airspeed was ca.45 cm s -1 in the middle of the chamber.Relative humidity was 55 ± 5% while light intensity was 2 lux during assays.
Males management, handling, and observation was described by Curkovic (2004).Trials were run in the first 2-4 h of the scotophase, which correspond to the sexual activity period for P. pyrusana (Knight and Turner, 1998).One treatment (a particular concentration for a given blend) was run per night.Male responses were categorized as staying in, taking off from the platform, or making source contact with the source cage.
Attracticide droplets were placed inside cages (hair rollers; 6 cm length, 1.5 diameter, L&N Sales and Marketing, PA), on a source platform held by a ring stand at approximately 10 cm from the upwind end, in the middle of the wind tunnel plume.In field trials, one drop (50 ± 0.1 mg) of the attracticide formulation was placed on a piece of aluminum foil in a hair roller that was pinned inside a Delta trap, and then placed on an apple tree (1.5-2 m) in an orchard at Wenatchee, central Washington.Traps (n = 4) were separated at least 30 m, then checked, serviced, and rotated clockwise after each examination to minimize the impact of location on captures.The orchard was not sprayed with conventional insecticides during the trial period.
A χ 2 test and an analogous of the Tukey test were used to identify multiple differences between propor-tions (p) of males responding to sources in the wind tunnel.ANOVA and the Tukey test were used to compare transformed proportions {arcsin[square-root(p)]} of the total captures per treatment per block in traps, in the field trial, P = 0.05 (Zar, 1996).
There were no significant differences in males staying or leaving the platform among treatments (Table 1).Source contact, however, was significantly different depending on sources (χ 2 = 16.92,df = 6, P<0.005).Responses to the attracticide containing 16% of the P. pyrusana 2-pheromone blend were signif icantly greater than any other source.The 16% 5-pheromone blend was not significantly different from the 0.16% of the P. pyrusana 2-pheromone blend, but was significantly greater than the 0.16% 5-pheromone blend.
Statistical differences were observed in P. pyrusana males total captures in the field in traps (Fig. 1) baited with a grease formulation containing the 2-pheromone blend or the 5-component blend at 1.6% or 16% concentrations (F = 19.33,df = 3,9, P < 0.001).These results agree with indoor bioassay data, i.e. captures in traps baited with 16% of the P. pyrusana 2-pheromone blend were significantly greater than other sources loaded with lower pheromone concentrations.Besides, in the field trial the 16% 5-pheromone blend source was not significantly different from the 1.6% of the P. pyrusana 2-pheromone blend, but was significantly greater than the 1.6% 5-pheromone blend.
The male approach to, and contact with the 16% two-pheromone blend source in a wind tunnel, was similar as they behave to females (Curkovic et al., 2006).However, the responses were different and reduced to any other evaluated source.Since it has been already demonstrated that lower concentrations of the conspecif ic blend signif icantly reduce the response in P. pyrusana males to sources (Curkovic and Brunner, 2006), the results reported in here (the 2-vs.the 5-pheromone blend at the same concentration) suggest that the C. rosaceana pheromone components added into sources act as an inhibitor for P. pyrusana males.It remains unclear, however, whether one or more minor C. rosaceana pheromone component(s), or other unknown mechanism, elicit this response.This effect is undesirable for a simultaneous attracticide approach for both species.Interestingly, the inhibitory effect decreased using the same blend but increasing pheromone concentration at the source.
The behavioral analysis indicates that only the last step (source contact) within the P. pyrusana male searching sequence was signif icantly reduced.A possible explanation for this type of response would be due to the activity of minor components, found once the male has already took off, as indicated by Sweeney   (1990).The inhibitory effect observed probably helps to avoid interspecific matings in nature.Overall, results are the first report for P. pyrusana pheromone inhibitors which might be useful to control this species, but do not support the development of an attracticide targeting P. pyrusana and C. rosaceana.