I. Why Puffers Work: Determining the Effects of Residual Releases on Control of Codling Moth Ii. Optimizing “meso-pheromone” Emitters for Codling Moth Management in Walnuts

Our results suggest that the level of pheromone applied per “puff” by the aerosol “puffer” dispenser can be reduced dramatically without any detectable change in the size or shape of the pheromone plume. Reductions by 50% in the active ingredient per puff did not result in any increased trap capture of sterile codling moths downwind of the puffer unit. A substantial, but smaller and narrower, plume was observed when rates fell to 10% of the standard active ingredient (ai) per puff. No clear plume was detectable at 1% of the standard ai per puff. Hence, there appears to be the potential for significant cost savings if lower amounts of pheromone can be used per puff, which leads to lower amounts of pheromone per acre. Within an unreplicated trial, no clear plume was observed when hand-applied dispensers were clustered together into a single location to produce an emission rate comparable to puffer emitting at 50% of the standard emission rate. Meso emitters provided significant suppression of codling moth traps and damage in all trials, but when pressures from codling moth were high, the ring dispenser applied at rates comparable to 50% of the standard program failed to provide similar levels of control. If codling moth pressures are high, then the number of ring dispensers would need to be increased to higher levels in the orchard. Excellent trap suppression was observed using the Suterra membrane dispensers at 20 per acre, which is roughly comparable to the traditional amounts of pheromone per acre as the standard hand-applied programs. INTRODUCTION Pheromone mating disruption has been shown to provide excellent control of low-moderate populations of codling moths using passive hand-applied pheromone dispensers or aerosol based “puffers”. While the performance is no longer questioned, issues of overall program costs and labor requirements remain a source of concern. In the past 3 years, our efforts have shifted to overall cost reductions (materials or labor) for both types of delivery devices. Based on earlier research, new hand-applied dispensers were developed which rely on a reduced number of dispensers per acre, and are referred to generically as “meso-dispensers”. Two commercial products have been developed; the Suterra meso membrane dispenser and the Pacific Biocontrol “Ring” dispenser. The primary advantage for these products has been the ease of application and reduced labor costs because only 20-40 units are placed per acre. As outlined below, research on puffers has focused on optimizing the product with potential changes in the timing of release or in the levels of active pheromone required per “puff”. The hope for this area of research will be reductions in overall program costs if the levels of pheromone required per acre can be reduced. Therefore, studies to understand how changes California Walnut Board 141 Walnut Research Reports 2010 in the levels of pheromone per puff influenced plume size and efficacy were the primary targets for 2010. Puffer Trials: Optimizing Aerosol Based Pheromone Systems High dose aerosol pheromone emitters, “puffers”, have been used successfully for a number of years for control of codling moth in pears, and are emerging as a leading mating disruption strategy in walnuts. While their success has been documented in large acreages, the exact mechanism by which they operate has not been adequately studied. Understanding how this type of dispenser works may provide opportunities for improving program performance as well as decreasing overall costs. In 2009, a series of studies were initiated which attempted to define the effective area of the pheromone plume from a puffer; understand its impact on female mate location; and enhance our understanding of the effects of direct release of pheromone from the unit as well as secondary release from foliage. In 2010 we continued on the same line of research by conducting laboratory and field studies related to the results from the previous year. Most of the activity in 2010 focused in continuing the wind tunnel studies of orientation of codling moth males towards pheromoneexposed foliage, and the field comparison of the effect of pheromone release rate by puffers on the plume shape and behavior. Additionally, we ran an assay to test for influence of pheromone puffers on within orchard movement of males, and a preliminary comparison of an aerosol device and a passive one with equivalent pheromone emission rate. In essence, we are attempting to address a fundamental issue that surprisingly remains unresolved for mating disruption as follows: “Does the intermittent delivery of the pheromone as an aerosol change the fundamental properties of the pheromone plume compared to a constant low level diffusion from the hand applied dispensers?” Data from both walnuts and pears are presented for the puffer plume studies since the larger combined datasets from similar types in both crops provides a more robust set of conclusions. OBJECTIVES 1. To study the attraction of male codling moth males toward pheromone-exposed leaves in the wind tunnel. 2. To compare the shape of the plume of puffers releasing the standard pheromone dose, and others releasing lower doses; 3. To initiate studies comparing the plumes of puffers and that of a passive device with equivalent release rates. 4. To determine the effects of puffers on the within orchard movement of codling moth males. EXPERIMENT 1. Upwind attraction of codling moth males to pear and walnut leaves from puffer-treated orchards. Leaves exposed to pheromone in mating disrupted orchards have been reported to adsorb sex pheromones and elicit antennal responses in conspecific males (Karg et al., 1994; Suckling et al., 1996), but no influence on male behavior in wind tunnel has been previously shown. Furthermore, it has been reported that mating disruption may be influenced by the abundance of foliage on the crop (Suckling et al., 1996). What is not clear is how the secondary release of pheromone from the foliage might influence the overall performance of the program and more specifically, is this an important part of how puffers work. The theory is that the California Walnut Board 142 Walnut Research Reports 2010 foliage may in fact be acting as a passive reservoir for the pheromone such that the number of point sources in a puffer exposed orchard might be dramatically underestimated, given that each leaf might be an effective point source. The first step was to determine if the pheromone was being release from exposed foliage could elicit a behavioral response in male codling moths. A second goal was to determine if foliage re-emissions can be used as a proxy for determining the size and strength of a pheromone plume. In our report in 2009 we showed partial results for attraction to pear leaves and very preliminary ones in attraction to walnut leaves. We herein present the more definitive results that we have obtained. PROCEDURES Pear foliage In early-September 2009 a puffer loaded with a standard codling moth pheromone canister (Puffer® CM-O, Suterra LLC, Bend, OR, USA) was deployed (12-h mode; 5 pm to 5 am) in a Bartlett pear orchard near Freeport, CA (38o 25’ 59” N, 121o 31’ 24” W). No other pheromone or pest management techniques were in use in this orchard. Three weeks later, foliar samples were taken at increasing distances downwind from the puffer (<1, 7, 35, 55, 75, 100, 115, and 140 m). An extra sampling point in the same orchard at 300 m perpendicular to the main wind direction from the puffer was added as a blank (negative control). Samples consisted of pear cuttings bearing 6 or 7 green leaves were collected around 2.5 m above ground. These samples were taken into the laboratory as soon as possible, where they were stored in ziplock bags in the freezer (-20 oC) until their use. Additional replicates were used in 2010 from the same sampling period. Pear cuttings were assayed in a wind tunnel for codling moth male attraction. The cuttings were removed from the freezer, allowed to reach room temperature (ca. 15 min) and then attached to a stainless steel pole, at ca. 25 cm above the floor of the wind tunnel. Batches of 14 to 20 codling moth males (replicate) were flown to each cutting. Males were flown individually, and they were allowed to respond for up to 3 min. However, if they started an oriented flight, they were allowed to finish their response, and then replaced with a fresh male. Male behaviors were recorded as follows: taking-off (TO), the male left the releasing platform and started flying; oriented (OR), the male finds the plume and starts the oriented flight; F1, oriented flight up to one half of the wind tunnel (around 1 m); F2, oriented flight up to 4/5th of the wind tunnel length (around 1.7 m); close-in (CI), the male approaches the cutting and zigzags closely (a few centimeters away); contact (CN), the male touches the cutting; and walking and wing-fanning (WW), the male lands on the cutting and starts walking and wing-fanning excited. Five replicates per leaf cutting distance (accounting for between 94 and 100 individuals) were conducted. Proportions of males responding to leaves at the different distances were analyzed by fitting a GLM to each behavior in the sequence. A step-wise model simplification was performed until reaching the minimal significant model. The groups with the smallest difference on effect size were aggregated, and loss of explanatory power was checked. A logistic link function and a quasibinomial error distribution were used. Data analysis was performed with the open-source R statistical data analysis environment (R Development Core Team, 2009). California Walnut Board 143 Walnut Research Reports 2010