Charles S. Burks

Unusual pheromone chemistry in the navel orangeworm: novel sex attractants and a behavioral antagonist

Using molecular- and sensory physiology-based approaches, three novel natural products, a simple ester, and a behavioral antagonist have been identified from the pheromone gland of the navel orangeworm, Amyelois transitella Walker (Lepidoptera: Pyralidae). In addition to the previously identified (Z,Z)-11,13-hexadecadienal, the pheromone blend is composed of (Z,Z,Z,Z,Z)-3,6,9,12,15-tricosapentaene, (Z,Z,Z,Z,Z)-3,6,9,12,15-pentacosapentaene, ethyl palmitate, ethyl-(Z,Z)-11,13-hexadecadienoate, and (Z,Z)-11,13-hexadecadien-1-yl acetate. The C23 and C25 pentaenes are not only novel sex pheromones, but also new natural products. In field tests, catches of A. transitella males in traps baited with the full mixture of pheromones were as high as those in traps with virgin females, whereas control and traps baited only with the previously known constituent did not capture any moths at all. The navel orangeworm sex pheromone is also an attractant for the meal moth, Pyralis farinalis L. (Pyralidae), but (Z,Z)-11,13-hexadecadien-1-yl acetate is a behavioral antagonist. The new pheromone blend may be highly effective in mating disruption and monitoring programs.

Effects of Mating Disruption Treatments on Navel Orangeworm (Lepidoptera: Pyralidae) Sexual Communication and Damage in Almonds and Pistachios

Abstract Two experiments in 2003 examined the effects of different ways of dispensing the principal sex pheromone component on sexual communication among and crop damage by the navel orangeworm, Amyelois transitella (Walker) (Lepidoptera: Pyralidae) in Nonpareil almonds and pistachios. A third experiment in 2004 compared the effect on navel orangeworm damage to several almond varieties using one of these dispensing systems by itself or with phosmet, phosmet alone, and an untreated control. Additional data are presented estimating release rates from timed aerosol release devices (PuffersNOW, Suterra LLC, Bend, OR) and hand-applied membrane dispensers. In 2003, puffers placed peripherally around 16-ha blocks, evenly spaced Puffers, and hand-applied dispensers reduced males captured in virgin-baited traps by ≥95% and mating in sentinel females by ≥69%, with evenly placed Puffers showing greater reduction of males captured and females mated compared with the other dispensing systems. Mating disruption with gridded Puffers or hand-applied devices in almonds resulted in an ≈37% reduction of navel orangeworm damage (not significant), whereas peripheral Puffers resulted in a 16% reduction of navel orangeworm damage to almonds. In pistachios neither peripheral nor gridded Puffers reduced navel orangeworm damage, whereas insecticide reduced damage by 56%. In 2004, Puffers alone, insecticide alone, and both in combination significantly reduced navel orangeworm damage in Nonpareil almonds. In other, later harvested varieties, the insecticide treatments reduced damage, whereas the mating disruption treatment alone did not. We discuss application of these findings to management of navel orangeworm in these two crops.

Sampling and pheromone trapping for comparison of abundance of Amyelois transitella in almonds and pistachios

The navel orangeworm, Amyelois transitella (Walker) (Lepidoptera: Pyralidae), is the primary insect pest of almonds, Prunus amygdalus Batsch (Rosaceae), and pistachios, Pistacia vera L. (Anacardiaceae), in California, USA. Abundance of A. transitella was compared between these crops by examining total and infested mummy nuts collected in trees and on the ground between January and March in 2003 and 2004, and by examining the number of males captured in sticky traps baited with virgin females as a pheromone source during the subsequent growing seasons. There was an 8–9‐fold greater density of total mummies (potential hosts) in pistachios compared to almonds. The proportion of mummies infested was not significantly different between the crops in 2003, but significantly more almond than pistachio mummies were infested in 2004. In 2003, the average density of infested mummies per hectare was greater in pistachios than in almonds, but in 2004 the converse was true. Examination of meteorological data did not suggest an explanation for more live A. transitella per infested mummy in almonds in 2004. The number of males captured in pistachios was consistently greater than the number captured in almonds, particularly during the second flight in June and July. The number of males captured in sticky traps in the summer was more strongly associated with the total mummy density in the sanitation survey of the previous winter than with the density of infested mummies. We conclude that the overall density of mummy nuts serving as potential oviposition sites prior to the next years crop has a greater impact on the abundance of A. transitella during the growing season and subsequent harvest than does the density of infested mummies. The implications for the ecology and management of this pest species are discussed.

Effect of Bait Formulation and Number of Traps on Detection of Navel Orangeworm (Lepidoptera: Pyralidae) Oviposition using Egg Traps

ABSTRACT Egg traps are the primary tool for monitoring egg deposition of the navel orangeworm, Amyelois transitella (Walker) (Lepidoptera: Pyralidae), and for timing treatments for this pest in almonds, Prunus amygdalus Batsch, and pistachios, Pistacia vera L. We compared, in almond and pistachio orchards, the number of eggs per trap in traps baited with almond meal, pistachio meal, or the current standard commercial bait. When considering cumulative eggs captured over an extended period, traps baited with pistachio meal prepared from previous-crop nuts generally captured a similar number of eggs compared with the commercial bait, and more eggs than those baited with almond meal prepared from previous-crop nuts. However, differences in eggs per trap between bait formulations were not as evident when examining individual weeks, particularly in weeks with few eggs per trap, as is typical when treatment decisions are made. The variance in eggs per trap was generally greater than the mean and increased with the mean and, when mean eggs per trap was low, most traps did not have eggs. We discuss implications of these findings for the relative importance of bait type and trap numbers for monitoring, and for experiments comparing egg trap performance.

Patterns of Flight Behavior and Capacity of Unmated Navel Orangeworm (Lepidoptera: Pyralidae) Adults Related to Age, Gender, and Wing Size

ABSTRACT The navel orangeworm, Amyelois transitella (Walker) (Lepidoptera: Pyralidae), is a key pest of almond, pistachio, and walnut tree crops in California. Understanding dispersal of adults between orchards is important to improving management options. Laboratory flight behavior of unmated navel orangeworm of ages 1, 2, 3, 5, and 7 d posteclosion was examined using flight mills. As a group, females flew farther and longer than males, but the differences were not statistically significant. Flight speed did not differ between sexes. Flight duration and distance did not differ with age, except that 7-d-old adults performed worse for these parameters than did 1- and 2-d-old adults. Females began their flights ≈1.5 h after the onset of dusk, and ≈1.5 h earlier in the night than males. Flight capacity and propensity were substantial for both sexes and all age classes tested. At least 20% of adults (except 7-d-old males) made a continuous flight ≥5.5 h, and median total distances flown during the 10.5-h night ranged from 7 to 15 km depending on age class. Thus navel orangeworm flight mill performance was greater than that of most pests tested from the families Pyralidae and Tortricidae. Surface area and length of forewings and hindwings were greater in females than males, but had little effect on flight performance. The results are generally consistent with field observations of navel orangeworm dispersal, but it will be important to characterize the effects of mating on flight, and flight on fecundity.

Demonstration and Characterization of a Persistent Pheromone Lure for the Navel Orangeworm, Amyelois transitella (Lepidoptera: Pyralidae)

The lack of an effective pheromone lure has made it difficult to monitor and manage the navel orangeworm, Amyelois transitella (Lepidoptera: Pyralidae), in the economically important crops in which it is the primary insect pest. A series of experiments was conducted to demonstrate and characterize a practical synthetic pheromone lure for capturing navel orangeworm males. Traps baited with lures prepared with 1 or 2 mg of a three- or four-component formulation captured similar numbers of males. The fluctuation over time in the number of males captured in traps baited with the pheromone lure correlated significantly with males captured in female-baited traps. Traps baited with the pheromone lure usually did not capture as many males as traps baited with unmated females, and the ratio of males trapped with pheromone to males trapped with females varied between crops and with abundance. The pheromone lure described improves the ability of pest managers to detect and monitor navel orangeworm efficiently and may improve management and decrease insecticide treatments applied as a precaution against damage. Awareness of differences between male interaction with the pheromone lure and calling females, as shown in these data, will be important as further studies and experience determine how best to use this lure for pest management.

Monitoring Amyelois transitella males and females with phenyl propionate traps in almonds and pistachios

We examined phenyl propionate as an attractant for trapping navel orangeworm, Amyelois transitella (Walker) (Lepidoptera: Pyralidae) adults, with the objective of developing a method of trapping both sexes more effectively than with almond meal. Two initial experiments maximized the total number of adults captured using phenyl propionate released from glass vials with cotton wicks. A third experiment compared the numbers of males and females captured using these glass dispensers in either bucket or sticky traps. The glass vial dispensers captured more adults than 0.1% phenyl propionate in water (as both attractant and killing agent), and far more adults were captured with glass vial phenyl propionate dispensers than with almond meal. On rare occasion, the glass vial dispensers captured as many adults as traps baited with virgin females, but usually phenyl propionate in glass vials captured fewer adults than virgin‐baited traps. Glass vial phenyl propionate dispensers were equally effective in sticky traps or bucket traps. The majority of females captured were mated, and the proportion of males captured increased over time within flights (generations). We conclude that phenyl propionate released from glass vials captured A. transitella adults more effectively than currently available options, and will be useful in research projects where capturing intact adults and comparing mating status are important. Developing a cost‐effective phenyl propionate‐based alternative to the egg traps currently used for commercial monitoring will be more difficult.

Effect of natural and artificial photoperiods and fluctuating temperature on age of first mating and mating frequency in the navel orangeworm, Amyelois transitella.

Abstract The effect of weak illumination during part or all of the scotophase on mating frequency of navel orangeworm, Amyelois transitella (Walker) (Lepidoptera: Pyralidae), was examined in environmental chambers under long photoperiods and constant warm temperature (colony conditions) or shorter photoperiods and a cooler thermoperiod intended to mimic spring conditions in our region. These data were compared to mating frequencies in sentinel females placed in the field during the first three weeks of May. Under colony conditions weak illumination in the final hour of the scotophase resulted in ∼90% mating on the first day after eclosion; significantly greater mating compared to complete darkness throughout the scotophase, weak illumination throughout the scotophase, or weak illumination for both the first and last hour of the scotophase. In an environmental chamber programmed to simulate spring conditions, little mating occurred on the first night after eclosion and three nights were required for more than 50% of the females to mate. There was no difference in mating frequency with between moths exposed to complete darkness throughout the scotophase and those provided with weak illumination in the last half hour of the scotophase or throughout the scotophase. This delay in age of first mating was consistent with field observations with sentinel females at May in the central San Joaquin Valley. The authors conclude that, along with greater longevity and later oviposition, first mating occurs at a later age in spring conditions compared to summer conditions in this species. Planned studies of the effect of delayed mating in first and second flights will need to take these factors into account.

Effect of abundance of the navel orangeworm on sampling range and interference between pheromone traps.

ABSTRACT The sampling range of pheromone traps for the navel orangeworm Amyelois transitella (Walker) (Lepidoptera: Pyralidae) and its association with abundance was investigated by examining mutual interference within cross-shaped arrays of nine wing traps baited with virgin females and placed at 400-m intervals in three 256-ha blocks of almonds (Prunus dulcis [Miller] D. A. Webb), and three of pistachios (Pistacia vera L.). The proportions of males captured in the different positions were compared with the mean males for all traps, used as an index for abundance. For means between zero and 50 males per trap per week, the distribution was unequal between trap positions and the greatest proportion of males were captured in the northern-most trap (i.e., the within-row direction). Between 50 and 100 males per trap per week, most males were captured in the western-most traps and fewest in the center, and proportions were equal in other trap positions. Above 100 males per trap per week, the proportion of males captured was more nearly equal for all trap positions. These results demonstrate that the sampling range of pheromone traps for navel orangeworm is density dependent and, at low densities, is >400 m. They also indicate that abundance affects the impact of direction (orientation) of trap interference. At low density, female-strength pheromone traps sample males from beyond the block in which they are placed for orchard blocks of <50 ha.

Phenyl Propionate and Sex Pheromone for Monitoring Navel Orangeworm (Lepidoptera: Pyralidae) in the Presence of Mating Disruption

Abstract The recent availability of sex pheromone lures for the navel orangeworm, Amyelois transitella (Walker) (Lepidoptera: Pyralidae), improves options for monitoring this key pest in conventionally managed almonds. These lures are, however, minimally effective in the presence of mating disruption. Experiments were conducted to determine if phenyl propionate (PPO), an attractant for the navel orangeworm, acts in an additive or synergistic manner when presented together with the pheromone. In the absence of mating disruption, traps baited with PPO captured significantly fewer adults than traps baited with a sex pheromone lure. There was no difference in the number of adults captured in traps with both attractants when mating disruption was not used. In the presence of mating disruption, pheromone traps were completely suppressed, yet traps with both pheromone and PPO captured significantly more adults than traps baited with only PPO. Traps with only PPO captured equal numbers of both sexes, whereas traps with both attractants had significantly more males. These findings demonstrate that PPO is likely to be useful for monitoring navel orangeworm in fields treated with mating disruption.