Pheromone lure for mating disruption.
A sex pheromone is used to help one sex (typically the male insects) orient toward and find the other sex for mating. Sex pheromones can be detected over hundreds of yards on wind currents, and by flying upwind in the pheromone plume, the male can almost always find the female.
Chemists have extracted and analyzed natural pheromones and have created processes to produce these complex chemicals in large quantities. This has given entomologists several new tools to use in pest management. To date, the most successful and widespread use of pheromones has been in monitoring traps. Monitoring traps consist of cardboard or plastic devices that contain a pheromone emitter and a sticky surface. A male moth, fooled into thinking that the emitter is a female releasing a pheromone, flies into the trap and is caught on the sticky surface.
Monitoring traps are placed in the orchard before the beginning of moth emergence. They are checked daily to record the first capture, or biofix, and then at weekly intervals. Each week the trapped insects and debris are removed. Traps and pheromones are replaced as necessary. The biofix can be used to begin accumulating degree days to predict future insect stage distribution. By recording the number of males found each week, a grower may monitor the development of a pest population over time.
Each season the information on moth capture in pheromone traps for codling moth, Oriental fruit moth, leafrollers, and various other insect species in Biglerville is available at the Penn State Fruit Research and Extension Center (FREC) website and published by Penn State Extension in the monthly newsletter Fruit Times. Degree days-based insect development models (eggs hatch models) are also used to track insect development and provide the information to growers so they will know the optimum timing to control the various pests. This information can be combined with scouting information from individual orchards and used in making pest management decisions.
Recently mating disruption, another pheromone-based tool, has emerged as a useful method in insect management. Mating disruption by pheromones takes place when enough artificial sources of pheromone are placed in an area that the probability of a female being found by a male, mating, and laying viable eggs is reduced below the point where economically significant damage occurs. Mating disruption pheromone systems are available for the codling moth, Oriental fruit moth, dogwood borer, peachtree borer and lesser peachtree borer as well as for some leafroller species. These are used extensively in western states and a number of growers are using them in the eastern seaboard.
Large-scale mating disruption implementation trials have yielded significant reductions in pesticide use while keeping crop damage levels acceptably low. Because of difficulties in managing high populations of pests, mating disruption programs should not be viewed as stand-alone strategies, but rather as one tactic within the toolbox of pest management options.
The advantages of pheromone-based pest management systems include the following:
- Negligible health risks to applicator and consumer.
- Virtually no detectable residues for some types of dispensing systems.
- No accumulation in groundwater or wildlife.
- Reduced worker reentry in orchards after application and shorter preharvest intervals
- Strong tool for managing insecticide resistance to other pesticides and no documented cases of resistance to the pheromone itself.
- Highly selective to the pest species being targeted for disruption without causing secondary pest outbreaks due to the elimination of biological control agents. This selectivity creates opportunities for the biological control of other pest species. Nontarget effects are generally not seen within or outside of the treated orchard.
- Improved control of the targeted pest if overlaid onto the standard insecticide program.
The disadvantages of pheromone-based pest management include the following:
- The high degree of selectivity can also be a disadvantage when other pests are able to move into orchards because insecticides targeted for the primary pest are eliminated and often unrealized collateral control of these other pests is released. For example, in apple, disruption of codling moth often releases leafrollers from pesticide control, and in peaches, mating disruption of the Oriental fruit moth has led to an increase of stink bug injury.
- High development and production costs often make these products significantly more expensive than the synthetic pesticides they may be replacing.
- Requirements exist for specialized application techniques or equipment with some types of pheromone products and possible increases in labor costs.
- There can be a need to supplement expensive pheromone programs in high pest pressure situations with other pesticides for the same target pest.
- Effectiveness is often directly related to the size of the orchards being disrupted, and products may be less effective in orchards fewer than 5 acres in size. Also effectiveness may be reduced along borders with other orchards/crops that are not being disrupted.
- Monitoring the target pest in a disrupted orchard can be a problem because the pheromones used to disrupt mating will prevent moths from locating pheromone traps. The use of high dose lures or combination of sex pheromone and kairomone that still attract some moths even under mating disruption is useful for tracking the flights of pests like codling moth and to assess effectiveness of the mating disruption (MD) program. Other moths like Oriental fruit moth do not exhibit this response to high dose lures, and other means for assessing effectiveness are needed.
- Treatment thresholds have been developed using these high dose lures, but in most cases they are dependent on levels of injury from previous seasons or on the trap catches of pest generations previous to disruption.
Special considerations are necessary for type of mating disruption product, rate, and application method being used. Borders of disrupted blocks are often at higher risk because of pest mating occurring outside the disrupted area, and therefore efficacy increases with the size of the block treated. Peach and apple orchards adjacent to each other benefit from disruption in both crops for pests like the Oriental fruit moth. The residual activities of many of these products vary greatly. Below are some of the types of pheromones and special considerations in use.
Microencapsulated pheromones are enclosed in a polymer capsule that controls the pheromone release rate. These capsules are small enough and durable enough to be applied in water through normal airblast sprays in the same manner as conventional pesticides. This makes them very attractive for use by many fruit growers. Residual activity is generally up to 4 to 6 weeks, which gives them some flexibility in pest management programs but also means they may need to be reapplied several times in a season for a target pest. Residual activity may be reduced by rainfall soon after application and a sticker type spray adjuvant is often recommended. Currently, the only available effective material is for the control of Oriental fruit moth (Check-Mate OFM-F). Several formulations for codling moth and several species of leafrollers and wood-boring insects have been tested and even sold commercially, but have not given reliable control.
These are systems with an impermeable reservoir fitted with an impermeable membrane for regulating pheromone release. Pheromone impregnated polymer spirals, ropes, dispensers, or tubes are the most commonly used products currently. Wires, clips, or circular twin tubes allow these dispensers to be twist-tied, clipped, or draped directly onto the plant. The larger reservoirs of these products allow for longer residual activity ranging from 60 to 140 days. This may allow early season applications to suppress mating for most or all of the growing season depending on the type of dispenser and pest species. Application rates vary from one to several dispensers per tree (2 to 400 dispensers per acre) and can be labor intensive. Costs for these products tend to be significantly higher than the chemical control programs they are replacing, especially in high pest pressure situations where supplemental insecticides would be needed for acceptable control. Hand-applied dispensers can be used to either control a single or multiple species of pests.