Organic producers are well aware of the crop production and protection challenges they face relative to their “conventional” counterparts. With these challenges, however, come great opportunities for exploration, development, and adoption of cutting-edge technologies. In recent years, there has been a great surge in the research and development of pest management alternatives to traditional synthetic chemical approaches. Regulation and consumer demand for organic and sustainable food and fiber has led industry to increase focus on biorational pesticides and other effective tactics for reducing pest populations and crop damage. Among those are the use of semiochemicals to impact normal behaviors of insect pests.
Semiochemical is a broad term used for chemical substances used for communication. Pheromones are a specific subset of these that mediate communication among individuals of the same species. Particular insect species may communicate using a wide range of pheromone signaling, including aggregation, trail, marking, alarm, and sex pheromones. For example, if you’ve ever observed ants traveling along a very specific path, this is a behavior mediated by a trail pheromone. One of the most widely used categories of pheromones used for monitoring and population suppression of crop-destructive insects are sex pheromones. Sex pheromones can be used by insects at all levels of the mating process (long- and short-distance mate location, courtship behaviors, partner acceptance, and the ultimate act of copulation).
Mating disruption is an integrated pest management (IPM) technique that has shown significant success and promise for a number of crop-destructive insect pests. Some examples of these in California cropping systems include: codling moth (apples, pears, and walnuts); oriental fruit moth (peaches, nectarines); tomato pinworm (tomatoes); pink bollworm (cotton); omnivorous leafroller (vineyards); navel orangeworm (almonds, pistachios, walnuts, fig); vine mealybug (grapes); European grapevine moth (grapes); California red scale (citrus); peach twig borer (apricot, peach, plum, prune); light brown apple moth (berries); as well as stored products pests (such as Indian meal moth). In some cases (e.g., pink bollworm and European grapevine moth), mating disruption has been used as part of large, regional-scale, multi-agency coordinated approaches involving a number of different management tactics, resulting in declared eradication of these pests from large geographic areas. In most of these examples however, mating disruption is used as part of an overall IPM approach to pest suppression on more localized scales (i.e., individual grower blocks, ranches, area-wide cooperatives).
Fundamentally, mating disruption acts to obstruct the pheromone-mediated sexual communication between individuals, ultimately resulting in fewer offspring in the subsequent generation. The reduction of subsequent offspring, and thus efficacy of mating disruption, can of course be achieved by completely blocking mating altogether. However, efficacy may also be achieved by delaying mating, reducing multiple matings, or causing an asynchrony in the mating behavior of males and females—all which can lead to a significant reduction in the overall numbers of subsequent generation offspring.
“Blanketing” The Environment
In practice, the way we achieve mating disruption in an agricultural setting is by “blanketing” the environment with synthetic pheromone to confuse the gender of the target species that responds to the sex pheromones. For the majority of insect species targeted for mating disruption in agricultural systems, females of the species are the producers and emitters of sex pheromones and males are the responders. This confusion, and ultimate disruption, of sexual communication in insects, is thought to be achieved by the following broad types of behavioral mechanisms:
- Competitive attraction (false-plume-following), in which males are diverted from orienting to females because they are attracted to competing ‘false’ trails emitted by synthetic pheromone dispensers.
- Non-competitive mechanisms, whereby exposure to synthetic pheromone inhibits or blocks the ability of males to sense and/or respond normally to pheromone emitted from females. These include camouflage, desensitization (i.e., adaptation and habituation), and sensory imbalance.
- Combinations of these mechanisms.
Technologies and Products
There are a number of technologies and products available for getting pheromone into the target cropping system for mating disruption purposes. In general, these are often classified based on the delivery mechanism. We often think of three common broad categories: (1) hand-applied (passive) dispensers, (2) aerosol (active) dispensers, and (3) microencapsulated (sprayable) formulations.
Hand-applied dispensers come in a variety of forms. Some of these are based on a pheromone-impregnated core sandwiched between films with permeable membranes to regulate pheromone release (Photo 1). Others are made of polymer- or plastic-based materials, again impregnated with pheromone, and designed with a particular matrix to allow the slow, even release of molecules (Photo 2). Hand-applied dispensers are considered passive, in that they provide a slow, constant release of pheromone over the entire 24-hour period for the duration of the season. The density of these types of dispensers needed for mating disruption depends on the cropping system, target species, and other ecological and operational factors. Early in the development of passive dispensers, rates were typically in the 100s (300 to 400 per acre was not uncommon). Some advances have been made in delivery mechanisms targeting certain insect species, whereby effective mating disruption can be achieved with much lower densities of passive dispensers (20 per acre for some pests and products). Again, the rate per acre will depend on the particular pest, product, and area to be treated. There are some fun versions of hand-applied formulations as well—one product can be “shot” into the tree canopy, another “splatted” onto the crop.
Aerosol dispensers (Photo 3) are considered active dispensers, in that pheromones are pressurized and emitted in metered “bursts.” The dispensers can be programmed to release pheromone only during the period of the day or night in which the target pest is sexually active (typically at night for moth pests). Further technological advancements have allowed remote-sensing of monitoring data (i.e., trap numbers) to be coupled with variable rate delivery. In other words, during periods of the year when trap catches are high (or more pests are active), a higher rate of pheromone is released from the canister. In tree crops in California, aerosol products are typically deployed at rates of 1 to 2 per acre, with increased densities around orchard edges or perimeters of mating disruption areas, and are designed to last season-long.
Sprayable (microencapsulated) formulations are not as common as hand-applied and aerosol dispensers, although there are some products available. A great benefit of sprayable mating disruption is that it is a technology that growers are familiar with in terms of the application method—it can be put directly in the spray tank and, in most cases, applied like any agrichemical. One of the challenges with sprayable formulations is stability of the material within the capsule from which it is designed to be released slowly over a period of a few to several weeks. Weather conditions, particularly excessive heat during summer months, can impact the longevity of these materials. In most cases, sprayable pheromone formulations require multiple applications during the season for most target pest species to achieve best efficacy.
There are many benefits to using mating disruption as part of an overall IPM strategy to suppress pest numbers and reduce damage, one of which is, of course, availability for use in organic systems. It is important to remember that not all mating disruptant products are registered for organic use. Always check product labels and discuss the use of any materials with your organic certifier.
“Set it and Forget it”
Other benefits include the “set it and forget it” aspect of the hand-applied or aerosol dispensers. Once deployed, they will remain active season-long, allowing you to focus other pest management efforts more specifically to other pests you may encounter in the system. Over the course of multiple seasons, population suppression using mating disruption has been shown to be compounding year after year, resulting in overall long-term reductions in pest pressure from a given species. In addition, issues common to conventional pesticide applications are mitigated or avoided, including resistance development and secondary pest outbreaks. Mating disruption is highly specific to the target pest, providing protection for non-target species such as pollinators and natural enemies (which can then be relied upon more heavily to provide biological control for a range of pests in the system).
Remember, like any pest management tactic, mating disruption is not a panacea, and is certainly not a replacement for critical cultural practices that should be employed in tandem to reduce pest numbers (for example, orchard sanitation for navel orangeworm). There are several important technological, biological, ecological, and operational factors to consider when adopting mating disruption and evaluating its efficacy. For example, mating disruption successes are often greatest when employed over large treatment areas, particularly if the target pest is highly mobile. Size and shape of the treated area can impact efficacy, as can overall pest pressure. Mating disruption as a stand-alone in most systems is most impactful at low to moderate pest densities. At higher pest pressure, supplemental treatments or management tactics of some kind may be needed, especially in the early years of employing mating disruption. Monitoring within mating disruption treated areas using pheromone-based traps may be difficult (as pheromone traps are often “shut down” or zeroed out as a result of the male confusion). Alternative monitoring strategies to detect pests and evaluate population pressures may need to be employed.
There is a wealth of information available to you as you explore adopting a new technology such as mating disruption. Your local University of California Cooperative Extension farm and IPM advisors will be able to discuss with you best practices for success, as can your pest control advisers/crop consultants, and technical representatives from the mating disruptant manufacturer.