Department of Entomology
Virginia Tech, Blacksburg
A wide array of arthropod pests in general and insect pests in particular always pose a serious threat to our fruit crops. Various strategies are recommended to combat the menace of these pests. However, heavy dependence on pesticides has created many problems such as environmental pollution, pesticide resistance, human health problems etc. However, most alternatives to chemical pest control have some other limitations. For example, complexes of parasites and predators give appreciable biological control of some pests in unsprayed orchards. However, in commercial orchards, the control by these biological agents may not be sufficient to provide effective population suppression. Consequently, insecticide applications are applied to reduce the infestations and protect the fruit. Repeated applications of insecticides to control pests may not be cost efficient in the long run. The natural balance may be upset in the orchard ecosystem, reducing the populations of natural enemies, and triggering the population build up of secondary pests. An environmentally friendly approach such as mating disruption (MD) could afford sufficient control of orchard pests while conserving natural enemies.
There may be many pests in an orchard but the origin of the pest control program was originally directed at the key pests. Some of the major key pests of apple orchards in Virginia are codling moth (CM), Cydia pomonella, tufted apple bud moth (TABM), Platynota idaeusalis, variegated leafroller (VLR), Platynota flavedana, redbanded leafroller (RBLR), Argyrotaenia velutinana, and oriental fruit moth (OFM), Grapholita molesta. Important direct pest on peach include OFM, peachtree borer, Synanthedon exitiosa, and lesser peachtree borer, Synanthedon pictipes, and on grape, grape berry moth (GBM), Endopiza viteana.
Sprays for the key pests release secondary pests
from natural controls. Important secondary pests are spirea aphid, Aphis
spiraecola, rosy apple aphid, Dysaphis plantaginea,
red mite, Panonychus ulmi, twospotted spider mite, Tetranychus
urticae, spotted tentiform leafminer, Phyllonorycter
and white apple leafhopper, Typhlocyba pomaria. Some of the
pests may have become annual pests in various apple orchards in
due to repeated applications of broad spectrum synthetic pesticides
against direct key pests of apple.
Mating disruption (MD) involves the use of pheromones, i.e. the chemicals produced by an insect which evoke a specific response in the other individuals of the same species. MD is based on the principle that when a specific pheromone is released in the air in an orchard in sufficiently high quantity, the males are unable to orient to natural sources of pheromone and fail to locate the calling female and the reproduction is prevented.
There are several ways in which MD could work and understanding of these mechanisms is important to the application of MD in the field. The various ways in which MD works are discussed as under:
1-Peripheral and central nervous system effects Olfactory receptors in moths concerned with the detection of pheromones are located on the antennae. When exposed to a constant stimulus, e.g., pheromone, the output from sensory organs declines rapidly; this condition is known as adaptation. The sensory organs recover fairly rapidly (in about 2-3 seconds) once the stimulus is removed. On the other hand a high and uniform concentration of the pheromone could effectively shut down the ability of sensory organs to detect the pheromone.
The exposure to high concentration of pheromone may result in the decline of behavioral response lasting several minutes or few hours. This effect is on the central nervous system and is refereed to as habituation. In this situation nerves do not recover in the normal manner. Thus habituation caused by the exposure of moths to high concentrations of pheromones could play an important role in suppressing normal male responsiveness in the mating disruption.
2 -False trails This phenomenon works when many sources of pheromones are placed in the field and male moths are attracted to false sources, wasting time and energy. Under these conditions, the likelihood of a male finding a calling female would be very low. Under these situations it may be important that all pheromone sources are releasing about the same amount of pheromone as a calling female. Male moths would cease to be attracted to a pheromone source when the concentration of pheromone gets too high i.e. above a response threshold. If this mechanism is important, it would be beneficial to have as many pheromone point sources as possible.
3-Masking In this mechanism the
level of the pheromone is often high enough to mask the odor trail from
a calling female. In this mechanism although, the sensory system of the
male moths is normally functioning but in the high background level of
the pheromone the relatively low concentration trails emitted by
cannot be perceived.
MD has been used for the control of CM and LR in Europe and North America for a long time, either experimentally or commercially. Although in many cases it has been found to be very effective for the control these pests, in certain cases the results have been variable or poor and the damage has been greater in MD orchards than in commercial orchards where conventional methods of pest control were being used. Hand-placed dispensers for leafrollers have become unavailable commercially. In the past few years, 3M Canada has produced a sprayable formulation containing (Z)-11-tetradecenyl acetate, that may be effective against obliquebanded, Pandemis, and redbanded leafrollers; this will not be effective against tufted apple bud moth or variegeted leafroller, the main leafroller species in commercial orchards of the mid-Atlantic states. Certain risk factors that hinder the use of mating disruption are set forth below. Products awere also available for codling moth, oriental fruit moth and grape berry moth. In 2005, however, 3M will cease production of these products. Hercon Environmental is developing sprayable products for mating disrupion of apple internal feeders.
MD has been registered for the control of oriental fruit moth and peachtree borer for several years, and has been used experimentally for lesser peachtree borer. Sccessful control has been obtained. Control of OFM has been equivalent with that provided by organophosphate sprays in Virginia, with elimination of moth capture in traps, and injury to shoots and fruit. Control of LPTB has exceeded that provided by chlorpyrifos (in terms of pupal skin counts), and total elimination of male captures.
1. Size of disruption block The size of the MD block is one of the most important factors. A disruption block of at least 5-10 acres is considered adequate for the successful MD program for CM and LR. MD is likely to fail in smaller-sized orchards. However, the minimal size of the orchard may vary with the pest and the species being controlled.
2. Distance from sources of immigration The disruption blocks should be adequately isolated from abandoned orchards. This is to reduce the chances of flight of mated females from the abandoned blocks to the mating disruption blocks. An isolation distance of 50-100 m is suggested for CM and LR. Again this distance may vary with the type of insect and its species because different insects have different flight ranges.
3. Application rate and dispenser release In order to have a continuously high concentration of pheromone in the orchard, two factors play an important role i.e. the application rate and the dispenser release rate. The rate of pheromone applied in the disruption block may be expressed in terms of pheromone released per area a function of release rate per dispenser and the density of dispensers in the orchard. A dispenser application rate of 1000 per ha or 400 per acre at a release rate of about 37 mg/ ha / h has been found to be effective for CM and LR. The application rate will however vary with the size of the disruption block and with the type of the dispenser. Release rate per dispenser is beyond the control of the grower; however, the grower can pay careful attention to pheromone rate per acre by basing dispenser placement on the number of trees per acre.
4. Placement of dispensers Placement of dispensers in an apple orchard at different heights has been found to have a variable effect on reducing damage to acceptable levels. It has been reported that lower pheromone heights do not give an effective control against a variety of apple orchard pests particularly against tortricids. Thus preferred placement height will vary with species. Ideally, CM dispensers should be placed in tops of trees. However, in situations with low CM pressure, placement at 6-8 feet will usually be sufficient. Since TABM and VLR do not spend most of their time in tree tops, dispensers need not be placed high.
5. Orchard edges The edges of orchards
diverse habitats. These habitats are the source of alternate hosts for
many pests which migrate to the orchards. Also these orchard edge
give shelter to many beneficial organisms which play an important role
in the biological control that is compatible with MD. Thus orchard
contribute both positive and negative forces in a MD program. It is
recommended to spray the edge rows of the orchard to prevent
of gravid females and other potential pests. Another approach could be
to manage the type of surrounding habitat so that it harbors desirable
populations preferentially to undesirable ones.
Monitoring is crucial to the successful use of MD in an IPM program. The number of moths captured not only gives an indication of how well MD is working, but it also gives information about the emergence times which may be used for timing the spray schedule in an orchard against a pest. For some pests, lures with high loading rates of pheromone are available for use in mating disruption blocks. Another type of monitoring would be the assessment of fruit damage. Weekly sampling is recommended; more frequent examination may be needed at times of anticipated population activity.
The importance of monitoring cannot be
it is more important than in a more conventional management program.
Different dispensing technologies are available for CM, OFM, GBM and LR. They are generally colored (to minimize photodegradation) and may be in polyethylene rope-style, plastic laminate or some other material. More designs will be available in near future. Different dispensers have different release rates and the selection of the dispensers will depend upon the requirements of growers. In addition to hand-placed dispensesrs, sprayable pheromone formulations are now available for oriental fruit moth, grape berry moth, codling moth and peachtree borer. Attract-and-kill technologies (e.g. Last Call) are also being developed for some species. Growers should consult fruit entomologists for exact information regarding dispenser technology and other aspects of mating disruption programs.
Labels for mating disruption products
Chugai Boyeki Co.
Suterra LLC (CheckMate mating disruption products)
3M Canada (lproducitn ends 2005)