Introduction

This page contains information on mating disruption, a technique to control or eradicate various types of moths. While the information is mostly specific to gypsy moths, the technique is similar for other genus/species. Click here for some specific information on light brown apple moth (LBAM).

European/American gypsy moth (EGM) infestations do not spread very quickly. The average increase in area is 50% to 100% for each year. The only unassisted modalities for spread are the crawling adult female moths (they cannot fly) or the "ballooning" of caterpillars (larvae) that spin a silk parachute and sail from trees.  Spread can also occur when females lay egg cases on vehicles or objects which are moved to another area.

In other words, there is plenty of time, when a small (less than 50 moths trapped/ha) infestation is discovered to try various safe methods for eradication before it is time to bring in the more dangerous pesticides. Note that mating disruption may not be as safe as was initially claimed. See the Safety section below.

NB: If you already know about mating disruption and think it is not suitable for eradication, you should look further on in this page.

Mating Disruption with Disparlure: A Smarter Answer

Recently, there has been some work in using mating disruption to control or eradicate smaller gypsy moth populations. The pheromone, or sex attractant that is used by the female to attract males, was synthesized in the early 1970's and is commonly used to lure males to gypsy moth traps. Now, pheromone "flakes", produced by putting a tiny drop of pheromone inside a plastic semi-permeable packet, can be spread over the infested area. The flakes stick (with the aid of a sticking agent similar to the adhesive for masking tape) to leaves and other surfaces and emit the pheromone, called disparlure (chemical name cis 7,8-epoxy-2-methyloctadecane). A cloud of pheromone blankets the area for three months and confuses the mature male moths' primary method for locating females.

The pheromone is legally considered a pesticide. However, it differs in that is is not a substance designed to destroy life, but is really a natural "perfume" and as such would be expected to have few human health effects. The concentration of pheromone in the air during the active disruption period is extremely low but it is more than enough to overwhelm the moths' sensitive olefactory system. Only gypsy moths (or the target moths of other pheromones) are affected by this very specific substance. This is not to say that it is completely harmless. Check the Safety section below.

Three objections raised to this method by some entomologists are that (1) it only acts to prevent mating and does not attack the earlier larval life stages (so that spread might still occur through ballooning), (2) it "blinds" gypsy moth traps (because traps use the same pheromone) during the adult flying season, so one year is lost before data can be gathered about the success or failure of the eradication, and (3) this method is for control of established populations and not for eradication.

In some infestations, ballooning can be the primary method of spread, so the first objection could have some merit. The second objection might carry more weight if mating disruption was less effective than pesticides and EGM infestation spread rates were higher than they are.

Is disparlure effective? The Wisconsin Department of Agriculture has done a fairly extensive comparison between Foray 48B (btk based) and disparlure flakes. The following chart shows the results:
About 53,000 acres (41 plots) were treated with btk insecticide in the recommended manner, and about 24,000 acres (24 plots) were treated with a single application of disparlure flakes. The graph shows the fraction of test plots for each method that had the population reductions given (The population reduction, T, is the ratio of moths trapped after treatment to moths trapped before treatment.) Left of the vertical line at 96% reduction is the region anyone would consider "eradication." You can see that both btk and disparlure eradicated the infestations about 35% of the time. Disparlure had even more success in total eradication (zero moths trapped the following year). The interesting thing is that both methods failed to eradicate more than half the time, and btk had more spectacular failures. 

  • Does "ballooning" behavior mean disparlure won't work? Ballooning might be the primary method of spread, but the Wisconsin study indicates that unless a sizeable number of larvae ballooned so far away that they were not detected in the subsequent year's delimiting survey, the larvae did not travel far enough  to escape eventual mating disruption by disparlure. Disparlure performed at least as well eradicating small (under 80 moths/acre) infestations as btk, even with the disadvantage of attacking only the adult stage. Along with the known data about the spread rates of infestations (they generally no more than double in size each year), one cannot help but conclude that spread by ballooning is not significant enough to discount disparlure's effectiveness. This answers objection (1) above.
  • Does "trap-blinding" mean disparlure should not be used? Even with the trap-blinding effect, Wisconsin appeared confident enough to declare figures for population reduction - this speaks to objection (2).
  • Can disparlure be used to eradicate and not just control gypsy moth infestations? From the data, it appears that a complete treatment of Foray48B is no more effective at eradication than disparlure - this answers objection (3).
  • Is disparlure too costly? Wisconsin found mating disruption, in a single aerial application, is less expensive than applying Foray 48B at the recommended 3 times spaced a week apart.

Extensive Research Published in 2002 Confirms Disparlure Can Eradicate Infestations

A thorough study of Btk-based insecticides versus mating disruption with disparlure was published in 2002 [Sharov, et. al.]. A large number of large plots (232) from Wisconsin to North Carolina  that were infested with European/American gypsy moth were treated with either Btk or disparlure flakes. The plots were followed for an additional year if treated with disparlure. The situation was the same as Wisconsin, in that areas surrounding the treated plots were sometimes infested to varying degrees. The authors determined that:
  • For lower-density infestations (<50 moths/ha) both Btk and disparlure were often able to eradicate infestations in the treated plots. The authors were specific in stating they determined that infestations were eradicated (that is, no moths were found the subsequent year (for disparlure) or the year of treatment (for Btk)).
  • Eventually, because of the surrounding infestations, some plots were reinfested and had to be retreated. However, disparlure proved to be markedly superior to Btk in completely eradicating  infestations and keeping moths from reinfesting the area in the subsequent year.
  • Even with the trap blinding effect (trapping cannot be done until the year after treatment) the authors were confident that they could show confirmed and statistically superior results when using disparlure.
  • Disparlure is easier to apply and is cheaper than Foray 48, and is getting even less expensive.
The authors made a point of stating that
"Out of the 232 blocks treated in 1993 through 2000, 64 (28%) were retreated later (through 2001) at least partially. Blocks that were initially treated with B. thuringiensis were retreated more frequently (54 out of 139, 38.9%) than blocks initially treated with disparlure (10 out of 93, 10.8%). The difference is statistically signifcant...  this gives an additional evidence that disparlure was more effective than B. thuringiensis applications."

"Results of treatment evaluation in the STS project demonstrated that mating disruption with disparlure was more effective against isolated low-density populations of the gypsy moth than B. thuringiensis treatments."

"...disparlure may appear effective even at higher population densities as indicated by four successful treatments ...in
colonies with maximum moth catches ranging from 52 to 107 [moths/ha] ."

"The current cost of disparlure treatments at 75 g (AI)/ha ($64/ha) is approximately the same as a double application of B. thuringiensis ($64-69/ha) ... The recommended dose for operational disparlure in the STS project has been recently lowered to 37.5 g (AI)/ha, thus reducing the cost to $42/ha...Tests are underway that could result in further cost reduction in the future by using lower doses of pheromone and/or wider swaths. Thus, pheromone treatments appear not only effective but also cost-effcient."

One of the downsides of Btk-based treatments is that the timing is critical -  the insecticide only remains active for a few days or weeks and must be consumed by larvae while active. Disparlure remains potent  for at least three months, and possibly more, and can disrupt mating of adult moths during the entire season.

The authors state clearly the primary limitation of disparlure:

"This is the first large-scale evaluation of gypsy moth disparlure treatments in an operational system, and it confirms the effectiveness of  this method. Disparlure can be used only as a preventive pest management tool because it does not disrupt mating in high-density populations that may defoliate the forest."
Precisely. They are saying that disparlure will not work as an eradication tool when a high-density (hundreds or thousands of moths/ha) infestation is present. In the western US, though, we do not have this situation. We only have isolated, very low-density infestations that are detected well before they exceed the threshhold where mating disruption no longer works and forests are being defoliated. In these conditions, this paper conclusively shows that eradication, not just control, is not only possible using disparlure, but more likely than with Btk.

The conclusions:

  • Mating disruption with disparlure is superior to Foray 48B or Foray 48XG.
  • Disparlure can be used to eradicate small, isolated infestations.
The reference for this discussion was:

Sharov AA, Leonard D, Liebhold AM, Clemens NS. Evaluation of preventive treatments in low-density gypsy moth populations
using pheromone traps.  J. Econ Entomol. 2002 Dec;95(6):1205-15.
 

An Example in Washington: How Effective is Foray 48B?

In Washington state, a small infestation (29 acres, less than 80 moths in total trapped) of EGM in a rural town (Vader) was treated with Foray48B in the spring of 2001. Trapping data showed that the treatment was not completely effective - the infestation grew somewhat in size geographically. The Dept. of Agriculture's answer is to aerially treat a square mile with the same Foray 48B again. Statistically, this might well be effective (and devastating to a number of insects outside of gypsy moths as well as possibly dangerous for the human population, not to mention costly to the taxpayers), but this incident shows that
  • btk-based insecticides are fallible and probably perform no better than disparlure. By the WSDA's own figures, since 1974 almost one in four aerial treatments has failed to eradicate gypsy moths in Washington.
  • It is actually quite possible that ballooning or bad timing of the application allowed this infestation to spread even though Foray 48B, which attacks the larval stage, was used. One could even postulate that had the WSDA used disparlure, this infestation might not have spread as it did, and certainly would be no worse than it is today.
Safety of Moth Pheromones

Moth pheromones are somewhat toxic to humans and mammals in large amounts and with direct contact (inhalation, skin, or eyes). The delivery mechanism (encapsulation) generally prevents exposure to acutely toxic amounts. The amount of pheromone released in a treated area from the flakes or beads is an extremely low concentration. Nevertheless, there is a concern that if a number of flakes or beads were consumed (for example, by a toddler playing on the ground outdoors), there could be some internal exposure to significant amounts of the pheromone.

Pheromones are not generally known to be carcinogens, and the LD 50/30 for rats exceeds 5 g/kg; it is extremely unlikely that there could be an accidental ingestion of anywhere near this amount. The lack of data for long-term exposures is a concern, as it is with Btk-based products such as Foray 48B.

Like other pesticides, commercial products that contain moth pheromones also are formulated with various other ("inert") chemicals. Some of these chemicals, present in the encapsulation or in the spray dispersant, could be harmful. For example, Checkmate OLR-F, a commercial mating disruptor (see below) contains a number of chemicals that are toxic not only to humans but also to the environment. The pheromone flakes may be of varying sizes, and some may be small enough that they can be inhaled during or after the application, with unknown long-term consequences to humans and pets. For more information, see the Califonia Alliance to Stop the Spray (CASS) Site.

Other Specific Pheromones

Both the invasive light brown apple moth (LBAM) (Epiphyas postvittana) and the native (to North America) omivorous leafroller (Platynota sultana) can be caught with the same pheromone (11-Tetradecen-1-yl acetate) . There is more than one manufacturer of this pheromone or a combination of pheromones used for LBAM. A good source for safety information is the Califonia Alliance to Stop the Spray (CASS) Site.

MSDS and Labels for Moth Pheromones

Disrupt II for Gypsy Moth Label
Disrupt II for Gypsy Moth MSDS
Checkmate OLR-F for LBAM Label
Checkmate OLR-F for LBAM MSDS
Isomate LBAM-Plus  MSDS

Natural Predators

Vertebrate predators such as birds account for most of the mortality in low density populations, so any disruption of bird habitat, especially  food sources, will affect this predation. Other predators are more significant mostly at higher moth densities than we have in Washington. A partial list is:
  • Entomophaga maimaiga is a fungus that attacks the caterpillars.
  • Ooencyrtus kuvanae is a wasp that attacks the eggs.
  • Cotesia melanoscela is another wasp that attacks the pupae.
  • NPV (a virus) attacks dense populations.
"The generally accepted hypothesis about natural regulation of gypsy moth populations has been that at low densities, the most important mortality factors are vertebrate predators, at medium densities parasitoids are most important (usually Diptera or Hymenoptera), and at high densities, the gypsy moth nuclear polyhedrosis virus (NPV), a baculovirus, is the most frequent agent regulating populations. NPV causes big crashes in the gypsy moth population (=epizootics) and people often tended to wait for these epizootics to control high populations. "
- Ann E. Hajek (Department of Entomology, Cornell University)

This statement can be verified by anyone living in the areas of the eastern US that have been infested with gypsy moth for more than a few decades. In these areas, no lasting damage to plants other than occasional partial defoliation is seen. The gypsy moth populations never reach the extreme peaks seen in the first few years. Most people say they are aware of gypsy moth as an infrequent nuisance but do not describe it as a serious pest.

 

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