The gypsy moth (Lymantria dispar) is a highly disruptive species that can, and has played a distinctive role in the lives of many organisms. Included in these organisms are various deciduous trees and shrubs, wildlife species that share the same environment, and even humans. The gypsy moth destroys the beauty of woodlands via defoliation, alters ecosystems and wildlife habitats, and disrupts our own lives. It should therefore come as no surprise that the U.S. Department of Agriculture and many other agencies have taken huge steps to help diminish populations of this small, yet persistent species. In an effort to control these overwhelming populations, five chemical control agents have been used to suppress and/or eradicate the gypsy moth. Following, is a discussion of each chemical and their potentially hazardous effects on humans.

The first chemical control agent is Bacillus thuringiensis var. kurstaki (B.t.k.); a bacteria isolated from diseased silk worms and flour moths. The potency of B.t.k. varies among insects and readily destroys lepidopteran larvae within approximately one hour of ingestion. More than 1 million pounds of B.t.k. is applied annually in the U.S., primarily via aerial spraying, but also by ground spraying. It does not persist long in the environment (losing its activity by 50% within 1-3 days), has not been seen to replicate in gypsy moth predators, and does not accumulate in the soil.

There seems to be a low level of concern regarding human B.t.k. exposure, although B.t.k. formulations have caused eye, skin, and respiratory tract irritations, especially in ground workers. Some claims reveal that a majority of these workers were not equipped with protective gear such as goggles and face masks. Ground workers are also exposed to other control agents of the gypsy moth simultaneously. It is unknown whether or not these agents effect B.t.k. formulations or the effects they may have towards the workers.

A variety of mammals have been tested for pathogenicity and other toxic effects of B.t.k. using several exposure routes. No evidence of pathogenicity was found in these experimental animals. However, viable B.t.k. has been recovered in humans up to several months after exposure. A few inconsistent studies were also reported in rats exposed to high B.t.k. levels. Symptoms included lethargy, frequent urination, hair loss and piloerection (hair stands up on end).

The most likely routes of exposure of B.t.k. to the general public include skin, oral, and inhalation. A small amount of blood or eye exposure may occur in workers, but even then there is no guarantee of risk. B.t.k. seems to be an effective and widely used chemical agent for suppression of the gypsy moth.

Nucleopolyhedrosis virus (NPV) is a chemical agent containing gypsy moth parts causing viral disease of insect larvae. NPV is sprayed aerially over relatively large areas and poses minimal risk to both workers and the general public. There is, however, a lack of both human toxicity and exposure data so most of the risk assessment concerning NPV come only from experimental mammals. From this data, there has been no evidence of systemic or respiratory disease conditions. Under certain conditions, NPV may cause eye and skin irritations. But, only when large quantities of NPV has been splashed directly into ones eyes (for a substantial period of time) has there been significant damage. However, a thorough washing immediately after such exposure will help prevent any such discomfort.

As previously mentioned, there are some uncertainties regarding NPV. For example, no air monitoring studies have been done so it is not known how long NPV stays in the air after spraying. Also, humans that are allergic to gypsy moth larvae may encounter allergic reactions since NPV is indeed made up of gypsy moth parts. The only major concern of NPV so far is potential skin and inhalation exposure. There is a very low risk of any infectious effects.

Another chemical control agent is Diflubenzuron (DFB). It controls gypsy moth populations by inhibiting formation of the outer skeleton of insects (chitin). This disrupts both growth and development. It has been indicated that this may interfere with the synthesis of connective tissue in vertebrates; however no evidence has yet been reported. The main concerns of DFB on workers and the general public are effects on blood (hematological), reproductive effects, and cancer.

DFB can induce a condition known as methemoglobinemia. This prevents hemoglobin in red blood cells from combining with oxygen. It is a reversible effect, but may become life threatening at high levels. DFB also causes sulfhemoglobemia - irreversible formation of dark granules (Heinz bodies) in red blood cells that cause dysfunction and hemolysis. Reproductive effects of DFB have only been reported in a few cases using experimental chicks. Growth was retarded for a few weeks in some of these specimens. Lastly, direct exposure to DFB has not been observed to cause cancer. It can, however, chemically change within the human body to produce a compound which may exert carcinogenic characteristics.

The dispersal rate of DFB is relatively fast, therefore multiple applications are used at lower doses. Spray programs last only a couple of weeks so exposure (to workers) is kept to a minimum. (Unless the workers choose to work several programs per season, which is likely.) Exposure rates and routes are also increased in workers who load, mix and apply DFB via ground application. Risk of exposure to the general public is fairly low, even for those who live within the control program area. Individuals particularly at risk for adverse effects are those with congenital methemoglobinemia or persons with diseased or damaged skin.

The fourth chemical agent used to monitor gypsy moth populations is DDVP, also known as Dichlorvos. It is placed in milk carton traps as short strips, usually along with Disparlure (discussed later). DDVP is a contact and stomach organophosphate insecticide. Organophosphate insecticides inhibit the production of acetylcholinesterase (AChE). AChE is an enzyme involved in regulation of the nervous system. Therefore, high levels of DDVP can cause serious toxic effects, neurological effects, paralysis, and death. Reproductive effects can occur with high doses of DDVP over longer periods of time. DDVP has also been shown to cause cancer in lab animals and humans. Recent studies have found a positive relationship between childhood brain cancer and exposure to DDVP. However, AChE inhibition seems to be the most sensitive effect of DDVP on humans.

Exposure risks to DDVP for workers depend on chemical handling techniques which may vary from state to state. Special work practices ensure minimal skin and inhalation exposure if properly abided by. Exposure to the general public is highly variable, but it is unlikely that significant exposures would occur under normal conditions. Children are of primary concern because it is they who unknowingly disassemble traps and handle the chemical strips. Very young children are at special risk because they do not have fully developed AChE systems. Handling of the DDVP strips may cause skin irritation and possible allergic reactions. Persons with asthma may also experience respiratory problems.

Although DDVP is a highly hazardous chemical, efforts have been made to minimize its rate of release from the strips. This helps to diminish oral toxicity and inhalation exposure. If proper handling techniques are followed by workers and traps are left undisturbed, DDVP traps pose no serious risk.

The last chemical control agent used against the gypsy moth is Disparlure. It is used to monitor populations and detect new infestations. Disparlure is a naturally occurring insect attractant (pheromone) produced by the female gypsy moth. Two forms of Disparlure are currently being used in the U.S. The racemic mix is sprayed aerially and disrupts gypsy moth mating by confusing male moths. Simultaneously, the positive Disparlure mix is used in association with DDVP in milk carton traps. As Disparlure attracts moths to the trap, the DDVP does the dirty work.

Insect attractants are generally nontoxic to mammals, including humans. Experimental data on various lab animals reveal that oral exposure is not lethal. However, some animals did experience local skin reactions including dryness, flaking, hemorrhaging and fissures. Contact with human skin revealed that Disparlure can persist for a long period of time. Although this poses no adverse health effects, it can cause male gypsy moth attraction for up to several years. This tends to be a nuisance more than anything. Overall, the use of Disparlure to control the gypsy moth is highly unlikely to be hazardous to humans. However, long term studies are yet to be conducted.

The five chemical agents used to control the gypsy moth vary in many ways. Some seem more hazardous than others, yet they all have specific pros and cons. All but DDVP are broadcast over large areas so workers in the field are most susceptible to exposure risks associated with these agents. Nonetheless, the gypsy moth has caused enough destruction and distress to both humans and nature that these attempts most be continuously maintained. Hopefully the control of gypsy moth populations will soon be in our hands and efforts will focus more specifically on reducing the effects of potentially hazardous chemical control agents.

References:

1) http://hortwww-2.ag.ohio-state.edu/odnr/Health/gypsymoth.htm

2) http://willow.ncfes.umn.edu/fhhissue/gyps_mth.htm

3) http://troy2.fsl.wvnet.edu/fhhissue/gyps_mth.htm

4) http://www.fsl.wvnet/gmoth/gmnews/gmnews.html

5) McManus, Michael L. and Roger T. Zerillo, TheGypsy Moth: An Illustrated Biography, U.S. Department of Agriculture, No. 225, 1974.

6) Houston, David R. and Harry T. Valentine, Classifying Forest Susceptibility to Gypsy Moth Defoliation, U.S. Department of Agriculture, No. 542, 1985.

7) McManus, Michael L. and Roger T. Zerillo, TheGypsy Moth: An Illustrated Biography, U.S. Department of Agriculture, No. 225, 1974.

8) U.S. Department of Agriculture, Forest Service, Northeastern Area State and Private Forestry, Summary: Final Environmental Impact Statement, Radnor, PA, 1995.

9) U.S. Department of Agriculture, Forest Service and Animal and Plant Health Inspection Service, Gypsy Moth Suppression and Eradication Projects, 1985.

10) U.S. Department of Agriculture, Forest Service and Animal and Plant Health Inspection Service, Gypsy Moth Managment in the U.S.: a cooperative approach. Environmental Impact Statement; Appendix F Human Health Risk Assessment, 1995.

11) Wargo, Phillip M., Defoliation by the Gypsy Moth: How it Hurts Your Tree, U.S. Department of Agriculture, No. 223, 1974.

12) White, William B., Hubbard, Schneeberger, and Raimo, Technological Developments in Aerial Spraying, U.S. Department of Agriculture,

No. 535, 1974.

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