The Food Quality Protection Act and Insecticide Alternatives
(or "Is There Life After the Loss of Dursban and Diazinon?")
David J. Shetlar
Urban Landscape Entomologist
The Ohio State University
As the United States Environmental Protection Agency implements the Food Quality Protection Act (FQPA), we are beginning to see the ultimate results - "voluntary" withdrawals, restrictions of usage areas and cancellations of various insecticides and miticides. Because of these actions, more landscape managers and nursery producers are asking if we have alternative products that will control key pests.
Actual cancellations of pesticides are quite rare under the FQPA review. This act was set up to reduce the exposure of children and child-bearing women to pesticides, especially ones suspected of being carcinogens, or having an influence on human nervous and hormone systems. EPA was assigned the task of determining the POTENTIAL life-time exposure of these pesticides (at current usage rates) and they were given the assumption that children are inherently at greater risk. Unfortunately, there are no good data on what an actual life-time exposure would be and there were little data that proved or disproved whether children were actually at greater risk from exposure.
To make things even more bazar, EPA was given a very short time period in which to perform its review of hundreds of pesticides. Therefore, EPA made some assumptions, whether based on sound scientific evidence or not! They lumped all pesticides together by their mode of action. Since organophosphates (of which Dursban, diazinon, and Orthene are the most commonly used around residential areas) and carbamates (like Sevin and Turcam) have the same mode of action on nervous systems, EPA grouped them together to determine the potential life-time exposures. They also made the assumption that children are ten times more susceptible to exposure (remember that the previous standard was 1/100th of the no observable effect level - NOEL). The result was that exposures were now to be considered at the 1/1000th of the NOEL! When EPA ran their "models," they quickly came to the conclusion that the easiest way to reduce exposure of the average citizen was to "encourage" the discontinued usage of organophosphates and carbamates from residential sites - both inside homes and buildings as well as in surrounding landscapes.
EPA determined that chlorpyrifos (=Dursban) was the most commonly used insecticide inside and outside homes. The gave DowAgroSciences little option other than to "voluntarily" withdraw Dursban from residential sites in order to keep its registrations in other areas. Therefore, existing stocks of Dursban can be sold and used until December 31, 2001. After that time, only chlorpyrifos products registered for other sites can be sold. You will still be able to use Dursban for golf courses, sod farms and in nursery plant production. The same thing has happened to diazinon, though a four year phase out was allowed for this insecticide.
Other insecticides and miticides, like Oftanol (isofenphos), Turcam (bendiocarb), and Morestan (oxythioquinox), were not supported (defended in front of the FQPA review) and the labels have been withdrawn. It takes millions of dollars to support these labels and there is little assurance that EPA would have allowed the labels to have remained. With the current mergers of the major chemical manufacturers, most have found that they have alternate products that can be used to replace their traditional compounds. Unfortunately, not all the new products are direct replacement and it will require end users to learn about the specific characteristics of each of these products. What follows is a listing of many of these newer compounds with some recommendations for maximizing their usage.
The pyrethroids are the synthetic counterparts to the natural, botanical insecticide - Pyrethrin. Some folks use the expression "synthetic pyrethroid" with is redundant. The earliest pyrethroids - permethrin and resmethrin - were general contact and stomach insecticides that were good at controlling a broad range of caterpillars, sawflies, aphids, foliar feeding beetles, scale crawlers and similar pests. The first pyrethroids had rather limited residual activity, usually five to seven days. Later generation pyrethroids seemed to have longer residual activity periods - 10 to 14 days, and they affected a broader spectrum of pests. Some now claim miticidal action. Though pyrethroids, as a group, are relatively less toxic than the organophosphates and carbamates, most pyrethroids can cause skin irritation if sprays land on the skin. Many of the latest generation of pyrethroids have much less tendency to cause skin irritation.
In general, for most surface-feeding insect pests, the pyrethroids are the pesticides that should be looked at first. For leafminer larvae, borer larvae and settled scales, pyrethroids have little or no systemic activity and are not good alternatives. Pyrethroids are also readily bound to organic matter and are a poor choice for control of soil-inhabiting pests.
This is one of the newest categories of synthetic insecticides. As the name suggests, the insecticides in this category affect the nicotinic receptor sites in the nervous system. Since insects use this type of receptor more than vertebrate animals (including humans!), neonicotinoids have a greater effect on insects. The specific mode of action is to block the transmission of the neural impulse to the receiving nerve. Organophosphates and carbamates cause uncontrollable and lethal transmission of neural impulses. When exposed to neonicotinoids, most insects simply stop doing what they would normally do! For very young insects, going without feeding for hours or a day can be lethal. Larger insects seem to get picked off by predators and parasites while others become infected with lethal microbes. Social insects (ants and termites) stop feeding each other or stop defending the colony. The end result is significant mortality.
Somewhat to the consternation of the manufacturers of the neonicotinoids, I often call these insecticides "mood-altering drugs for bugs!" Insects that don't behave normally are soon eliminated!
There are three subclasses of neonicotinoids - chloronicotinyls, thianicotinyls and nitromethylenes. At present, Merit or Marathion (imidachloprid) from Bayer is the only chloronicotinyl registered for turf and ornamentals. Syngenta is developing a thianicotinyl which will be called Meridian or Flagship. Merit and Meridian have broad spectrum activity and can have significant systemic action, depending on how they are applied. When sprayed, the systemic action is only by being absorbed into the leaf tissues. When soil drenched, soil injected or trunk injected, the active ingredient is translocated upward throughout the plant.
Because of their mode of action, neonicotinoids are most effective against the earliest stages of insects. In other words, they are better used in "preventive" as opposed to "curative" control approaches. Merit also seems to be rather slow to be taken up in plant tissues, often 30 to 40 days are needed for effective residues to be in place after a soil application. Therefore, if you want to prevent leafminer attack or borer invasion, applications have to be made in anticipation of these pests. For early spring pests (e.g., birch leafminers or bronzed birch borers in May) applications have been successful when made the previous October or November! Another useful attribute of many of the neonicotinoids is that they have long effective residuals, often 90 days or more.
To illustrate the usage of neonicotinoids, a study performed under USDA direction in the Chicago area where the Asian longhorn beetle has gained a foothold, soil and trunk applications of Merit to UNINFESTED trees kept the trees from becoming infested. Infested trees were not cleaned up by Merit applications. This is to be expected because this borer only moves through the sapwood as young invading larva. Larger larvae burrow into the heartwood which does not conduct most systemic insecticides.
Insect Growth Regulators
The term Insect Growth Regulator (IGR) is a rather inexact one, but it includes those pesticides that affect the growth and development of insects or mites. The two most common types of IGRs are the juvenile hormone (JH) mimics or inhibitors and the molting hormone disruption compounds. As an insect grows, glands produce juvenile hormone that keep the insect in a juvenile stage. Once the juvenile hormone stops, the insect proceeds to molt into an adult form. Therefore, when a compound mimics JH, the insect may not be able to molt into the adult form. The giant immatures that result die when their body structures collapse. Obviously, few of these products have been developed because no one wants giant caterpillars! On the other hand, JH inhibitors cause the immature insect to attempt to molt into an adult before its time. Any adult that survives is usually sterile or too small to reproduce normally.
The molt-affecting IGRs are the most commonly encountered. These IGRs usually interfere with the proper formation and hardening of a new cuticle after an insect molts or they disturb the hormone system that initiates the molting process. Azatin (azadirachtin or neem oil) and Dimilin (diflubenzuron) interfere with the proper formation of new cuticle. Insects affected by either chemical appear normal until the next molt. They split the old skin but rarely successfully emerge. If they do, the new cuticle does not harden and they eventually collapse into a pile of "goo." MACH2 (halofenozide) is a molting agonist or Molt Accelerating Compound (commonly called "MACs"). When an immature insect ingests or absorbs halofenozide, the molting process is initiated. This often occurs before the insect's body and physiology is ready so the result is a deformed insect that does not survive. Obviously, MACs are most effective when used on young insects that are going to molt several times. Near adult or adult insects may not be affected, though there is some evidence that contact with these compounds may cause defects during egg formation - essentially sterilizing females.
IGRs generally have low or non-toxic effects on non-arthropod organisms (remember that many of the aquatic invertebrates are arthropods!). However, some anti-pesticide groups often raise the question: "Aren't IGRs hormones?" The implication is that these hormone-like compounds might cause "little Johnny to grow breasts!" or "little Susie to grow hair!" which has been a concern of feeding hormones to livestock. Since humans do not molt (shed their skin) or have similar juvenile hormones, IGRs have no affect.
In order to maximize the action of IGRs, you should determine how it really works - what system does it affect? As with the neonicotinoids, small stage insects are usually the best target, though adult insects exposed to the IGRs are often sterilized. Many of the first IGRs were quickly degraded by sun or other weathering factors and most had no systemic action. Therefore, they had to be applied when and where the insects would be most likely to contact or ingest the compounds. Newer IGRs, like halofenozide, have systemic action and appear to leave effective residuals in soils for 90 or more days.
Spinosyn is a new category of biologically-derived insecticides/miticides. The active ingredients are derived from the soil-dwelling microbe, Saccharopolyspora spinosa, and Conserve is the registered product. Originally, spinosyns (the microbe seems to produce several of these compounds with similar chemical structure) were though to have an effect on the insect nervous system that was similar to the neonicotinoids - inhibit with the reception of the nerve impulse, post-synapse. We now know think that spinosyns somehow stimulate the post-synaptic receptor. The interesting feature is that spinosyns affect arthropod (insects and mites) post-synaptic receptors but have little affect on vertebrate nerves.
Conserve is currently registered to control a variety of caterpillars and spider mites. The compound must come into contact with the target or be ingested within a day or two after application. Residues appear to remain for only three to seven days. Because of this short residual action, satisfactory spider mite control may require two applications at a 7 to 10 day interval. This is because resistant stages of the mites may not come into contact with the material.
Bacillus thuringiensis - Bt -endotoxin
Though commonly considered a biological control material, the Bt -endotoxin is not much different than spinosyns in origin - both are chemicals produced by a microbe. The Bt -endotoxins are complex protein crystals that can adversely affect the gut lining of cells in insect digestive tracts. Since insect gut linings are directly exposed to these chemicals (remember that we have a mucous membrane lining in our guts), the cells break open and leak gut contents into the body cavity of the insect. This causes secondary infections that are lethal to the insect.
Bt products contain live and dead spores as well as the Bt -endotoxin crystals. Live spores are not necessary for the proteins to kill insects.
The first Bts discovered were found to have activity on caterpillars only. However, not all Bt strains contained protein crystals that could kill caterpillars. Soon strains were found that contained proteins that attacked the gut linings of aquatic fly larvae (like mosquito and black fly larvae), and leaf beetles (especially Colorado potato beetle and elm leaf beetle). Since the advent of genetic fingerprinting, nearly 10,000 distinct strains have been identified, many of which contain protein crystals that have yet to be characterized as to the insect they may affect. The original Bt kurstaki strain (caterpillar-active strain) has been subdivided and other strains have been identified that also affect caterpillars. Some of these newer strains have been developed for gypsy moth control and some can affect the larger caterpillars (the traditional kurstaki strain only kills the first to third instars).
Bt formulations still provide the landscape and nursery manager a truly non-toxic insect control option. For predictable insects such as gypsy moth, bagworms and elm leaf beetles, Bt formulations can be easily timed to wipe out developing larvae. This is why the Ohio Department of Agriculture uses Bt as its primary control material when aerial sprays are applied. An application of kurstaki Bt in the first or second week of June to shrubs previously infested with bagworms will eliminate the problem for the season.
The Bt israelensis strain can be purchased in pellet or floating brick formulations. These are spread or tossed into ponds or temporary pools of water that may be breeding mosquito larvae.
Unfortunately, Bt toxins are being given a bad reputation since the genes that make the toxins have been isolated and these can be inserted into plants through genetic engineering. The Starlink™ fiascos of 2000 involved corn that has a kurstaki Bt gene. Scientists are concerned that growing vast acres of such corn may lead to development of pest resistance to the toxin and the general public is unsure of what it means to have a "foreign protein" in their food. Plant breeders are inserting these genes into turf and possibly ornamental plants.
Insecticidal Soaps and Oils
Soaps and oils, while very different in chemistry, essentially have the same mode of action - they disrupt cell membranes of insects and mites. Cell membranes are a lipo (fat)-protein matrix. As you can probably guess, soaps emulsify fats and oils dissolve fats. Therefore, if these soaps or oils come into direct contact with cell membranes, the membranes are broken apart and the cell contents leak out. While insect and mites have what appears to be an impervious exoskeleton, this exoskeleton has numerous micropores and insects have breathing holes (spiracles) that attach to a system of tubules (trachea) that lead inside the body, down to the cellular level.
Soaps are fatty acid salts and not all soaps have insecticidal/mitical activity. Soaps containing long-chain fatty acids can kill insects. Short-chain fatty acid soaps can be dangerous to use because these also kill the cell membranes of plants. In fact, the herbicidal soap currently on the market is based on these short-chain soaps.
Horticultural or dormant oils are simply mineral oils that are of a certain molecular weight which is determined by the temperature at which they distill. Horticultural oils distill at 412 to 435 F and these oils can be used on the green leaves of plants. Oils that distill above this range do not evaporate well and can remain on the plant tissues too long. However, these higher weight oils can be used when the plant is dormant, thus the term "dormant oil." Because of problems with end users of dormant and horticultural oils, most manufacturers now only provide horticultural oils though these oils can also be used as dormant sprays.
Soaps and oils kill most insects that do not contain overly thick exoskeletons. Caterpillars, sawflies, beetle larvae, aphids, scale crawlers, mites, and eggs, etc. are all good candidates for soap or oil applications. The only requirement for success is that the soap or oil spray must contact the insect, mite or egg to be controlled. The residues of soaps or oils on leaf surfaces have no affect on the target pests. Therefore, thorough coverage and pest contact with the sprays is essential for success. If scales or mites are located on leaf undersurfaces, the sprays must be directed to these places.
Soaps and oils also appear to help in the penetration and action of many pesticides. Many companies now regularly use a 1% horticultural oil mixed with the lower rates of their pyrethroid insecticides.
Biologicals as Alternatives to Insecticides and Miticides
The true biological controls include predators, parasites and pathogens (diseases). Most Ohio landscapes provide satisfactory habitat for a variety of predators and parasites. As long as landscapes are not regularly sprayed with broad-spectrum insecticides, these predators and parasites usually keep most plant pests in check. In short, there is generally no reason to release predators (lady beetles, green lacewings or preying mantids) or parasites (small wasps and flies) because these are already present and releases often require considerable training to be successful.
When using non-selective insecticides - like the organophosphages, carbamates and pyrethroids - only treat the plant or plants that have an actual problem. If possible, use more selective insecticides - like neonicotinoids, spinosyns, IGRs, etc. Or, use pesticides in a selective manner, such as soil or plant injections of systemics.
There are three predator/parasites that you should be aware of - predatory mites, insect-parasitic nematodes and fungi.
Predatory mites are available from several supply companies (search the Internet!), but be careful of what you order. Your supplier should ask you which spider mite (or thrips) you are trying to control and what are the environmental conditions - hot-cool, dry-moist. If released when spider mite populations are beginning to build, the predatory mites can provide season long control. Remember that most of the pyrethroids and traditional miticides - Kelthane or Morestan - also kill predatory mites. If an insecticide must be used after release of predatory mites, select a neonicotinoid, IGR or use soil-applied systemics. Soaps and oils can also kill predatory mites.
Insect parasitic nematodes are also covered on several Internet sites, but visit the one hosted by Ohio State: http://www2.oardc.ohio-state.edu/nematodes/
There are about a half dozen nematode species that are available from large and small suppliers. The nematodes are generally termed "cruisers" or "ambushers" depending on their behavior. "Ambusher" nematodes tend to move slowly or they remain inactive until an insect is detected nearby. The "cruiser" nematodes are much more active and will seek out insects in the soil. The most common nematode, Steinernema carpocapsae (an ambusher) can kill a large number of insects, but it is best at controlling soil-inhabiting caterpillars - cutworms and sod webworms. It has been used successfully to control black vine weevil larvae in containers, though Heterorhabditis bacteriophora is a better choice. S. feltiae has performed well in controlling fungus gnats in greenhouse flower pots. It is also used to kill fly larvae in mushroom production facilities! Where hotter soil conditions are encountered, S. riobravis (a cruiser) has been more successful. H. bacteriophora is also the best grub to use for control of white grubs.
The insect parasitic nematodes kill their host insect by entering the body, normally through natural openings like the mouth, anus or breathing holes, and releasing a lethal bacterium. This bacterium, specific to each nematode species, rapidly kills the insect host and also produces antiobiotics that keep other bacteria from colonizing the carcass. The nematodes then undergo reproduction with their offspring feeding on the bacteria. Several generations can occur, depending on the insect host size. Eventually, new infective juveniles are produced that leave the host and seek out other insects.
The main problem with using the nematodes has been the lack of understanding that these parasites are tiny, living organisms that can be easily killed by sunlight, rapid drying and other environmental extremes. If they are to be used, obtain fresh material from the vender and check them after mixing to see if they are alive. Again, information available on the Internet covers proper usage techniques.
Many producers of container perennials eventually run into problems with black vine weevil infestations. The black vine weevil larvae are easily controlled with nematodes. However, the most common mistake made when using the nematodes is to apply them while the pots are too cold. Most producers first discover that they have the weevil problem when they uncover their polyhouses in March or April. At this time the soils may be 45 to 60F. While H. bacteriophora can operate at 60F and above, S. carpocapsae works best when the temperatures are 70F and above. Either keep the poly on until the soil temperature rises or use a registered insecticide drench. Once black vine weevil has been discovered, apply the nematodes as a preventive treatment in Sepember or October when temperatures are naturally higher. The nematodes have not been successful in controlling black vine weevil larvae in landscape plants, most likely because the extensive use of mulches keep the nematodes from reaching the soil.
Insect pathogenic fungi are commonly found in nature. In the past, the only two fungi deemed worthy of development were Beauveria bassiana (the "white" fungus of insects) and Metarrhizium anosopliae (the "green" fungus of insects). A couple of companies in the United States developed commercial preparations of Beauveria and products are still available. Metarrhizium formulations have not been commercialized in the United States though products are available in New Zealand and Europe. Unfortunately, in most field tests, there has been little efficacy that could be attributed to the application of the Beauveria spores. Since Beauveria is a rather common fungus, when soils or near-soil habitats are kept moist (a major requirement for achieving spore germination and infection), most susceptible insects get infections.
The rather recent discovery that another fungus, Entomophaga maimaiga, was killing gypsy moth caterpillars begged the question - can this fungus be cultured and spread? Apparently, this fungus is rather "fastidious" which means that it will only grow on gypsy moth caterpillars and not on an artificial medium. Therefore, there are no commercial preparations of this fungus. However, there is evidence that infected caterpillars (they are easily spotted hanging on tree trunks) can be collected, placed in paper or plastic bags and transported to other areas. These "vectors" are spread around the bases of trees and the emerging spores will remain until the next season. This should only be done if gypsy moths are known to be in the area to be innoculated since the spores will likely die after a season or two without appropriate hosts.
Other Biological Controls
The other commercial preparation of a bacterium that is sold is the milky disease of white grubs. This product, based on active spores of Paenibacillus popilliae "Japanese beetle strain," is produced by collecting live Japanese beetle grubs, infecting them with the bacterium (by injection), incubating them for a period, and then grinding them up and mixing the residue with talc. The resulting "spore powder" is applied to turf areas where Japanese beetle grubs are likely to occur. Unfortunately, the commercial strain is only active against Japanese beetle grubs while there are several other grub species that may be present. Other strains of this bacterium have been found in the other grub species, but no commercial preparations have been made using these strains. In Ohio and Kentucky tests, infections from this bacterium rarely exceed 25% which is fairly commonly found naturally, especially where Japanese beetle grubs have been active for several years.
You may discover numerous "alternate" products on the Internet and in trade magazine advertisements. These "organic" products often contain oils of garlic, eucalyptus, peppermint, spearmint, citrus, and hot peppers. In most replicated, published studies, none of these materials (except for d-limonene) have provided consistent control of insects or mites that attack ornamental, greenhouse or field crops. In fact, some of these oils have caused more phytotoxicity damage than the pest would have caused! Be careful of the advertisements of these products. If they claim to control (or even suppress) insects or mites, they must have an EPA registration number. If there is no such registration number, pesticidal claims are illegal. Also, remember that an EPA registration number is no confirmation of efficacy!
Feb, 2001 - DJS