CHANEY, WILLIAM EUGENE. PhD., Purdue University, August 1988. The Effect of Synthetic Pyrethroid Insecticides on Honey Bees in Indiana: Laboratory Studies and a Survey of Beekeepers and Pesticide Applicators.

Insecticides are applied annually to a high percentage of the cultivated acres in Indiana. Some of these insecticides are applied in a manner and at a time as to expose non-target organisms, including the honey bee, to direct sprays or residues (Atkins 1979, E.H.Erickson 1983a). Concern over the impact of pesticides on the beekeeping industry has been expressed by leaders of that industry (Ambrose 1983; Atkins 1980; Crane 1983; E.H.Erickson 1983a, B.J. Erickson 1984a, 1984b; Knol 1983; Stevenson 1978, and others). The public is also becoming more concerned about the impact of pesticides on the environment as evidenced by increased regulation pesticide applicators face arid the removal of products from the marketplace (Adkinsson 1971, Pimentel 1980). As many older, more persistent, chlorinated hydrocarbons were removed from use, farmers turned to newer shorter lived insecticides and often found more applications were necessary to achieve acceptable control.

One class of insecticides that contains many of the newly registered insecticides is the synthetic pyrethroids. As a group, the synthetic pyrethroids are loosely related by their chemistry and mode of action on the target pests. Within the group are a wide range of products that have diverse target pests. Most of these products are characterized by their relatively low mammalian toxicity and their effectiveness against invertebrate pests at low doses (Sine 1988). In Indiana, these products are being utilized in the pest management programs of a growing number of corn, soybean and alfalfa farmers.

Some synthetic pyrethroids are reported to be quite safe to honeybees in some areas of the United States (Atkins 1979, Johansen 1983, Moffet 1982, Stoner 1984). Early evidence indicates that the toxicity of some synthetic pyrethroids to honeybees may be greater in Midwestern areas than in warmer more arid parts of the country (B.J.Erickson 1983; E.H.Erickson 1983b,1984; Smart 1982). The fact that the toxicity of some synthetic pyrethroids is inversely related to temperature (Georghiou 1964, Morton 1979) and may be important in a contaminated honey bee colony’s ability to overwinter in the midwest. It was also evident from early studies that the toxicity of this group to any particular species was very diverse (Atkins 1981, Moffet 1982, Smart 1982). For example, some of these products are highly toxic to mites and are used as miticides (Herbert 1988, Witherell 1988), while others are so safe to mites as to actually increase their population (Flaherty 1981, Flint 1985).

As farmers have become more specialized producers of a declining range of crops, the direct importance of bees as pollinators on the farm has also been declining. While some studies indicated that soybean yields might benefit from insect pollination (Abrams 1978, Erickson 1978, Mason 1979), other crops such as corn, alfalfa grown for hay and wheat require no insect pollination. As these crops captured an increasing proportion of the acreage, the number of nectar producing plants plummeted. The decrease in forested acres, the intensive planting of non-nectar producing plants such as fescue and crown vetch on roadsides and in pastures, the intensive use of herbicides in cropland and the increasing urban demand for land, seriously reduced the nectar resources available to bees. This combined with the low world honey price over the past several years, has driven nearly all commercial beekeepers from many parts of Indiana.

Most of the remaining beekeepers in Indiana are hobbyist or part-time beekeepers who keep bees for pleasure as well as profit. For these beekeepers, the impact of pesticides on their bees is a highly-charged, emotional issue. Much misunderstanding exists between beekeepers and applicators and there is considerable misinformation on both sides. Since discontinuation of the federal governments Beekeeper Indemnification Program, there has been very little effort to evaluate, document, or record reports of pesticide poisonings of honey bee colonies, unless litigation was instituted or threatened (Coleman 1979, Pimentel 1981). It is generally believed, but undocumented, that beekeepers have overestimated the severity of the problem, while pesticide applicatiors have underestimated the extent of the problem.

In Indiana, application of those products which have been classed by the United States Environmental Protection Agency (EPA) as “Restricted Use Pesticides is regulated by the State Chemist’s Office. This office has the responsibility for enforcing the laws and regulations relating to pesticides including pesticide applicator testing and certification.

Because many individuals who apply pesticides may never use a restricted product, many private applicators are not required to be trained or show competency in pesticide use. The Indiana Cooperative Extension Service and the Office of the State Chemist have worked together to train pesticides applicators in the safe handling and application of pesticides, as well as safety to the environment. Pesticide applicators are further divided into those who apply pesticides for hire and those who use the products only in conjunction with their own crop production operation. These groups are referred to as Public Pesticide Applicators and Private Pesticide Applicators, respectively.

Among the information which is required for certification is knowledge of the safe handling and use of pesticides, including their toxicity to non-target organisms such as the honey bee. The issue of honey bee poisoning is a complicated one and can not be covered in depth during applicator training due to time constraints.

The factors which determine the extent to which a given colony of honey bees will be affected by the application of a pesticide to a given field are complex (Atkins 1981, Johansen 1977, Lieberman 1964, Quatitlebaum 1983). The single most important factor is the number of bees from a particular hive that are foraging in the treated area (Nowakawski 1982). This is influenced by many factors such as attractiveness of the crop treated, presence or absence of blooming weeds in the area, distance from the treated field to the colony, strength of the colony, weather, needs of the particular colony, genetic make-up of the colony, etc (Atkins 1977, B.J. Erickson 1983a, Mayer 1983, Mayland 1970, Smirle 1987, Ross 1981, Wailer 1984).

In addition to factors relating to the honey bee colony, factors relating to the pesticide such as the active ingredient, the formulation, the time of application, the method of application, the weather conditions during and following application, etc., will all influence the extent to which a given colony will be affected. There is the additional complicating factor that some pesticide products may cause no observable damage at the time of application, but may cause delayed mortality of the overwintering colony during a period of greater stress.

The synthetic pyrethroid insecticides are of particular concern in this regard due to the inverse relationship between their toxicity and temperature (Yu 1984). Lehner (in press) has shown that the toxicity of permethrin to bees dramatically increases at 20 degrees C over the toxicity at 26 degrees C. Delayed mortality may often not be detected or identified as a result of earlier pesticide exposure. The insecticide stored in the hive may not singularly cause colony mortality, but may act in conjunction with other factors to increase the stress on the hive and cause a decline of the population. This decline may or may not be reversed by the colony as weather and other conditions improve, depending on their reserve strength and size of the initial population.

An understanding by both beekeepers and pesticide applicators of the factors that influence poisoning of colonies of honey bees by pesticides is critical to establishing a situation in which the two groups can operate without conflict. Because this is such an emotional issue, it is often difficult to separate emotion from fact when discussing this subject with either side. Given the complexity of the problem and the limited resources available to try to deal with the situation, a multi-faceted approach to the problem was undertaken. This included laboratory work to examine some the the most critical questions relating to synthetic pyrethroids and bees as well as an examination of the groups of people directly involved; that is beekeepers, farmers and public pesticide applicators in Indiana.