Bringing new insecticides to market:
Although the Food Quality Protection Act of 1996 (FQPA) has resulted in restrictions on the use of OP insecticides in pome fruit production, it has allowed for expedited registration of new insecticides under the “reduced risk” and “OP alternative” programs. An unanticipated consequence of this action is that new insecticides often receive registration before researchers have had the opportunity to fully understand their role in the orchard environment. It is our hope that growers appreciate the measured steps researchers take before recommending a new insecticide for a specific pest.
Four methods are used to evaluate the potential of new insecticides:
• Laboratory bioassays
• Field-Aged bioassays
• Small-plot field trials
• Large-plot field trials
Laboratory bioassays:Using a variety of techniques (e.g. direct sprays, apple-dip or leaf-dip bioassays) the toxicity of candidate insecticides is evaluated in the laboratory. These bioassays provide a means of determining relative toxicity and whether further testing is warranted. Insecticide manufacturers have a general idea as to which group of insects are affected by their experimental product, but local researchers have the ability to test new insecticides against the pests common to a specific region. Laboratory bioassays can also be used to screen new insecticides against a variety of beneficial insects. Further, these bioassays form the basis of resistance monitoring. A concentration of an insecticide that kills 50% of the pest is called the LC50. These LC50 values are determined for new insecticides using a susceptible laboratory maintained population and provide “base-line” data on the pest’s susceptibility. This information can then be compared to LC50 values obtained from field-collected populations of the pest to see if resistance to the new insecticide is present or has changed over time. Any significant shift in toxicity noted in field-collected populations suggests that tolerance or resistance could limit the efficacy of a new insecticide in commercial orchards.
Field-aged bioassays:This technique involves spraying a candidate insecticide onto individual trees and then collecting and returning foliage or fruit to the laboratory at regular intervals to assess residual toxicity. Field-aged bioassays are used to identify the best rates and treatment intervals to use.
Small-plot field trials:Once a good idea of an insecticides rate range is determined from field-aged residue bioassays field-trails are initiated. In these trials the insecticide is applied to replicated, single-tree plots using a handgun sprayer. A relatively large and uniformly distributed pest population is needed for this type of trial. To maintain standardization among all treatments they are applied at full dilute rates to ensure excellent coverage of foliage and fruit. Thus, confounding factors of coverage or concentration are eliminated and the results tend to be consistent and repeatable. An effort is made to evaluate candidate insecticides in a number of different locations under a variety of pest pressures. This allows researchers to adjust rates and modify timing intervals gaining an understanding of how the insecticides perform in different situations. Small-plot field trials targeted for one pest allows a glimpse at the selectivity of the insecticide. It can take three years or more of testing before researchers are confident of recommending a use pattern that best fits the conditions and pest complexes of the region.
Large-plot field trials:Large-plot field trials are an important step in understanding how a new insecticide will fit into a pest management program. The small-plot trials can determine rate and interval information for a particular pest but are not robust in identifying other positive or negative effects on the orchard ecology. In these tests an insecticide is applied by an air-blast sprayer at rates and volumes used commercially. The effect of a new treatment program is then evaluated by carefully sampling all pest and beneficial arthropods. These trials are labor intensive and costly but reveal the full impact of a new insecticide implemented as a grower would. These kinds of trials need to be evaluated at the same location for more than one year to gain a true understanding of any long-term changes in orchard ecology.
A consequence of rule changes under FQPA is that pesticide companies
no longer obtain Experimental Use Permits (EUP) to allow for large
plot field testing prior to final registration. That is because
they would have to give up a position in the EPA registration cue,
replacing another insecticide they want registered, and the data
required for an EUP is essentially the same as for full registration.
The result has been to limit the ability of researcher to evaluate
new insecticides using typical grower practices. Due to this limitation,
the impact of a new insecticide is typically not fully understood
at the time of registration. Therefore, large-plot field trials
are generally conducted after an insecticide is registered delaying
the optimized recommendations on how to use them coming from unbiased