The original article was published by the Environmental Protection Agency March 21, 2019 and can be found here.
RT25 Data: What They are and Where They Come From
The residual time to 25% mortality (referred to as the RT25) values provided in the table below were compiled from registrant-submitted data submitted in order to fulfill the data requirement for Honey Bee (Apis mellifera) Toxicity of Residues on Foliage study (OCSPP Guideline 850.3030). This study may be conditionally required if the honey bee acute contact (or oral) median lethal dose (LD50) value (obtained from a honey bee acute toxicity test such as OCSPP Guideline 850.3020) is less than 11 µg/bee1.
The honey bee toxicity of residues on foliage study is a laboratory test designed to determine the length of time over which field weathered foliar residues remain toxic to honey bees, or other species of terrestrial insects. The test substance (e.g., a representative end-use product) is applied to crop foliage, the foliage is harvested at predetermined post-application intervals (i.e., aged residues), and test adult bees are confined on foliage with aged residues for 24 hours. Three treatment intervals (different durations of time that residues are aged between application and harvest) are typically used (e.g., 3, 8 and 24 hours post-application). At a minimum, the test substance should be evaluated at the maximum application rate specified on the product label. If mortality of bees exposed to the foliage harvested 24 hours after the application is greater than 25%, bees should continue to be exposed to aged residues on foliage samples collected every 24 hours (i.e., 48, 72, 96, 120 hours, etc. after the application) until mortality is 25% or less.
The table below represents all available RT25 values from studies submitted to the Agency which have undergone quality assurance reviews to ensure that the data are scientifically sound. Depending on the chemical tested, either the technical grade active ingredient or a specific formulation was tested using either the honey bee, alfalfa leaf cutting bee, or alkali bee; the table lists the test material and species tested. The table also denotes the plant species on which residues were aged.
RT25 values are a function of a number of factors including application rate, physical-chemical properties, dissipation, crop, and pesticide formulation. Thus, there is considerable variability in RT25 values within a single formulation, between formulations, between crops, and across application rates. The values included in the table are chemical and formulation specific. EPA plans to update this table as a more robust data set becomes available.