THIRD WORLD NETWORK BIOSAFETY INFORMATION SERVICE
Dear Friends and Colleagues
2,4-D and Dicamba Found to Have Lethal and Sub-lethal Effects on Lady Beetles
Currently, nearly all soybeans, cotton, and maize grown in the USA are tolerant to the herbicide glyphosate. A growing number of weeds have evolved resistance to glyphosate, and in response, there have been recent increases in the use of 2,4-dichlorophenoxyacetic acid (2,4-D) and dicamba alongside glyphosate to sufficiently control the resistant weeds.
2,4-D-resistant crops were registered by the US-EPA in 2014 and dicamba-resistant crops are undergoing registration. One risk posed by these pesticides is the potential lethal or sub-lethal hazards that their active ingredients may pose to non-target species and the ecosystem services that these species provide. Past studies have found harmful effects of 2,4-D on honey bees, dung beetles, earthworms and amphibians.
Lady beetles, which are beneficial insects, have been used as an indicator species for the testing of non-target effects of pesticides. A recent study has found that 2,4-D and dicamba active ingredientsand commercial formulations can cause both lethal and sub-lethal effects on a lady beetle species. The study found that commercial formulations of 2,4-D were highly lethal to lady beetle larvae. In this case, the “inactive” ingredients were a key driver of the toxicity. So-called “inactive’’ ingredients in pesticide formulations typically constitute the majority of a pesticide’s volume and can sometimes be more toxic to non-target species than the active ingredients.
Meanwhile, the dicamba active ingredient significantly increased lady beetle mortality and reduced their body weight. Lady beetles administered the dicamba active ingredient were significantly smaller than the control beetles and larvae administered the combined herbicides produced significantly smaller pupae than the water-treated control. The commercial formulations of both herbicides also reduced the proportion of males in the lady beetle population.
With best wishes
Third World Network
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UNINTENDED EFFECTS OF THE HERBICIDES 2,4-D AND DICAMBA ON LADY BEETLES
by Laurène Freydier and Jonathan G. Lundgren
EcotoxicologyVolume 25, Issue 6
DOI: 10.1007/s10646-016-1680-4
Abstract
Weed resistance to glyphosate and development of new GM crops tolerant to 2,4-dichlorophenoxyacetic acid (2,4-D) and dicamba is expected to lead to increased use of these herbicides in cropland. The lady beetle, Coleomegilla maculata is an important beneficial insect in cropland that is commonly used as an indicator species in safety evaluations of pesticides. Here, we examined the lethal and non-lethal effects of 2,4-D and dicamba active ingredientsand commercial formulations to this lady beetle species, and tested for synergistic effects of the herbicides. Second instars of lady beetles were exposed to an experimental treatment, and their mortality, development, weight, sex ratio, fecundity, and mobility was evaluated. Using similar methods, a dose-response study was conducted on 2,4-D with and without dicamba. The commercial formulation of 2,4-D was highly lethal to lady beetle larvae; the LC90 of this herbicide was 13 % of the label rate. In this case, the “inactive” ingredients were a key driver of the toxicity. Dicamba active ingredient significantly increased lady beetle mortality and reduced their body weight. The commercial formulations of both herbicides reduced the proportion of males in the lady beetle population. The herbicides when used together did not act synergistically in their toxicity toward lady beetles versus when the chemistries were used independently. Our work shows that herbicide formulations can cause both lethal and sublethal effects on non-target, beneficial insects, and these effects are sometimes driven by the “inactive” ingredients. The field-level implications of shifts in weed management practices on insect management programs should receive further attention.