Unintended effects of the herbicides 2,4-D and dicamba on lady beetles

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 ingredients and 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.

Exposure of the African mound building termite, Macrotermes bellicosus workers to commercially formulated 2,4-D and atrazine caused high mortality and impaired locomotor response

“…For example Hill et al [51] reported that the recommended concentration of a commercially formulated 2,4-D caused up to 80% mortality in the mirid, Ecritotarsus catarinensis (Carvalho) (Hemiptera: Miridae) after the insect was exposed for 72 hours. In addition, Freydier and Lundgren [14] reported 80% mortality in ladybug, Coleomegilla maculata De Geer (Coleoptera: Coccinelidae) larvae due to exposure to 2,4-D. Furthermore, Adam [52] reported four times mortality in three species of coccinelid beetle larvae, Coccinella transversoguttata (Fald.…”

“…Atrazine works by inhibiting photosynthesis by blocking electron transfer at the reducing site (plastoquinone binding site) of photosynthesis complex II in the chloroplasts in higher plants [10,11]. Although 2,4-D and atrazine based herbicides are among the most commonly used herbicides in many parts of the world (including Nigeria) due to its low cost, selectivity, efficacy and broad spectrum, their negative effects on beneficial and none target organisms are well documented in the literature [12][13][14][15][16].…”

“…Martinez et al [25] correlated the population declines in three dung beetles with the use of a 2,4-D commercial formulation. Furthermore, commercial formulations of 2,4-D has been reported to be highly toxic, increase development time and decrease male population in larvae of lady beetle, Coleomegilla maculata DeGeer (Coleoptera: Coccinellidae) [14].…”

Assessment of ecological risks of agrochemicals requires a new framework.

“…Examples include the lower fecundity of the pea aphid (Acyrthosiphon pisum) exposed to sublethal concentrations of Margosan-O extracts (active ingredient, azadirachtin) [66] and that of the cotton aphid (Aphis gossypii) exposed to cycloxaprid [67], both of which can help reduce the populations of those pests and achieve their effective long-term control. However, similar negative effects can be observed in beneficial, predatory and parasitoid arthropod species, such as the decrease in fecundity of predatory Coleomegilla maculata lady beetles after exposure to commercial formulations of 2,4-D and dicamba herbicides [68] and reduced ovipositions of Eriopis connexa lady beetles exposed to the insecticides teflubenzuron and cypermethrin [69]; the severe reduction in fecundity of predatory thrips (Scolothrips longicornis) exposed to abamectin [70]; or the reduced fecundity of the generalist predatory bug Orius armatus exposed to spinosad [71], amongst many others. Other non-target organisms also experience impaired reproductive effects; for example, the reduced fecundity of queen honey bees (Apis mellifera) exposed to sublethal doses of bifenthrin and deltamethrin [72] or to field relevant residues of imidacloprid [73,74]; the reduced spawning of Australian crimson-spotted rainbowfish (Melanotaenia fluviatilis) and medaka fish (Oryzias latipes) exposed to sublethal concentrations of esfenvalerate insecticide in water [75,76]; or the reduced population growth rate of Daphnia spp.…”

Preliminary Reports on Comparative Weed Competitiveness of Bangladeshi Monsoon and Winter Rice Varieties under Puddled Transplanted Conditions

“…Sometimes, herbicides have indirect effects on the phytophagous beneficial insects through destruction of their habitat or reduction of the nutritional value of their host plants [21][22][23]. Herbicides also have lethal and sublethal effects on ladybird beetles [24], green lacewings [25], earthworms [26], parasitic wasps, and honeybees [27] when they come into direct contact with herbicides either topically or through ingesting treated food materials. Furthermore, application of the same herbicide frequently over the years may produce herbicide-resistant weeds [28][29][30][31][32][33][34].…”