Use of glyphosate and glyphosate-based herbicides is ubiquitous in US agriculture and widespread around the world. Despite marketing efforts to the contrary, numerous studies demonstrate glyphosate toxicity to non-target organisms including animals, primarily focusing on mortality, carcinogenicity, renal toxicity, reproductive, and neurological toxicity, and the biochemical mechanisms underlying these physiological outcomes. Glyphosate toxicity also impacts animal behavior, both in model systems and in agricultural and environmentally relevant contexts. In this review, we examine the effects of glyphosate and glyphosate-based herbicides on animal behaviors, particularly activity, foraging and feeding, anti-predator behavior, reproductive behaviors, learning and memory, and social behaviors. Glyphosate can be detected both in food and in the environment, and avoided through activity and feeding strategies. However, exposure also reduces activity, depresses foraging and feeding, increases susceptibility to predation, interferes with courtship, mating, fertility and maternal behaviors, decreases learning and memory capabilities, and disrupts social behaviors. Changes in animal behavior as a result of glyphosate toxicity are important because of their sometimes severe effects on individual fitness, as well as ecosystem health. Implications for human behavior are also considered.

Herbicide use has increased dramatically since 2001, particularly Roundup^®. Effective in agricultural practice, Roundup^® adversely affects non-target organisms, including reproductive and endocrine systems. We exposed fruit flies, Drosophila melanogaster, to either Roundup^® Ready to Use, containing pelargonic acid and glyphosate, or Roundup^® Super Concentrate, that includes glyphosate and POEA, at sublethal concentrations. Both Roundup^® formulations reduced ovary volume with fewer mature oocytes, most adversely at the highest concentration tested. Flies exposed within 2 h of eclosion were affected more than at 4 h, suggesting a critical period of increased ovarian sensitivity. These results support multi-species evidence that glyphosate-based herbicides interfere with normal development of the reproductive systems of non-target organisms.

In a wild-type strain of Drosophila melanogaster Meigen, the antijuvenoid precocene I reduced primary sexual receptivity in a dose-dependent manner; exposure to 0.80 μmol halved mating by virgin females in a 1-h test. Precocene-treated females rejected courting males for longer times than control females, but the rates of rejection signaling per unit time were unaffected. Precocene I slowed ovarian growth and markedly reduced oviposition; exposure to 0.14 μmol of precocene decreased oviposition by about half. Protein deprivation severely reduced ovarian volume and lowered primary receptivity in 3-d-old flies. Protein-starved females decamped from courting males more than yeast-fed females did at all the ages tested, whereas both age and diet affected the rates of stereotyped rejection signals. Precocene II did not affect sexual receptivity, whereas exposure to 70–140 μmol of ethoxyprecocene reduced sexual receptivity significantly.

Genetically modified foods have become pervasive in diets of people living in the US. By far the most common genetically modified foods either tolerate herbicide application (HT) or produce endogenous insecticide (Bt). To determine whether these toxicological effects result from genetic modification per se, or from the increase in herbicide or insecticide residues present on the food, we exposed fruit flies, Drosophila melanogaster, to food containing HT corn that had been sprayed with the glyphosate-based herbicide Roundup^®, HT corn that had not been sprayed with Roundup^®, or Roundup^® in a variety of known glyphosate concentrations and formulations. While neither lifespan nor reproductive behaviors were affected by HT corn, addition of Roundup^® increased mortality with an LC₅₀ of 7.1 g/L for males and 11.4 g/L for females after 2 days of exposure. Given the many genetic tools available, Drosophila are an excellent model system for future studies about genetic and biochemical mechanisms of glyphosate toxicity.

Glyphosate is an active ingredient in the plethora of glyphosate-based herbicide (GBH) products available, such as Roundup, and is the most commonly used pesticide worldwide. Studies recognize that genetic and environmental factors contribute to the development of Autism spectrum disorder (ASD) in children, with a notable correlation between the increased use of glyphosate and reported ASD cases. ASD is a neurological disorder characterized by social impairments, anxiety, repetitive behavior, etc. Animal models simulating ASD - like behavior exhibited changes in behavior, such as increased repetitive behavior and social deficits, after prenatal glyphosate/GBH exposure. Furthermore, geographic and human surveys identified correlations between glyphosate/GBH exposure and development of ASD in children. Taken together, results demonstrate a strong relationship between the deleterious effects of glyphosate/GBH exposure and ASD development in children. Even if the individual contribution of GBH exposure represents only one of many environmental risk factors, ubiquitous exposure to GBH in public spaces, through occupational exposure, and as food residue contribute to its importance. Additional research is needed to distinguish glyphosate's impact during prenatal and postnatal exposure, test differences between pure glyphosate and various GBH formulations, and further elucidate the relationship between exposure and ASD development in humans.

With the rise in concern about GMOs and pesticides on human health, we have utilized Drosophila melanogaster as a model organism for understanding the effects of Roundup-Ready^® GMO diets on health. We recorded dietary behavior during and after exposure to a medium containing GMO or non-GMO corn, Roundup^® in organic corn medium, and sucrose with or without one of the two Roundup^® formulations. No differences in behavior were observed when Drosophila were exposed to a medium containing Roundup-Ready^® GMO or non-GMO corn. Drosophila can detect and refrain from eating sucrose containing one Roundup^® formulation, Ready-to-Use, which contains pelargonic acid in addition to glyphosate as an active ingredient. Drosophila exhibited dose-dependent increased consumption of sucrose alone after exposure to a medium containing either Roundup^® formulation. This may indicate that flies eating a medium with Roundup^® eat less and were thus hungrier when then given sucrose solution; that a medium with Roundup^® is more difficult to digest; or that a medium with Roundup^® is less nutritious, as would be the case if nutritionally important microbes grew on control medium, but not one containing Roundup^®.