Neuroactive Insecticides – Death by Default

Neonicotinoid insecticides are neuroactive insecticides that are used for insect management on agricultural crops, lawns, and gardens, and in flea and tick pet treatment. They were once considered a breakthrough (Fairbrother et al., 2014) for getting rid of a broad range of insect pests (Gu et al., 2014) and they are still the most popular insecticides among farmers. The way that neonicotinoids work is related to the central nervous system (CNS) and that is the reason they are called neuroactive.

According to Hopwood et al. (2012), neonicotinoids are directly absorbed by plant tissues. Insect pests that feed on any part of the plant ingest the insecticides that permanently bind to their nerve cells causing hyperactivity, paralysis, and eventually death (Tingle et al., 2003). Other secondary effects of neonicotinoids are insects’ immune system, navigation, memory, stamina, and fertility. The problem with neonicotinoids is that their action is indiscriminating. They kill any insect, pest, or other, including honeybees. Consequently, neuroactive insecticides are also a major concern for honeybees as they accumulate in the pollen and nectar that bees are fed from or come in contact with (Codling et al., 2015).

Honeybees have broad food preferences thus foraging at many different types of flowers. The efficiency of this foraging is a direct result of their ability to learn, remember, and communicate sensory information. When the bees fly from flower to flower to collect pollen and nectar, they either die immediately from the insecticides, or if they are lucky enough, they manage to reach the hive with the insecticides on their body and the contaminated pollen. As a result, the insecticides are transferred to the entire population (young bees, drone, worker bees, queen), as well as the wax, pollen, honey, and royal gel, resulting in continuous exposure of all life stages (embryo to adult, Alaux et al., 2010).

Neonicotinoids also have a detrimental neurological effect on the bees such as motor, memory, and behavioral abilities which are related to the bees’ daily lives (Thompson, 2003; Blanken, van Langevelde, & van Dooremalen, 2015). For example, bees are mapping potential food locations using their navigation system and olfactory association learning to locate flowers. Neonicotinoids impair foraging behavior, short-and long-term memory, and weaken the bees’ immune system, stamina, and fertility. Nosema is one type of disease that colonies are faced with in the U.S. (Alaux et al., 2010). Therefore, to provide maximum protection for honeybee populations, the application of pesticides should be avoided, especially during the bloom season, and, if necessary, applied in such a way that minimizes damage to honeybees. However, even when restrictions on neonicotinoids are placed by governmental bodies during bloom season, farmers ignore these.

References:
Alaux, C., Ducloz, F., Crauser, D., Le Conte, Y. (2010). Diet effects on honeybee immunocompetence. Biol Lett, 6: 562–565. https://doi.org/10.1098/rsbl.2009.0986 PMID: 20089536
Blanken, L. J., van Langevelde, F., van Dooremalen, C. (2015). Interaction between Varroa destructor and imidacloprid reduces flight capacity of honeybees. Proc R Soc B Biol Sci., 282. https://doi.org/10.1098/ rspb.2015.1738 PMID: 26631559
Fairbrother, A., Purdy, J., Anderson, T., & Fell, R. (2014). Risks of Neonicotinoid Insecticides to Honeybees. Environ. Toxicol. Chem. 33:719-731.
Gu, M., Merchant, M., Robbins, J., & Hopkins. J. (2014). Crape Myrtle Bark Scale: A New Exotic Pest. Tex. A&M AgriLife Ext. Bul. EHT-049.
Hopwood, J., Shepherd, M. (2012). Neonicotinoids in Your Garden. Wings Mag Newsl. (Fall):1–7.
Tingle, C. C. D., Rother, J. A., Dewhurst, C. F., Lauer, S., King, W. J. (2003). Fipronil: environmental fate, ecotoxicology and human health concerns. RevEnviron Contam 176:1–66
Thompson, H. M. (2003). Behavioural effects of pesticides in bees—Their potential for use in risk assessment. Ecotoxicology, 12: 317–330. https://doi.org/10.1023/a:1022575315413