The Problem with Fipronil

Many beekeepers are using fipronil to control small hive beetles (SHB). Even those who do not use fipronil are at risk of getting bees from yards where it is used. Studies show that even trace doses of fipronil can be lethal and bioaccumulate in honey bees. Beekeepers struggle to find natural ways to eliminate SHB. Milwaukee, WI based company Strong Microbials Inc has a product in the pipeline that offers natural, microbial based solutions for SHB.


Figure 1. Small hive beetle larvae destroy the frames of stored honey and pollen (above) and cause bees to abscond the hive. Small hive beetles cause roughly 4.8 million dollars in damage each year.

There is no treatment for
Small Hive Beetle infestations

The small hive beetle (SHB), Aethina tumida, is native to sub-Saharan Africa but has spread to most of the world and has become a serious problem for beekeepers. SHB lay large numbers of eggs which hatch into larvae that feast on brood, pollen and honey. Control is often difficult as the maturing larvae burrow into the soil to pupate. SHB populations are usually controlled in strong hives but will wreak havoc on weak hives in a few days and force bees to abscond the hive.

In some countries, the presence of any SHB results in total hive destruction. In America, migratory hives are not allowed to cross state borders with SHB infestations. These precautions are necessary to avoid the transmission of SHB to neighboring hives. Unfortunately, there are a lack of effective methods to completely resolve the SHB problem which has also become a financial burden for beekeepers needing to replace expensive equipment and entire colonies from SHB damage. From an economic standpoint, SHB cause roughly 4.8 million dollars in damage assuming 1% of hives ($200/hive) in the US are lost each year to SHB.

The problem with fipronil

Fipronil is widely used as a broad-spectrum insecticide that acts on the central nervous system to control pests. According to entomologist Dr. Reed Johnson, fipronil is highly toxic to bees (LD50 = 4 ng/bee), blocking GABA, the primary inhibitory compound in the central nervous system, thus causing hyperexcitation and eventual death (Johnson 2015). Fipronil is being used as a non-EPA approved substance in the beekeeping industry to control in-hive SHB infestations. Research shows Fipronil has lethal and sublethal effects on honeybees, impairing drone and queen fecundity and colony collapse (Kairo et al. 2018, Holder et al. 2018).  

Research conducted by Kairo et al. placed drones in colonies that were fed either sugar syrup or fipronil (1 µg·L-1) contaminated syrup in small time intervals for 20 days. After 20 days, sexually mature drones were removed from exposed colonies and their semen was collected for quality assessment (spermatozoa concentration, spermatozoa mortality rate, reducing potential, ATP content). Queens were then artificially inseminated with the semen from control or exposed drones.

Experimental findings did not detect observable amounts of fipronil or associated metabolites in chemical analysis. Individual assessment of worker and drone survival did not appear to be negatively affected by exposure. These results are likely due to low levels of fipronil exposure. Behavioral effects are only observed at concentrations greater than 1 µg·L-1. Fipronil exposure decreases total spermatozoa concentration, increases spermatozoa mortality rate (Figure 2AB), and alters cellular function resulting in physiological disruptions, oxidative stress and reduced fecundity (Figure 2CD). Queens inseminated with fipronil exposed drones stored fewer spermatozoa with higher levels of dead spermatozoa compared to the control (Figure 3BD). These results indicate impaired fecundity in queens indirectly exposed to fipronil.


Figure 2. Drones exposed to fipronil for 20 days resulted in decreased spermatozoa (A), increased spermatozoa mortality (B) and increases in metabolic stress (C,D) leading to high rate in spermatozoa mortality.

Figure 3. Following fipronil exposure, drone semen was collected and used to artificially inseminate queens. The results show reduced spermatheca content (B) and viability (D) in queens inseminated with fipronil exposed drones.

Additional research by Holder et al.  placed honey bees into cages and were fed syrup containing different dosages of fipronil (0, 3.2, 8, 20, 50, 87.5, 125 µg·L-1). Colonies were monitored daily for mortality. The functional relationship between dietary concentration of pesticide and mean longevity were compared. Simulated population dynamics were used to validate experimental results of environmentally realistic fipronil exposure (5ppb) on adult workers compared to a control population.  


Figure 4. Longevity is reduced at a dose dependent rate in fipronil exposed colonies (closed circles) compared to control (open circles).

Figure 5. A represents simulated honey bee mortality associated with fipronil exposure over a 7-day period in control colonies (closed circles) and environmentally realistic exposure to fipronil (open circles). B represents colony size reduction associated with fipronil exposure over a 7-week period. Closed circles represent control colonies not exposed to fipronil. Open circles represent environmentally realistic exposure to imidacloprid. Closed squares represent environmentally realistic exposure to fipronil (2013 trial), open squares represent a replicated trial from 2015. Dashed line is the assumed minimum colony survival. Fipronil exposure increases honey bee mortality and decreases colony size

The experimental exposure to fipronil caused a dose dependent reduction in longevity (Figure 4). Simulated exposure resulted in mass mortality (20-50% of original population) during the first week (Figure 5). Prolonged simulated exposure resulted in colony collapse within a 3-week period. Additional results suggest that a single exposure to fipronil syrup persisted at the full dosage strength for at least 6 days. These results suggest bioaccumulation of fipronil metabolites are responsible for observed toxicity.

Is there another way?

Greater understanding of microbial community and ecology brought about the return of natural products as a means of biological control. Strong Microbials Inc are exploring a natural, microbial based, honey bee friendly product that wards off SHB without compromising the health and fertility of hive reproductive castes. BioBeetle is a new product that will be introduced to beekeepers in 2019. BioBeetle is toxic to SHB larvae and repels adult SHB from laying eggs in the hive. Extensive field testing indicates that this product can be safely applied inside the hive. In addition to in-hive application, BioBeetle can be applied to soil to repel SHB from propagating near the hives. BioBeetle will be the first safe, natural remedy to the SHB problem.

References:


Kairo, G., Provost, B., Tchamitchian, S., Ben Abdelkader, F., Bonnet, M., Cousin, M., Sénéchal, J., Benet, P., Kretzschmar, A., Belzunces, L. P., … Brunet, J. L. (2016). Drone exposure to the systemic insecticide Fipronil indirectly impairs queen reproductive potential. Scientific reports, 6, 31904. doi:10.1038/srep31904

Holder, P. J., Jones, A., Tyler, C. R., & Cresswell, J. E. (2018). Fipronil pesticide as a suspect in historical mass mortalities of honey bees. Proceedings of the National Academy of Sciences, 201804934. http://doi.org/10.1073/PNAS.1804934115

Johnson, R. (2015). Honey Bee Toxicology. Annual Reivew of Entomology, 60:22.1-22.20. 10.1146/annurev-ento-011613-162005

Author: Jennifer Gordon

Honeybee Research Scientist, Farmer

2 thoughts on “The Problem with Fipronil

  1. When will your “natural remedy” for SHB be available? I discovered going into Fall that I have a serious problem with SHB, and I want to hit them hard as soon as it warms up.

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