What is the Problem?
Pollinator health has recently been the focus of popular media, environmentalists, apiary specialists, and scientists. In 2006, unusually high honeybee colony losses were reported by beekeepers in the United States and other countries. This syndrome is now known as colony collapse disorder. In addition to issues with honeybees, attention to bumblebees and other bees has raised concerns of declines in the number of species and abundance of these pollinators.
What is the Cause?
Numerous scientific studies, both laboratory and to a lesser extent, field studies, have been conducted to identify causal factors of changes in honeybee and bumblebee populations, which vary between the two species. In recent reviews of the data, scientists have identified the interaction of multiple primary factors that affect honeybee health that include parasites (Varroa mites), pathogens (fungi, viruses), nutrition, and colony maintenance. To a lesser extent, pesticides may interact with the above factors, resulting in sublethal effects that may affect colony health.
Data suggest that pesticides in general, and neonicotinoids in particular, are not primary factors in colony collapse disorder. For bumblebees, data suggest that pesticides may play a role, but there is still a need for more field level studies. There are many “issues” associated with the interpretation of the data from research studies. For example, laboratory studies tend to evaluate levels of pesticides that are greater than bees are likely exposed to under field conditions. This questions the accuracy of inferences from lab to field situations. Because of the variable results from different lab and field studies, interpretation can be quite variable.
What About Neonicotinoid Insecticides?
Some groups have focused on the class of insect neurotoxicants called neonicotinoids (neonics), citing them as a major cause of the problem with bee health.
In the green industries, these include imidacloprid, thiamethoxam, clothianidan, acetamiprid, and dinotefuran. They have many desirable features such as broad-spectrum activity, low application rates, low mammalian toxicity, systemic movement upward in plants, and multiple application methods (soil drenches, foliar sprays, or injected into plants). They have proven to be very effective, and generally safe in controlling many sucking, plant boring, and turf-feeding insects.
Their distribution throughout the plant, and long residual activity have contributed to their effectiveness, and wide use for controlling plant damaging insects. Neonics are especially useful for tree conservation and invasive insect species management. For invasive species such as emerald ash borer, Asian longhorned borer, and hemlock wooly adelgid, neonicotinoids are one of the only effective tools towards preventing massive loss of trees in our urban landscapes.
These benefits also suggest they may result in greater risk to pollinators. Statements have been made that higher rates of these chemicals are applied in ornamental systems, and that this increases risk to pollinators. Of particular concern is neonicotinoids sprayed on open flowers of insect-pollinated plants, or the potential of some plant species to move the chemical systemically into pollen, nectar, and guttation fluids, posing particular concern for exposure to pollinators.
There is still a lot we do not know about the effects of all pesticides, including neonics, on pollinators and other beneficial insects, and their movement into and residual activity in various plant parts.
Regulations restricting the use of neonicotinoid have been implemented in Europe, and are under discussion in Canada. In the United States, the EPA has accelerated their reviews, and mandated the addition of a “bee advisory box” on all products containing them. There is pressure from various groups to remove or further restrict their use, especially from ornamental and turfgrass systems.
First, neonicotinoids are in the spotlight as a major factor affecting bee health, regardless of what the data suggest. In addition, complete information is still lacking on their impacts on pollinators. Second, the green industry tends to rely on products that contain neonics for managing a wide array of pests. In some situations these are the best or only choices, for other pests there are alternatives management tactics that could be used. Third, there is the potential for EPA to remove or greatly restrict the use of neonicotinoid insecticides, especially use in ornamental and turf systems.
Therefore, it would be wise to reduce the use of and reliance on neonicotinoids, and to be sure you and your employees are aware of risks of the insecticides they’re applying to pollinators and non-targets in general. Many other insecticides are also toxic to pollinators and non-targets. Be sure to READ THE LABEL thoroughly and follow the directions.
Pest Management Considerations
Choose non-chemical management tactics whenever possible. Select pesticides that have low impact on and risk to pollinators. Use neonics only when other effective products do not exist (reduce reliance on neonicotinoids). Avoid their prophylactic use (e.g. do not make applications unless you actually have an insect at levels likely to cause damage to the plant). Know which plants are wind-pollinated vs. insect-pollinated. Do not apply foliar sprays to insect-pollinated plants until after petal drop. Similarly, try to avoid trunk and soil injection of neonicotinoids on insect-pollinated plants, as not enough is known on their residual levels of in nectar and pollen.
One of the causes of honeybee and bumblebee troubles is a small parasite called a varroa mite. Varroa mites were first found in Maryland in the early 1990s. Since then they have been found in honeybee colonies worldwide. They spread from colony to colony by drifting workers and drones within an apiary. Honeybees can also acquire these mites when robbing smaller colonies. The pest is also moved about by transporting honeybee colonies from one state to another.
Varroa mites (Varroa jacobsoni) are external parasites that attack adults and the brood, with a distinct preference for drone brood. They suck blood from both the adults and the developing brood, weakening and shortening the lifespan of the ones on which they feed. The emerging brood may be deformed with missing legs or wings. Untreated and increasing infestations of varroa mites will kill entire honeybee colonies. This mite has also been found to transmit disease to bees.
The adult females are reddish-brown, flattened, oval, and measure about 1 to 1.5 mm across. They have eight legs. They are large enough to be seen with the unaided eye, most commonly on the bee’s abdomen, sometimes on the thorax. Their flattened shape allows them to hide between the bee’s abdominal segments.
Under field conditions these mites were shown to be highly effective vectors of deformed wing virus (DWV) between bees. This causes bees to have deformed wings that do not allow flight. A relationship was found between increasing numbers of mites on individual bees and the incidence of morphological deformity and death.
If one colony is found to be infested, all colonies at the site are generally treated with Apistan strips. These strips contain the miticide fluvalinate and are not to be used during honey flow, or when there is surplus honey present in the colony that may be removed for human consumption at a later date. This use of a miticide in a honeybee colony is not completely desirable for honeybees, but the varroa mite is considered the greater threat to bee colony health.
A predatory mite that has been used for fungus gnat control is now being used in honeybee colonies to reduce varroa mite populations. Hypoapis miles was tested by Canadian researchers and honeybee keepers in 2013 and 2014 for its effects on the numbers of varroa mites in infected hives. Positive results have been found so far.
Neonicotinoid and Fungicide Impact on Bees
Several researchers are examining the impact of neonics, and classes of fungicides including chlorothalonil and how they impact bees. Researchers in England have developed a small transmitting antenna that weighs one-tenth the weight of the honeybee female, and can be attached to the upper thorax. The female honeybee can carry up to half of her body weight in nectar and pollen, so the weight of the antenna does not impinge on her flight. The researchers used a radar disc and computer software to track the flight of the honeybee.
Honeybee researchers in Germany are using this system to track honeybees exposed to the product under lab conditions. They found that exposing bees to 5-50 parts per billion of neonicotinoids results in behavior modification and in some cases, death. Untreated honeybees were released, along with bees fed the nectar with neonicotinoid added at 6 ppb. The bees appear to have an internal tracking system that allows to find their hive. When they are released in unfamiliar surrounding they will use visual cues to locate the hive. The treated and untreated bees return with little trouble.
The trials were varied by moving the honeybees to an unfamiliar location and releasing neonic-treated bees along with control honeybees. The untreated honeybees found the hive 100% of the time in the trials. Honeybees treated with neonics had greater difficulty locating the hive with the visual cues and many did not return to the hive. Keep in mind these honeybees were artificially treated in lab conditions, then released.
Researchers in England are mounting the micro-antennae on honeybees and tracking their foraging patterns. The purpose is to determine whether in field conditions honeybees dilute the neonic nectar with other nectar sources and what impact this has on bee health. Research is continuing into 2015, with results will possibly available that year.
In France neonicotinoids were banned more than ten years ago, but beekeepers continue to experience colony bee health issues even in their absence. Neonicotinoids are widely used in agriculture in Australia where bee colonies so far appear to be doing fine.
Land use researchers are looking at historical use of rural land and comparing it to modern agricultural practices. In the early 20th century, land use involved multiple crops with many open areas with diverse pollen sources. In the 21st century, large plantings of a limited number of crops planted in large blocks is the norm. Many of these crops are poor pollen sources for pollinators. Bee colony health appears to be tied to honeybee foraging on multiple sources of nectar. British researchers are conducting field trials, planting strips of various flowers to serve as diverse nectar sources. They are finding bumblebee species population are up to six times greater in number at the farm featuring pollen-rich and diverse flower sources.
This practice of planting pollen source planting strips, at least based on early stages of investigation, appears to be a good way to improve pollinator health.
The University of Maryland Extension will continue to provide information on all alternative control materials and tactics. We will be posting relevant publications of research or reviews of research on the UME IPMNet web site extension.umd.edu/ipm
Photo 1 – Healthy, working bumblebee.
Photo 2 – Varroa mite on a bee nymph
Stanton Gill is an extension specialist (professor-ranked principal agent) in IPM and entomology with the University of Maryland Extension, based at the Central Maryland Research and Education Center in Ellicott City. He is also a professor in the Landscape Technology Program at the Germantown Campus of Montgomery College. Contact him at [email protected]