Pollinator Partnership works with diverse stakeholders representing various perspectives with the goal of creating positive change for pollinators. We work with farmers, gardeners, land managers, scientists, and industry to develop tools and programs that help keep pollinators safe from pesticides, habitat loss, climate change, and other threats.

Threats to Pollinators And why they need our help

Below are some pollinator trends by the numbers:

• Monarch overwintering loss in the western population has risen from between 35-49% to a 58% seasonal decrease;

• Several species of native bumble bees have exhibited declines in geographic range and number in the last twenty years, including common bumble bee, western bumble bee, and Rusty-patched bumble bee;

• The number of managed honey bee colonies in the United States has dropped from 5 million in the 1940’s to approximately 2.68 million in 2023, according to the USDA Animal and Plant Health Inspection Service

Habitat Loss

Agricultural Intensification

Agricultural intensification refers to the process of changing agricultural practices that make use of an area more frequently or more intensely in order to increase the yield per unit of farmland. This process can have unexpected impacts on pollinators, increasing residual pesticides, reducing habitat connectivity, and decreasing the botanical biodiversity. These multiplying factors have negative effects on pollinator health by reducing or eliminating important food sources, decreasing the carrying capacity for pollinators across the landscape and nesting habitat.

Human Development

The interactions between human development, biodiversity, and conservation are complex and multifaceted. The rapid spread of human development can lead to habitat fragmentation of important species groups including pollinators. Other factors associated with human development such as the Introduction of non-native and invasive plants and animals can also negatively impact the ecosystem by outcompeting native plants for resources. Studies show the linkage between the increase of impervious surfaces with reduced bee and butterfly species richness, reducing the overall biodiversity within urban areas.

Expansive Lawns and Increased Use of Non-Native Plants

Pollinators rely on certain flower species for nectar and host sites. Native plants, or plants that have historically been a part of the natural environment of a region, provide the most benefit to pollinators. The introduction and expansion of non-native plants, or plants that have not historically been part of a region, impact the abundance of native plants required by pollinators such as bees, butterflies, and birds to forage and reproduce. Non-native plants such as cultivar and hybrid plant species are, in most cases, not good for pollinators as they can result in double flowers, changes in flower color, and sterile flowers with no pollen. Furthermore, the expansion of grass lawns reduces plant species richness and the overall biodiversity of developed areas.

Climate Change

Climate change is the result of increased greenhouse gas emissions, primarily carbon dioxide, from the anthropogenic burning of fossil fuels into the atmosphere . Climate change effects such as increased temperatures and more severe weather events have potential negative impacts on important pollinator species. These effects include destruction of habitat and range shifts of native species. Climate change is thought to be a key cause of pollinator decline across the globe. Pollinators, plants, and their interactions will continue to be impacted by a warming climate.

Increased Temperature and Range Shifts

The potential impacts of increased temperatures on pollinators may widely alter their range and distributions. As temperatures increase, suitable habitat for nectar resources and nesting sites become limited. To combat this change, pollinators have begun shifting their ranges north and into higher altitudes. For example, bumble bees are more common in cooler regions due to their cold-adapted fuzzy bodies; however, climate change is resulting in populations disappearing from the southern parts of their range, suggesting that these populations are getting squeezed out of suitable habitats. Additionally, some bumble bee populations are not shifting their range north, but rather shifting towards higher altitudes in mountainous regions. Migration towards mountain areas may result in increased resource competition with existing bumble bee populations.

Higher temperatures are also associated with increased aridity, potentially reducing available forage and water sources. This is a greater concern to pollinator populations located in already arid regions. For example, bats require specific temperature ranges for their roosting habitat and are not well adapted to even slightly higher temperatures. These bats must drink every night to stay hydrated, especially nursing females in the summer season. Increased aridity implies a stress on the reproductive ability of bats, leading to bat population declines.

Mis-matched Phenology of Plants and Pollinators

Climate change effects include warmer temperatures, less snow cover, more frequent droughts, and less predictable frost and flowering times. Research suggests that the mismatching of flowering time and pollinator visitation leads to decreased pollination and starving pollinators. For example, temperature increases impacts the blooming periods for a number of host plants and in the case of the Karner blue butterfly, increasingly warmer temperatures are causing its host plant, the wild blue lupine (Lupinus perennis), to emerge sooner in the year, leading to a decline in the larval success rate of the Karner blue.

Increased Extreme Weather Events

The most critical factor affecting pollinator populations is weather: precipitation and temperature. It has been found that climate change-induced higher temperatures and heavier rainfall is associated with lower native bee abundance. This is because weather factors directly impact the growing season thus limiting flight time for foraging due to heavy rain and reducing forage availability due to hot summer weather. This can impact the ability to forage provisions for the next generation of bees, resulting in population declines. Research also shows that changing weather patterns cause an earlier spring onset, resulting in higher pre-emergence weight and higher mortality rates post emergence. In 2023, severe rain and wind storms moved through California that caused a 60% die-off of western monarch butterflies. This population was overwintering in non-native eucalyptus tree groves on the California coast. Monarchs usually experience a die-off rate between 38-49%, however severe climatic events may result in increased overwintering mortality.

Extreme Drought

Like humans, pollinators require water to survive. Current climate predictions suggest that average annual temperatures will rise in temperate zones, leading to exasperated summer droughts and overall water deficits. This can have negative implications for plant-pollinator interactions because pollinators require the nectar from native plants for growth and reproduction. Reduced floral resources can potentially cause pollinator population declines. This is for two reasons: reduced pollinator attraction to flowers and decreased nectar volume. Drought may compromise floral signaling, possibly eluding visiting pollinators as a result of less vibrancy or reduced size of flowers. Additionally, drought directly impacts the volume of nectar available for pollinators to harvest as drought reduces the rate of photosynthesis. Overall, drought impairs the productivity of floral resources, potentially altering important plant-pollinator interactions, which may result in loss of nectar and pollen resources imperative to pollinator populations.

Misuse of Pesticides

A pesticide is a substance used to control unwanted plants, insects, rodents, or plant diseases. Pesticides include herbicides, insecticides, rodenticides, and fungicides. Insecticides have the biggest impact on pollinators. Using proper application practices when applying any pesticide is very important in keeping pollinators (and people) safe. Most pollinator poisoning occurs when pesticides that are toxic to pollinators are applied to crops during the blooming period. Poisoning of pollinators can also result from:

• Drift of pesticides onto adjoining crops or plants that are in bloom

• Contamination of flowering ground cover plants when sprayed with pesticides.

• Pesticide residues being picked up by foraging pollinators and taken back to the nest/colony.

• Pollinators drinking or touching contaminated water sources or dew on recently treated plants.

Home use of herbicides and insecticides may inadvertently remove important plants required for pollinators to survive. Habitat alteration or reduction may impair a pollinator’s ability to navigate and reproduce. Reduced immune response in bees is also associated with pesticide use.

Agricultural use of pesticides has a significant impact on the landscape and pollinators. Used to optimize production, agricultural pesticides target unwanted pests and weeds. However, pollinators are often caught in the crossfire. Direct impacts such as exposure to toxic substances can kill common pollinators such as the honey bee. Agricultural use of pesticides may also harm non-target plants that are important to pollinators for nectar and reproduction. Indirect impacts of pesticides include contaminated soil and waterways.

It’s important to review the effects of pesticides in terms of timing, concentration, and location. The use of pesticides may be implemented as a part of Integrated Pest Management (IPM). The goal of IPM is to solve pest problems at a small or large scale while reducing risk to the environment. IPM plans benefit from a combination of management approaches that use different modes of action and strategies, taking advantage of physiological, ecological, and behavioral characteristics of the target pests. By utilizing non-pesticide approaches first, this reduces potentially toxic exposure to pollinators. The means of applying chemicals are also important in mitigating exposure to pollinators. Growers are encouraged to use a multi-faceted approach that combines physical, biological, chemical, and cultural control methods. In addition, biocontrol is an emerging alternative to common pesticides. Biocontrol is the use of natural enemies to manage unwanted pest populations. The benefits of biocontrol include:

• Easy and safe to use

• Cost-effective

• Environmentally sound compared to conventional pesticides

• Can be implemented as a component of IPM

• Can be target-specific

Click here to learn more about how you can protect pollinators from pesticides: https://www.pollinator.org/pesticide-education

Parasites and Pathogens

Pollinators also face pressures from parasites and pathogens that can infect their colonies, decrease their health and lower their numbers. A parasite is an organism that lives on or in a host organism and gets its food from or at the expense of its host. A pathogen is a bacterium, virus or other microorganism that can cause disease. Like the other mentioned pressures, the prevalence of parasites and pathogens are linked to and worsened by other pressures. The threats from parasites and pathogens look slightly different depending on if the pollinator is managed by a human versus if they are in a wild colony.

Native Pollinators

Monarchs and Ophryocystis elektroscirrha (OE)

Monarchs are susceptible to the damaging effects of the parasite, Ophryocystis elektroscirrha, otherwise known at OE. Parasite spores from OE on monarch adults are deposited onto eggs and milkweed and then ingested by the larvae. The parasite can reduce larval survival, butterfly size, life span, mating success, and the ability to fly. The prevalence of infection by OE increases with monarch density at local scales and is negatively correlated with the ability to migrate. As infection prevalence is highest in sedentary monarch populations, this has led to speculation that the use of non-native milkweeds such as the introduced Tropical milkweed species, Asclepias curassavica, leads to higher incidence of OE in Monarch populations. However, there is debate about this and further research is needed to confirm the relationship.

Bumble Bee Parasites

Bumble bees face health challenges from parasites such as Crithidia bombi, a widespread parasite which can infect colonies, and reduce reproductive ability and lifespan. C.bombi infects the gut of the host bee and impairs the bee’s ability to forage. There is some evidence that transmission can happen to bees who forage on flowers previously visited by infected individuals. Additionally, there is some evidence of spillover between managed and wild populations. Further research is needed to monitor this disease in bumble bee populations as they are being increasingly utilized for commercial pollination services.

Monitoring efforts can help track parasites and pathogens in pollinator populations and give scientists an idea of how widespread these diseases are in both managed and wild populations. Resources are needed to study these parasites and pathogens so that treatments can be developed or prevent their spread all together.

Managed Bees

Parasites

One of the most well-known parasites of managed bees is the Varroa mite, or Varroa destructor, a leading cause of colony mortality in North American honey bee colonies. It is a non-native and invasive species introduced into the U.S. from Asia. Varroa is widely spread, detected in over 90% of the colonies in the U.S. sampled by the APHIS National Honey Bee Disease Survey. Varroa feeds on the blood of honey bees which leads to smaller and cognitively impaired bee individuals and less honey production. Not only does Varroa decrease physical fitness in honey bees by causing direct damage, they also compromise bee immune systems making them more susceptible to viruses. For more information please visit https://www.pollinator.org/miteathon

Pathogens

One of the viruses that can be introduced into managed bee colonies is the Deformed Wing Virus (DWV), which damages worker bees in the hive. Bees that are infected with DWV as larvae will have curly deformed wings as an adult and thus are incapable of flight. While this effect does not usually kill the bee directly, it does mean they cannot forage. There is no known cure for this virus so proper monitoring must be done regularly to avoid infestation of the hive.

Managed bees are susceptible to damage from bacteria as well. Paenibacillus is a bacteria that causes American Foulbrood disease. The disease can be recognized by the foul odor and sunken brood cell caps. The bacteria is transferred by the spores being fed to young larvae from the nurse bees which then germinate in the gut of the larvae. As the dead larvae cells are cleaned by the house bees, the spores can spread to the rest of the hive, causing infection.

Nosema ceranae is a fungus that can infect managed bee colonies and reduce reproductive fitness, suppress immune function, cause increased hunger and increase mortality. N.ceranae was first identified in the Asian honey bee in 1975 and eventually the fungus spilled over into honey bee (Apis mellifera) colonies in North America sometime in the early 2000s. Today, it can be found on all continents where A.mellifera resides and has a similar prevalence in both managed and wild bee populations.

Non-Native and Invasive species

Native plants and their pollinators have coevolved over thousands of years, thus the presence of ecoregionally-appropriate native plants provide the most benefit to pollinators while non-native and invasive species can negatively impact pollinators. For instance, while some pollinators are generalists and can forage on many different plant groups, other pollinators are more specialized and rely on certain native plant species for their nutrition. As those native plants disappear, get over taken by non-native plants or damaged by non-native species, these relationships between pollinators and native plants start to deteriorate, lowering biodiversity and the ability of ecosystems to thrive.

Non-native species and invasive species often refer to similar land management issues. However, these terms mean different things and it’s important to distinguish these differences when implementing species management strategies. A non-native species is a plant or animal that has been introduced into an area either deliberately or accidentally by human activities. Invasive species can be either native or non-native, but are unique given that they must do harm to the existing ecosystem in order to be considered invasive. Non-native invasive plant species are not native to the region and reproduce freely on their own. They invade natural or disturbed areas, outcompete native plants, and disrupt the ecosystem. For all concepts, it’s important to consider the location; a species that is native in one region may be non-native invasive in another.

A great example of how a non-native invasive species can impact pollinators is garlic mustard (Alliaria petiolata). Garlic mustard threatens native plants in forests of the eastern and midwestern U.S. by out-competing native species in the mustard family, known as “toothworts” (Genus Cardamine). Toothworts provide the primary source of food for caterpillars of the rare West Virginia White Butterfly (Pieris virginiensis). Besides damaging native toothworts, the chemicals in garlic mustard have a toxic effect on the White Butterfly’s eggs, keeping them from hatching when butterflies unwittingly lay their eggs on the plant’s foliage.

As mentioned previously, increasing temperatures often coincide with range shifts not only for pollinators but other insect groups as well. As invasive insect pests start moving into areas where they were not found previously, this can also damage the relationship between pollinators and their native host/ nectar plants. New pests in agricultural areas can lead to increased use of pesticides posing damage to host plants and a shortage of native plants.

For more information about how to select plants for pollinators, visit the Selecting Plants to Support Pollinators brochure.