Pesticide use reduces population numbers of native foraging pollinators.  The extent of damage on native bees, wasps, beetles, moths and butterflies is largely unknown as most of the studies have been done on the european honey bee.  However, it is known  that pesticides are in general worse than herbicides.  Herbicides have a more indirect effect by changing the foraging environment of the pollinator rather than effecting the pollinator itself.

Spreading Pesticide
Phot credit: Flickr user IFPRI Images

Pesticide poisoning can occur from direct absorption, drinking tainted nectar, gathering contaminated pollen or accidental foraging of micro-encapsulated insecticide. Toxins can also be transferred to the nest through contaminated larval food brought in for brood cell nourishment.

Less than lethal doses can cause colony failure in bees by causing impaired navigation, difficulty with flight, and an inability to forage or tend to their young.

Pesticides are not just an agricultural problem. Pesticides are frequently used in urban habitats such as home gardens, municipal parks, and large public gardens.  Although it is anticipated that these urban environments will not pose as large a threat as agricultural lands, this is not true in some cases.  The majority of agriculturalists are trained and certified to spray, they are familiar with minimal dosing rates, and often prescribe to integrated pest management schemes.   Their lands may also be monitored for runoff.

A study in the Pugent Sound basin of Washington state, which is considered a fairly “green conscious” area of America, found that more pesticides were applied per acre in urban neighborhoods than on farmland (Xerces, Attracting Native Pollinators).

Click here and see the “Be informed” segment for more information on how pesticides affect native bee populations. There you can also learn how to enjoy a pollinator garden that is pesticide free by employing pest management alternatives.

Case Study: Systemic pesticides pose new threat to pollinators

Neonicotinoids are a relatively new class of insecticides. They affect the central nervous system of insects, resulting in paralysis and death. They include pesticides such as imidacloprid, acetamiprid, clothianidin, dinotefuran, nithiazine, thiacloprid and thiamethoxam.  These pesticides are systemic, meaning that a treated plant uptakes the insecticide into their vascular system, and the insecticide remains in the plant’s system as the plant grows. Most recent fears are concerned with the systemic pesticide making its way into the plant’s by-products. For pollinators, this would mean that the pollen and nectar may be tainted with the pesticides toxic compounds.

These insecticides can be applied as a seed treatment, foliar spray or root treatment. So imagine the problem when a toxic chemical is present in a plant but cannot be seen! Problems arise when commercial nurseries begin to use these insecticides. Because unless plants available for commercial sale are labelled with treatments used, plants treated with such insecticides have begin to make their way into the market.

Many countries such as France and Germany have already banned the use of neonicotinoids on bee pollinated crops. Italy’s suspension of neonicotinoids during 2009’s corn growing season halted bee mortality completely in apiaries around the crops. This had not happened since 1999.

The transference of toxic compounds from neonicotinoid treated plants to pollen and nectar is the major concern. However, there is another concern. Systemic pesticides are  transported throughout the plant to the roots and leaves. Therefore, there is also a threat to butterflies whose caterpillars eat leaves during their larval stages. These pesticides are often applied as a seed treatment or a foliar spray when plants are young and then sold commercially. If consumers are not made aware, they may be purchasing such plants for their gardens.

Below is a list of two neonicotinoid pesticides used commonly and their effects on the European honeybee, from

1. Imidacloprid

Is the most common used neonicotinoid, used in agriculture as a foliar or seed treatment and also in home gardening.  First registered in 1994 it has been found to be highly toxic to bees and other beneficial insects.  Studies show that this chemical produces sub-lethal effects in honeybees, which include mobility, navigation, and feeding problems. Imidacloprid has been scheduled for review of its registration in 2016.  The Environmental Protection Agency states that they currently do not have enough information on the potential for exposure to invertebrates who rely on plant flower parts for foraging or nesting. The agency is currently requesting field residue testing for leaves, nectar, and pollen.

Mini case study:   In the United States, a group of beekeepers from North Dakota is taking Bayer, a well known agricultural chemical company, to court after losing thousands of honeybee colonies in 1995, during a period when oilseed rape in the area was treated with imidacloprid.

2. Clothianidin

is highly toxic to bees and other insects.  It was given registration in the US in 2003 and, according to some groups, is claimed to have been registered without sufficient test data to support its registration.

Mini case study: In 2008, bee decline in Germany was attributed to the use of this chemical and a move to ban it and other neonicotonides pending further investigation was put forth (see here).  Tests on bees during this period showed that 99% of them contained a buildup of this product.

For more information, see the following three websites that detail neonicotinoids and their uses, effects, and bans across the world in the agricultural industries. See here, here, and here.