The star pollinators

January 11, 2010
Written by Angela Gradish, Cynthia Scott-Dupree, Les Shipp, Ron Harris, Gillian Ferguson
Bumblebees (Bombus impatiens Cresson) (Figure 1) have become increasingly common in Canadian vegetable greenhouses as most growers rely on them to provide supplemental pollination. Tomatoes and sweet peppers are self-pollinating, but supplemental pollination results in larger, more attractive fruit. When a bumblebee colony is placed in the greenhouse, female worker bees begin to collect pollen to feed to the developing larvae. More worker bees then emerge, resulting in further pollen collection. Therefore, successful pollination is partially dependent on the bees’ ability to produce large numbers of workers to forage.

In essence, bumblebees can be considered the stars of the greenhouse pollination world.

Compared with manual pollination, bumblebee pollination is less labour intensive and results in higher yields. Bumblebees also are superior to honey bees for a variety of reasons. Their hairy bodies allow them to collect and carry more pollen, they are active at lower temperatures and light intensities, and they are capable of “buzz” pollination (vibrating the flower to release pollen), which is required for tomatoes.

A Bombus impatiens worker
A micro-colony containing: a) a feeder filled with honey/water solution; b) a wax-coated pollen ball; and c) the nest with larvae.  
FIGURE 3. Average corrected per cent mortality (± SE) of bumblebee workers 72 hours following exposure to
technical grade imidacloprid, abamectin, metaflumizone, or chlorantraniliprole using a Potter spray tower. Insecticides were applied at 0.001, 0.01, or 0.1% w/v. Columns with the same letter are not significantly different.
FIGURE 4. Average worker lifespan (days) and pollen consumption (g) (± SE) of bumblebee micro-colony workers. Queen-less micro-colonies received pollen contaminated with formulated imidacloprid, abamectin, metaflumizone, chlorantraniliprole, myclobutanil, potassium bicarbonate, or cyprodinil+fludioxonil. Control colonies were provided with pollen mixed with honey and water only. Columns with the same letter are not significantly different. 
FIGURE 5. Average number of days to first egg-laying and number of larvae ejected (± SE) by bumblebee micro-colony workers. Queen-less micro-colonies received pollen contaminated with formulated imidacloprid, abamectin, metaflumizone, chlorantraniliprole, myclobutanil, potassium bicarbonate, or cyprodinil+fludioxonil. Control colonies were provided with pollen mixed with honey and water only. Columns with the same letter are not significantly different.
In addition to pollination, effective pest management is crucial for maintaining high yields of marketable fruit. Insecticides are occasionally used for control of insect pests and fungicides are routinely applied for powdery mildew. The problem is that some pesticides may be harmful to bumblebees. While bumblebees are foraging, they may come into contact with pesticides as a foliar spray, residues on plants, or by consuming contaminated pollen. This exposure may result directly in bee mortality or in sub-lethal effects, such as reduced lifespan, reduced ability to reproduce, or behavioural changes. Additionally, contaminated pollen may be fed to developing larvae, which can result in larval mortality or changes in development. In either case, the result is fewer bees, less pollination, and a reduction in yield and fruit quality. Therefore, as new pesticides are developed for greenhouse vegetable use, it’s important to determine their potential impact on bumblebees.

To accomplish this, a study was recently conducted at the University of Guelph by Angela Gradish under the supervision of Drs. Cynthia Scott-Dupree (University of Guelph) and Les Shipp (Agriculture and Agri-Food Canada), and in collaboration with Dr. Ron Harris (University of Guelph) and Gillian Ferguson (Ontario Ministry of Agriculture, Food and Rural Affairs). The study examined the toxicity of some insecticides and fungicides currently used or in the process of being registered for use in Canadian greenhouse vegetable production to bumblebee health and reproduction. The objective of the study was to identify and use pesticides that are safe to apply in greenhouses in the presence of bumblebees.

The insecticides tested included imidacloprid (Intercept®, Bayer CropScience Canada), abamectin (Avid®, Syngenta Crop Protection Canada Inc.), metaflumizone (Alverde™, BASF Canada), and chlorantraniliprole (Coragen®, Dupont Canada). Alverde is being registered for lygus bug in pepper and cucumber beetle in cucumber, while Coragen is registered for cabbage looper. The fungicides tested included myclobutanil (Nova®, Dow Agrosciences Canada), potassium bicarbonate (Milstop®, Bioworks Inc.), and cyprodinil + fludioxonil (Switch®, Syngenta Crop Protection Canada Inc.).
In the first experiment, adult female worker bumblebees were exposed to a direct spray of the active ingredient of each pesticide using a Potter spray tower (a type of specialized spray chamber). Each pesticide was applied at 0.001, 0.01, and 0.1 per cent w/v. The impact on adult mortality was then assessed. In the second experiment, possible sub-lethal effects of each formulated pesticide were determined. In a normal bumblebee colony, only the queen lays eggs. However, if a group of workers is isolated from the queen, one dominant worker will begin laying eggs, while the other workers provide food for the developing larvae. For this study, bumblebee “micro-colonies” were created by isolating groups of three workers in cages (Figure 2). Each micro-colony was then provided with pollen treated with an insecticide or fungicide at label rate for 30 days, on which they reared their larvae. Time to first egg laid, larval ejection rates, amount of pollen consumed, and adult worker lifespan were monitored for 60 days.

When directly applied to adult bumblebees, imidacloprid and abamectin both caused high mortality (Figure 3). Metaflumizone also caused mortality at high concentrations (Figure 3). However, chlorantraniliprole did not cause any mortality (Figure 3). Similarly, all fungicides tested were harmless as a direct spray, causing less than five per cent mortality. In the sub-lethal study, Intercept and Avid increased time to first eggs laid, reduced worker bee lifespan, and reduced pollen consumption (Figures 3 and 4). Metaflumizone and chlorantraniliprole had no effect on egg-laying, larval ejection, worker bee lifespan, or pollen consumption (Figures 4 and 5). Finally, none of the fungicides tested caused sub-lethal effects (Figures 4 and 5).

These results suggest that imidacloprid and abamectin have the potential to severely impact bumblebee health and reproduction and therefore greenhouse pollination. If Intercept or Avid must be used, steps can be taken to protect bumblebees. Exit holes on the colonies can be closed in the evening until all foraging workers have returned. The colonies should then be completely closed prior to insecticide application and not re-opened until the recommended re-entry period. Metaflumizone and chlorantraniliprole appear to be safer alternatives for greenhouse insect pest management. The fungicides myclobutanil, potassium bicarbonate, and cyprodinil + fludioxonil appear to have no impact on bumblebees and can be safely used in greenhouses where bumblebees are released. Choosing to use these reduced risk pesticides will help ensure that the bumblebees remain healthy and able to provide effective pollination.

Funding for this research was provided by the Pest Management Centre of AAFC and a CORD IV grant provided to the Ontario Greenhouse Vegetable Growers by the Agricultural Adaptation Council.

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