Issue 14, August 26, 2013

Turf Insecticides and Pollinators

Insecticides, particularly neonicotinoids, have been receiving some heavy hits recently about effects on honey bees and other pollinating insects. Other pollinating insects include bumblebees, sweat bees, ground bees, flower flies, bee flies, butterflies, moths, and various beetles. Last week, I attended the National Turfgrass Entomology Workshop held in South Kingston, Rhode Island where this topic came up.

There are several types of insecticides used in turf. Most organophosphates, such as trichlorfon (Dylox), are very toxic to bees and other pollinators. Like pyrethroids, they kill the insect quickly, resulting in less impact on the hive or nest.

Pyrethroids, such as cyfluthrin (Tempo), bifenthrin (Onyx), permethrin (Astro, Pounce), and lambda-cyhalothrin (Scimitar) have long been known to be very toxic to bees and other insect pollinators. They are so toxic, that insects coming into contact with them are killed very quickly. This trait actually reduces their effects on honey bee hives and bumblebee nests as the insect and thus the insecticide does not get back to the colony to be spread around to the larvae and other adults.

Neonicotinoids are perhaps more damaging to pollinators as they are typically slow-acting, which allows exposed bees to get back to the hive or nest, move systemically within the plant to contaminate nectar and pollen, and low doses insufficient to kill the insect still affect behavior. These include imidacloprid (Merit), thiamethoxam (Meridian), and clothianidin (Arena). Bifenthrin is sold in combination with imidacloprid as Allectus and with clothianidin as Aloft.

Chlorantroniliprole (Acelepryn) is of different chemistry, being an anthraniic diamide. It affects insect muscles rather than the insect nervous system as do most other turf insecticides. It has a lower toxicity to birds, mammals, fish, and other vertebrates and has been found to have less of an effect on bees and other insect pollinators.

Bees and other insect pollinators are not attracted to turfgrasses. Being wind-pollinated, there is no nectar attractant. They do not collect turfgrass pollen, even though honey bees do collect pollen from corn, another grass. For these reasons, turf applied insecticides’ impact occurs primarily through the flowering plants in turf that we call weeds including dandelions, white Dutch clover, and creeping Charlie. Highly maintained turf contains almost none of these weeds due to herbicide applications and other management. However, many home lawns and lesser maintained turf areas in parks and similar areas do contain flowering weeds.

Research conducted by University of Kentucky entomologists with white Dutch clover showed that neonicotinoids such as thiamethoxam, clothinidin, and imidacloprid reduced the number of bumblebees contained over treated turf by one-third while Acelepryn had no effect on mortality.

Bumblebees exposed for as little as six days to Clothianidin initially lost weight and had fewer individuals. Because only the largest bumblebee hives produce queens, clothianidin exposed hives did not produce queens. Bumblebees are annual, relying on queen production to survive from year to year, so no queen production equates to no long term survival. Acelepryn exposure did not cause weight loss, hive size reduction, or reduced queen production.

So should we only use Acelepryn for white grub control? No, the use of a single insecticide is almost surely going to result in resistance problems. It was determined that neonicotinoids do not move well systemically into white Dutch clover flowers and that most of the exposure was from the flowers being directly sprayed. Using granular formulations avoided the effects seen with spray applications. Mowing before or immediately after spray application removes the flowers and avoids deleterious effects on bees. A little communication with clientele to ensure that lawns with flowering weeds are mowed before or immediately after application will allow neonicotinoids to be sprayed without serious harm to pollinators. (Phil Nixon)

Phil Nixon

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