Honey Bee Colony Collapse Disorder is Possibly Caused by a Dietary Pyrethrum Deficiency

Richard J Sharpe, MD, Lisa C Heyden

This paper is the author's personal version of an article published in Bioscience Hypotheses, received 6 January 2009; received in revised form 29 January 2009; accepted 30 January 2009; published online 18 July 2009; doi:10.1016/j.bihy.2009.01.004

Abstract

Industrialized farming relies on bee keepers transporting hives to the vicinity of large areas of monocrops for crop pollination. Hives are typically moved multiple times per growing season to satisfy the pollination need. A phenomenon wherein colonies of honey bees collapse in large numbers has been threatening crops in North America. Honey bees are hosts to at least two pathogenic mites; Varroa destructor and Acarapis woodi (a tracheal mite). Pyrethrums are a group of flowering plants which include Chrysanthemum coccineum, Chrysanthemum cinerariifolium, Chrysanthemum marschallii, and related species. These plants produce potent insecticides, also named pyrethrums, which are powerful mite toxins. We believe that a honey bee dietary deficiency of pyrethrums and other micronutrients from pyrethrum producing plants allows parasitic mites to either kill the honey bees directly or reduce honey bee resistance to other pathogens. Intermittent feeding of honey bees on pyrethrum producing plants might reverse or prevent colony collapse disorder.

Introduction

Honey bees live in a complex social network in hives with from 10 to over 80,000 bees. Industrialized farming practices, which are increasing, include planting very large areas with a mono-crop. The wild honey bees (Apis mellifera) and to a lesser degree bumblebees (Bombus sp.) are not usually present in sufficient numbers to pollinate the crops. The solution to this problem has been to transport multiple large colonies of honey bees to the crop sites to facilitate pollination. Hives are typically moved multiple times per growing season to satisfy the pollination need. Over the last several years many commercial honey bee keepers in North America have noted widespread collapse of their bee colonies. Europe and the Middle East are also experiencing problems with similarities to CCD. [1] The cause of this phenomenon, now known as colony collapse disorder (CCD), is unknown.

Honey bees are hosts to the pathogenic large ectoparasitic mite Varroa destructor (Varroa mites). These mites feed on bee hemolymph (bee blood) and can kill bees directly or by increasing their susceptibility to secondary infection with fungi, bacteria or viruses. Tracheal mites (Acarapis woodi) infect bee trachea and also feed on hemolymph. These mites can cause death by suffocation or induction of secondary infection (1-3). Little is known about the natural defenses that keep the mite infections under control.

Pyrethrums are a group of flowering plants which include Chrysanthemum coccineum, Chrysanthemum cinerariifolium, Chrysanthemum marschalli,  and related species. These plants produce potent insecticides with anti-mite activity. The naturally occurring insecticides are also known as pyrethrums. A synonym for the naturally occurring pyrethrums is pyrethrin and synthetic analogues of pyrethrums are known as pyrethroids [4, 5]. In fact, he human mite infestation known as scabies (Sarcoptes scabiei) is treated with a topical pyrethrum cream.

The Hypothesis

We suspect that the bees of commercial bee colonies which are fed (used to pollinate) mono-crops are nutritionally deficient. In particular, we postulate that the problem is a diet deficient in anti-mite toxins; pyrethrums, and possibly other nutrients which are inherent in such plants. Without, at least, intermittent feeding on the pyrethrum producing plants, bee colonies are susceptible to mite infestations which can become fatal either directly or due to a secondary infection of immunocompromised or nutritionally deficient bees. This secondary infection can be viral, bacterial or fungal and may be due to one or more pathogens. In addition, immunocompromised or nutritionally deficient bees may be  further weakened when commercially produced insecticides are introduced into their hives by beekeepers in an effort to fight mite infestation. We further postulate that the proper dosage necessary to prevent mite infestation may be better left to the bees, who may seek out or avoid pyrethrum containing plants depending on the amount necessary to defend against mites and the amount already consumed by the bees, which in higher doses could be potentially toxic to them.

Evaluation of the Hypothesis

This hypothesis can best be tested by a trial wherein a small number of commercial honey bee colonies are offered a number of pyrethrum producing plants, as well as a typical bee food source such as clover, while controls are offered only the clover.  Mites could then be introduced to each hive and note be made as to the choices of the bees, and the effects of the mite parasites on the treated colonies versus controls.

It might be beneficial to test wild-type honey bee colonies in this manner as well, in case there could be some genetic difference between them that affects the bees' preferences for pyrethrum producing flowers.

Discussion

As global food shortages increase, the need for high productivity in agriculture is necessary to feed the growing global population. Honey bee colony collapse disorder is now threatening crops throughout North America and may be taking hold in other parts of the globe. A solution to this problem is needed without delay [6].

We believe the anecdotally higher risk of collapse in commercial honey bee colonies versus wild or organically managed commercial colonies [6] seems to support a possible nutritional source for the disorder, as commercial honey-bee colonies are heavily transported from place to place and are used mainly to pollinate mono-crops. Pyrethrums, are naturally occurring insecticides that are toxic to mites. For this reason, they are a possible candidate as a source of a natural honey bee defense.

In animal populations as well as human populations diversity in the diet confers an advantage, with some seemingly toxic compounds being essential to the health of an organism in micro dosages. The necessity of these micro-nutrients may not always be obvious, especially when they are considered generally to be toxic, such as pyrethrums to honey-bees. In addition, some plants may offer, along with the apparently toxic compound, a ready-made defense against that toxicity when the compound is consumed with other plant material. Because of this, refined nutrients, such as commercially produced pyrethrums or pyrethroids, may cease to have the beneficial effect or may in fact be harmful.

Competing Interests

The author declares that he has no competing interests.

Acknowledgement

This paper is dedicated to the memory of Dr. Dan E. Pratt, a brilliant scientist and teacher.

References

[1] Watanabe ME (2008) Colony Collapse Disorder: Many Suspects, No Smoking Gun. BioScience: Vol. 58, No. 5 pp. 384–388

[2] Martin SJ. The role of Varroa and viral pathogens in the collapse of honeybee colonies: a modelling approach. J. Applied Ecology 2001; 3815) 1082-1093

[3] Sammataro D, Gerson U, Needham G. Parasitic mites of honey bees: life history, implications, and impact. Annu Rev Entomol. 2000;45:519-48.

[4] Haustein UF. Pyrethrin and pyrethroid (permethrin) in the treatment of scabies and pediculosis] Hautarzt. 1991 Jan;42(1):9-15.

[5] Hartzell, A. Pyrethrum Culture in Dalmatia with some applications to the Americas. Jour. Econ. Ent. 1943. 36: 320-325.

[6] Oldroyd BP. What's killing American honey bees? PLoS Biol. 2007 Jun;5(6):e168.