Bee Culture – June, 2002
With growing concern about pollen transfer from genetically modified crops and with continued concern about pesticide poisoning of bees, it is becoming increasingly important to know the answer to the question posed above.
The flip answer, “as far as they have to” is also the best answer.
Imagine a large wreath of flowers, encircling a hive (or an apiary) in a barren desert. Gradually expand that wreath and you will find that bees will forage up to seven miles, but that the law of diminishing returns (where hives lose weight) kicks in at about four miles.
In what has been termed a “classic experiment”, J. E. Eckert essentially did the “wreath experiment” in a three year study (1927-1929) that was published in 1933(1). This study should answer the title question for all time. Eckert picked two irrigated areas in Wyoming that were separated by a 17 mile stretch of barren badlands, then placed colonies at increasing distances from the irrigated wares. Roger Morse summed up his study in the table on the next page.
What’s striking about this experiment is that colonies can make a living when the nearest food source is four miles away. From this, it is easy to see that a two mile buffer zone is not sufficient to protect bees from pesticides (or to prevent pollen transfer from two different varieties of plants grown several miles apart).
The area covered by bees increases exponentially with distance from the apiary since the area of a circle is a function of the square of the radius:
|Flight range||Acres covered|
I have had personal experience learning about the flight range of honey bees as determined by pesticide applications. Around 1981, bee colonies in an almond orchard in Kern county suffered severe poisoning from a spray (parathion) on blooming nectarines well over two miles away. There were approximately 5,000 bee colonies on 2,500 acres of almonds located over two miles south of about 200 acres of nectarines that were in full bloom. The poisoning occurred at the tail end of the almond bloom when pollination was essentially completed and when almond bees greatly expand their foraging radius. The bee kill pattern in the almonds conformed exactly to the distance from the nectarines: the closest bees, a little over two miles from the nectarines, showed a severe kill while bees four miles away suffered what would be considered a “light” kill.
Bees placed on alfalfa seed pollination will travel great distances to get pollen rather than work alfalfa flowers for pollen(2). In an extensive test in the 1980′s, David Chaney (U. C., Davis) found that bees placed for alfalfa pollination collected 10 times as much safflower pollen as alfalfa pollen even though the nearest safflower field was five miles away!(3) a distance greater than the breadth of Celine Dion’s ego!(4).
California laws (and laws in some other states) require pesticide notification to beekeepers within a mile of hazardous spray. Since the nectarine incident described above, I have requested notification for sprays on blooming crops up to two miles away; my request has not been fulfilled and probably never will be although I have made it every year since the incident (saying, essentially, “attention must be paid”).
|DISTANCES HONEY BEES WILL FORAGE|
|Distance from irrigated area (sweet clover and alfalfa)
||Average change in Hive Weight over 18 days
|0.0 miles||+25.3 pounds|
A number of variables affect the hazard of a given pesticide application including the attractiveness of the sprayed crop, the total acreage to be sprayed and the dilution of bees (on other flower sources) in the area. When all conditions are right (“wrong” from the beekeeper’s standpoint) severe pesticide kills can occur from sprays applied well over a mile from apiaries.
It is probably not practical to inform beekeepers of sprays within four miles, or even two miles of apiaries, but area-wide restrictions on pesticide applications could be made. These restrictions could ban the use of a few extremely hazardous materials (e.g., Penncap-M, Sevin, Furadan) in bee “areas” and restrict the use of others.
How far do bees fly? The answer still is . . as far as they have to.
Joe Traynor is a crop consultant and pollination specialist from Bakersfield, CA. He is afrequent contributor to these pages.
1. Eckert, J. E. 1933. The flight range of the honeybee. J. of Agricultural Research 47:257-285.
2. Morse, Roger 1984. Research Review (How far will bees fly?). Gleanings in Bee Culture, September 1984, p. 474.
3. Chaney, David circa 1985. Bloom dynamics in alfalfa: Implications for pollination and seed production. M. S. Thesis, International Agricultural Development, University of CA. Davis, CA.
4. Carroll, Jon. San Francisco Chronicle, April 9, 2002. Carroll estimated Dion’s ego at more than a mile, but gave no exact figure.
Filling Your Buckets
Time, distance and reward are important in foraging.
Its raspberry picking time and you take a couple of buckets out to your favorite patch in back of your house. To your dismay, you find it overgrown with prickly nettles – there are ample raspberries underneath but it will be a chore to extract them. You start picking anyway but soon get discouraged; you sit down and calculate that it will take you all day to fill your buckets.
What to do? You then remember a raspberry patch you stumbled across a few years ago – its an hour drive by car, followed by a mile walk through the woods, but your appetite for raspberries has been whetted and you consider this only a minor inconvenience. You hop in your car, make the journey and after losing your way several times on the trail you finally arrive at the secret patch and discover, to your delight, a bumper crop of ripe raspberries that obviously hasn’t been touched. You fill your buckets in 15 minutes and quicken your pace back to your car as you see someone approaching with a shotgun. You make it to your car and when you arrive back home you calculate that even though you just spent four hours, you’d still be picking raspberries if you’d stayed at the patch in back of your house.
Now, you’re a worker bee in a hive surrounded by blooming alfalfa as far as the eye can see. As alfalfa nectar pours into the hive, your appetite for pollen becomes uncontrollable but you soon find that you have to visit 350 alfalfa flowers to get a load of pollen (about 20 mg)(1). Alfalfa pollen is abundant (because of the millions of flowers per acre) and nutritious(2) but this is far different from that almond orchard this Spring where you only had to visit 20 almond flowers to get a load of pollen(3) and different, also, from that mustard patch you were in yesterday before some unthinking individual moved you last night. To add injury to insult, you get whacked on the head every time you get a smidgen of alfalfa pollen. Anything is better than this, so you fly zigzag upwind two or three miles to where you chance on a field of corn in full tassel. You land, and it only takes 15 minutes to fill your pollen buckets – you’re in honey bee heaven!
When you get back to the hive, you use your language skills to inform your fellow workers of your (their) newly found bounty(4). For the next two days you and your worker kin fill the hive with corn pollen and lift a cup or two each evening to toast your good fortune.
On the third day, you visit the corn field en masse and while you’re in the midst of your chores, you see a low-flying plane approaching. Something buried deep in your genes makes you feel uneasy, but you go on with your work. You feel the spray drench you and find yourself twisting helplessly on the ground. As things get black, you hear a fallen comrade gasp with her dying breath, “there oughta be a law.”
1. Vansell, G. H. and F. Todd. (1946) Alfalfa tripping by insects. Amer. Soc. Of Agronomy Journal. 38:470-488
2. Peng, C. S. 1985 The nutritional value of alfalfa pollen to honey bees p. 23-28 in Proceedings, Alfalfa Seed Production Symposium, Fresno, CA, March 12, 1985. U of CA Extension & CA Alfalfa Seeds Production Research Program.
3. DeGrandi-Hoffman, Gloria, Gerald Loper, Robbin Thorp and Dan Eiskowitch (1991) The influence of nectar and pollen availability and blossom density on the attractiveness of almond cultivars to honey bees. Acta Horticulturae 288, 6th Pollination Symposium.
4. Wenner, Adrian and Patrick H. Wells. Anatomy of a Controversy. 1990. Columbia University Press