APIS Volume 4, Number 6, June 1986
In this issue
- Florida Citrus Honey: Is It Unique?
- Pesticide Kills: Sublethal Doses; Aldicarb and Detoxification
FLORIDA CITRUS HONEY--IS IT UNIQUE?
Historically, there have been problems with the unique composition of Florida citrus honey. Shipments of the sweet have been refused abroad when found to contain excess sucrose. This was not purposefully added sucrose, but the shipments were returned in any case. The United States Department of Agriculture (USDA) is now taking a closer look at honey coming into Commodity Credit Corporation warehouses. Recently, some Florida citrus honey has been rejected because it appeared to be adulterated with corn syrup.
The testing process, known as isotope ratio analysis, was developed by Dr. J. White. It detects the ratios of carbon atoms derived from cane and corn (monocot grasses) versus carbon atoms derived from nectar secreting (dicot woody flowering) plants. According to "13C/12C Ratios of Citrus Honeys and Nectars and Their Regulatory Implications," Journal of the Association of Official Analytical Chemists, Vol. 66, Jan. '83, by J.W. White and F.A. Robinson, the average ratio value of 119 honey samples was -25.4, whereas corn syrup was -9.7. Unfortunately, the variability found in authentic samples of honey precludes accurate calculation of a composition of unknown mixtures, according to the paper, and samples with values between -23.5 and -21.5 should be confirmed as adulterated by an independent test.
Florida citrus honey can fall into the independent testing range. During the 1980 marketing season, according to the paper, a citrus sample with a -23.8 value was declared 10% adulterated, resulting in considerable confusion and economic loss. The authors conclude that Florida citrus honey has significantly less negative values than other U.S. honey and this was not the result of purposeful adulteration, but characteristic of the plant species.
The present level set by the USDA at -23.4 appears to cover most U.S. honey. However, some citrus honey, according to the paper above, may have as low a figure as -22.0. Experience this season suggests that a lower figure may also be characteristic of mesquite honey. All this suggests that the USDA should reexamine its policy on the issue. A major problem with this is loss of reliability, as suggested above, in the value range of -23.5 to -21.5; performing an independent test makes taking Florida citrus and mesquite honey a more costly process by the CCC. Representatives of the beekeeping industry are hard at work in the political realm on the issue.
[Editor's Note 5/12/1997--the CCC loan program no longer exists. The above shows how variable a commodity honey can be and why standardized tests can be problematic.]
ANALYZING PESTICIDE KILLS
Conventional wisdom suggests that bees poisoned in the field seldom make it back to the hive and this precludes contaminating either comrades or stores. However, the fact that many pesticide kills are discovered by beekeepers when they see piles of dead and dying bees at the entrance runs counter to this notion. Presumably, these bees have been detected and thrown out of a colony, reducing contamination possibilities. Complicating the issue is the fact that we now know bees can be exposed to low dosages of pesticide and persist in living for longer periods than previously supposed. In addition, evidence suggests adult bees have the capacity of detoxicating themselves by use of gut enzymes.
The latter study, "Detoxication Capacity in the Honey Bee, Apis mellifera L.," Pesticide Biochemistry and Physiology 22, 360-368 (1984), by S. Yu, F. Robinson and J. Nation, Department of Entomology and Nematology, University of Florida, revealed various enzymes capable of detoxifying certain pesticides. Sublethal doses of at least one pesticide, permethrin, stimulated production of glutathione S-transferase enzyme. A further conclusion suggested that high susceptibility of honey bees to insecticides does not appear to be due to low detoxication capacity.
The same authors along with A. Bolten have recently completed a study which will soon be published, "Influence Upon Honey Bees of Chronic Exposure to Very Low Levels of Selected Insecticides in Their Diet." Pollen cakes were fed to small colonies in screened cages. The diets contained 0.017 parts per million (ppm) permethrin, 0.16 ppm malathion, or 0.17 ppm carbaryl, all considered highly toxic to bees. In addition, diets also contained 5.12 methoxychlor or 10 ppm diflubenzuron, considered relatively nontoxic to bees. All chemicals except diflubenzuron were set at concentrations representing one-third of the LC1 value (LC1 = lethal concentration that will kill 1.0% of the population). In other words, on the average some one- third of one percent of the bees were predicted to die of pesticide poisoning.
Directly measured by the study were food consumption, stored syrup and brood rearing. Of the materials tested, only methoxychlor resulted in a statistically significant decrease in brood rearing and stored syrup. A possible explanation provided by the authors is that methoxychlor, a chlorinated hydrocarbon, may have become concentrated in the comb wax. All treated, but no control, colonies exhibited (observed, but not quantified) a decline in house keeping, resulting in accumulation of debris and dead bees on the hive bottom. In addition, wax moth often gained a foothold in colonies receiving malathion and methoxychlor, even though populations were strong. Bees in colonies being fed methoxychlor almost ceased foraging for sugar syrup and began using their stores rather than actively gathering and storing sugar syrup provided.
The above study is important when assessing potential damage to bees from nectar that might be contaminated with systemic insecticides, because it mimics to some degree conditions found in the field. E. Jaycox, as far back as 1964 in "Effect on Honey Bees of Nectar from Systemic Insecticide Treated Plants," Journal of Economic Entomology, Vol. 57:31-35, warned that systemic insecticides can penetrate floral nectar in sufficient quantity to kill bees. Of the two specific pesticides used, phosphamidon appeared more hazardous than dimethoate.
G. Waller and R. Barker, Carl Hayden Bee Research Center, in a paper entitled, "Effects of Dimethoate on Honey Bee Colonies," Journal of Economic Entomology, Vol. 72:549-551 (August, 1979) sprayed onion plants with dimethoate; largest concentration seen in nectar was 7 ppm four days after treatment, declining about 25% each day thereafter. Experimental colonies were fed dimethoate in both sugar syrup and pollen patties, in concentrations ranging from 5 ppm to 0.2 ppm. All treated colonies fed 5 ppm died the first week; those fed 1.0 ppm were dead at the end of the second week. Colonies fed 0.2 ppm consumed less pollen, but stored as much syrup as the controls; their population declined during the third week. Queens from the latter group (0.2 ppm) survived and continued to lay eggs normally, when transferred to other colonies. All treated colonies were allowed to forage on jars containing contaminated and pesticide free syrup. Results appear to show the bees unable to distinguish between contaminated and non contaminated syrup. Also revealed is that dilution from uncontaminated syrup (or nectar in the field) will reduce toxic effects on colonies.
Concern over the past several years has suggested that toxic nectar in citrus groves may be responsible for bee losses. The pesticide Temik® (aldicarb) has been blamed by some beekeepers, but little experimental evidence has corroborated their reports. Recently, H.A. Moye, Food Science and Human Nutrition Laboratory, University of Florida, analyzed citrus nectar and super samples for aldicarb metabolites by two independent methods. Both metabolites retain much of the toxicity of the parent compound, with the results frequently expressed as "total toxic residue."
Sample from L. Wyrosdick, Archer, FL:
Metabolite Method 1 Method 2
aldicarb sulfoxide 1.25 ppm 0.77 ppm
aldicarb sulfone 0.09 ppm interferences
Total toxic residue 1.34 ppm 0.77 ppmSamples from R. Bullock, Ft. Pierce Agricultural Research and Education Center:
Orange Nectar
Metabolite Method 1 Method 2
aldicarb sulfoxide 0.58 ppm 0.50 ppm
aldicarb sulfone 0.02 ppm interferences
Total toxic residue 0.60 ppm 0.50 ppm
Grapefruit Nectar
Metabolite Method 1 Method 2
aldicarb sulfoxide 0.16 ppm 0.14 ppm
aldicarb sulfone 0.09 ppm interferences
Total toxic residue 0.22 ppm 0.14 ppmA sample from the same supplier from honey super was negative for metabolites.
Do these data support the contention that aldicarb is responsible for large bee losses? It's difficult to say. Aldicarb is reported to be less toxic than permethrin or dimethoate based on L. Atkins' work at the University of California, Riverside. Those studies, however, were based on external application of pesticide, not ingestion. In fact, Atkins states that aldicarb, highly toxic to bees as a contact poison, is used only in granular form, and extensive field usage has not caused bee loss.
The levels of aldicarb metabolites found in samples of citrus nectar are generally greater (1.34 to .22 ppm) than levels fed bees in the study above reporting on chronic low dosages (0.017 ppm permethrin to 0.17 ppm malathion). Aldicarb, however, according to Atkins, is less toxic than permethrin by .2 micrograms per bee, but more toxic than malathion by .7 micrograms per bee (again this is by contact, not ingestion). In addition, the amounts fed were predicated on only one-third of one percent of the population dying due to the chemicals. Dimethoate, according to Atkins' work, is close in contact toxicity to aldicarb. The levels found by Moye above are in the lower range of 1.0 to 0.2 ppm reported above in the study by Waller and Barker, where significant damage was seen at the 1.0 ppm level for dimethoate, but much less at the 0.2 ppm level.
Complicating the issue is the range in ppm found in the samples of citrus nectar reported above, from a high of 1.34 total toxic residue to only 0.14. Certainly the higher range would be potentially more damaging to bees than the lower. Nectar in one blossom or from one tree, however, may not be representative of the grove. Many other factors also come into play: dilution factor by uncontaminated nectar, environmental conditions, size of the colony and its brood rearing area, and in extreme cases, misuse. The latter issue was addressed by J.H. Kirch, Vice President for Sales and Technical Services, Union Carbide Agricultural Products Co., Inc. who recently said:
As most of you are aware, misuse of our product Temik brand aldicarb pesticide on watermelons in 1985 received a great deal of publicity... We spend a great deal of time and money researching performance and toxicology of our products...if we direct that it be used in a certain way on the crop, there is a sound scientific reason for doing so. For example, the product may leave excessive residues in the edible portion of the crop... None of us want to be a party to anything that threatens the health or well-being of people or our environment...To ensure this I urge you to read all labels and carefully follow all directions, cautions, and warnings.
In the final analysis, concentrating on potential bee losses from pesticide may really be diversion of energy from a more pressing problem. This is the potential presence of any pesticide residue in honey for which at the present time, NO ACCEPTABLE LEVELS ARE ALLOWED! Although A. Moye found no detectable levels of aldicarb metabolites in the sample taken from a super, we are far from knowing the extent of this possible problem. However, as Jaycox warned as far back as 1964,
"We can no longer accept, without proof, the oft-repeated statements that the purity of honey is assured because bees gathering poisoned nectar are killed in the field or die in the hive without giving up their contaminated load."
Sincerely,
Malcolm T. Sanford
Bldg 970, Box 110620
University of Florida
Gainesville, FL 32611-0620
Phone (352) 392-1801, Ext. 143 FAX: (352)-392-0190
http://www.ifas.ufl.edu/~mts/apishtm/apis.htm
INTERNET Address: MTS@GNV.IFAS.UFL.EDU
©1986 M.T. Sanford "All Rights Reserved
