RESULTS AND CONCLUSIONS OF USING PESTICIDES WITH THE ALFALFA LEAFCUTTING' BEE IN THE PRODUCTION OF ALFALFA SEED'

D. A. George and C. M. Rincker' Yakima Agricultural Research Laboratory

USDA, Agricultural Research Service Yakima, WA 98902

Abstract: High initial residues of oxydemeton-methyl (Metasytox R«l) and oaJed (Dibroml») on alfalfa leaf surfaces did not affect the foraging and reproduction activities of alfalfa leafcutting bees (Megachile rotundata Fabricius). Naled treatments gave the best "long term" control of detrimental insects, followed by oxdemeton-methyl. Exposure of the bee larvae to insecticide residues in the reproductive cell did not adversely affect percent live larvae nor emergence and flight of bees in the succeeding year.

Key Words: Alfalfa leafcutting bee, pesticides, residue, oaled, oxydemeton-methyl.

J. Agric. Enlomol. 2(1); 93·97 (January 1985)

The completion of the research project on the effect of insecticide residues on alfalfa leafcutting bees (Megachile rotundata Fabricius) resulted in several basic conclusions that will prove beneficial to the alfalfa seed growers. Leafcutting bees are one of the most important pollinators of alfalfa grown for seed in the Pacific Northwest (McGregor 1976). The use of nn insecticide, and its resulting residue, is more of a concern to seed growers using leafcutting bees since they are more susceptible to most insecticides than either honey bees (Apis mellifera Linnaeus) or alkali bees (Nomia melanderi Cockerell) (Johansen 1984; Capizzi et aI. 1982). Johansen et aL (1984) conducted toxicity test with several insecticides on the leafcutting bee and alkali bee. They found the minimum toxic dosages were well above those residues found by George and Rincker (1982) in the alfalfa leaf, pollen, nectar, or the bee cell when the alfalfa plant had been treated with the insecticide during the growing season.

This paper is an extension of the work of George and Rincker (1982), and reports on residues of additional pesticides, nsled and oxydemeton-methyl, and presents the conclusions drawn from the completed project.

METHODS AND MATERIALS

Field Treatment Each field plot of "Arc" alfalfa (3.6 X 6.0 m in size) was covered with a Saran

screen cage to prevent the bees from becoming contaminated with unknown insecticides from outside their test area. Laminated wooden bee nesting boards for nesting purposes were provided in insulated shelters inside each cage. Known

I Mtga~hilt rotl/.fldalo (HYMENOI>TERA; Megll~hilidlle) 2: This paper I"tportl the relUlta or research only. Mention or II proprietary product or II pelticide dotl not eQl\lltil.U~ In

em:lonement by the USDA, nor doel it impl)· rep.lnItion under F1FRA 1lI amended. Recei"ed for publication 13 October 1984; llccepted 17 January 1985.

3 Irrigllted Agriculture Relelll'Ch lind EJ~nlion Center. USDA. ARS. Prouef. WA 99350.

93

94 J. Agric. Entomol. VoL 2, No. 1 (1985)

numbers of bees were periodically introduced into the cages. Formulations of naled (Dibrom@) and oxydemeton-methyl (Metasystox R®) were applied singly as a foliar spray at 1.12 kg AI/ha and 0.56 kg AI/ha, respectively. Each insecticide was also applied at 1.5 X the recommended treatment rate. Each plot received three applications at approximately 2-wk intervals, beginning in June.

Freshly emerged bees were sanitized (quick dip in a 0.5% sodium hypochlorite solution) to control chalk brood, and released into the treated cages. A total of about 140 bees were released over a period of a month in groups of 10· 15/ release. Pollination activities of the bees were visually observed at least twice a week to determine if bee numbers were declining or pollination was not being achieved due to a loss of bee vigor.

Sampling Samples taken for residue analysis included the alfalfa leaf at fOUf to six

different time intervals (Tables 1 and 2), pollen and nectar at 1 and 5 d after the

Table 1. Residues of naIed and its metabolite, dichlorvos, found in alfalfa leaf, pollen, nectar, and the pollen-nectar ball and leaf from the bee cell.

Sampling Residue found (PPM)-

Amount interval leaf pollen nectar p·n ball leaf-cell

(kg AI/ha) (days) Nt Ot N 0 N 0 N 0 N 0

1. 12 2d spray 0 0.32 8.44 1 0.63 1.37 NOI 3.99 0.20 NO 5 NO 0.02 NO NO NO ND

13 ND 0.34 NO ND ND NO 3d spray 4 NO 0.17 2.64 ND NO NO

8 NO NO 0.17 ND 0.35 0.22 1.68 2d spray 0 0.37 8.53

1 0.54 3.78 NO 2.87 NO ND 5 NO 0.05 NO NO NO ND

13 NO 0.40 NO NO 0.53 NO 3d spray 4 NO 0.06 1.30 ND 4.06 0.30

8 NO NO NO NO 0.14 0.05

• H~sulta have beon corrected for 8\'erllce re~'() ..ery found: nnled, 83Ar,;,; dichlorvn~, 93."%. t N - naled; D - dil;hlorvoa. .::: None detected.

Table 2. Residues of oxydemeton-methyl and its metabolite, sulfone, determined as the sulfone, in alfalfa leaves and the pollen-nectar ball and leaf from the bee cell.

Amount Sampling interval Residues found (PPM)' (kg AI/ha) (days) leaf p-n ball leaf-cell

0.56 2d spray 0.5 56.4 3 16.6 0.1 15.8 14 1.2 0.3 28.6

3d spray 3 6.2 0.7 49.2 0.84 2d spray 0.5 81.2

3 [6.9 0.2 NDt [4 0.6 1.3 ND

3d spray 3 23.3 1.1 l4.9 • Heaulta hnvc becn cnrrected fur 8Vl'fIl~e recovery found; 89.2%. t None detecl.::d.

GEORGE and RINCKER: Pesticides-Leafcutting Bee-Alfalfa Seed Production 95

second spray application, and the bee cell at three different time intervals. The bee cell was then cut open and separated into its individual components (pollen­neclar ball and leaf). All samples were immediately frozen until analyzed.

Naled Residue Analysis The samples were weighed, blended with methylene chloride plus 1 rol

concentrated HCI, filtered through anhydrous sodium sulfate, and then concen­trated on a rotary evaporator (35 - 38°C bath) to a 10 ml volume. It was then chromatographed through 2 g Norit A@ {neutral, prewashed with methylene chloride}. The sample was added, the flask rinsed and naled and its metabolite, dichlorvos, residues were eluted with methylene chloride. The eluate was then evaporated on a rotary evaporator and made to volume with 1:1 acetone/hexane for gc analysis. The residues were determined using a Hewlett-Packard 5840A gas chromatograph equipped with a flame photometric detector using a phosphorus filter. The 2-ft (60 em) by 3/16-in (0.47 em) glass column was packed with 10% DC-200 on 80/100 mesh GCQ@ and held at a temperature of 150'C for 2 min and then programmed at 20°C per min to 180°C and held at that temperature for 10 min.

Oxydemelon-Melhyl Residue Analysis The samples were blended with methylene chloride, filtered through anhydrous

sodium sulfate, and evaporated on a rotary evaporator (40°C bath). They were then oxidized to the sulfone by adding 2 ml acetone, 5 ml 20% magnesium sulfate, and 20 ml 2% potassium permanganate, heated for 30 min at 70°C, and then cooled in an ice bath for 10 min. The samples were then filtered through Ottawa® sand in a separatory funnel, and the nask and filter washed with water. The sample was then extracted 3 X using 25 ml methylene chlol'ide each time, filtering each through anhydrous sodium sulfate. They were then evaporated on a rotary evaporator and made to volume with benzene for gc analysis. Residues were determined using a Hewlett-Packard 5840A gas chromatograph equipped with a flame photometric detector using a sulfur filter. The 2-ft (60 em) by 3/16-ln (0.47 em) glass column was packed with 2% OV-IO] on 80/100 mesh Ultrabond@ and used at a temperature of 200Q C.

RESULTS

No/cd Leaf samples for residue analysis of naled and its metabolite, dichlorvos, were

taken at O·hr, I, 5, 13 d after the second treatment, and 4 and 18 d after the third treatment. Naled residues were found in the O-hr and 1 d samples, for both the 1 X and 1.5 X treatments, with no residues being detected in any of the other samples (Table 1). Residue"s of the metabolite, dichlorvos, ranged from a high of 8.4 ppm at the O·hr treatment, to below the detection level 18 d later. Naled residue of 3.99 ppm was found in one nectar sample and dichlorvos residue of 0.20 ppm was found in the pollen sample, both were sampled 1 d after the second treatment. No residue was detected in the rest of the pollen and nectar samples. Naled residues in the pollen-nectar ball from the ceU ranged from a high of 2.6 ppm to nothing detected. Both nsled and dichlorvos were detected in leaf from the cell. The·naled treatment gave excellent Lygus bug control. The total number of bee cells recovered from treated bee cages was nearly twice that of the controls.

96 J. Agric. Entomol. Vol. 2, No.1 (1985)

Orydemeton-Methyl Leaf samples for residues of oxydemeton~methyl and its sulfone metabolite

were taken 12 brs to 14 d after the second spray treatment Bnd 4 d after the third treatment (Table 2). Residues ranged from a high of 56.4 ppm (12 hrs) to 1.24 ppm (14 d) after treatment at the recommended rate and 81.2 ppm to 0.61 ppm, respectively, at the 1.5 X treatment. While high residues were found in O.5-d nectar samples analyzed in a previous experiment (unpublished data), these were found to diminish by 90% in 3 d. However, this large residue did not carry over into the pollen~nectar ball, and we did not find a large carry-over of residue in this experiment. High residues were found in the leaf from the bee cell, but had no apparent effect on the larvae or adult bee. In spite of these levels of residues, the bees performed well in the treated plots and the insecticide provided good control of the detrimental insects in the alfalfa. The number of bee cells constructed averaged 13% above the control. Also, the percent good cells, the percent live larvae, and the percent pollen balls reflected no adverse affect from oxydemeton­methyl residues on the bees or their pollination activities.

DISCUSSION

Control of detrimental insects is one of the three most crucial factors in producing high yields of alfalfa seed (Rincker 1979). However, the use of insecticides to control detrimental insects can be harmful to maintaining adequate populations of pollinators, which is another critical factor in seed production. In earlier tests (George and Rincker 1982), demeton, trichlorfon, dimethoate, and carbofuran ·produced very little mid-season control of detrimental insects. All were applied as foliar sprays. Dimethoate and carbofuran were applied once prior to bloom while demeton and trichlorfon were applied either three or four times during bloom at 2-wk intervals. Demeton residues were initially high, but decreased to approximately 10% of the initial residues in 14 d. Trichlorfon treatments also yielded high initial residues, but these rapidly decreased to 1% in 4 d. While we found residues of naled and oxdemeton-methyl in alfalfa pollen, nectar, leaf, and the pollen-nectar ball collected hy the alfalfa leafcutting bees (Table 1 and 2), levels were not high enough to be deleterious to either adult bee foraging in treated plots or to bee larvae feeding on residue contaminated stores. While initial residue deposits of Daled were low, those of its toxic metabolite, dichlorvos, were quite high, indicating rapid conversion after application to the alfalfa leaf surfaces. The oxydemeton-methyl residues were also initially high, but were rapidly degraded.

Reduced flowering and vigor of the alfalfa plant, due largely to the effects of harmful insects was a major factor in reduced seed yield and in the reduced numbers of bee cells recovered in our test plots. Observations of these test plots indicated that treatment with naled provided better control of detrimental insects than treatments with oxydemeton-methyl or any of the other four insecticides tested and reported on previously.

To determine whether residues of the six insecticides tested might have a long­term negative effect, bee larvae from a particular insecticide were observed the following year in the same plots. These observations indicated there were no adverse effects resulting from the insecticide treatments, the adult bees appeared to be vigorous and to be as effective a pollinator as those from the untreated plots.

GEORGE and RINCKER: Pesticides-Leafcutting Bee-Alfalfa Seed Production 97

Our observations of leafclltting bees foraging in alfalfa plots treated individually with registered insecticides allowed us to draw several conclusions: treatment at recommended rates with the insecticides demeton, trichlorfon, dimethoate, carbofuran, naled, or oxydemeton-methyl yielded no detrimental effects on foraging leafcutting bees; treatment of alfalfa with naled provides the best control of detrimental insects; oxydemeton-methyl provides less effective control of detrimental insects. These observations and conclusions are supported by insecticide residue determinations in alfalfa pollen, nectar, and the pollen-nectar ball from the leafcutting bee reproductive cell. These residues have not been previously reported.

REFERENCES CITED

Capizzi, J., G. Fisher, J. Homan, C. Baird, A. Retan, and A. Antonelli. 1982. Pacific Northwest Insect Control Handbook. p. 23.

George, D. A., and C. M. Rincker. 1982. Residues of commercially used insecticides in the environment of MegaclJile rQtwldata. J. Econ. Entomo!' 75: 319-323.

Johansen, C. L984. How to reduce bee poisioning from pesticides. Western Region Extension Publication (WREP) 15: 1-12.

Johansen, C., C. M. Rincker, D. A. George, D. F. Mayer, and C. W. Kious. 1984. Effects of aldicarb and its biologically-active metabolites on bees. J. Environ. Entomol. Accepted for publication.

McGregor, G. S. 1969. Susceptibility of an alfalfa leafcutting bee to residues of insecticides on foliage. J. Econ. Enwmol. 62: 189-192.

Rincker, C. M. 1979. Alfalfa seed production in the Pacific Northwest. Proc. Twenty-fifty Annual Farm Seed Conf. of ASTA. Nov. 1979: 13-19.