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10-1970
Onion Pollination as Affected by Different Levels of Pollinator Activity
George E. Bohart Utah State University
William P. Nye Utah State University
L. R. Hawthorn
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Recommended Citation Bohart, G. E., W. P. Nye, and L. R. Hawthorn. 1970. Onion Pollination as Affected by Different Levels of Pollinator Activity. Utah Agr. Exp. Sta. Bull. 482, figs., tables.
This Bulletin is brought to you for free and open access by the Pollinating Insects Research Unit at DigitalCommons@USU. It has been accepted for inclusion in All PIRU Publications by an authorized administrator of DigitalCommons@USU. For more information, please contact [email protected]. ONION POLLINATION- AS AFFECTED Utan State University BY DIFFERENT LEVELS 'OF POLLINA1:0R ACTIV
G. E. Bohart, W. P. Nye and L. R. Hawthorn
Bulletin 482 - October, 1970 Utah Agricultural Experiment G. E. BOHART and W. P. NYE are with the Entomology Research Division, Agricultural Research Service, USDA, logan, Utah 84321. 1. R. HAWTHORN was formerly with the Crops Research Division, Agricul tural Research Service, USDA, Logan. He is presently at 113 Wiggins Street, West Lafayette, Indiana 47906.
/ - ACKNOWLEDGl\t!ENTS
Weare indebted to Mr. John R. Pease now at the University of Utah Medical School in Salt Lake City; Dr. Charles 1. Graham, now at the U. S. Army Biological Laboratories at Fort Dietrick, Maryland; and Mr. Ross A. Nielsen, now at the Southeastern Bee Research Laboratory at Baton Rouge, Louisiana, for making many field counts and measurements during the course of these studies. Dr. Lynn Kerr, now at the Charter Seed Company at Twin Falls, Idaho provided most of the plot management and could be counted on when needed. Many of the insects collected on the plots were identified by specialists, including the following:
Hymenoptera Aculeata (except Apoidea) - R. M. Bohart Apoidea - G. E. Bohart Braconidae - P. March Chalcidiodta - B. D. Burks
Diptera
Bombiliidae - J. C. Hall Stratiomyidae - W. J. Hanson Syrphidae - H. S. Telford Therevidae - 1. Knutson Muscoidea, Chloropidae - C. Sabrosky Otitidae, Tephritidae - G. Steyskal
1 CONTENTS
ACKNOWLEDGEMENTS 1 INTRODUCTION 3 1958 4 Methods and Materials 4 Conditions Affecting the Experiment . 6 Results · 11 1959 • 14 Methods and Materials · 14 Conditions Affecting the Experiment . · 15 Results • 17 1960 • 21 Methods and Materials · 21 Conditions Affecting the Experiment . · 22 Results • 28 1961 • 29 Methods and Materials • 29 Conditions Affecting the Experiment . · 30 Results · 34 DISCUSSION AND CONCLUSIONS · 39 SUMMARY · 45 LITERATURE CITED .46 APPENDIX A . • 48
2 ONION POIJJNATION AS AFFECTED BY DIFFERENT LEVELS OF POIJJNATOR ACTMTY
G. E. Bohart, W. P. Nye, and L. R. Hawthorn
According to Jones (1937), the pollination of onion (Allium cepa Linnaeus) is effected mainly by insects that visit the nectaries at the base of the three inner stamens. Muller (1833) and Jones (1937) stated that cross-pollination is the rule, although self-pollination between flowers of the same umbel is undoubtedly of frequent occurrence. Muller (1883) and Hayward (1938) reported that the flowers are imperfectly proterandrous the anthers of the inner whorl of stamens dehisce before those of the outer. Both whorls dehisce before the stigma is receptive. Moll (1953) stated that the normal receptive period of the stigma is 3 days.
Several investigators have noted that onion flowers are visited freely by many kinds of insects, including honey bees. (Apis melli/era Linnaeus) (Muller, 1883; Jones and Emsweller, 1934; Shaw et. at. 1935; Kordakova, 1956). For this reason, it has often been taken for granted that pollination is not a limiting factor in onion seed production in spite of the tremendous variation known to occur in yields from different fields, seasons, and cul tural practices (Morse, 1923; Hawthorn, 1951). The recent development of hybrid seed grown on male-sterile inbreds pollinated by male-fertile inbreds has intensified the pollination problem. Pollinating insects are required to disseminate pollen over 6 to 12 or more rows from two pollen parent rows Complicating problems are the supposed relative unattractiveness of male sterile plants to pollen-collecting insects and the possibility that their receptive period will not coincide with the pollen dehiscence period of the pollen parents. Another problem, and one particular to the Treasure Valley of Idaho and Oregon (the most important onion seed producing area in the U. S.) has been the great increase in alfalfa seed production, resulting in thousands of acres of alfalfa bloom which drain off populations of honey bees and other pollinators. Finally, increased use of insecticides has reduced the populations of pollinators. In Treasure Valley, the wide spread use of Dylox (sometimes called Dipterex) for alfalfa insect control has probably had a particularly disastrous impact on dipterous pollinators.
3 In 1958, we started a 4-year program to learn more about the pollin ation factor as it affects onion seed production. In the following discus sion, the methods, conditions, and results for each year will be treated separately, and a general discussion will follow. Handling of the plots and methods of measurement were the same from year to year unless otherwise stated.
1958 Methods and Materials
Location
White farm, northeast bench, Logan, Utah.
Treatments
The three treatments (randomized within the row of plots) were as follows: (1) Plots caged to admit only tiny insects; (2) plots without cages (open pollination); and (3) plots caged to enclose a small (four-frame) colony of honey bees. The cages (Pedersen et aI., 1950) were 21.5 feet long, 11 feet wide, 6 feet high, and covered with 12-mesh clear lumite screen. As soon as flowering began in late June, the cages were erected and the hives of bees installed.
Plot layout
In 1958, there were 12 plots that measured 10 x 20 feet arranged in a single row. Each plot contained five rows, each planted with 40 onion bulbs. The rows were 2 feet apart, and the plants were spaced ab()ut 6 inches apart in the rows. The center row was plante:! with U-16-3-10- 2B, a male-fertile inbred line. The other four rows were planted with the following three male-sterile inbreds: B-1900A, B-2147A, and B-2267A. Two rows of the B-2267 A were planted in each plot and the positions of all the male-sterile rows were randomized. More than one male-sterile line was used merely because we were unable to obtain enough bulbs of a single line. When the bulbs were obtained, we anticipated that male steril ity would be complete, but at least a small amount of pollen was present in all of the lines.
Irrigation and insect control
The plots were irrigated once each week throughout the growing season.
4 The onion maggot [(Hylemya antiqua (Meigen)] was controlled by the application of Dieldrin in the furrow at the time the bulbs were plantl~d. Onion thrips (Thrips tabaci Lindeman) were controlled with a foliage ap plication of 10-percent DDT dust just prior to spfitting of the sheath on the umbel. No insecticides were applied after blossoming started. Eriophyid mites were not recognized as a potential problem, and, hence, no attempt was made to determine their presence or to control them.
Measurements
1. In 1957, in the course of a series of experiments on carrot pollination (Hawthorn et aI., 1960), the effect of the cages on air movement, air tem perature, and light intensity at the flower level, and on temperature at the soil mrface, was studied in detail. In 1958, we made another series of readings in our onion pollination studies to find the effect of the cages on relative humidity and soil surface temperature.
2. Nectar sugar concentration in the flowers was measured on July 18 on all plots (except those excluding large insects) by reading the sugar concentration of the nectar in the honey stomachs of bees taken directly from the flowers. A Bausch Lomb'*' low rang.e (0-60 percent) hand re fractometer was used for this purpose.
3. Flowering was measured 12 times throughout the season on the basis of the number of flower heads on which at least half of the flowers had opened. The duration of bloom was not measured.
4. On the mornings and afternoons of July 18 and 21, the relative numbers of nectar-collecting and pollen-collecting honey bees were meas ured in the cages with bees enclosed.
5. Counts of each species of pollinator were made on each row in the open plots. Four counts were made on each of 12 days th:o:.I.shout the season. The ob~erver 's route from plot to plot and row to row was changed for each observation. Tiny flies were difficult to see and their p~pulations were undoubtedly understated by the counts. Populations of tiny flies in the cages excluding bees were cnly evaluated in general terms.
6. A pollination efficiency rating for each pollinator was assigned by estimating the quantity of loose pollen grains fro.:n a representative sample and combining this factor with the size, hairiness, and a:tivity pattern of the insect. This type of rating, used previously br carrot pollin ators (Bohart and Nye, 1960), is admittedly subjective, but whea it is mul tiplied by the populations to give a pollination index, it should give a truer
5 picture than population figures alone. In the case of honey bees, separate ratings were given to nectar and pollen collectors, and the overall rating for the species was based upon the proportion of the two activity patterns taking place.
7. The seed heads were dried in September and threshed on a small rubbing board. The yield data in 1958 and subsequent years were sub jected to analysis of variance. The significance of mean differences was determined by the application of Duncan's (1955) multiple-range test.
Conditions Affecting the Experiment
Soil conditions
The soil was classified as Timpanogos silt loam. The moisture level was adequate for the row spacing throughout the growing season.
Plants
Some of the bulbs were decayed and, as a result, a number of plants failed to develop and others were onlY" partially productive. Since spacing in the rows was wide, it was possible to correct the data for missing plants without being concerned about increased yield on plants adjacent to the missing ones.
Harmful insects
The populations of onion maggot and onion thrips were held at a low level by the insecticide treatments used. Mirid bugs (Lygus spp. and Orthops scutellatus Utler) were present in the bloom stage but did not ex ceed one or two per flower head.
Cage effect
The principal effect of the cages was to reduce light intensity by about 39 percent and air movement by abc:.lt 45 percent (table 1). Th~ temperature and humidity in the cages and in the open were nearly the same, apparently as a result of the offsetting effe~ts of shading and reduced air movement. The temperature at the soil surface was somewhat lower in the cages in both the carrot and onion studies, perhaps because air move ment differences were less pronounced at this level.
6 Table 1. Air movement, relative humidity, air temperature, an d light intensity at flower height, and soil temperature at the ground level in the open and caged plots. Carrot and onio n pollination experiments, Logan. Utah, 1957 and 1958, re spectively
Relative Air Soil Air movement* humidity** temperature Light intensity* * * temperature Treatment Year ft. per min. (percent) (oF) (meter readings) (oF)
Open 1957 500 20 86.6 22.5 100
" 1958 14 85 86
Caged 1957 275 20 87.6 13.8 98
1958 15 86 83
* Effect of cage measured in a closed room in which a fan created an artificial breeze of 500 feet per minute. Measured with Electric Hygrometer indicator, American Instrument Co., Inc., Silver Springs, Maryland. Measured with Weston Master light meter (model I) directed toward a neutral gray (18% reflectance) card. Weather
In July of 1958, when flowering took place, temperatures were un usually low for the Logan area and precipitation was moderate (table 2.)
Nectar sugar concentration
The sugar in the nectar of the plants in the open plots was nearly twice as concentrated as that in the plants in the cages with honey bees (table 3). Greater air movement in the open plots probably increased nectar evaporation to cause this result. More rapid removal of nectar in the bee cages, with consequent less time for evaporation, was probably also involved (Nye and Pedresen, 1962). In support of this, we noted that the cage with the weakest colony of bees had flowers with the highest nectar sugar concentration (29 percent).
Progress of bloom
The cumulative progress of opening blossoms on the open plots is shown in figure 1. The point of decline in total bloom appeared to occur on or about July 15 when the cumulative curve flattened out. There was little difference among inbred lines in the progress of bloom.
Table 2. Temperature (OF) and precipitation data for the Logan, Utah area in July 1958-1961
Temperature No. of days Total Average Average 90 0 F or precipitation Year maximum minimum Highest above (inches) ------1958 85.7 52.9 92 8 .55 1959 88.1 54.0 97 16 .12 1960 92.3 56.5 102* 21 .03 1961 89.5 55.4 98 20 .53
* 7 days over 100° F.
Table 3. Sugar concentration in the nectar" of onion flowers on open plots and plots with honey bees enclosed, onion pollination experiment, Logan, Utah, 1958
___P_ercent sugar concentration Treatment By replication Average Open plots 44 45 46 44 45 Plots with honey bees enclosed 21 29 22 24 24
* Nectar taken from the honey stomachs of honey bees collected from the onion flowers. Each figure represents 16 samples (four bees collected four times during the season). 8 All1naecta
Honey bees Number of onion heads ~ per plot
40 I I~ I,,' "-/ , ----,.....-- ~ 350 ~' \ -~- 30 LA I ~ --.~ / \ "- of 300 , 250 ! 5! , .£0. .!3· t ·8 \ , Qj'"' \0 ~ ~ 0. , CIl 20 4 , , 200 -g Qj II '\ .d 1'1 / " , 0 /T " 150 § ...... " 0 '"'Qj 10 1-2 I I ./ ,,~ J 100 1l z::j
50
2 4 5 6 8 9 10 11 12 16 17 18 19 20 21 22 23 24 25 26 27 28 Days
Figure 1. Seasonal fluctuations of honey bees and all insect populations compared with accumula tive total of open flower heads, 1958. /
Pollination population-tiny insects only
In the cages of treatment 1, the only potential pollinators seen were small Diptera, including ceratopogonids, sciarids, cecidomyiids, chloropids, milichiids, and a few small spyphids [(mostly Syritta pipiens (Linnaeus)] The populations of tiny flies in the cages were small and few of the in dividuals examined carried pollen grains.
Pollination population-open plots (number per 100 feet of row)
Throughout the season, the average number of insects per 100 feet of row per observation was 32. The corresponding pollination efficiency rating was 52. The most abundant order of insects was Diptera (average, 22). Next was Hymenoptera (11). All other insects (principally Lepidop tera) were relatively scare (0.1). In terms of pollination efficiency, the above groups averaged 27, 15, and 0.12, respectively (tables 4, 5).
The most abundant insect was a syrphid fly (Syritta pipiens (9» and next was a chloropid fly [Thattmatomyia glabra (Meigen) (6)]. Both of these were ineffective pollinators and together they contributed only 10 percent to the total efficiency rating. Drone flies [Eristalis tenax (Linneaus) and E. brousii Williston (4.6)] were next in abundance among the flies. but because of their greater effectiveness as pollinators, they contributed almost half of the total efficiency rating for all insects.
Among Hymenoptera, honey bees were the most abundant, but be cause most of them were nectar collectors, their contribution to the total efficiency rating (about 23%) was less than that of the drone flies. A species of sweat bee, Halictus farinosus Smith, was only one-fifth as abundant as the honey bee but contributed about half as much ( 11 % ) to the total efficiency rating. The only other insect species contributing to a marked degree (about 5%) was a sand wasp, Bembix amoena Hand lirsch. The many other insect visitors assumed importance only in the ag gregate.
Pollinator populations tended to follow the curve of flower develop ment. The plateau of high population from July 9 to 21 coincided with the period of greatest bloom. By July 28, bloo:n had deteriorated to a point lower than at the beginning of the counts but pollinators were still mod erately abundant, perhaps because they were accustomed to visiting the plots.
Population curves of some species of pollinators did not follow the curve. It can be assumed that these were strongly influenced by their own
10 seasonal population curves, or perhaps by the flowering periods of more attractive blooms within their flight range. For example, Hatietus !arinosus gradually increased its visitation to the plots until July 25, whereas Bembix amoena was most abundant on July 9. Variation in the population curves of different species resulted in a broad plateau of high insect population. (See appendix A for complete list of insect visitors to onion plots.)
Pollinator population-caged plots with honey bees
Unfortunately, accurate measurements of bee populations in the cages were not taken. The average number present during the majority of the blooming period was roughly estimated to be between 10 and 200 per plot, which, at slightly less than one bee per flowering umbel, was much higher than all insects combined in the open plots. In one replicate, the population was at least one-third lower than in the others.
Table 6 shows the relative numbers of pollen and nectar-collecting honey bees in the caged plots with honey bees. There was a slight, but prob ably nonsignificant, increase in the percentage of nectar collectors through out the day (85% to 93%).
R-esults
Seed yields
In 1958, the overall seed yields from the enclosed plots with bees was 171 pounds per acre compared with 355 in the open plots and no seed in the plots with only tiny insects (table 7). Yields from the pollen parent were not significantly different between the plots with bees enclosed and the open plots, but yields from the male-sterile inbred lines were much higher in the open plots. Relative yields from the male-sterile lines were entirely different in the open and in the caged plots. Line B-2149A gave the highest yield in the cages but the lowest in the open plots.
11 Table 4. Average populations of insects per 100 feet of row on open onion
Species of pollinators 2 3 9 10 11 Apis mellifera .50 2.06 9.00 8.72 8.44 Halictus farinosus .10 .31 0.0 .50 .25 Other bees .59 .25 .17 0.0 .13 All bees 1.19 2.62 9.H 9.22 8.82 Bembix amoena .33 .44 3.50 2.63 1.69 Vespula spp. 0.0 0.0 0.0 0.0 0.0 Other wasps .33 1.07 1.52 3.75 .19 All wasps .66 1.51 5.02 6.38 1.88 All Hymenoptera 1.85 4.13 14.19 15.60 10.70 Thaumatomyia glabra .33 .44 12.08 6.13 9.56 Syritta pipiens 5.75 8.56 12.75 10.25 9.25 Eristalis tenax .33 3.94 7.17 7.63 7.69 Other Diptera .34 1.08 1.43 .64 1.31 All Diptera 6.75 -14.02 33.43 24.65 27.81 All Lepidoptera .10 .06 0.0 0.0 0.0 All insects 8.70 18.21 47.62 40.25 38.51
Table 5. Average population X efficiency of insects per 100 feet of row
Species of pOllinators 2 3 9 10 11 Apis mellifera 1.00 4.12 18.00 17.44 16.88 Halictus farinosus .50 1.55 0.0 2.50 1.25 Other bees 1.43 .63 .17 0.0 .39 All bees 2.93 6.30 18.17 19.94 18.52
Bembix amoena .83 1.10 8.75 6.58 4.23 Vespula spp. 0.0 0.0 0.0 0.0 0.0 Other wasps .50 1.14 2.02 5.25 .19 All wasps 1.33 2.24 10.77 11.83 4.42 Ail Hymenoptera 4.26 8.54 28.94 31.77 22.94 Thaumatomyia glalJra .03 .04 1.21 .61 .96 Syritta pipiens 2.88 4.28 6.38 5.13 4.63 Eristalis tenax 1.32 15.76 28.68 30.52 30.76 Other Diptera .78 1.84 2.59 1.14 3.93 All Diptera 5.01 21.92 38.86 37.40 40.28 All Lepidoptera .10 .06 .10 0.0 .06 All insects 9.37 30.52 67.90 69.17 63.28
12 plots, onion pollination experiment, Logan, Utah, 1958. July 14 15 16 18 21 25 28 Average 8.00 8.94 10.44 6.42 4.14 2.81 1.75 5.94 .19 1.61 1.19 2.00 2.39 3.13 2.00 1.14 .94 .31 2.44 .50 .68 .63 .13 .56 9.13 10.86 14.07 8.92 7.21 6.57 3.88 7.64 1.00 0.0 0.0 .92 1.29 .56 .75 1.09 0.0 0.0 0.0 0.0 0.0 2.19 1.13 .28 .19 1.82 .38 1.75 2.35 3.51 2.14 1.58 1.19 1.82 .38 2.67 3.64 6.26 4.02 2.95 10.32 12.68 14.45 11.59 10.85 12.83 7.90 10.57 8.06 10.56 9.00 9.56 4.07 3.25 .13 6.10 7.50 18.06 10.13 7.08 7.36 7.75 8.88 9.44 7.63 5.50 9.63 3.50 1.68 .56 .50 4.65 .31 1.88 3.07 2.17 2.67 1.93 1.39 1.52 23.50 36.00 31.83 22.31 15.78 13.49 10.90 21.71 .06 0.0 .70 0.0 .40 0.0 0.0 .11 33.88 48.68 46.98 33.90 27.03 26.32 18.80 32.41
on open plots, onion pollination experiment, Logan, Utah, 1958 July 14 15 16 18 21 25 28 Average 16.00 17.88 20.88 12.84 8.28 5.62 3.50 11.88 .95 8.05 5.95 10.00 11.95 15.65 10.00 5.70 2.82 .93 7.32 1.50 2.94 2.51 .52 1.74 19.77 26.86 34."15 24.34 23.17 23.78 14.02 19.32 2.50 0.0 0.0 2.30 3.23 1.40 1.88 2.73 0.0 0.0 0.0 0.0 0.0 6.57 3.39 .83 .19 1.89 .38 1.75 2.35 3.61 2.14 1.79 2.69 1.89 .38 4.05 5.58 11.58 7.41 5.35 22.46 28.75 34.53 28.39 28.75 35.36 21.43 14.68 .81 1.06 .90 .96 .41 .33 .01 .61 3.75 9.03 5.07 3.54 3.68 3.88 4.44 4.73 30.52 22.00 38.52 14.00 6.72 2.24 2.00 18.59 3.88 5.13 6.76 3.57 4.96 2.88 3.15 3.41 38.96 37.22 51.25 22.17 15.77 9.33 9.60 27.32 0.0 0.0 .70 0.0 .40 0.0 0.0 .12 61.42 65.97 86.48 50.56 44.92 44.51 31.03 52.09
13 Table 6. Percentages* of nectar and pollen-collecting honey bees on the plots caged with honey bees, onion pollination experiment, Logan, Utah, July 21, 1958 Time of day Nector collectors Pollen collectors 8-10 am 85 15 10-12 am 92 8 12-2 pm 91 9 2-4 pm 93 7 Average 90 10 * Averages of 190 bees examined on the four replications at each time of day
Table 7. Onion seed yields in pounds per acre by inbred line and pollination level, onion pollination experiment, Logan, Utah, 1958 .Inbred lines Open plots Bees caged B-1900A 423 A* 154 0 B-2149A 310 BC 214 CO B-2267A 387 AB 109 0 B-2267A 387 AB 109 0 Pollen parent 270 C 266 C Average 355 170 * Means not followed by the same letter are significantly different at the 1-percent level.
1959
Methods and Materials
Location
Greenville farm, North Logan, Utah
Treatments
In 1959, when it was apparent that plots caged to admit only tiny insects would not produce seed, we established instead plots covered with cages (modified-open) designed to allow free passage of pollinators. This was done primarily to determine whether differences in yields between open and caged plots might be associated with cage effect rather than pol linator activities. The three treatments (randomized within the row of plots) were as follows: (1) Plots without cages (open pollination); (2) plots provided with cages partially rolled up on the sides and open at the upper corners to allow free passage of pollinators (modified-open); and (3) plots caged to enclose a small (eight-frame) colony of honey bees.
14 Plot layout
The 12 plots were randomized in two rows. The center row of each plot was planted with U-16-3-10-2B, a male-fertile inbred line. The other four rows were planted with the following four male-sterile inbreds: B-2264A, B-2267A, B-2190A, and U-23-92-5-3A. Only the male-sterile inbred B-2267 A was the same used in the 1958 study. The other sterile lines used had no counterpart in 1958. As in 1958, male sterility was not complete; a small amount of pollen was present in all of the lines.
Measurements
1. Progress of bloom on each row was measured on July 13 by count ing the total number of heads and the number not yet open. On July 23, the percent of the bloom was estimated on each of 10 heads at the north end of each row on the first three replications.
2. Populations and pollination efficiencies of insect VISItors were measured on mornings and afternoons of July 10 and July 13, and morn ings only of July 16 and August 7.
3. The population of honey bees in the caged plots with bees was roughly estimated but not accurately counted.
Conditions Affecting the Experiment
Soil and soil moisture
The soil was classified as Millville silt loam. The moisture level was adequate for the row spacing throughout the growing season, and cultiva tion was uniform in the nursery.
Plants
The bulbs were in good condition and the stands were excellent. lIarnnful insects Populations of onion maggot and onion thrips were held at a low level by the insecticide treatments used. Mirid bugs (Lygus spp.) were present in the bloom stage, but they did not exceed one or two per flower head.
15 Weather
In July 1959 when flowering took place, temperatures were high and precipitation was below normal, less than one-fourth that of 1958 (table 3).
Progress of bloom
The cumulative progress of opening blossoms on all plots was similar to that shown in figure 1 for 1958. The point of decline in the total bloom was not accurately determined, but it appeared to occur shortly before July 23.
Pollination population-open plots
Insect populations per 100 feet of row per observation were much higher (128.5) than in 1958 (29.5) in spite of the fact that the number of species observed in the regular counts was smaller. The corresponding pollination efficiency ratings were 276.6 and 52.1. The smaller number of species observed in 1959 was in part accounted for by the smaller num ber of counts. The fact that most of the 4 counts in 1959 were taken during the peak bloom accounts to a slight extent for the disparity between aver age populations for the 2 years, but nearly as strong a difference is ap parent when only the days of peak population are compared. The most abundant order of insects in 1959 was Hymenoptera (average 108). Next, about one-fifth as abundant, was Diptera (18). All other insects, princi pally Lepidoptera, were relatively scarce (2.7). In terms of pollination efficiency, the above groups averaged 239.8, 34.1, and 2.7, respectively (table 8). Honey bees were more than twice as abundant as all other visitors combined. This contrasts sharply with the previous year when honey bees were only about one-fourth as abundant as all other insects combined. Approximately the same relationships held for pollination indices as for pollinators. In other words, honey bees appeared to be about average in efficiency both years. Based on accumulation of loose pollen grains, Halictus farinosus and Andrena prunorum were the most efficient pollin ators. Pollen-collecting honey bees were next, followed by two species of drone flies (Eristalis).
Pollination population-modified-open plots
The populations in the modified-open plots were slightly lower (aver age, 111 per plot) than in the open plots (average, 128) on all counting
16 days but one (table 9). The difference was nearly all accounted for by the smaller honey bee populations in the modified open plots. Other species of pollinators did not appear to be affected by the presence of the rolled-up cages.
Honey bees and solitary bees reached their peak populations on July 13 (table 8), but Diptera reached a sharp peak on July 16. On August 7, when little bloom remained, wasps (primarily Chlorion ichneumonium) and butterflies were much more abundant than they had been during peak bloom (table 8). Trends according to date were much the same on the open plots as on the modified-open plots (table 9).
Most of the insects were more abundant during the afternoon than the morning counts (table 10. However, drone flies (Eristalis spp.) were more abundant in the morning, just as they were on carrot plots in previous years.
The relative attractiveness, based on pollination indices, of the inbred lines on the open and modified -open plots is shown in table 11. On both types of plots, the order of attractiveness was the same. The pollen parent ranked fourth among the five lines represented. Pollinator populations - caged plots with honey bees
Honey bee populations were high. On July 16 the population was estimated at 300 to 100 feet of row. Nectar collectors outnumbered pollen collectors on this occasion by about four to one.
Results
Seed yields
Yields were considerably higher in 1959 (table 11) than in 1958 on the open plots (567 pounds per acre, compared with 356). From the analysis of variance (table 11), it indicates that yields from the modified-open plots were significantly higher than those from the open plots with bees enclosed. Table 11 shows that yields from the inbred male-sterile lines were significantly different, and the regression shown in figure 2 indicates that (1) yields benefited from increased pollinator activity within the ranges encountered on the open and modified-open plots, and (2) line differences in seed yield were at least partially accounted for by differences in attrac tiveness to insects.
17 Table 8. Average population and their pollination efficiency of insects per 1959 July 10 July 13 Pollinator No. Index No. Index Apis mellifera 72.3 144.5 160.0 320.0 Halictus farinosus 5.8 28.8 13.3 66.3 Andrena prunorum 0.0 0.0 3.0 15.0 Other bees .3 .3 .3 .3 All bees 78.4 173.6 176.6 401.6 Bembix amoena 1.0 2.5 2.3 5.7 Chlorion ichneumonium 1.0 2.0 1.3 2.5 Vespula spp. 0.0 0.0 0.0 0.0 Other wasps 1.6 3.0 1.0 1.3 All wasps 3.6 7.5 4.6 9.5 All Hymenoptera 82.0 181.1 181.2 411.0 Syritta pipiens 7.5 4.8 10.0 5.0 Eristalis tenax 1.8 7.0 .5 2.0 Other Diptera 0.0 0.0 0.0 0.0 All Diptera 9.3 11.8 10.5 7.0 All Lepidoptera 1.0 1.0 .3 .3 All insects 92.3 193.9 192.0 418.3 ~
Table 9. Average population and their pollination efficiency of insects per Utah, 1959 July 10 July 13 Pollinator No. Index No. Index Apis mellifera 59.5 119.0 141.0 282.0 Halictus farinosus 6.0 30.0 16.5 82.5 Andrena prunorum 3.0 15.0 Other bees .5 .5 All bees 65.5 149.0 161.0 380.0 Bembix amoena 2.0 5.0 1.0 2.5 Chlorion ichneumonium 1.5 3.0 Vespula spp. Other wasps 1.0 1.5 All wasps 3.0 6.5 2.5 5.5 All Hymenoptera 68.5 155.5 163.5 385.5 Syritta pipiens 8.5 4.3 7.5 3.8 Eristalis tenax Other Diptera All Diptera 8.5 4.3 7.5 3.8 All Lepidoptera All insects 77.0 159.8 171.0 389.3
18 100 feet of row on open plots, onion pollination experiment, Logan, Utah,
July 16 August 7 Average No Index No. Index No. Index 126.0 252.0 11.0 22.0 92.3 184.6 6.5 325 .5 2.5 6.5 32.5 4.5 22.5 0.0 0.0 1.9 9.4 0.0 0.0 0.0 0.0 .3 .3 137.0 307.0 11.5 24.5 101.0 226.6
0.0 0.0 10.5 26.3 3.4 6.9 .5 10 4.5 9.0 1.8 3.6 0.0 0.0 1.0 3.0 .2 .8 .5 1.0 2.0 2.5 1.3 1.9 1.0 2.0 18.0 40.8 6.7 13.2
138.0 309.0 29.5 65.3 107.7 239.8 20.5 10.3 3.0 1.5 10.3 5.1 20.5 82.0 1.0 4.0 6.0 23.8 4.0 11.5 3.0 8.3 1.8 5.2 45.0 103.8 7.0 13.8 18.1 34.1 0.0 0.0 9.5 9.5 2.7 2.7 183.0 412.8 46.0 88.6~ 128.5 276.6
100 feet of row on modified-open plots, onion pollination experiment, Logan,
July 16 August 7 Average No. Index No. Index No. Index 71.0 142.0 15.0 30.0 71.6 143.2 8.0 40.0 7.6 38.1 3.0 15.0 1.5 7.5 1.0 1.0 .3 .3 83.0 198.0 15.0 30.0 81.0 189.1 9.0 22.5 3.0 7.5 1.0 2.0 9.0 18.0 2.9 5.8
2.0 2.5 .8 1.0 1.0 2.0 20.0 43.0 6.7 14.3 84.0 200.0 35.0 73.0 87.7 203.4 21.0 10.5 3.0 1.5 10.0 5.0 20.0 80.0 1.0 4.0 5.0 21.0 13.0 48.0 3.0 8.0 4.0 14.0 54.0 138.5 7.0 13.5 19.2 40.0 17.0 17.0 4.3 4.3 138.0 338.5 59.0 103.5 111.2 247.7
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Table 11. Seed yields in pounds per acre by inbred line and pollination level, onion pollination experiment, Logan, Utah, 1959 Onion inbred Modified- Bees line open open enclosed Average Male-steriles B-2264A 932 1222 820 991 A B-2267A 564 1061 407 677 A B-2190A 309 565 260 378 C U-23-92-4-3A 337 548 362 416 C Pollen parent U-16-3-10-2B 693 724 596 671 B Average 567 B* 824A 507 B 633 * Means followed by same letter are not significantly different at 1-percent level.
1960
Methods and Materials
Location
Greenville farm, North Logan, Utah. Treatments
The four treatments, randomized within two rows of plots, were as follows: (1) Plots without cages (open pollination); (2) modified-open plots; (3) plots caged to enclose a small (four-frame) colony of honey bees; and (4) plots caged without insects for 2 days and provided with a small honey bee colony the third day. Plot layout
There were 16 plots composed of the four above-described treatments replicated four times. The center row of each plot was planted with
21 inbred male-fertile pollen parents-U-16-3-11B. The other four rows were planted with the following four male-sterile inbreds: B-2267 A, B-2264A, U-16-3-11A, and B-5546A. Only the male-sterile inbred lines B-2264A and B-2267 A were used in the 1959 study. The pollen parent and the other two male-sterile lines had no counterpart in the previous studies. As in previous years, male sterility was not complete; a small amount of pollen was present in all of the lines.
Measurements
1. Information about air and soil temperature, relative humidity) and light intensity was gathered as follows: (1) air temperature at flow'-;r height was measured by using a chemical mercury-filled thermometer, shaded to keep direct sunlight from the bulb. (2) The soil surface tem perature was measured by a chemical mercury-filled thermometer with the column section mounted on a board and the free bulb held in contact with the soil by means of a spike connected to the board and thrust into the soil. (3) The percent relative humidity was measured in the center of each plot with an electric humidity and sensing element placed 6 inches above the ground surface. (4) The foot candles of light were measured with a photo light meter directed toward #a neutral gray card. 2. Percent of sugar in the nectar. 3. Percent of flowers with pollen on the stigmas from each row during peak bloom. 4. Percent of blasted (straw-colored) florets in the center of the flower beads. 5. Counts of insect visitors on 12 days spaced throughout the flower ing season. Percentage of pollen-collecting honey bees was measured in all plots. 6. Seed yields.
Conditions Affecting the Experiment
Plants, soil, soil moisture Equivalent to those in 1959.
Harmful insects Insect populations were held at a low level. The highest lygus bug count recorded was 0.6 per umbel.
22 Weather
The weather was clear and unusually warm, with a number of days surpassing 100 F.
Air temperature at flower height (table 12)
The average of four maximum temperature readings in the open plots was 94.5 F., and in the modified open plots it was 95.5 F. The average temperature in both treatments with bees enclosed was 96.9 F. The analysis of variance indicates that there was no significant differ ence between treatments or replications. However, the increased tem perature in the bee cages may have been more drastic during the 100 F. plus periods. This may have been enough to kill many of the florets and reduce the seed yields.
Surface soil temperature
The surface temperatures by treatment and plot are summarized in table 12. The analysis of variance shows that treatments were significantly different at the I-percent level. The modified-open plots and those caged continuously wjth bees had the older, darker screen, whereas those with bees caged intermittently had new clear screen, which allowed more light penetration. The lowest surface soil temperatures were recorded in the modified-open plots.
Relative humidity
Table 12 shows the relative humidity for each treatment. The analy
StS of variance shows that the replications, but not the treatments, were Table 12. Nectar sugar concentration, air temperature, and soil surfaae temperature by treatment. Onion pollination experiment, Logan, Utah, 1960 Sugar Soil Relative nectar* Air temp surface temp humidity Treatment (percent) (0F)** (OF)*** (percent) Open plots 32 B* *. * 94.5 A 113.0 A 16.5 A Modified open plots 35 B 95.5 A 102.5 B 15.8 A Honey bees continuously 26 C 96.8 A 104.5 B 14.8 A Honey bees inter- mittently (1 day in 3) 45 A 96.8 A 112.0 A 16.6 A * Readings taken from four honey stomachs of honey bees collected from . each plot. * * Four readings taken at flower height from each plot. * * * Four readings taken 3 inches from plant base in center row of each plot. * * * * Means in a column not followed by the same letter are significantly different at the 1-percent level.
23 significantly different at the 5-percent level. The difference between replications probably resulted from the presence of slightly more soil mois ture in some plots than others.
Blasting of florets
A number of flower heads on all plots were observed with a circular patch of straw-colored (blasted) florets in their centers. The patches var ied in size from a few central florets to areas an inch across. Blasted florets were observed in previous years but only in inconsequential numbers. In 1960, they were more abundant in some lines (especially B-5546A) than others, but the differences between treatments were much greater. The plots enclosing bees continuously had 40 percent of the florets blasted; those with bees 1 day in 3 had 23.8 percent, the open plots 2.9 percent; and the modified-open, 1.6 percent. Seed was not produced in blasted florets. The percentages of blasted florets are summarized in table 13.
Nectar sugar concentration
The data for sugar concentration ip the nectar of the onion flowers are summarized in table 12. The analysis of variance based on the total of four nectar readings for each plot was significant at the I-percent level for treatments and not for replications. There was no difference between open and modified-open plots. The sugar in the nectar of the plants in the plots caged with bees 1 day in 3 was nearly twice as concentrated as that in the plants continuously caged with bees. Apparently, the bee visitation 1 day in 3 allowed evaporation to occur in the nectaries.
The amount of pollen on the stigmas
Although it was difficult to select stigmas in the same development condition in the different inbred lines, the percent of stigmas observed
Table 13. Percent of florets blasted in the center of onion umbel by pol lination level and inbred line, onion pollination experiment, Logan, Utah, 1960 Open Modified- Bees caged Bees caged Inbred lines plots open continuously 1 day in 3 Average B-2264A 1.1 C* 1.4 C 30.2 A 36.4 A 17.28 B-2267A 2.9 C 1.6 C 40.0 A 23.8 AB 17.08 B-5546A 8.1 BC 1.0 C 20.0 B 21.9 B 12.75 U-16-3-11-A 0.1 C 0.1 C 3.1 C 3.2 C 1.62 U-16-3-11-B 0.0 C 0.0 C 0.24 C 1.5 C 0.42 Average 2.44 0.82 18.70 17.16 9.78 * Means not followed by the same letter are significantly different at the 1-percent level.
24 with pollen was nearly te same for all treatments [bees caged continu ously (38), bees 1 day in 3 (33), and modified-open plots (37)J.
Pollination populations-open plots
The overall figure for insect visitors per 100 feet of row (595) was about five times as high as in 1959, but the corresponding figure for pol lination index (293) was only about twice as high (table 14). A high percentage of the insects in 1959 were tiny flies with a low pollination efficiency. Since the efficiency rating assigned them (0.1) was probably too high, the pollination efficiency rating for all insects was probably also too high.
Honey bees were more abundant on the open plots than in previous years (159 per 100 feet compared with 92 in 1959 and 59 in 1958). How ever, only 3 percent of them were pollen collectors. The population of bees other than honey bees (7.4 per 100 feet) was comparable to that in 1959, but wasps (20 per 100 feet) were three times as abundant.
Differences in attractiveness among inbred grown lines were extreme. For example, B-2267 A and B-2264A each had 850 visitors per 100 feet in the open plots. This was three times as many.as on the pollen rows (250) and nine times as many as on B-5 546A.
Figure 3. Onion pollination, open plot, 1960.
25 Table 14. Numbers and pOilination indi.:es of various kinds of pollinators in Utah, 1960
B-2267A B-2264A Pollinator No. Index No. Index Apis mellifera (pollen) 1.0 3.0 1.0 3.0 Apis mellifera (nectar) 335.6 335.6 328.0 328.0 Other bees 15.9 73.8 13.2 54.4 All wasps 38.6 52.5 44.2 64.4 Large Diptera 26.1 87.4 13.9 45.8 SyriHa pipiens 214.7 107.4 184.4 92.2 Tiny Diptera 523.6 52.4 573.8 57.4 Other insects 31.0 37.2 19.9 23.8 All insects 1186.5 749.3 1178.4 669.0 Insects less honey bees 849.9 410.7 849.4 338.0
Pollination population-modified-open plots
Population trends of the various insects were similar to those in the open plots, but the figures averaged only about half as high (table 15). The overall figure was 293 per 100 feet compared to 595 in the open plots. The relative order of attractiveness of the lines was also the same in both treatments.
Pollination populations-continuously enclosed honey bees
The plots enclosing honey bees continuously had insect vlsltation levels comparable to those in the open plots, but the pollination indices were much higher because of the high proportion of tiny flies in the open plots.
Pollination population-honey bees enclosed 1 of 3 days
Visitation levels on the plots enclosing bees 1 day of 3 were only one fifth as high, even on the days when the bees were present, as on those with honey bees continuously.
Analysis of the data for insect populations (table 16) shows that all treatments were significantly different at the I-percent level, the order be ing as follows: Plots enclosing bees continuously, open plots, modified open plots, and plots with bees enclosed 1 day of 3. The same order held for pollination indices.
26 the open plots (per 100 feet of row), onion pollination experiment, Logan,
Inbred line U-16-3-11B (pollen parent) U-16-3-11A B-5546A Average -- -- No. Index No. Index No. Index No. Index 20.8 85.9 1.3 6.4 1.0 3.0 5.0 20.0 41.6 41.6 37.7 37.7 26.1 26.1 154.0 154.0 4.016.0 1.0 5.0 3.0 11.0 7.4 32.0 7.7 11.3 5.0 7.5 6.1 8.4 20.3 28.8 16.8 60.0 11.0 38.6 4.5 15.0 14.5 49.4 134.3 67.1 84.1 42.1 39.3 19.6 131.4 65.7 82.4 8.2 27.7 2.8 36.1 3.6 248.7 24.9 5.3 8.9 8.4 10.1 2.6 3.1 13.4 16.6 312.9 299.0 176.2 150.2 118.7 89.8 594.5 391.5 250.5 171.5 137.2 106.1 91.6 60.7 267.7 217.4
Table 15. Numbers of various kinds of pollinators per 100 feet of row in the modified-open plots, onion pollination experiment, Logan, Utah, 1960
Inbred line 8-2267A B-2264A U-16-3-11-8 U-16-3-11-A 8-5546A Pollinator ~. No. No. No. ~Average Apis mellilera (pollen) 1 1 12- 1 1 3.2 Apis mellifera (nectar) 151 120 23 26 12 66.4 Other bees 14 13 4 3 1 7.0 All wasps 15 17 14 10 7 12.6 Large Diptera 16 13 10 5 3 9.4 Syritta pipiens 115 103 72 58 33 76.2 Tiny Diptera 328 142 33 21 12 107.4 Other insects 18 20 7 5 71 292.6 All insects 658 430 175 129 71 292.6 Insects less honey bees 506 309 140 102 58 223.0
Table 16. Insect populations and pollination indices by treatment, onion pol lination experiment, Logan, Utah, 1960 Insect visitors per Pollination index Treatment 100 ft. of row* per 100 ft. of row Honey bees continuously 642.5 A ** 714.7 A Honey bees 1 day of 3* * ,. 162.9 D 194.9 D Open 594.5 B 391.5 B Modified-open 292.6C 249.1 C * Four replications each counted on 15 separate days. * * Different letters signify differences significant at the 1-percent level. * * * Figures refer to coun:s made on the day bees were in the caged plots. Visitation the other 2 days was O.
27 Results
Seed yields
Seed yields in pounds per acre by treatment and inbred lines are summarized in table 17. The highest yields were obtained in the modi fied-open plots (389 pounds per acre). The open plots were next (309), the plots of bees caged 1 day of 3 were third 228), and the plots with bees caged continuously (162) were lowest.
The analysis of variance shows a significant difference between all treatments at the I-percent level and no difference between replications.
Table 17. Onion seed levels In pounds per acre by imbred line and pollina- tion levels, onion pollination experiment, Logan, Utah, 1960
Open Modified- Bees caged Bees caged Inbred line plots open continuously 1 day in 3 B-2264A 771 AB* 838 A 379 CDE 538 BCD B-2267A 364 CDEF 585 BC 114 G 196 EF B-5546A 78 G 128 F 62 G 73 G U-16-3-11A 119 G 174 EF 105 G 157 EF U-16-3-11 B 211 EF 219 DEF 149 F 176 EF Average 309 389 162 228 * Means not followed by the same letter are significantly different at the 1 percent level.
Figure 4. Onion pollination, modified-open plot, 1960.
28 Yield differences between inbred lines were also significant, and the same trend of differences occurred in all treatments.
The order of attractiveness to insects of the various inbred lines (based on the open and modified-open plots) coincided with the order of seed yields for every treatment except the one with honey bees continuously caged. In this treatment, the yields of two lines were reversed (table 17).
1961
Methods and Materials
Location
Evans Experimental Farm, south Logan
Treatments
We established the same four treatments as in 1960 except that in the treatment enclosing honey bees intermit~ently, the bees were present 1 day in 4 instead of 1 day in 3. In addition, the eight plots caged with bees were divided into halves, the south half with 16-mesh cheesecloth sewed to it. The halves receiving shade could not be randomized because of the angle of the sun.
Plot layout and onion lines
The plot layout was the same as in 1960. The male-sterile lines were B-5546A, B-2264A, and U-23-92-5-3-4A, and the pollen parent line was U-161613-10-2B. Lines B-2264A and B-5546A were the same as used in 1960. The pollen parent and line U-23-92-5-3-4A had no counterpart in the previous studies.
Planting, irrigation and insect control
The onion bulbs were set out on April 17. Irrigation water being scarce, the plants were only watered once each in May and June and not at all in July and August. Onion maggots and onion thrips were controlled before flowering began, as in previous years.
~feasurements
1. Readings of temperatures at flower height in the shaded and un-
29 shaded halves of the caged plots were made by the same methods used previously.
2. Nectar sugar concentrations were measured six times in each plot.
3. Counts on insects and pollination efficiency ratings were also taken six times during the season on the open and modified-open plots. The same number of population counts of honey bees were made in the plots enclosing honey bees, with separate counts being made in the shaded and unshaded halves.
4. The percentage of germination after 14 days was measured on the cleaned seed by the Vegetable Seed Investigations Laboratory, Agriculrural Research Service, Beltsville, Maryland.
Conditions Affecting the Experiments
Soil and soil moisture
The soil was classified as Nibley silt loam. Soil conditions were drier than in previous years, especially late ih the season.
Plant condition
The onion bulbs were in good condition, and the plant growth was generally uniform from plot to plot. Since the plants were only irrigated twice, they did not grow as much as in previous years, but the difference was not obvious.
Harmful insects
Populations of harmful insects were held at a low level with insecticides applied before the onions began flowering. In July, with other crops drying up from lack of water, thrips and lygus bugs built up on the onions. The increase of these insects may have affected the seed yields in the open and modified-open plots.
~Veather and atmospheric conditions
The weather was generally warm and clear. The average maXImum temperature of 89.5 in a weather shelter was 3 degrees lower than in 1960. The average of four maximum temperature readings at flower height in the unshaded halves of the caged plot was 91.5 F., which was 4 degrees higher than that in the shaded halves. This difference was
30 significant at the I-percent level of probability. The average relative humidity was 12 percent, a few inches above the ground in the plots, as compared to 16 percent in 1960.
Nectar sugar concentration
The data on percent sugar in the nectar obtained from the contents of the honey stomachs of four nectar collectors per plot taken six times during the season can be summarized as follows: Open plots, 38.3; modi fied plots, 43.3; bees continuously, 26.8; bees intermittently, 66.0. Except for the two uncaged treatments, all treatments were significantly different from each other at the I-percent level.
Polinators in open and modified-open plots
Tables 18 and 19 show the numbers and pollination indices of the insea visitors on the open and modified-open plots for each inbred line. The numbers in general were about the same as in 1959, several times as high as in 1958, and much lower than in 1960. Honey bees were about twice as abundant on the . open plots as on the modified-open plots, and other kinds of bees were nearly twice as abundant on the modified open plots. Other insects generally showed ltttle in the way of differential response to the treatments.
Differences in attractiveness between lines were less apparent than in previous years. In addition, for the first time, the pollen parents were as attractive as the most attractive male-sterile line.
Figure 5. Onion pollination, enclosed plot with honey bees.
31 Table 18. Numbers and pollination indices of various kinds of pollinators per 1961
B-5546A B-5546A Pollinator No. Index No. Index Apis mellifera (pollen) 4.4 20.2 4.8 24.6- Apis mellifera (nectar) 44.1 44.1 37.0 37.0 Other bees 4.7 10.3 2.5 5.9 All wasps 1.9 3.0 1.0 1.5 Large Diptera 1.0 2.0 1.6 2.7 Syritta pipiens 52.6 26.4 42.3 21.2 Tiny Diptera 1.0 0.1 1.9 0.2 Other insects 10.2 15.2 11.3 14.1
--~------All insects 119.9 121.3 102.4 107.2 --_... - Insects less honey bees 71.4 57.0 60.6 45.6
Table 19. Numbers of various kinds of pollinators in the modified-open plots
B-5546A B-5546A ---- Pollinator No. Index No. Index Apis mellifera (pollen 0.0 0.0 2.6 12.7 Apis mellifera (nectar) 16.2 16.2 24.6 24.6 Other bees 3.6 9.5 8.1 23.4 All wasps 2.2 2.7 4.0 6.0 Large Diptera 1.0 5.0 1.0 5.0 Syritta pipiens 31.9 19.7 32.8 19.1 Tiny Diptera 1.0 0.5 1.0 0.5 Other insects 5.4 5.4 10.3 10.3 All insects 61.3 59.0 84.4 101.6 Insects less honey bees 45.1 42.8 57.2 64.3
Table 20. Average number of insects and their efficiency per treatment per Logan, Utah, 1961
B-5546A B-5546A ---- ._- ---- Treatment No. Index No. Index Open 19.9A * 19.5B 16.5C~- 17.7B Modified-open 14.8A 12.9B 19.8BC 23.48 Bees 1 day in 4 (north side of cage not shaded) 9.18 13.08 5.7C 9.78 Bees 1 day in 4 (south side of cage shaded) 4.2B 5.48 3.2C 4.68 Bees continuously (north side of cage not shaded) 4.28 48.9A 52.5A 54.5A Bees continuously (south side of cage shaded) 35.7A 38.1AB 42.8AB 56.2A ------_.. _------* Means not followed by the same letter are significantly different at the 1-percent level.
32 100 feet of row in the open plots, onion pollination experiment, Logan, Utah,
Inbred line U-16-3-10-2B (pollen parent) B-2264A U-23-92-5-3-4A Average No. Index No. Index No. Index No. Index 15.9 79.5 0.2 1.7 5.0 16.4 6.1 28.5 61.9 61.9 54.4 54.4 64.1 64.1 52.3 52.3 4.4 10.6 4.4 10.6 3.4 9.7 3.9 9.4 2.2 3.1 3.1 4.8 1.9 2.8 2.0 3.0 1.9 3.8 1.9 5.7 2.5 4.5 1.8 3.7 50.8 25.4 39.9 16.1 60.3 30.1 49.2 23.8 1.0 0.1 1.0 0.1 1.0 0.1 1.2 0.1 11.9 19.3 7.8 13.3 12.1 19.9 10.7 16.4 150.0 203.7 112.7 106.7 150.3 147.6 127.1 137.3 72.2 62.3 58.1 50.6 81.2 67.1 68.7 56.5 per 100 feet of row, onion pollination experiment, Logan, Utah, 1961 Inbred line --U-=-16-3-10-2B (pollen parent B-2264A U-23-92-5-3-4A Average No. Index No. Index No. Index No. Index ---- 3.4--17.2 '1.0 2.8 2.2 9.7 2.8 8.5 31.9 31.9 45.0 45.0 24.7 . 24.7 28.5 28.5 8.1 23.4 6.0 13.5 5.3 14.1 6.2 ·i6.8 1.0 1.4 2.8 4.1 1.1 1.6 2.2 3.2 1.0 5.0 2.2 11.0 3.8 19.0 1.8 9.0 50.0 25.5 52.5 26.2 49.4 24.7 43.3 23.0 1.0 0.5 1.0 0.5 2.0 1.0 1.2 0.6 10.9 10.9 18.1 18.1 12.5 12.5 11.4 11.4 107.3 115.8 128.6 121.2 101.1 107.3 97.4 101~ 72.0 66.7 82.6 73.4 74.2 72.9 66.1 64.0
100 feet of row on imbred lines bp treatment, onion pollination experiment,
Inbred line U-16-3-11B (pollen parent) B-2264A U-23-92-5-3-4A Average No. Index No. Index No. Index No. Index ------24.58 34.08 17.78 15.8B 24.88 25.78 20.78 22.58 22.38C 23.78C 15.98 16.68 21.88 21.78 18.98 19.78
6.78 12.8C 13.68 14.38 8.4B 9.78 8.78 11.98
4.28 9.8C 5.18 5.18 4.48 5.48 4.28 6.18
65.1A 87.8A 77.6A 79.8A 67.5A 75.0A 51.8A 69.2A
53.2A 70.9A 63.5A 64.7A 51.9A 55.2A 49.4A 57.0A
33 Pollinators in the plots enclosing bees
Visitation to the onions was very low in the cages with bees enclosed 1 day our of 4 (an average of 6.5 per 100 feet of row) (table 20). In the cages with bees continuously enclosed, the populations were much higher (average 55.6 per 100 feet of row). In both treatments, the populations were higher in the unshaded than the shaded halves of the cages.
Results
Blasted florets
The percent of blasted florets was generally lower than in 1960 (table 21). Some lines (for example, B-5546A and U-16-3-10B) had more blasting in the bee cages than in the open or modified-open plots, but in B-2264A the reverse was true in small measure. The shaded end of the plots caged with bees showed more blasting than the unshaded half, con trary to expectations.
Seed yields
Yields were lower than in 1959 and differences among treatments and among inbred lines were the smallest of the 4 years of study. Unlike 1959 and 1960, the plots with honey bees continuously enclosed had yields equivalent to this in the open and modified-open plots. The plots with honey bees enclosed 1 day of 4 (very light population) had significantly lower yields. In both honey bee treatments, the extra shading on the south halves of the cages resulted in increased yields (table 22).
Seed germination
The average 14-day germination of seeds from the four basic treat ments ranged from 89.5 percent in the plots caged with honey bees con tinuously to 94.4 percent in the modified-open plots. Only the latter fig ure was significantly different from the others (table 23). There were significant differences in the seed germination of the inbred lines and these tended to be consistent from treatment to treatment. The inbred with the lowest germination was B-5546A (83.5 percent) and that with the highest was B-2264A (97.1 percent).
Correlations
When eight variables were matched with the seed yields, the follow-
34 ing were significantly positively correlated with the yields within treatment (table 24): (1) Pollination index (all treatments), (2) insect visitation (open and modified -open), (3) 14-day germination (all treatments), (4) pollen collecting honey bees (open, bees enclosed continuously and inter mittently), (5) nectar-collecting honey bees (open and modified-open), (6) Syritta pipiens (open), and (7) Eristalis tenax (open). Blasted florets (all except modified-open) were significantly negatively correlated on the same basis.
When matched with yields within lines, the following correlations were significant (table 25): Pollination index (three lines negative), (2) insect visitation (same three iines negative), (3) blasted florets (all lines negative), (4) 14-day germination (two lines negative and one line posi tive), (5) pollen-collecting honey bees (two lines negative and one line positive), (6) nectar-collecting honey bees (all lines negative), (7) Syritta pipiens (two lines negative and one line positive, and one line with a neg ative correlation from one row (bulb source) and positive from another (the two rows from different bulb sources». In a correlation between pollination index and blasted florets, there was a significant negative cor relation within all treatments except modified-open and a positive correla tion within two lines.
Figure 6. Onion pollinator, nectar-collecting honey bee.
35 Table 21. Percent of florets blasted in center of umbel by pollin ation level and inbred line, onion pollination experiment, Logan, Utah, 1961 Bees caged 1 day In 4 Bees caged continuously Inbred line Open Modified-open Light Shade Light Shade Average
8-2264A 7.85 8C* 3.52 C 0.0 D 0.0 D 0.0 D 0.0 D 1.90 8-5546A 0.0 D 0.0 D 0.0 D 2.62 0.0 D 7.30 C 1.65 8-5546A 0.0 D 0.0 D 2.37 16.41 A8 0.0 D 18.77 A 6.26 U-23-92-5-3-4A 0.0 D 0.0 D 0.0 D 0.0 D 0.0 D 0.0 D 0.0 U-16-3-10-28 0.0 D 0.0 D 2.81 C 11.34 A8C 0.0 D 9.63 A8C 3.96 (pollen parent) Average 1.57 0.70 1.04 6.07 0.0 7.14 2.75
\.)) * Means not followed by the same letter are significantly diffe rent at the 1 percent level. 0\
Table 22. Seed yields in pounds per acre by inbred line and pollination level, onion pollination experiment, Logan, Utah, 1961
Bees caged 1 day in 4 Bees caged continuously Inbred line Open Modified-open Light Shade Light Shade Average
8-2264A 214 A* 309 A 104 8 100 8 204 8 252 A 197 8-5546A 334 A 339 A 102 8 222 8 291 A 407 A 282 8-5546A 392 A. 442 A 156 8 236 8 406 A 430 A 344 U-23-92-5-3-4A 243 A 269 A 136 8 135 8 303 A 333 A 236 U-16-3-10-28 218 A 275 A 181 8 232 A 222 A 290 A 236 (pollen parent) Average 280 327 136 185 285 342 259 * Means not followed by the same letter are significantly different at the 1 percent level. Table 23. Germination (14 days) percentages of seed produced under levels of pollination, onion pollination experiment, Logan, Utah, 1961 U-16-3-10-2B B-5546A B-5546A (pollen parent) B-2264A U-23-92-5-3-4A Average Bees intermittently 82.88 C* 91.00 B 96.38 A 97.00 A 87.75 B 91.00 B Bees continuously 79.62 C 91.50 B 97.50 A 96.12 A 83.00 C 89.54 B Open 82.62 C 94.50 A 95.38 A 97.50 A 89.25 B 91.85 B Mod ified-open 88.88 B 97.38 A 97.38 A 97.88 A 90.62 B 94.42 A Average 83.50 93.60 96.66 97.12 87.66 91.71 * Means followed by the same letter are not significantly dif ;erent from each other.
Table 24. Correlations between variables obtained from the analysis by pollination levels, onion pollination experiment, Logan, Utah, 1961 I.).) Correlation coefficients ""-J Modified- Bees Beees Variables Open open intermittent continuous Index X seed yields .712** .447* * .322* * .373** Insects X seed yields .501 * * .317* * .143 .054 Arc sine blast X seed yields -.245* .144 -.390* * -.705** Germination (14 days) X seed yields .556* * .613** .695* * .717** Honey bees (pollen) X seed yields .587* * -.029 .374* * .502** Honey bees (nectar) X seed yields .259* * .372* * .022 -.116 Syritta pipiens X seed yields .530* * .134 Eristalis tenax X seed yields .543* * -.001 Index X blasting -.283* -.052 -.500* * -.405** * Correlation coefficients significant at the 5-percent level. Correlation coefficients significant at the 1-percent level. Table 25. Correlations between variables obtained from the an alysis by inbred onion lines, onion pollination experiment, Logan, Utah, 1961 Inbred line U-16-3-10-2B Variables B-5546A B-5546A (pollen parent) B-2264A U-23-92-5-3-4A Index X seed yields -.608* * -.520* -.213 -~584* * .040 Insects X seed yields -.310* * -.290* .135 -.617** .021 Blast X seed yields -.738* * -.759** -.398* * -.418** -.313* * Germination (14-day) X seed yields .594 .644* * -.423* * .060 .408* * Honey bees (pollen) X seed yields .198 -.370* * -.386* * .365* * .152 Honey bees (nectar) X seed yields -.766** -.727** -.412** -.638* * -.305* * Syritta pipiens X seed yields -.857* * -.491 * * .572* * -.640* * .037 Eristalis tenax X seed yields -.318** .513** .553* * -.586* * .592* * Total index X blasting .476* * .216 -.020 .450** -.059 * Correlation coefficients significant at the 5-percent level.
\,)) Correlation coefficients significant at the 1-percent level. 00 Table 26. Numbers of various kinds of pollinators per 100 feet of row on open and modified-open plots, onion pollination experiment, Logan, Utah, 1958-1961 1958 1959 1960 1961 Species Open Open Modified-open Open Modified-open Open Modified-open
~.----"- Apis mellifera (pollen) 5.0 3.2 6.1 2.8 Apis mellifera (nectar) 5.9* 92.3* 71.8 154.0 66.4 52.3 28.5 Other bees 1.7 8.7 9.4 7.4 7.0 3.9 6.2 All wasps 3.0 6.7 6.7 20.3 12.6 2.0 2.2 Large Diptera 6.2 6.0 5.0 14.5 9.4 1.3 1.8 Syritta pipiens 9.4 10.3 10.0 131.4 76.2 49.2 43.3 Tiny Diptera 6.1 1.8 4.0 248.7 107.4 1.2 1.2 Other insects 0.1 2.7 4.3 13.4 10.4 10.7 11.4 All insects 29.5 128.5 111.2 594.5 292.6 127.1 97.4 Insects less honey bees 26.6 36.2 39.6 267.7 223.0 68.7 66.1 * Total honey bees for 1958 and 1959
~---~-~---~,,-.----.. ~.... DISCUSSION AND CONCLUSIONS
The experiments from 1958 to 1%1 were successful in terms of achieving significant differences between treatments in insect visitation and seed yields. One treatment, that excluding all insects except tiny flies, resulted in no seed and was not used after 1958. The modified-open plots (1959-1961), which allowed insects to come and go but subjected the plants to other aspects of the cage effect, reduced insect visitation some what and, hence, was not an ideal control treatment for the cage effect. This modified-open treatment reduced overall insect visitation about 20 percent to 50 percent during the 3 years (table 26).
In spite of the lower insect visitation to the modified-open plots, seed yields were higher in these plots than in the open plots all 3 years. This indicated that the shading effect (possibly coupled with reduction in air movement) had a beneficial effect on yields. It also could indicate that reducing the insect visitation below that in the open plots tended to increase yields. However, insect visitation was positively correlated with seed yields on individual lines in 1959, even when the reverse influence of shading on populations was included by con~idering both open and modi fied-open plots together. The regression coefficient indicated that about 40 percent of the variation in yields was accounted for by differences in insect VIsitation. Thus, it would appear that, although insect visitation levels were important, the environmental condition brought about by the cages was more important within the ranges of insect visitation encountered.
In a comparison of yields and pollination indices from year to year on the open and modified-open plots (table 27), it can be seen that in 1958 and 1961, these plots had the lowest yields and the lowest pollination in dices. However, within the 2-year groups (198, 1961 and 1959, 1960), the yields and pollination indices were inversely related. Possible explan ations are: (1) in 1961, irrigation water was severely limited, thus limiting plant capacity, and (2) in 1960, the pollination indices were probably over estimated as a result of overestimating the value of the tiny flies that made up a high proportion of the insect visitors that year.
The results obtained from the enclosed plots with honey bees do not bear out the positive association between insect visitation and seed yields (table 28). Each year the plots with honey bees continuously enclosed had higher pollination indices than the modified-open plots, but they had lower yields (except in 1961 on the halves of the plots receiving extra shading). In 1960, reducing the exposure of the plots to honey bees to 1 day in 3
39 Table 27. Comparison of yields and pollination indices by yea.r on open and modified-open plots, onion pollination experiment, Logan, Utah, 1958-1961 Open plots Modified-open plots Yield Pollination index Yield Pollination index Year Ibs/acre per 100 ft. of row Ibs/acre per 100 ft of row 1958 356 52 1959 567 277 824 248 1960 309 392* 389 298* 1961** 280 137 325 101 * Including indices from high percentage of tiny flies (probably overrated). * * Only two irrigations (adequate in previous years).
Table 28. Comparisons of pollination indices and yields in open and caged plots by treatment and year, onion pollination experiment, Logan, Utah. 1958-1961 Pollination index Yield Year Treatment (per 100 ft of row) Ibs/acre 1958 Open 52 355 Honey bees continuously 228* 170 1959 Open 277 567 Modified-open 248 824 Honey bees continuously 450* 507 1960 Open 392 309 Modified-open 293 389 Honey bees continuously 715 162 Honey bees 1 day in 3 195 228 1961 Open 137 280 Modified-open 101 325 Honey bees continuously unshaded 135 285 Honey bees continuously shaded 97 342 Honey bees 1 day in 4 unshaded 18 136 Honey bees 1 day in 4 - shaded 8 185 * Based upon population estimates and measured percentages of pollen and nectar collectors. resulted in a three-fold reduction in VIsItation even on the days of ex posure. In spite of this there was a seed yield increase. However, in 1961, when the exposure was further reduced to 1 day in 4 and there was a 6-fold population reduction on the day of exposure, yields were reduced by about half.
Apparently, the caged honey bees had a harmful effect on pollination superimposed on their necessary basic role as pollinators. Probably, when the visitation was extremely low, as in the plots with bees present 1 day out of 4 greater visitation would have increased yields. On the other hand, increased visitation in the cages with honey bees above an index of 100 per 100 feet of row appeared to reduce yields. The greatest reduction occurred in 1960 when the yields were moderate in the modified-open plots but poor in the caged plots with bees. Since there were a number of very
40 hot days in 1960 (above 100 F.), it seems likely that excessive heat compounded the harmful effect of the bees. Further evidence for an inter action between heat and honey bee activity in the cages was provided by the blasting that occurred in the centers of many flower heads (table 16). Blasted florets were especially prevalent in 1960 in the cages enclosing bees. They were more prevalent in the cages with bees continuously present than in the ones in which visitation was intermittent (and light). The possibility of blasting being caused by eriophyid mites cannot be ruled out completely since we made no pertinent observations. However, it would appear that, if eriophyids were involved, their effect was greatest under conditions of high temperatures in cages with honey bees.
Some studies were undertaken to find out what the honey bees in the cages were doing to depress yields. Physical injury to the stigmatic sur face and stripping of pollen from the stigma were not observed but may have occurred.. There is no evidence that honey bees were harmful when not confined to cages. For example, honey bees were the dominant pol linators in the modified open plots in 1959 when the yields on these plots were the highest we obtained in the 4 years of our experiments.
The high yields generally obtained in 1959 probably resulted from a combination of good weather (warm and sunny, but not hot), good
Figure 7. Onion pollinator Sphex ichneumoneus.
41 bulbs, adequate irrigation, and adequate pollination. In 1958, there waS some bulb decay (although yield figures were adjusted to make up for missing plants) and pollinators may have been in short su.pply in the open plots. In 1960, the exceptionally hot days were probably responsible for a general reduction in yields as well as a special reduction in the bee cages. The generally low yields in 1961 were probably caused by inade quate irrigation, perhaps offset to some extent by extra shading in the south halves of the cages with honey bees.
The various inbred lines differed widely in their attractiveness to pollinators (table 29). In nearly every instance, the lines held the same relative order of attrativeness to honey bees as to other insects. Since we changed many of the lines from year to year, it was difficult to determine how their attractiveness held up from year to year. Lines B-2264A and B-2267 A were relatively attractive for 2 years in a row, but the former lost its ranking in the third year.
The most surprising result in the line comparisons was the relatively low ranking of the pollen parents. In 1959, pollen parent U-16-3-10:-2B was fourth among the five lines. In 1960, U-16-3-11B was third and at tracted only one-fourth as many insects as the two leading lines. In 1961, pollen parent U-16-3-10-2B was equal to the most attractive male-sterile line and slightly more attractive than B-2264A which had been highly at tractive in the preceding years. Apparently nectar was the principal at tractant since rankings were generally independent of the presence or absence of pollen.
Table 29. Average number of honey bees and other insect visitors per 100 experiment, Logan, Utah, 1959-1961 1959 Open Modified-open Honey Other Honey Other Inbred line bees visitors bees visitors B-2190A 179 51 124 46 B-2264A 185 50 184 89 B-2267A 170 48 148 55 B-5546A U-16-3-11A U-23-92-4-3A 74 40 68 28 U-23-92-5-3-4A U-16-3-10-2B 129 29 114 41 (pollen parent) U-16-3-11-B (pollen parent)
42 Honey bees tended to visit the pollen parent lines for pollen much more than they did the male-sterile lines (table 30). Treatment seemed to have little effect on the percentage of pollen collectors except in 1961 when the percentage of pollen collectors visiting male-steriles was high in the cages where bees were present 1 day in 4. Althou.gh there were more nectar collectors than pollen collectors at all times and on all inbreds, even a small increase in the number of pollen collectors was probably im portant to seed production because of the greater efficiency of bee col lectors carrying pollen to the stigmas. Although females of most of the bees other than honey bees were collecting pollen, they showed no more preference for the pollen parent inbreds than G-id nectar-collecting honey bees or other insects. The same was true of Eristalis, which fed on pollen as well as nectar in the flowers. Apparently, these insects do not learn to discriminate between pollen-rich and pollen-poor plants as quickly as honey bees do. Another possibility is that they were more transient and did not have as much opportunity to learn.
During the 4 years of observation on the open and modified open onion plots, we identified 267 species of insect visitors (appendix A). Hymenoptera and Diptera were by far the 1Jlost numerous in species and individuals. Size and hairiness were the most important factors affecting the number of pollen grains carried, but activities on the flowers were also important. For example, nectar-collecting honey bees carried fewer pollen grains than did Eristalis flies of equivalent size and halictid bees of much
feet of row on inbred lines of open and modified-open plots, onion po iii natiotJ
1960 1961 Open Modified-open Open Modified-open Honey Other Honey Other Honey Other Honey Other bees visitors bees visitors bees visitors bees visitors
329 845 121 309 54 59 46 83 337 849 152 506 27 92 13 58 45 66 22 51 39 . 137 27 102
69 81 27 74 78 72 35 72
63 250 35 140
43 Table 30. Percent pollen collectors by inbred line and pollination level, onion pollination experiment, Logan, Utah, 1960-1961
1960 1961 Modified- Bees Bees Bees Modified- Bees Bees Inbred line Open open continuously intermittently Open open continuously intermittently
B-2264A 0.30 0.83 0.19 0.85 0.37 2.17 0.69 2.60 BI-2267A 0.30 0.66 0.01 0.26 ~ B-5546A 3.83 7.69 0.43 1.92 9.07 0.0 1.64 17.39 ~ B-5546A 11.48 9.56 3.61 21.91 U-16-3-11A 3.33 3.70 0.77 6.80 U-23-92-5-3-4A 7.24 8.18 0.59 6.67 Average of male steriles 1.94 3.22 0.35 0.93 7.04 4.98 1.63 12.14 pollen parent U-16-3-10-2B 20.44 9.69 9.18 33.33 U-16-3-11-B 33.33 34.29 32.00 38.24 smaller size. Taking both efficiency and abundance (all 4 ye:us) in to con sideration, the most important pollinators on the open and modified-open plots were (in order) as follows: 1. Apis mellifera 2. Syritta pipiens 3. Eristalis tenax 4. Halictus farinosus 5. Eristalis brousii 6. Bembix amoena
SUMIVIARY
From 1958 to 1961, we studied insect visitation to experimental onion plots by manipulating visitation levels, giving the insects a choice of inbred lines to visit, and comparing yields. We compared the following treat ments (but not all in the same year): (1) open plots; (2) plots caged with wide-mesh screen to exclude all but small insects; (3) caged plots with a small honey bee colony; (4) plots caged to include a small honey bee colony intermittently (1 day of 3 and 1 day of 4); (5). plots with cages modified to provide cage effect but to allow full passage of insect visitors. In addi tion, in 1961, the plots enclosing honey bees were given extra shading with cheesecloth on the south half. Each plot had five 20-foot rows of plants, the middle row being a pollen parent inbred and the others being different male-sterile inbreds. Some inbreds were used year after year but others were different each year.
The treatments succeeded in causing significant differences in both insect visitation and seed yields, but there was no positive correlation ap parent between the two on a treatment basis (except that in the caged plots allowing only tiny insects, seed setting was precluded. Plots with cage effect (but presumably free access to pollinators) reduced visitation somewhat but had higher yields than the open plots. Benefit from shading was also apparent from increased yields in the more heavily shaded halves of the plots caged with honey bees. Damage by honey bees when confined to the plots was apparent from the relatively low yields in such plots. Fur thermore, in 1960, yields were lower when the honey bees were continu ously rather than intermittently present. Only in 1961, when visitation was extremely light in the intermittent (1 day in 4) cages, was reduced visitation associated with reduced yields.
It was possible to positively correlate insect visitation with seed yields
45 in a comparison between inbreds in the open and modified-open plots. Thus, it appears that the shading benefits of cages on the one hand and the damage caused by confined honey bees on the other hand overrode the benefits of increased visitation (except where only tiny insects were pres ent). Pollen parent inbreds were less attractive to insects than some of the male-sterile inbreds (except in 1961 when the pollen parent was equal to the most attractive male-sterile). Pollen-collecting honey bees appeared to be more efficient than nectar collectors (based upon their activi ties and contamination with pollen), and they showed a preference for the pollen parent inbreds. During the four seasons of observation, 267 species of insect visitors to the open and modified open plots were identified. Based upon criteria of activities on flowers and contamination with pollen, the larger pollen collecting bees and pollen-feeding flies (mostly Eristalis) appeared to be the most efficient pollinators. The most important insect visitors based on efficiency ratings and abundance were (1) honey bees, (2) small syrphid flies (very abundant but possibly overrated), (3) halictid bees (especially Halictus farinosus) , and (4) drone flies (Eristalis spp.).
LITERATURE CITED
Bohart, G. E., and W. P. Nye. Insect pollinators of carrots in Utah. Utah Agr. Exp. Sta. Bul. 419. 1960. Duncan, D. B., Multiple range and multiple F tests. Biometrics 11 (1): 1-42. 1955. Flemion, R., and E. T. Hendrickson. Further studies on the occurrence of embryoless seeds and immature embryos in the umbelliferae. Boyce Thompson Inst. Contrib. 15:291-297. 1949. Flemion R., and P. Olsen. Lygus bugs in relation to seed production and occurrence of embryoless seeds in various umbelliferae species. Boyce Thompson Inse. Contrib. 16:36-46. 1950. Hawthorn, 1. R. Studies of soil moisture and spacing for seed crops of carrots and onions. USDA Cire. 892, 26 pp. illus. 1951. Hawthorn, 1. R., G. E. Bohart, E. H. Toole, W. P. Nye, and M. D. Levin. 1960. Carrot seed production as affected by insect pollination. Utah Agr. Exp. Sta. Bul. 422. 18 pp.
46 Hayward, Herman E. The structure of economic plants. The Macmillan Company, New York. Chapter 7 Liliaceae-Allium cepa 1. p. 179- 213. 1938.
Jones, H. A. Onion improvement, USDA Yearbook 1937: 233-250. 1937.
Jones, H. A., and S. 1. Emsweller. The use of flies as onion pollinators. Am. Soc. Hort. Sci. Proc. 31:160:164. 1934.
Kordakova, Z. M. Medonosnye pchely i opylenie semennikov repchatogo luke [Honey bees and pollination of seed plants of the common onion]. In Krischchunas, 1. V. and A. F. Gubin, eds., Opylenie sel' skokho ziaistvennykh rastenii [Pollination of agricultural plants], p. 163-171, fig., tables. Moska, Gos. Izd-Vo Selkhoz Lit-ry, 1956.
Moll, R. H. A study of seceptivity in the onion flower (Allium cepa 1.) and some factors affecting its duration. M. S. thesis. Univ. of Idaho, Moscow, Idaho, 1953.
Morse, 1. 1. Field notes on onions. C. C. M~rse and Co., San Francisco, Calif. 1923.
Muller, Hermann, Prof. The fertilization of flowers (translated by D. W. Thompson) Macmillan & Company, London. 1883.
Nye, W. P. Management of honey bee colonies for pollination in cages. Bee World 43(2):37-40. 1962.
Nye, W. P., and M. W. Pedersen. Nectar sugar concentration as a measure of pollination of alfalfa (Medicago satit/a 1.). J. Apic. Res. 1:24-27.
Pedersen, M. W., F. E. Todd, and F. V. Lieberman. A portable field cage. USDA Bur. Ent. and PI. Quar. ET. 289 1950 (mimeo.).
Shaw, F. R., A. I. Bourne, and C. 1. Lothrop. Notes on insects pollinating onions. J. Econ. Ent. 28(5) :836-837. 1935
47 APPENDIX A
Insect visitors to onion plots, Logan, Utah, 1958-1961 0
Hymenoptera Sphecidae 2 d Bembix amoena Handlirsch 2 e Steniolia elegans Parker 2 e Bicyrtes ventralis (Say) 1 c Philanthus gibbosus (Fabricius) 1 c Philanthtts anna Dunning 1 e Philanthus polittts psyche Dunning 1 e Philanthus fla~lifrons Cresson 1 e Cerceris convergens Viereck & Cockerell 1 d Cerceris nigrescens Smith 1 e Cerceris conifrons Mickel 1 e Cerceris sextoides Banks 1 e Ectemnius spi1liferus (Fox) 1 e Ectemnius dilectus (Cresson) 1 e Ectemnius chrysargyus (Lepeletier & Brulle) 0.5 d Lindenius colombianus (Kohl) 1 e Lestica interrupta (Lepeletier & Brulle) 0.5 e Diodontus rugoStis Fox 1 e Trypoxylon sculleni Sandhouse 2 e Stiziodes unicinctus (Say) 1 e Gorytes simillimus Smith 1 e H oplis 0 ides spilopterus (Handlirsch) 0.5 e OxybeitJs uniglumis quadrinotatum Say 0.5 e Oxybelus emarginatum Say 1 e Lyroda subita (Say) 1 e Liris argentata (Palisot de Beauvois) 1 e T achysphex fusus Fox 1 e T achysphex ashmeadii Fox 1 d Tachysphex tarsatus (Say) 1 e T achysphex terminatus (Smith) 2 e T achytes spatulatus Fox
* Arabic numerals (0.1, 0.5, 0.5, 1, 1.5, 2, 3, 4, 5) preceding each name refer to the estimated efficiency of individuals as pollinators (0 being the least efficient). Letters a, b, c, d, e following the numerals refer to abundance (a - most abundant e - rare or seen only once). (P) appearing after the names means that ~ome or all of the individuals seen were collecting pollen.
48 2 d T achytes distinctus Smith 2 d T achytes sayi Banks 1 e Ancistromma capax Fox 5.0 e Mimesa cressonii Packard 0,. 5 e Solierella sp. 1 e Astata nubecula Cresson 1 d Zanysson texanus (Cresson) 1 c Ammophila azteca Cameron 1 c Ammophila aberti Haldeman 1 c Podalonia luctuosa (Smith) 2 c Sphex (Pernaldina) lucae Saussure 2 b Sphex ichneumoneus (Linnaeus) 2 e Isodontia elegans Smith 2 c Sceliphron caementarium (Drury)
Vespidae 2 d Polistes fuscatus utahensis Hayward 3 e Vespula maculata (Linnaeus) 3 d Vespula arenaria (Fabricius) 3 d Vespula pennsylvanica (Saussure) 2 d Euodynerus annulatus ~e1/ectus (Cresson) 2 e Euodynerus discogaster (Bequart) 2 e Euodynerus exoglyphtts (R. Bohart) 2 e Euodynertts dorsalis (Fabricius) 1 e Ancistrocerus tuberculiceps sutterianus (Saussure) 1 e Ancistrocerus catskill albophaleratus (Saussure) 3 e Pterocheilus quinquefasciatus Say
Sapygidae 1 e Sapyga pumila Cresson
Pompiliidae 2 e Priocnemioides unifasciatus (Say) 1 e Anoplius aethiops (Cresson) 1 e Paracyphononyx funereus (Lepeletier) 2 d T achypompilus torridus (Smith)
Chrysididae
1 e Parnopes edwardsi (Cresson) 1 e Chrysura pacifica (Say) 0.5e Hedychrum violaceum Brulle
49 Colletidae 3 e Colletes fulgidus Swenk t 4 e Colletes mandibularis Smith !? (P) 4 d Colletes simulans Cresson t !? 1 e Hylaeus verticalis Cresson !J 1 e Hylaeus cressoni (Cockerell) ~!? Andrenidae 5 e Andrena prunorum Cockerell !? (P) 3 e Andrena candida Smith !? 3 e N omadopsis anthidius lutea Rozen ~ 2 d Nomadopsis scutellaris (Flower) ~ !? Halictidae 5 b Halictus farinosus Smith ¥ (P) 5 c Halictus rubicundus Christ !? (P) 4 c Halictus ligatus Say !? (P) 3 c Halictus tripartitus Cockerell ~!? (P) 3 d Halictus confusus arapahonom Cockerell !? (P) 2 d Dialictus incompletus (Crawford) ~ !? 2 d Dialictus zephyrus (Smith) !? (P) 2 e Dialictus nevactensis (Crawford) !? (P) 2 e Dialictus veganus (Cockerell) !? 4 d Lasioglossum sysimbrii (Cockerell) !? (P) 2 c Sphecodes arvensiformis (Cockerell) ~!? 1 e Sphecodes sp. nr. confertus Say ~ 1 e Sphecodes sp. nr. phosphorus Lovell & Cockerell ~ 1 e Sphecodes sp. nr. solonis Graenicher ~ 5 c N omia melanderi Cockerell ~ !? (P) 4 e Agapostemon texanus Cresson !? (P) 4 e Agapostemon angelictlS Cockerell !? (P) 4 e Agaspostemon femoratus Crawford ~ 5 e Agaspostemon virescens (Fabricius) ~!? (P) Anthophoridae 5 e Anthophora occidentalis Cresson !? (P) 5 e Anthophora urbana Cresson!? 3 e Melissodes rivalis Cresson ~ 3 e Melissodes tepida Cresson ~ 3 e Melissodes lupina Cresson !? (P) 2 e Nomada (Gnathias) sp. !? 2 e Nomada (Nomada) sp. !? 2 e N omada (A1icronomada) sp. !? 2 e Nomada Heminomada sp. !?
50 2 e Triepeolus arizonensis Cockerell ~ 2 e Epeolus pusillus Cresson 3 3 d Megachile rotundata Rabricius ~ 3 d Megachile angelarum Cockerell ~ 5 e Megachile perihirta Cockerell ~ (P) 4 e Megachile onobrychidis Cockerell ~ 4 e Osmia atrocyanea Cockerell ~ (P) 4 e Osmia indeprensa Sandhouse ~ (P) 2 e C oelioxys texana Cresson ~ 2 e C oelioxys moesta Cresson ~ 2 e H eriades carinata Cresson 1; ~ Apidae 5 e Bombus hunti Greene ~ (P) 5 e Bombus rufocinctus Cresson ~ (P) 5 e Bombus nevadensis Cresson ~ 4 e Bombus fervidus (Fabricius) ~ (P) 5 e Bombus morrisoni Cresson ~ (P) 5 e Bombus griseocollis (Degeer) J ~ (P) 5 e Bombus occidentalis Greene ~ (P) 5 d Bombus centralis Cresson ~ (P) 4 e Psythirus insularis F. Smith ~ 2 a Apis mellifera Linnaeus ~ (P) Ichneumonidae 1 e Pterocormus ambulatorius (Fabricius) 1 e Pterocormus longulus (Cresson) 1 e Compsocryptus fletcheri (Provancher) 1 e Exeta.rtes ruficoxalis Cushman 0.5 e Hyposoter fugitivus (Say) 0.5 d Diplazon lattatorius (Fabricius) 0.5 e Homot,.opus maculifrous (Cresson) 0.5 e Diadegma sp. 1 e lschnobatis baldufi (Walkley) 1 e Cryptus laborator altoni Dalla Torre 1 d Cryptus albitarsis (Cresson) 1 e Patrocloides montanus (Cresson) Braconidae 0.5 e Ascogaster sp. 0.5 e Chelonus muesebecki McComb 0.5 e Bracon nuperus Cresson 0.5 e lphiaulax sp. 0.5 e Tetrasphaeropyx piloJUS (Cresson)
51 Chalcididae 0.5 e Brachymeria coloradensis (Cresson)
Eurytomidae 0.1 e Eurytoma sp.
Torymidae 0.1 e Ditropinotus aureoviridis Crawford
Cynipidae 0.1 e Eucoila impatiens (Say)
Dlptera
Bombyliidae
1 e Villa lateralis semifulvipes Painter 1 e Villa melasoma (Wulp) 1 e Villa hypomelas (Macquart) 1 e Villa sp. fiT. molitor (Loew) 1 e Villa sp. nr. muscaria (Coquillett) 1 d Heterostylum laticeps (Bigot) 0.5 e Aphoebantus mus (Osten Sacken) 0.5 e Toxophora virgata Osten Sacken
Therevidae 1 e Psilocephala aldrichii Coquillett
Nemestrinidae 1 e N eorhynchocephalus sackenii (Williston)
Stratiomyidae 3 e Stratiomys barbata Loew 3 e Stratiomys normula unilimbata Loew 3 e Stratiomys adelpha Steyskal 3 e Odontomyia communis James 3 e Odontomyia alticola James 3 e Odontomyia pilimana Loew 3 e Hedriodiscus truquii (Bellardi) 1 e Sargus cuprarius (Linnaeus) 2 e Odontomyia pubescens Day 1 e Myxosargus knowltoni Curran
52 Conopidae 1 d Physocephala burgessi (Williston) 1 e Zodion fuh1ifrons Say 0.5 e Thecophora occidensis (Walker) 0.5 e Thecophora nigripes (Camras)
Tabanidae 2 e Tabanus lineola Fabricius 2 e Pilimas californicus (Bigot)
Sepsidae 0.1 e Themira putris (Linnaeus)
Tephritidae 0.5 e Eutreta jonesi Curran 0.5 e Gymnocarena diffusa (Snow)
Milichiidae 0.1 a Madiza glabra Fallen
Ephydridae 0.5 e Ochthera pilosa Cresson
Piophilidae 0.1 c Phiophila casei (Linnaeus)
Anthornyiidae 0.5 d Hylemya platura (Meigen)
Muscidae 1 e Musca domestica Linnaeus 1 e Graphomya maculata (Scopoli) 1 e Morellia micans (Macquart)
Calliphoridae 1.5 d Pollenia rudis (Fabricius) 1.5 e Lucilia illustris (Meigen) 1.5 c Phaenicia sericata (Meigen) 1.5 d Phormia regina (Meigen)
Syrphidae 0.5 a Mesograpta marginata (Say) 0.5 d Xylota (Syritta) pipiens (Linnaeus) 0.5 d Eumerus strigatus (Fallen)
53 0.5 d Chrysogaster parva Shannon 0.5 d Paragus bieolor (Fabricius) 0.5 e Paragus tibialis (Fallen) 0.5 d Mesograpta sp. 0.5 d Allograpta obliqua (Say) 4 b Eristalis tenax (Linnaeus) 4 d Eristalis anthophorinus (Fallen) 4 b Eristalis brousii Williston 4 e Eristalis latifrons Loew 2 c H elophiltts latifrons Loew 1 c Eupeodes volueris Osten Sacken 2 c Syrphus (Syrphus) opinator Osten Sacken 0.5 c Syrphus (Sphaerophoria) menthastri (Linnaeus) 0.5 e Syrphus (Platyeheirus) sp. 2 e Spilomyia interrttpta Williston 1 e Helophilus lunulatus Meigen 2 e Asemosyrphus polygrammus (Loew) 2 d Polydontomyia eurvipes (Wiedemann) 0.5 e Baeehet lemur Osten Sacken
Chloropidae 0.1 d Chlorops lituratt"s Adams 0.1 d T haumatomyia glabra (Meigen) 0.1 d Thaumatomyia annulata (Walker)
Otitidae 0.5 e Melieria eana (Loew) 0.1 c Physiphora demandata (Fabricius) 0.5 d Pseudotephritis inaequalis Malloch
Lauxaniidae 0.5 e Camptoprospella sp.
Sarcophagidae 2 c W ohlfartia vigil (Walker) 1 d Sareophaga sp. 1 1 d Sareophaga sp. 2 1 e Sareophaga sp. 3 1 e Senotainia flavieornis (Townsend) 0.5 d Senotainia trilineata (Wulp) Tachinidae 2 d Gonia sp.
54 1 c Cylindromyia armata Aldrich 1 c Gymnosoma fuliginosum Robineau-Desvoidy 1 e Gymnoclytia immaculata (Macquart) 2 c N owickia sp. 1 2 c N owickia sp. 2 2 e Peletaria iterans (Walker) 0.5 e Ryalomya aldrichii Townsend 1 e Myiophasia oregonensis Townsend 1 e Phoronthella punctigera (Townsend)
Lepidoptera Aegeriidae 1 e Synanthedon bibionipennis (Boisduval) 1 e Paranthrene robiniae (Hy. Edwards) Olethreutidae 1 e Eucosma sp. Noctuidae 1 d Agrotis ipsilon (Hufnagel) 1 e Anagrapha falcifera "(Kirby) 1 d Anagrapha californica (Speyer) 1 e Ettxoa sp. 1 e Acontia abdominalis (Grote) 1 e Tarachidia candefactra (Hubner) 1 e T arachidia tortricina (Zeller) 1 d Reliothis zea (Boddie) 1 e ProtorthodeJ sp. 1 e Peridroma saucia (Hubner) Pyralidae 0.5 e Loxostege sticticalis (Linnaeus Yponomeutidae 1 e Plutella xylostella (Linnaeus) Galechiidae 0.1 e Chrysopora hermannela (Fabricius) Pieridae 1 e Pieris protodice Boisduval & LeConte 1 d Pieris rapae (Linnaeus) 1 d Colias eurytheme Boisduval
55 Nymphalidae 1 e Vanessa cardui (Linnaeus) 1 e Nymphalis antiopa (Linneaus) 1 d Phyciodes mylitta (Edwards) Satyridae 1 d Cercyonis pegala (Fabricius) Lycaenidae 1 d Strymon melinus (Hubner) 1 c Lycaena helloides (Boisduval) 1 e Lycaena nivalis (Boisduval) 1 e Lycaena editha (Mead) 1 c Lycaedes melissa (Edwards) Hesperiidae 1 d Pyrgus communis (Grote) 1 d Poanes taxiles (Edwards) 1 e Pholisora cattalNs (Fabricius) 1 e Amblyscirtes tJialis (Edwards) Coleoptera Cerambycidae 1 e BatJ'le ignicollis (Say) 1 e T etraops femoratus LeConte Chrysomelidae 0.5 e Monoxia debilis LeConte Coccinellidae 0.5 d Hippodamia glacialis lecontei Mulsant 0.5 d Hippodamia convergens Guerin-Meneville 0.5 d Hippodamia quinquesignata (Kirby) 0.5 e Hippodamia apicalis Casey 0.5 e Hippodamia americana Crotch 0.5 e Coccinella transversoguttata Faldermann
Cleridae 2 d T rich odes ornatus Say Dermestidae 0.5 e Trogoderma simplex Jayne MeJyridae 1 d C ollops bipunctatus Say
56 Meloidae 1 e Nemognatha lurida LeConte Homoptera Cicadellidae 0.1 e Macropsis hesperia Break Hemiptera Lygaeidae 0.1 e Lygaeus reclivatus Say 0.1 d Nysius ericae (Schilling) Rhopalidae 1 e Liorhyssus hyalinus (Fabricius) 1 d Leptocoris rubrolineatus Barber Pentatomidae 1 e Euschistus in/latus Van Duzee 1 e Carpocoris remotis Horvath Miridae 0.5 c Lygus elisus Van D~zee 0.5 c Lygus hesperus Knight Phymatidae 1 e Phymata americana coloradensis Melin. Anthocoridae 0.5 c Orius tristicolor (White) Nabidae 0.5 d Nabis alternatus Parshley Neuroptera Chrysopidae 0.5 c Chrysopa sp.
57 COVER: Onion Pollinator - Halictus mililoti