CITRUS
Citrus spp., family RutaceaeThe kind of citrus crop produced, its volume, area of profusion; and dollar value are shown in table 8. As this table shows, the bulk of the citrus crop is produced in Florida, and oranges and grapefruit account for more than 80 percent of all fruit produced.
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TABLE 8. - Estimated U.S. production of citrus by State, type, number of boxes, and total value in 1970-71Plant:
The cultivated citrus plants are mostly shrubs or small trees with dense foliage; sweet-smelling, whitish to purple flowers that are often produced in great profusion; and greenish to golden fruit. The trees may live for more than 100 years, but citrus groves more than 50 years old are rare. Depending on the kind involved, the fruit may mature from fall until summer of the year following flower development. Some fruits, for example certain mandarins, fall shortly after they mature. Others, such as the 'Valencia' orange or the grapefruit, will remain on the tree several months after maturity. Citrus has little cold resistance and is not grown in areas where the temperature is likely to fall below 20 deg F.
A high degree of cross-fertility exists between the species of Citrus as well as between the genera of Citrus, Fortunella, and Poncirus. This has permitted breeders to develop the various simple and multiple hybrids, some of which have become of considerable economic importance (Cameron and Soost 1969).
The common and scientific names of the more well-known cultivars are shown in table 9. The species frequently mentioned but of minor value or used as rootstock or in breeding work are as follows:
Common name Scientific name:
Calamondin..........................................................Citrus reticulata var. austera Swingle X Fortunella spp. Citrange................................................................C. sinensis X Poncirus trifoliata Citrangequat.......................................................P. Trifoliata X Citrus spp. X Fortunella spp. Citron....................................................................Citrus medica L.Common nameÑ(Con.) Scientific nameÑ(Con.) Cleopatra mandarin............................................................C. reticulata Blanco Kumquat.................................................................................. Fortunella margarita (Lour.) Swingle Meyer lemon...........................................................................Citrus limon x C. medica Pummelo (Shaddock)..........................................................C. grandis (L.) Osbeck Rough lemon...........................................................................C. Iimon (L.) Burm. Sour Orange............................................................................C. aurantium L. Trifoliate orange.................................................................Poncirus trifoliata (L.) Raf. TABLE 9.ÑCommon and scientific names and important cultivars of U.S. citrus crops __________________________________________________________ Common Scientific Important name name cultivars __________________________________________________________ Grapefruit Citrus paradisi ÔBurgundyÕ, DuncanÕ,ÔMarshÕ, Macf. ÔRedblushÕ, ÔThompsonÕ. Lemon C. limon (L.) ÔEurekaÕ, ÔLisbonÕ Burm. f. Lime C. aurantifolia ÔKeyÕ (Mexican or West (Christm.) Indian group), ÔBearssÕ Swingle (Tahiti or Persian group). Orange (sweet) C. sinensis (L.) ÔHamlinÕ, ÔMediterranean Osbeck SweetÕ, ÔParson BrownÕ, ÔPineappleÕ, ÔValenciaÕ, ÔWashington NavelÕ. Mandarin and ÔAlgerianÕ (ÔClementineÕ) mandarin-hybrid ÔDancyÕ, ÔKinnowÕ, ÔK- complex EarlyÕ, ÔMinneolaÕ, ÔMurcottÕ, ÔOrlandoÕ, ÔPageÕ, ÔRobinsonÕ, ÔTempleÕ, ÔWilkingÕ. __________________________________________________________
Inflorescence:
The outstanding characteristics of citrus flowers are the pleasant fragrance, the pleasing contrast between the whitish (to pink or purple in lemons) petals and the dark-green background of the leaves, and the attractiveness of the flowers to bees. Blossom size varies in grapefruit, lemon, lime, orange, and the mandarin and mandarin-hybrid complex, ranging from about three-quarters of an inch for the smaller flowers to 1 1/2 inches for the largest (fig. 78).
The flowers usually open in one great flush of bloom in the spring, although lemons and acid limes are particularly noted for their tendency to flower throughout much of the year. The flowers are mostly hermaphrodite, releasing pollen when the stigma is receptive; however, staminate flowers occur in the lime, lemon, and citron (Purseglove 1968*) and pistillate flowers occur in 'Satsumas' (Kihara 1951). The pollenless flowers of the 'Washington Navel' are well known for their ability to set parthenocarpic fruit (Webber et al. 1943).
The flowers are in small clusters in the leaf axil of a preceding growth flush but single in the axils of a just-completed growth flush (Coit 1916, Chandler 1958*, Reece 1945). The four to eight, but usually five, oblong, glossy, flared petals arise from the base of the sexual column. The staminate portion consists of 20 to 40 upright white filaments, sometimes united into several groups at the base, with yellow anthers on the tip.
The globose yellowish stigma terminates the style. At the base, the style unites with the greenish ovary, with its 9 to 13 locules, which stands well above the disk.
Nectar is secreted from the nectary or floral disk just within and above the point of attachment of the stamens. Vansell et al. (1942) stated that secretion of nectar continues at least 48 hours after flower opening. Also, a thick viscous stigmatic fluid is secreted from papillose hairs on the stigma. This material serves to catch and hold pollen grains and provides suitable media for their germination. A similar material can sometimes be seen inside the style, apparently providing a route and media by which the pollen tube may reach the ovary.
The flowers open primarily from 9 a.m. to 4 p.m. with the peak period about noon (Randhawa et al. 1961). They never close; the petals merely shed a few days later. The stigma becomes receptive just before the bud breaks open, but the stamens usually do not release pollen until several hours later, after the flower is fully open (Wright 1937).
To determine if bee visitation altered the period of time the flower is open, I kept records of development on 20 'Clementine' ('Algerian') tangerine flowers at Yuma, Ariz., in 1954 (previously unpublished data). Ten flowers were on a tree enclosed in a cage with a colony of honey bees and 10 on a tree in a cage that excluded bees. Shedding of the petals and stamens in the no-bee cage was slightly slower than in the cage with bees but only because they became stuck in the uncollected nectar. Anther dehiscence was completed by the end of the second day, and normal petal fall was completed on the third day. Whether this applies to all other citrus or even to the same cultivar in other areas is not known but probably it is similar.
The difference in the appearance of the stigmas in the cages was significant. Pollination apparently occurred shortly after flower opening in the bee cage, after which the stigma color changed to brown. In the no- bee cage, the stigmas remained cream-colored and apparently receptive at least 4 days. This might explain the observation by Climenko (1936) that stigmas are receptive for 6 to 8 days.
Citrus generally yields nectar copiously. Vansell et al. (1942) stated that some blossoms contained 1.5 bee-loads of nectar, averaging 20 microliters, compared to 0.8 to 2.4 microliters per blossom for an alfalfa flower, another important nectar source. Because of the large amount and superior quality of honey that citrus blossoms produce, many beekeepers place their colonies in or near most groves.
The value of citrus as a source of pollen is influenced by the kind involved. Hamakawa (1967) reported that less than 1 percent of the bees foraging on 'Satsuma' mandarin (C. unshiu Marc.) carried pollen loads as compared to 95 percent on 'Hassaku' orange (C. hassaku Hort. ex. Y. Tanaka). In general, citrus is not considered to be an excellent source of pollen by beekeepers. Only a small percentage of citrus flowers set and develop into mature fruit. For example, Reuther et al. (1968) showed that one 'Washington Navel' tree had 102,350 blooms but matured only 419 fruit, and a 'Valencia' tree with 47,112 blooms matured 708 fruit. Reed (1919) reported 4,440 buds on one lemon tree, 52 percent of which set, but only 6.6 percent (294 fruit) reached maturity.
Moss (1971) studied the relation of flowering and the tendency toward biennial bearing in the sweet orange. He recorded twice as many flowers on the trees in "on" years as in "off" years, but the percentage of flowers that set was the same. Although more flowers usually equal more fruit, if the grower can take steps to increase this percentage during the "off" years, he should do so.
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FIGURE 78. - Longitudinal section of citrus flowers, x 3. A, 'Red Blush' grapefruit; b, 'Meyer' lemon; C, 'Algerian ('Clementine') tangerine; D, 'Washington Navel' orange.Pollination Requirements:
In general, citrus has been considered as a crop with little or no need for insect pollination. However, that which was said about a crop years ago may not be true today for, as Webber et al. (1943) pointed out, no variety is likely to remain entirely static over long periods, even when propagated asexually. The likelihood that pollination requirements of citrus have changed in this way is minor. More likely, our increased knowledge, obtained through continued studies, has enlightened us as to the range of pollination needs.
Furthermore, economic conditions may require maximum production of a crop if a net profit is to be realized. Under such conditions, a slight benefit, derived from better pollination of the crop, can become highly significant economically. Considerable attention has been given to citrus pollination recently. Krezdorn (1970) stated that a growing number of citrus cultivars are known to be self-incompatible and, in some cases, cross incompatible. With such cultivars, an appropriate pollen supply and pollinating agents is needed.
The pollination requirements of the different kinds of citrus are quite diverse. In some there is almost complete self-sterility. Pollen must be transferred to these flowers from those of another compatible type for maximum fruit production. In others, the plant is benefited if pollen is moved from flower to flower within the cultivar or within the species. In still others, there is no known benefit from transfer of pollen to the stigma by external agents over production caused by the plant's own pollen coming into contact with the stigma without the aid of such insects. In addition, there are varying degrees of parthenocarpic development of the fruit. Because of such diversity, the more important kinds of citrus are discussed separately.
GRAPEFRUIT:
Authorities on citrus in the United States have consistently stated that cross-pollination is not required in grapefruit, and that grapefruit production presents no pollination problem (Coit 1915, Frost and Soost 1968, Krezdorn 1970, 1972, Soost 1963, Webber 1930). This does not necessarily mean that no benefit is derived from insect transfer of pollen within the cultivar.
Wright (1937) studied the effect of cross-pollination on seed development and fruit set of the 'Marsh' grapefruit. Although some of his data on unpollinated (emasculated and bagged) flowers are open to question, he reported that open pollinated flowers set about twice as many seeds, but more importantly four times as many fruit, as selfed flowers. The presence of seeds is generally undesired by the canners and other consumers, although the 'Duncan' grapefruit is preferred by canners in spite of its seeds. The difference in fruit set could be of considerable economic importance. Satisfactory crops of grapefruit are normally harvested from solid blocks of a single cultivar.
LEMONS:
Richter (1916) stated that without question (but also without showing data) all the blooms of the lemon could be protected from insect visitation without the slightest reduction in set of mature fruit. Webber (1930) also concluded that pollination by bees was probably a negligible factor in the production of citrus fruits, at least for the 'Eureka' and 'Lisbon' lemons, the 'Valencia' and 'Washington Navel' oranges, and the 'Marsh' grapefruit. However, Webber et al. (1943) stated that although self-pollination occurs rather commonly without insects, seedlessness sometimes results, and seedlessness is rather generally a handicap to setting of fruit. Frost and Soost (1968) and Soost (1963) concluded that supplying pollen of another variety does not appear necessary for most of the major types of citrus.
In Russia, however, where numerous tests have been conducted on caged citrus trees, Glukhov (1955) stated that lemon trees isolated from bees produced only one-fourth as much fruit as trees exposed to cross- pollination by bees. Burnaeva (1956) reported that lemons receiving supplemental pollen from other cultivars or citrus species, produced more than trees not exposed to cross-pollination. Zavrashvili (1964) reported that lemon trees caged without bees produced 42.5 percent less than open-pollinated trees, whereas the trees caged with bees produced only 10 percent less, indicating that bees contribute by distributing the self- pollen on the tree. Later, Zavrashvili (1967b) stated that the 'Novogrusinskii' requires cross-pollination by bees for fruit production. Randhawa et. al. (1961) obtained four mature 'Malta' lemon fruit from 25 cross-pollinated flowers but none from 50 selfed flowers.
LIMES:
There has been little research on the pollination requirements of limes. Krezdorn (1970) stated that the Tahiti lime is strongly parthenocarpic, and, although cross-pollination might increase the number of seed, the increase in production of fruit, if any, would be negligible. However, Motial (1964) reported that 80 to 100 percent of the open pollinated flowers he observed on sweet limes (C. limettoides Tan.) set fruit, but only 40 to 60 percent of the emasculated and hand pollinated flowers set. This indicates that strong pollinator activity might increase the set and total production of sweet limes. Motial concluded, however, that sweet lime is not self-incompatible but is merely a shy bearer because of the high percentage of staminate flowers the plant produces.
ORANGES:
A general statement about the pollination of oranges is difficult because of the variation among cultivars. Coit (1915) stated that certain oranges require pollination to set fruit, others will set fruit parthenocarpically without the stimulus of pollination, and some will not accept pollen from some other cultivars. Because of this difference, the 'Washington Navel' and 'Valencia' and other sweet oranges will be discussed separately.
'Washington Navel'. - The anthers of 'Washington Navel' blossoms produce no pollen and the embryo sac may degenerate before tubes of pollen from other cultivars can penetrate to it, yet fruit sets and develops if conditions are favorable. However, if the tree is stressed by desiccating winds or moisture shortage, drop of young fruit can be severe. Surr (1922) caged six 'Washington Navel' trees to increase the humidity around them, which also excluded pollinating insects. He found that by doing this the production was not increased but instead decreased as much as 86 percent. The cages may have influenced fruit set for reasons other than pollination. Krezdorn (1970) stated that cross-pollination in 'Washington Navels' does not increase the yield, yet he (1965) obtained the following results from hand-pollinating the flowers, which would indicate that cross-pollination might influence set:
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No. of flowers No. of Pollen Source pollinated fruit set 'Pineapple' orange 1,000 2 'Temple' orange 1,000 3 'Duncan' grapefruit 1,000 5 Self (None) 3,000 0
El-Tomi (1964, 1957) reported that cross-pollination of 'Washington Navels' significantly minimized the dropping of immature fruit.
An interesting report on pollination made by Zavrashvili (1967b) stated that 'Washington Navel' trees caged to exclude bees yielded fewer fruits than trees caged with bees or open plots. The flowers set the most fruit when crossed with the 'Grusinian' orange. He also reported that the transfer of stigmatic fluid between stigmas increased the percentage of set. No reason for this effect was given, and its significance has not been determined.
The effect of pollination on production of 'Washington Navel' oranges seemed to be summed up by Atkins (1963), who stated that there is a possibility that cross-pollination by bees may cause them to retain more fruit.
'Valencias.' - Richter (1916) stated, without showing data, that if all insects were kept off 'Valencia' flowers there would be no less production. Francke et al. (1969) also concluded that bees have no effect on production of 'Valencias', but Cameron et al. (1960) reported that fruit size of 'Valencias' was increased as the seed number increased and that 'Pearl' tangelo pollen may increase both seed number and fruit set on 'Valencias'. This would indicate that, with cross-pollination, fruit size and possibly number of fruit set might be increased.
Other sweet oranges. - Soost (1963) stated that commercial plantings show no obvious reduction of yield in the absence of other varieties, but this does not mean that cross-pollination is of no benefit. Khan and Chandhri (1964) concluded that five unidentified cultivars were self-pollinating. Oppenheimer (1935) (cited by Oppenheimer 1948) came to the conclusion that "citrus can be planted in large blocks with no admixtures of other varieties, without the least misgiving."
Conversely, Glukhov (1955) reported that orange trees (cultivar not given) pollinated by bees produced four times as much fruit as trees isolated from bees. Zavrashvili (1964) reported that the orange crop in cages without bees was 54.4 percent lower than that on trees in the open. The cultivar was not identified nor was there a measure of cage effect on the plant other than pollination effect. Wafa and Ibrahim (1960) obtained 31 percent increase in set of fruit on the 'Elfelaha' orange, 22 percent increase in fruit weight, 33 percent more juice, and 36 percent more seeds from fruits on trees visited by bees than on trees from which bees were excluded. Zacharia (1951) reported partial self-incompatibility in the 'Shamouti' orange.
Hassanein and Ibrahim (1959) reported a set of 2.6 percent of flowers of the 'Khalili' orange where insects were excluded, 10.4 percent set where honey bees were present, and 7.4 percent on control (open) blooms. Krezdorn (1967) showed that the 'Hamlin', 'Parson Brown', 'Pineapple', and 'Valencia' orange size increased linearly with fruit set.
Although the results of tests are meager, some beneficial effects of pollination on oranges are indicated.
PUMMELO:
Soost (1963, 1964), working with 11 different accessions and Nauriyal (1952) concluded that the pummelo, which is grown commercially only in the Orient, is self-incompatible.
Aala (1953) conducted pollination studies on the Siamese pummelo 'Siamese 3442' in the Philippines. It produces both complete and staminate flowers. Some of the flowers were left to visits by bees, some were selfed, and some were crossed with pollen of 'Sour', 'Siaver 14', and 'Valencia' orange, and 'Batanga' mandarin. He concluded that most pummelo trees were self-incompatible and should be inter-planted with other cultivars. He stated: "Bees or other insects are necessary for proper pollination and setting of fruits, whether a cultivar is self-fertile or self-sterile." He also noticed that a higher percent set of open-pollinated flowers was obtained during off seasons than regular seasons, which may indicate that an inadequate pollinator population existed at flowering time. Of course, it could also mean there was an interaction with unfavorable environmental or physiological factors.
MANDARIN AND MANDARIN-HYBRID COMPLEX:
More research has been conducted on the pollination requirements of this group than of all the other citrus species combined, because the pollination problem is more acute. The problem has been recognized since Lacarelle and Miedzyrzecki (1937) reported that fewer fruits of the 'Clementine' mandarin set on a tree enclosed for self-pollination without bees than on 30 others enclosed with bees, either with or without pollen of other cultivars. Oppenheimer ( 1948) also showed that production of the 'Clementine' tangerine was increased when it was cross-pollinated by bees with pollen from 'Dancy', 'Temple', 'Duncan', or some other seedy cultivars. He found that the 'Valencia', 'Eureka', 'Marsh Seedless', and 'Satsuma' were ineffective pollinators.
Van Horn and Todd (1954) caged 'Clementine' ('Algerian') tangerine trees with and without pollinating insects (honey bees) and with and without bouquets of other cultivars. They showed that trees having both bees and bouquets yielded 16 times as many tangerines as those with no bees, had double the yield of those provided with bees only, and had better fruit quality. Miwa (1951) showed that the 'Hyuganatsu' mandarin was self-sterile but cross-fertile. Lynch and Mustard (1955), Coste and Gagnard (1956), Soost (1956,1963), Mustard et al. (1957), and Barbier (1964) concluded that the 'Clementine' tangerine was self-incompatible. Minessy (1959) found that grapefruit pollen was highly effective in fertilizing 'Clementines'. Blondel and Barbier ( 1963) accepted the fact that pollination increased production but stated that it also increased the pips or seeds present. Hilgeman and Rodney (1961) and Krezdorn (1970, 1972) stated that yields of 'Clementine' can be improved with bee pollination.
Hearn et al. (1969) reported that the 'Lee', 'Page', 'Nova', and 'Robinson' were self-incompatible, but Reece and Register (1961) stated that the 'Osceola' was not completely so. Furr (1964) and Moffett and Rodney (1971b) reported that cross-pollination was necessary and should be provided for 'Fairchild'. Later (1973) they reported that bees increased the yield of 'Orlando' tangelo. Also, Moffett and Rodney (1973) showed that honey bee visits increased yields of 'Orlando' tangelo. Hearn et al. (1968, 1969) and Hearn and Reece (1967), concluded that the 'Lee', 'Nova', 'Page', and 'Robinson' were all self-incompatible. Krezdorn (1972) included the 'Orlando', 'Minneola', and 'Osceola' in this group, but questioned the inclusion of the 'Lee'. Hearn et al. (1969) also reported that the 'Page' fruits were larger if they developed from 'Lee' pollen, the first well-defined metazenic effects reported in citrus.
Krezdorn and Robinson (1958) showed that crossing 'Orlando' with pollen from 'Temple' or 'Dancy' increased yields. Krezdorn (1959, 1967) also reported a significant correlation between fruit size and number of seeds of the 'Orlando'. Krezdorn (1970) stated that the 'Orlando', and 'Minneola' were self-incompatible, the 'Nova', 'Osceola', and 'Robinson' require cross-pollination, and at least in the 'Orlando' the fruit size increases with seed number. Soost (1963) reported that 'Minneola', 'Orlando', 'Osceola', and 'Robinson' were self-incompatible and that 'Lee' and 'Osceola' were suspect. Krezdorn (1970) stated that there is a growing number of self-incompatible cultivars.
The 'Satsuma' is variously referred to as 'Satsuma' mandarin (Hamakawa 1967), 'Satsuma' orange, 'Unshiu' orange (Kresdorn 1970), or 'Unshiu' tangerine (Mchedlishvili 1962). Several tests indicate that it is benefited by bees- 6.3 percent according to Zhgenti (1956); 7 to 11 percent, Zavrashvili (1967a, b). Soost (1963) recommended that the plants be set in solid blocks, although there was some risk of excessive fruit drop under some conditions. Mchedlishvili (1962) showed the importance of insect pollination. At varying distances from an apiary, he observed that near the apiary 42.5 percent of the flowers set and 14.6 percent were harvested. At 150 m from the apiary, 29.3 percent of the flowers set and 10.6 percent were harvested. At 350 m from the apiary, however, only 13.6 percent of the flowers set, and 5 percent were eventually harvested. This showed the value of having the colonies of bees near the trees to be pollinated. Although a few research workers have obtained substantially the same set of fruit from no pollination, self-pollination, and cross- pollination of 'Satsuma', the data indicate that for best production, an ample bee population is needed.
CALAMONDIN, CITRANGE, CITRON, KUMQUAT, MEYER LEMON, PONDEROSA LEMON, SOUR ORANGE, AND TRIFOLIATE ORANGE:
No pollination problems have been observed on citron, kumquat, Meyer lemon, and trifoliate orange, but there have been problems of seed set in 'Morton' end 'Troyer' citrange (Soost 1963).
In summary, insect transfer of pollen within the flower, between flowers of a cultivar, or between cultivars may be of slight value to oranges, grapefruit, and lemons. Many, if not all, of the mandarin and mandarin-hybrid complex are dependent upon or greatly benefited by insect pollination. The pummelo is dependent upon pollinating insects.
Pollinators:
The honey bee is unquestionably the primary pollinating agent of citrus; wind is not a major factor. Other pollinating insects are minor. Beekeepers readily place their colonies near citrus groves for the delicious honey the bees store. and citrus specialists frequently intimate that an ample supply of bees is always in the groves (Krezdorn 1972). Moffett and Rodney (1971a) showed this may not be true. They observed an average of slightly less than one bee per 100 blossoms at Yuma, Ariz., and concluded that the population was so low that growers of most orchards needing insect pollination should have rented colonies for that purpose. During the peak bloom, the ratio was much less than one bee per 100 flowers. Such a population would not be likely to visit individual flowers more often than about once per hour. By contrast, Mchedlishvili (1962) reported 12 bee visits per blossom per hour.
P. M. Packard (personal commun., 1972), State apiary inspector for Florida, estimated that only 220,000 colonies of honey bees were in the prime citrus area during bloom time in 1972Ñabout one colony per 4 acres. He stated distribution is not systematic, with some areas overcrowded with bees and others having practically none.
Butcher (1955) observed a zonal production effect in relation to distance of 'Minneola' tangelos from the apiary with the most marked effect 200 to 300 feet away. However, Robinson (1958) stated that honey bees worked equally well in all directions and were evenly spread to 400 feet.
Honey bees collect both pollen (if it is produced) an nectar from citrus. The flower is so constructed that if the bee has visited a previous pollen-producing flower, some pollen is likely to be transferred to the next stigma visited.
Depending upon the cultivars involved, the results of insect pollination may have no effect, increase the number of fruits set, increase the size of the fruit, cause seed to be present, increase the number of seeds, or cause an overloading of the tree.
Pollination Recommendations and Practices:
Little work has been done on the number of bee visits per flower, or the effect of cross-visitation between cultivars in relation to fruit set on citrus cultivars either dependent upon or benefited by bee pollination. Some recommendations have been made, without support or data, on colonies per acre and suggested placement.
Oppenheimer (1948) suggested bringing bees in, if they were not present, to pollinate 'Clementine' mandarins in Palestine. He did not indicate how many bees should be brought in or where the colonies should be placed.
The placement of colonies of bees in citrus orchards for pollination has often been recommended. Baldwin (1916) without concrete data to support his statement recommended five colonies per acre. Van Horn and Todd (1954) recommended one colony per acre of 'Clementines'. The Florida Agricultural Extension Service (1961) recommended the use of bees and pollenizer cultivars to increase the number and size of tangelos. Robinson and Krezdorn (1962) recommended a minimum of one strong colony of honey bees per acre of 'Orlando' tangelos. Soost (1963) stated that most commercial kinds of citrus set adequate crops without cross-pollination, but where insect pollination is needed "one hive per 2 acres may be sufficient although this is not certain." Zavrashnli (1967b) stated that one colony per 2.5 acres doubled the crop. His research dealt with 'Washington Navels', 'Novogrusinskii' lemons, and 'Unshiu' tangerines. Haynie (1968) recommended one colony per 2 acres, the colonies in groups and properly spaced, for cultivars benefiting from bee pollination.
There seems to be no uniformity in these recommendations, probably because each dealt with only one or a few cultivars in different areas of the citrus world and under different conditions.
The weakness of the recommendations is that there is no indication given as to the relative bee population per unit of flowers and also no relation is shown between colonies per acre and bees per flower.
For most efficient pollination of citrus, the meager data indicate that if bees are needed they should be distributed at the rate of one-half to five colonies per acre at about 1/4- to l/10-mile intervals. Consideration in the recommendation should be given to vigor of the colonies, other colonies in the area, acres of citrus, and other nearby plants attractive to bees, size of the citrus trees, and blooms per tree. For greatest benefit, the colonies probably should be present throughout the citrus flowering period.
Beekeepers place their bees near citrus groves for the honey they obtain; however, these colonies may not be placed strategically or in aufficient numbers for most effective pollination of all areas of a particular grove. The grower would profit most by arranging for the appropriate number of strong colonies properly placed and managed for citrus pollination although the honey obtained could be a factor in relation to locations and pollination fees. The citrus grower can gain far more than the beekeeper from such an arrangement.
LITERATURE CITED:
AALA, F. T.
1953. EFFECTS OF HAND POLLINATION ON THE PRODUCTION OF SIAMESE PUMMELO. Philippine Jour. Agr. 18(1-4): 101 - 113.ATKINS, E. L.
1963. HONEYBEES AND AGRICULTURE. Calif. Citrog. 49(2): 81 - 82.BALDWIN, E. G.
1916. PERFECT POLLINATION OF CITRUS GROVES. Gleanings Bee Cult. 44: 269-271.BARBIER, E. [C. ]
1964. [POLLINATION AND FRUITING OF THE CLEMENTINE (ORANGE).] Ann. de l'Abeille 7(1): 63-80. [In French, English summary.]BLONDEL, L., and BARBIER, E. [C.]
1963. [THE PROBLEM OF PIPS IN CLEMEMTINE ORANGES.] Fruits et Primeurs de l'Afrique du Nord 33(2): 153-156 [In French.] AA-538/64.BURNAEVA, N. L.
1956. [AN EXPERIMENT ON SUPPLEMENTARY POLLINATION OF CITRUS FRUITS.] Agrobiologiya 3: 124-128. [In Russian, abstract translated.]BUTCHER, F. G.
1955. HONEY BEES AS POLLINATORS OF MINNEOLA TANGELOS. Fla. Hort. Soc. Proc. 68: 313.CAMERON, J. W., and SOOST, R. K
1969. CITRUS. In Ferwerda, F. P., and Wit, F., eds., Outlines of Perennial Crop Breeding in the Tropics, pp. 129-162. H. Veenman and Zonen, N. V. Wageningen, The Netherlands.______COLE, D., JR.. and NAUER, E. M.
1960. FRUIT SIZE IN RELATION TO SEED NUMBER IN THE VALENCIA ORANGE AND SOME OTHER CITRUS VARIETIES. Amer. Soc. Hort. Sci. Proc. 76: 170 - 180.CLIMENKO, K.
1936. [PERIODICITY OR THE RECEPTIVITY OF STIGMAS OF ORANGES.] Batum Subtrop. Bot. Gard. Bull 1: 127-129. [In Russian, English summary.]COIT, J. E.
1915. CITRUS FRUITS. 520 pp. The Macmillan Co., New York.COSTE, A., and GAGNARD, J. M.
1956. [STUDIES ON THE POLLINATION OF CLEMENTINES.] Fruits et Primeurs de l'Afrique du Nord 26: 246 - 252. [In French.] Cited by Reuther, Batchelor, and Webber (1968).EL-TOMI, A. L.
1954. EFFECT OF CROSS-POLLINATION ON FRUIT SETTING IN WASHINGTON NAVAL ORANGE. Citrus lndus. 35(8): 5-6.______ 1957. EFFECT OF CROSS-POLLINATION OF JUNE-DROP PRE-HARVEST DROP, AND CROPPING IN WASHINGTON NAVEL ORANGE. Ann. Agr. Sci. 2(2): 249 - 265.
FLORIDA AGRICULTURAL EXTENSION SERVICE.
1961. YOUR 1961 AGRICULTURAL EXTENSION SERVICE ANNUAL REPORT. Fla. Agr. Ext. Serv., Gainesville, 7 pp.FRANCKE, R., JORGE, A., and MATHIEU, J. M.
1969. [EFFECTS OF INSECT POLLINATORS ON THE PRODUCTION OF VALENCIA ORANGES: THE HONEY BEE AND ITS EFFECT ON CITRUS PRODUCTION.] Agronomia (Monterrey) 122, 7 pp. [ In Spanish. ]FROST, H. W., and SOOST, R. K.
1968. SEED REPRODUCTION: DEVELOPMENT OF GAMETES AND EMBRYOS. In Reuther, W., Batchelor, L. D., and Webber, H. J. The Citrus Industry, V. 2, pp. 290-324. The University of California Press, Berkeley and Los Angeles.FURR, J. R.
1964. NEW TANGERINES FOR THE DESERT. Calif. Citrog. 49(7): 266.GLUKHOV, M. M.
1955. [HONEY PLANTS.] 512 pp. Izd. 6, Perer. i Dop. Moskva, Gos. Izd-vo Selkhoz Lit-ry. [In Russian.]HAMAKAWA, H.
1967. [ON THE BEHAVIOUR OF HONEYBEES IN CITRUS FLOWERS OF FOUR SPECIES.] Jap. Jour. Breed. 17 Suppl. 2: 143-144. [In Japanese.] AA-368/71.HASSANEIN. M. H., and IBRAHIM, M. M.
1959. STUDIES ON THE IMPORTANCE OF INSECTS, ESPECIALLY THE HONEY BEE IN POLLINATION OF CITRUS IN EGYPT. Agr. Res. Rev. 37(3): 390-409.HAYNIE, J. D.
1968. BEES AND CITRUS BLOSSOMS. Amer. Bee Jour. 108: 397. 156HEARN C. J., and REECE, P. C.
1967. POLLINATION NEEDS OF PAGE, LEE, NOVA AND ROBINSON CITRUS HYBRIDS. Citrus lndus. 48(4): 19, 23.______REECE, P. C., and FENTON, R.
1968. EFFECT OF POLLEN SOURCE ON FRUIT CHARACTERISTICS AND SET OF 4 CITRUS HYBRIDS. Fla. State Hort. Soc. Proc. 81: 94-98.______REECE, P. C., and FENTON, R.
1969. SELF-INCOMPATIBILITY AND THE EFFECTS OF DIFFERENT POLLEN SOURCES UPON FRUIT CHARACTERISTICS OF FOUR CITRUS HYBRIDS. 1st Internatl. Citrus Symposium Proc. 1: 183 - 187.HILGEMAN R. H., and RODNEY, D. R.
1961 COMMERCIAL CITRUS PRODUCTION IN ARIZONA. Ariz. Agr. Expt. Sta., and Ext. Serv. Spec. Rpt. 7, 31 pp.KHAN, M., and CHANDHRI, M. K. H.
1964. POLLINATION STUDIES IN CITRUS SINENSIS. Punjab Fruit Jour. (Lyallpur) 1962-64: 26-27, 97-107.KIHARA, H.
1951. TRIPLOID WATERMELONS. Amer. Soc. Hort. Sci. Proc. 58: 217-230.KREZDORN, A. H.
1959. FACTORS AFFECTING THE UNFRUITFULNESS OF TANGELOS. Fla. Agr. Expt. Sta. Ann. Rpt.: 228-229, 1960: 207.______ 1965. FRUIT SETTING PROBLEMS IN CITRUS. Amer. Soc. Hort. Sci. Carribean Reg. Proc. 9(13): 85-92.
______ 1967. THE INFLUENCE OF SEEDS AND POLLEN SOURCE ON THE SIZE OF FRUIT. Fla. State Hort. Soc. Proc. 80: 37-43.
______ 1970. POLLINATION REQUIREMENTS OF CITRUS. In The Indispensable Pollinators, Ark. Agr. Ext. Serv. Misc. Pub. 127, pp. 211-218.
______ 1972. POLLINATION REQUIREMENTS OF CITRUS Citrus Indus. 53: 5 - 7, 28.
______and ROBINSON, F. A.
1958. UNFPUITFULNESS IN THE ORLANDO TANGELO. Fla. Hort. Soc. Proc. 71: 86 - 91.LACARELLE, A., and MIEDZYRZECKI, C.
1937. [NEW CONTRIBUTIONS ON THE STUDY OF CLEMENTINES IN MOROCCO.] Experimentation Fruitiere et Maraichere, Rabat, Morocco. Edition Terre Marocaine, 22 pp. [In French.] Cited by Webber et al. (1943).LYNCH, S. J., and MUSTARD M. J.
1955. STUDIES ON THE UNFRUITFULNESS OF MINNEOLA TANGELOS IN DADE COUNTY. Fla. State Hort. Soc. Proc. 68: 299-301.MCHEDLISHVILI, G. I.
1962. [POLLINATION OF CITRUS TREES BY BEES.] Pchelovodstvo 39(9): 17. [In Russian.]MINESSY, F. A.
1959. EFFECT OF DIFFERENT POLLINIZERS ON YIELD AND SEEDINESS IN CLEMENTINE TANGERINE. Alexandria Jour. Agr. Res. 7: 279-287.MIWA, T.
1951. [ON POLLINATION, FERTILIZATION PHENOMENA AND PROBLEMS CONNECTED WITH FRUIT DROP IN THE HYUGANATSU MANDARIN.] Miyazaki Daigaku Jiho (Shizenkagaku) Bul. Miyazaki Univ. (Nat. Sci.) 2: 2 - 67. [In Japanese, English summary, pp. 66-67.]MOFFETT J. O., and RODNEY, D. R.
1971a. HONEY BEE VISITS TO CITRUS FLOWERS. Ariz. Acad. Sci. 6: 254-259.______and RODNEY, D. R.
1972b. FAIRCHILD TANGERINES NEED BOTH: HONEY BEES, POLLINATOR TREES. Prog. Agr. in Ariz. 23(5): 6 - 7.______and RODNEY, D. R.
1973. HONEY BEE VISITS INCREASE YIELDS OF `ORLANDO' TANGELO. Hort Science 8: 100MOSS, G. I.
1971. EFFECT OF FRUIT ON FLOWERING IN RELATION TO BIENNIAL BEARING IN SWEET ORANGE (CITRUS SINENSIS). Jour. Hort. Sci. 46: 177 - 184.MOTIAL, V. S.
1964. FRUIT-SET STUDIES IN SWEET LIME. Indian Acad. Sci. Proc. Sect. B. 60(6): 371 - 379.MUSTARD, M. J., LYNCH, S. J., and NELSON, R. O.
1957. POLLINATION AND FLORAL STUDIES OF THE MINNEOLA TANGELO. Fla. State Hort. Soc. Proc. 69: 277 - 281, 1956.NAURIYAL, J. P.
1952. SELF-INCOMPATIBILITY IN PUMELO (CITRUS MAXIMA MERR.). Current Sci. [India] 21: 347.OPPENHEIMER, C.
1935. ON CITRUS FERTILIZATION WITH SPECIAL REFERENCE TO SEEDINESS AND SEEDLESSNESS OF THE JAFFA ORANGE. Hadar 8(10): 261-262, 265-267 (11): 291-292, 295-296.OPPENHEIMER, H. R.
1948. EXPERIMENTS WITH UNFRUITFUL CLEMENTINE MANDARINS IN PALESTINE. Agr. Res. Sta. Rehovoth (Israel) Bul. 48: 1-63.RANDHAWA, G. S., NATH, N., and CHOUDHURY, S. S.
1961. FLOWERING AND POLLINATION STUDIES IN CITRUS WITH SPECIAL REFERENCE TO LEMON (CITRUS LIMON BURM.). Indian Jour. Hort. 18: 135-147.REECE P. C.
1945. FRUIT SET IN THE SWEET ORANGE IN RELATION TO FLOWERING HABIT. Amer. Soc. Hort. Sci. Proc. 46: 81.______and REGISTER, R. D.
1961. INFLUENCE OF POLLINATORS ON FRUIT SET OF ROBINSON AND OSCEOLA TANGERINE HYBRIDS. Fla. State Hort. Soc. Proc. 74: 64-106.REED, H. S.
1919. CERTAIN RELATIONSHIPS BETWEEN THE FLOWERS AND FRUITS OF THE LEMON. Jour. Agr. Res. 17: 143 - 166.REUTHER, W., BATCHELOR, L. D., and WEBBER, H. J.
1968. THE CITRUS INDUSTRY. 2 v., rev. University of California Press, Berkeley and Los Angeles.RICHTER, C. M.
1916. FROM THE CALIFORNIA STANDPOINT. Gleanines Bee Cult. 44: 271.ROBINSON F. A.
1958. FACTORS AFFECTING THE UNFRUITFULNESS OF TANGELO. Fla. Agr. Expt. Sta. Rpt. 1957-58: 102.______and KREZDORN. A. H.
1962. POLLINATION OF THE ORLANDO TANGELO. Amer. Bee. Jour. 102: 132-133.SOOST, R. K
1956. UNFRUITFULNESS IN THE CLEMENTINE MANDARIN. Amer. Soc. Hort. Sci. Proc. 67: 171 - 175.______ 1963. CITRUS POLLINATION. Calif. Citrog. 48: 447 - 452.
______ 1964. SELF-INCOMPATIBILITY IN CITRUS GRANDIS (LINN.) OSBECK. Amer. Soc. Hort. Sci. Proc. 84: 137-140.
SURR, G.
1922. GROWING ORANGE TREES IN TENTS. Calif. Citrog. 7: 103, 125.VAN HORN, C. W., and TODD. F. E.
1954. BEES, BOUQUETS AND BETTER TANGERINES. Prog. Agr. Ariz. 6(1): 11.VANSELL, G. H., WATKINS, W. G., and BISHOP, R. K.
1942. ORANGE NECTAR AND POLLEN IN RELATION TO BEE ACTIVITY. Jour. Econ. Ent. 35: 321-323.WAFA, A. K, and IBRAHIM, S. H.
1960. [EFFECT OF THE HONEYBEE AS A POLLLNATING AGENT ON THE YIELD OF ORANGE.] Elfelaha (Jan.-Feb.), 18 pp. Cairo University, Egypt. [In Arabic. ] AA-448/63.WEBBER, H. J.
1930. INFLUENCE OF POLLINATION ON SET OF FRUIT IN CITRUS. Calif. Citrog. 15(7): 304, 322-323.WEBBER, J., BATCHELOR, L.D., and collaborators.
1943. THE CITRUS INDUSTRY. Ed. l, 2 v. University of California Press, Berkeley and Los Angeles.WRIGHT, N.
1937. POLLINATION AND THE SEEDINESS OF MARSH GRAPEFRUIT. Agr. Soc. Trinidad and Tobago, Proc. 51-60.ZACHARIA, D. B.
1951. FLOWERING AND FRUIT SETTING OF THE SHAMOUTI ORANGE. Palestine Jour. Bot. (Rehovoth) 8: 84-94.ZAVRASHVILI, R. M.
1964. [BEES AND THE CITRUS CROP.] Pchelovodstvo 84(8): 19. [In Russian. ] AA-347/66.______ 1967a. [IMPORTANCE OF NECTAR IN FLOWERS OF MANDARIN ORANGE UNSHIU.] Akad. Nauk. Gruz. SSR Soobshch. [Tiflis] 45(1): 205-212. [In Georgian, Russian summary.] AA-789/70.
______ 1967b. [INFLUENCE OF BEES ON THE YIELD OF CITRUS TREES ON THE COMMERCIAL PLANTATIONS OF GEORGIA.] In 21st Internatl. Apic. Cong. Proc., College Park, Md. Aug., pp. 450-451. [In Russian, EngIish summary.]
ZHGENTI, S. K.
1956. [POLLINATION OF THE JAPANESE PERSIMMON AND MANDARIN ORANGE.] In Krishchunas, I.V. and Gubin, A. F., [Pollination Of Agricultural Plants.] pp. 193-199. MoskVa, Goz. Izd-vo. Sel-khoz. Lit-ry. [In Russian.]
