MACADAMIA
Macadamia integrifolia Maiden & Betche and M. tetraphylla L. A. S. Johnson, family ProteaceaeAbout 4,000 acres of macadamia trees were in production in Hawaii in 1970 with another 4,700 acres of new but not yet producing trees (Wallrabenstein 1971). About 140 acres were in California, mostly in San Diego County (Swedberg and Nelson 1970), and a few acres on trial in Arizona. Coit and Miller (1951) stated that new cultivars were producing 1.5 tons of nuts (825 pounds of meat) per acre. Hamilton and Storey (1956) reported 500 tons of nuts harvested from 2,721 acres (1,395 of which were nonbearing acres) in HawaiiÑabout 700 pounds per productive acre. Production of as much as 7,000 lb/acre have been obtained (W.C. Mitchell, personal commun., 1971). The grove must be about 15 years old before the income from it pays the investment and expenses (Keeler and Fukunaga 1968).
The specific name of macadamia was formerly considered to be M. ternifolia Maiden & Betche (Hamilton and Fukunaga 1959), but now there are considered to be two species involved (Krause and Hamilton 1970), although only M. integrifolia nuts are processed commercially.
Plant:
The macadamia is an evergreen tree, native to Australia, where it may grow to a height of 50 to 60 feet. Elsewhere, however, it rarely exceeds 30 feet. The leathery leaves of M. integrifolia are narrow and long, up to 20 inches, serrate, with many spines along the edges. Those of M. tetraphylla are shorter, with few or no spines. The fruit is a fleshy exocarp or husk, enclosing a spherical l/2 to 1-inch hard brown shell or nut, a true seed, which contains the oval kernel or sometimes two hemispherical kernels (Hartung and Storey 1939). On maturity, the exocarp splits and the nut falls to the ground (Mowry et al. 1967*). The shell is tough and difficult to crack. The kernel is delicious with high energy value (9.3 percent protein, 78.2 percent fat, and 8 percent carbohydrate) (Kennard and Winters 1960*). The plants are grown about 20 feet by 35 feet apart (62 trees per acre) (Hamilton and Fukunaga 1959). They come into bearing in 5 to 7 years. The macadamia is also an excellent dooryard ornamental.
Inflorescence:
The l/4 to l/2-inch tubular flowers are borne in groups of three to four, with 100 to 500 of them on a whiplike terminal or axillary pendulous raceme about as long as the leaf (fig. 128). Urata (1954) stated that one short stamen is attached to each of four petals, but Storey (1957) stated that the flowers were without petals, the stamens being attached to the petallike sepals. Kennard and Winters (1960*) also referred to them as petalless flowers. The flowers on M. integrifolia are ivory white, on M. tetraphylla they are pink. The ovary with two ovules, bears a long straight style with a small terminal stigma. The style forms a sharp loop in its midsection just before the flower opens. The pollen is shed within the flower 1 to 2 days before it opens, then 1 to 2 hours before opening, which is about 7 to 8 a.m., the sepals curl back exposing the anthes closed over the tip of the style. Then, the anthers separate, and 5 to 10 minutes later the style breaks free and straightens, extending beyond the now empty anthers, but its stigma does not become receptive until some time later. The stigma comprises only the very apex of the style, approximately 1 mm across. It is capable of receiving only 10 to 12 grains of pollen (Schroeder 1959). The pollen of a specific flower, however, is generally removed by insects before the stigma is receptive (Knuth 1909*, p. 356 ), so pollen must come from another flower. The main flowering months in Hawaii are January and February.
Honey bees collect pollen freely from macadamia (Urata 1954 and Gary et al. 1972). Nectar is secreted at the base of the blossom. Schroeder (1959) commented that secretion of nectar is not in any quantity to attract insects. One report (Anonymous 1958) stated that macadamia flowers produce a gas that is highly toxic to bees, with the suggestion that this gas might have a somewhat repelling effect on bees. Apparently, the bees are not repelled.
[gfx] FIGURE 128.- Flower of macadamia (macadamia integrifolia), x 20. A, Complete flower with reflexed style just before petal-like sepals seperate to release stamens; B, longitudinal section of the open flower; C, style straightened after pollination has occured.
Pollination Requirements:
Urata (1954) and Schroeder (1959) stated that most trees are at least partly self-sterile but are cross-compatible; therefore, pollen must be moved from tree to tree for good fruit set. Knuth (1909*, p. 356) concluded that self-pollination was unlikely in the Proteaceae. Hamilton and Storey (1956) stated that usually only 1 to 20 flowers on a raceme set fruit, but no reason was given for this small percentage of set. Later, Storey (1957) stated that only 1 to 2 percent set fruit. The minuteness of the stigma indicates that wind is not a factor in pollen transfer.
Pollinators:
Urata (1954) stated that honey bees are the most common pollinating insects on macadamia flowers, primarily collecting pollen. He gave no indication of the relative number of bees per flower or tree, or the relative bee population in the area. Shigeura (1967) and Shigeura et al. (1970), working with 100, 75, and 20 trees of three cultivars of M. integrifolia concluded that moving commercial apiaries beside the plantings caused 59 percent increase in production over previous years without bees, although one cultivar showed no increase. Nothing was said about the activity of the bees on the flowers, and no suggestions were made as to how the bees might be used to increase production.
Pollination Recommendations and Practices:
There are no recommendations on the use of bees or other pollinating insects on macadamia flowers. The evidence strongly indicates that for highest production the use of honey bees as pollinators should be encouragedÑsufficient bees to provide ample cross-visitation between trees throughout the flowering period. There is no evidence as to the number of bees needed nor of the relative competition between flowers of macadamia and of other plants in the vicinity. Two to three colonies per acre are recommended for the pollination of the highly attractive almond trees and probably as many are needed on macadamia. A study of this phase of macadamia production is badly needed.
LITERATURE CITED:
ANONYMOUS
1958. MACADAMIA POLLINATION. In Hawaii Agr. Expt. Sta. Bien. Rpt. [or 1956-58, p. 40.COTT, J. E., and MTLLER, W. W.
1951. WHAT ABOUT THE MACADAMIA? Calif. Citrog. 36: 300 - 302.HAMILTON, R. A., and FUKUNAGA, E. T.
1959. GROWING MACADAMIA NUTS. Hawaii Agr. Expt. Sta. Bul. 121, 51 pp.HAMILTON, R. A., and STOREY, W. B.
1956. MACADAMIA NUT PRODUCTION IN THE HAWAIIAN ISLANDS. Econ. Bot. 10: 92 - 100.GARY, N. E., MAU, R. F. L., and MITCHELL, W. C.
1972. A PRELIMINARY STUDY OF HONEY BEE FORAGING RANGE IN MACADAMIA (MACADAMIA INTEGRIFOLIA MAIDEN AND BETCHE). Hawaii Ent. Soc. Proc. 21: 205-212.HARTUNG, M. E., and STOREY, W. B.
1939. THE DEVELOPMENT OF THE FRUIT OF MACADAMIA TERNIFOLIA. Jour. Agr. Res. 59: 397 - 406.KEELER, J. T., and FUKUNAGA, E. T.
1968. THE ECONOMIC AND HORTICULTURAL ASPECTS OF GROWING MACADAMIA NUTS COMMERCIALLY IN HAWAII. Hawaii Agr. Expt. Sta., Agr. Econ. Bul. 27, 47 pp.KRAUSS, B. H., and HAMILTON, R. A.
1970. BIBLIOGRAPHY OF MACADAMIA. PT. 1. AUTHOR INDEX. Hawaii Agr. Expt. Sta. Res. Rpt. 176, 112 pp.SCHROEDER, C. A.
1959. SOME OBSERVATIONS ON THE POLLINATION OF MACADAMIA IN CALIFORNIA. Calif. Macadamia Soc. Yearbook 5: 49 - 53.SHIGEURA, G. T.
1967. VARIETAL NUT SET AND SUGGESTION OF POLLINATION REQUIREMENT IN MACADAMIA. Hawaii Macadamia Prod. Assoc. 7th Ann. Mtg. Proc: 28-32.____ LEE, J., and SILVA, J. A.
1970. THE ROLE OF HONEY BEES IN MACADAMIA NUT (MACADAMIA INTEGRIFOLIA MAIDEN AND BETCHE) PRODUCTION IN HAWAII. Amer. Soc. Hort. Sci. Proc. 95: 544 - 546.STOREY, W. B.
1957. THE MACADAMIA IN CALIFORNIA. Fla. State Hort. Soc. Proc. 70: 333 - 338.SWEDBERG, J. H., and NELSON, G. A.
1970. CALIFORNIA FRUIT AND NUT ACREAGE, BEARING AND NON- BEARING AS OF 1969. Calif. Crop and Livestock Rptg. Serv. and U.S. Dept. Agr. Statis. Rptg. Serv. 23 pp.URATA, U.
1954. POLLINATION REQUIREMENTS OF MACADAMIA. Hawaii Agr. Expt. Sta. Tech. Bul. 22, 40 pp.WALLRABENSTEIN, P. P.
1971. STATISTICS OF HAWAIIAN AGRICULTURE, 1970. U.S. Dept. Agr., Statis. Rptg. Serv., and Hawaii. Crop and Livestock Rptg. Serv., 77 pp.
