By Walter Ebeling
Dr. Ebeling is a Professor of Entomology, UCLA, Los Angeles.
Reprinted From the CMS Yearbook, 1956
Although a limited number of Macadamia trees have been under observation in California for at least a half a century, there has never been a sufficient number of trees in this state to enable us to assess the full potentialities of insect pests. With the present interest in more rapid expansion of this crop in California, it is to be expected that a number of insect species from native vegetation or from other cultivated crops will adapt themselves to the Macadamia. This is in addition to the few that are already known to infest the Macadamia in this state.
At the experimental subtropical fruit orchard of the University of California, Los Angeles, the writer has observed severe infestation of Macadamia trees on two occasions. The greenhouse thrips, Heliothrips haemorrhoidaIis Bouche once became abundant on mature trees and was causing severe defoliation. The infestation was effectively controlled with 5 per cent DDT dust and has never reoccurred. This insect may also attack citrus, avocado, sapote and cherimoya. On another occasion Macadamia seedlings grown in a lathhouse and 3 to 8 inches in length were attacked by larvae of the tobacco budworm, Heliothis virescens (Fabricius), which were rapidly devouring the leaves. The multi-colored larvae changed from predominantly greenish, with yellow stripes, to a beautiful rose-bronze color before pupating. They attained a length of about 1 1/2 inches. The adult moths had a wingspread of about 1 1/2 inches. The light-green front wings were crossed by oblique light bands edged with black. The infestation was wiped out with a 5 per cent DDT dust.
The orangeworms, Argyrotaenia citrana (Fernald) and Holcocera iceryaeella (Riley), may also be found infesting Macadamia trees in California. Aphids are sometimes abundant on tender twig terminals and the inflorescence.
In Florida, in addition to greenhouse thrips and aphids, the mining scale, Howardia biclavis (Comstock), may be a pest. This large, circular, whitish or grayish scale may be partly or entirely covered by the bark, which the scale covering resembles. The scale has been controlled with parathion, 1 1/2 pounds of 15 per cent wettable powder to 100 gallons of water.
Judging from experience in areas in which Macadamias have long been a commercial crop, this tree is as susceptible to certain types of destructive pests as are other nut varieties. It is hoped that quarantine restrictions will be successful in preventing their entry into California.
In Australia the Macadamia is attacked by a number of serious pests. A coreid, the fruit spotting bug, Amblypetta lutescens Distant, feeds on the young shoots, causing them to wilt and die, and on the nuts, causing them to fall prematurely, with shriveled kernels, if they are attacked while still soft. If attacked when the shell is beginning to harden, the nuts do not fall, but are rendered unmarketable. This bug is known as a pest of the papaya, the seedlings of which are sometimes killed. (Brimblecombe, 1948). Another species, A. nitida, called the fruit pitting bug, is associated with shedding of nuts and shriveling of kernels. The pyralid moth, Homoesoma vagella Zeller, lays its eggs in the flower spikes of the Macadamia and the larvae feed on the flower buds (Anonymous, 1945-46). The larvae of a gelechiid called the twig girdler moth, Phthonerodes luteotactella Walker, girdle the twigs or skeletonize the basal halves of the leaves under cover of a silk webbing (Wallace, 1936).
A tortricid moth, Anotrophora ombrodelta Lower, also is recorded as a pest of Macadamias (Brimblecombe 1948) and the pyralid moth, Dichoeroeis punctiferalis Guenee, infests the nuts (Anonymous, 1949). The armored scale, Chrysomphalus rossi, also attacks the Macadamia in New South Wales.
In Hawaii, the Macadamia nut husk borer, Cryptophlebia illepida (Butler), is a pest that can infest a high percentage of the nuts. This moth is somewhat similar to the codling moth in appearance and habits, being in the same family (Eucosmidae). The larvae may (1) cause a premature drop of fruit, (2) bore into the nut completely, or (3) bore only through the shell, allowing fungi or nitidulid beetles to gain entrance. It is also believed that the insect damages some shells while they are still soft, causing a subsequent scar formation that keeps shells and kernels from growing larger. The kiawe moths, Anacamptodes fragilaria Gross and a membracid bug, Vanduzea segmentata Fowler, have been observed feeding on Macadamia.
Literature Cited.
Anonymous, 1945-46. Annual Report of the Department of Agriculture and Stock for the Years 1945-46. (Queensland).
Anonymous, 1949. Insect Pest Survey, Entomological Branch, N.S.W. Dept. of Agriculture. (Australia).
Brumblecombe, A. R. 1948. Fruit spotting bug as a pest of the Macadamia or Queensland nut. Queensland Agr. Journal. 67(4): 206-11.
Wallace, C. R. 1936. The twig girdler moth of Australian nut trees. Agric. Gaz. N.S.W. 47(10): 566-8.
Editors Note:
Since this article was written in 1956 or earlier, the insecticide DDT has been banned. This article being 42 years old needs updating on the correct insecticides to be used today.