Ecological studies on Polydesma umbricola Boisd. in Hawaii (Lepidoptera: Noctuidae)

Abstract

The noctuid moth, Polydesma umbricola Boisd., commonly known as the monkey pod caterpillar, was first discovered in the Hawaiian Islands by Van Zwaluwenburg (1945) on Oahu (Figure 1). In quick succession it was reported from the other islands: Mo1okai (Williams, 1945), Maui (Pemberton, 1945), Kauai (Fullaway, 1945), Hawaii (Williams, 1946), and Niihau (Fullaway, 1946). In the Hawaiian Islands P. umbricola is a well-known serious defoliator of the monkey pod tree, Samanea saman (Jacq.) Merrill (Figure 2). In recent years, this tree has considerably gained in economic importance due to its tough and light- and dark-colored wood which has become very popular for hand-carving platters and bowls (Neal, 1948). The large influx of tourists to Hawaii has helped to identify these carvings as exclusively Hawaiian products. The demand for the wood exceeds the supply to such an extent that monkey pod wood is now imported from Fiji. The tree and its products have been brought to other uses in remarkably different ways in the various places where it is grown. In Central America, its place of origin, the pods are fed to cattle and the wood, especially cross sections of the trunk, is used for cart wheels (Nea1, 1948). In India and Ceylon the leaves and pods have been reported to be quite nutritious food for horses and cattle (Tempany and Girst, 1958). The wood, originally thought to be useful as railway fuel (Cowen, 1952), is now considered to be of no value (Blatter and Millard, 1954), except as household fuel (Randhawa, 1957). Gill (no date given), in the Carribean, reports the wood to be useful for construction of posts, etc. From Bermuda (Britton, 1918) to China (Sauer, 1947) it is prized as an ornamental and roadside-shade tree. In India the monkey pod's shade has been utilized to protect delicate plants in their early stages of development (Cameron, 1894). In New Caledonia (Sarlin, 1954), and the Carribean it has been employed as a shade tree in plantations of coffee and cacao, though its use is very much less at present than formerly (Little and Wadsworth, 1964). Williams (1949) in East Africa and Worthington (1959) in Ceylon report the wood to be excellent for furniture construction. A review of the literature indicates that little work has been done on g. umbricola. The reason for this is that this insect is not a pest in the areas outside of Hawaii. Very little is known about its life-history and behavior, much less about the influence of various environmental. conditions upon its abundance. The objective of this investigation is to make a study on some of these aspects of this insect, and, in addition, to probe into the interrelationships between seasonal abundance and the various environmental factors. It is envisioned that a study of this sort would contribute towards (1) an understanding of the population ecology of the noctuids, and (2) the development of control procedures based on the ecology of the moth.