Larval Defoliators of Monkeypod (Samamea Saman) Strike Again

The Monkeypod, is a popular landscape tree in Hawaii.  It grows in many other tropical areas of the world, although it‘s native range is the northern region of South America and Central America south of El Salvador.  The Monkeypod is recognized for its umbrella-like canopy and leaflet closure which allows sunlight and rain to filter down to its roots so that the grass grows right up to its massive trunk.  Because of the tree’s dominant place in the landscape, it becomes readily apparent if this giant is under siege and looses its foliage.  Unfortunately, since the 1970’s, this is what occurs nearly every year somewhere in Hawaii’s landscape when the Monkeypod defoliators strike.Melipotis indomita (female)[1]

The triad of defoliators which attack the Monkeypod tree are the Monkeypod-kiawe caterpillar (Melipotis indomita (Walker)), the black witch caterpillar (Ascalapha odorata (L.)) and the caterpillar of the Monkeypod moth (Polydesma umbricola Boisduval).  Of the three, the most severe pest of Monkeypod is the Monkeypod-kiawe caterpillar which usually makes up more than 98% of the larvae collected on Monkeypod.  Trees can remain defoliated for as long as two years but sometimes die due to prolonged leaf-loss.

The life cycle of these three defoliators is very similar in habit and duration.  Female moths lay their eggs in crevices in the tree’s bark and upon hatching, the larvae crawl up to the tree’s foliage to feed at night.  In the early morning hours, the larvae migrate back down the trunk of the tree and hide under the bark or in the soil at the base of the tree during the day.  Development from egg to adult can take from one to two months for the three defoliators.

In order to disrupt this cycle, in a 1987 study, Tamashiro and Mitchell of the University of Hawaii sprayed the trunk of Monkeypod trees with five different insecticides and then tied carpet around the trunk to collect the larvae.  Of the insecticides which proved effective, only two are available for use today; carbaryl and diazinon.  Today, when an outbreak of Monkeypod defoliators occurs, the remedy is to apply carbaryl (Sevin) as a dust to a swath of carpet and tie it around the trunk of the Monkeypod tree so that the dusty side of the carpet is facing the tree’s bark.  The top of the carpet is tied loosely so that the caterpillars can crawl in to hide early in the morning while the bottom of the carpet is tied tightly to secure it to the trunk.  Sevin is refreshed bi-weekly and usually if the remedy is applied for six weeks, it is sufficient to control the caterpillar attack.

Linda Burnham Larish is a Survey Entomologist with the Pacific Cooperative Studies Unit, the Hawaii Department of Forestry and Wildlife and the Hawaii Department of Agriculture.

References:

Staples, G.W., and C.R. Elevitch.  Samanea saman (rain tree).  Species Profiles for Pacific Island Agroforestry.  April, 2006.  www.traditionaltree.org.

Tamashiro, M. and W.C. Mitchell.  Control of three species of caterpillars that attack Monkeypod trees.  College of Tropical Agriculture, Hawaii Agricultural Experiment Station, Misc. Publications 123.  1987.

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