Molting in workers of the Formosan subterranean termite (coptotermes formosanus)

Authors: Raina, Ashok; Park, Yong; Gelman, Dale

Submitted to: Journal of Insect Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/30/2007
Publication Date: 1/1/2008
Citation: Raina, A.K., Park, Y.I., Gelman, D. 2008. Molting in workers of the Formosan subterranean termite (coptotermes formosanus). Journal of Insect Physiology 54:155-161.

Interpretive Summary: Study of the molting process in the Formosan subterranean termite, including the role of various hormones, had not been studied primarily because of the cryptic nature of this serious urban pest. We studied these events in field collected colonies under laboratory conditions. Observations revealed that workers stop foraging approximately 10 days before molting and about 1% of the workers molt each day. Five days before molting, the workers empty their guts including the microorganisms present therein. These microorganisms are reacquired on the fourth day after molting through feeding on the excretion of other workers. Juvenile hormone and ecdysteroid, the key developmental hormones in insects increase dramatically six and five days before molting. The information will be useful to researchers involved in termite control through the use of chemicals that inhibit molting process and in the study of colony development.

Technical Abstract: The Formosan subterranean termite, Coptotermes formosanus, with its huge colonies, is a major urban pest in several southern states and Hawaii as well as in South Asia. Because of their cryptic nature (underground habitat) and very long life cycle, not much is known about molting in termite workers. In C. formosanus, the workers stop foraging and lose their gut fauna, respectively approximately 10 and 5 days prior to ecdysis. In any given colony an average of 1.01% (range 0.6-1.8) of the workers were found to molt each day under laboratory conditions. Workers destined to molt become sluggish and their head capsules developed a mottled texture one day prior to ecdysis. Ecdysis was generally accomplished with the assistance of other workers which also fed on the exuviae. Immediately after molting worker mandibles were light pink in color and became fully melanized approximately two days later. Gut fauna was acquired on the fourth day after molting. Flagellates were transferred as small encysted cells from other workers through proctodeal feeding. Juvenile hormone III titer ranged between 30-41 pg/mg bodyweight in all stages except in workers sampled 6 days prior to ecdysis. In these workers the titer was 80.5pg/mg. The high JH titer may also be involved in causing defaunation. Ecdysteroid titer increased from 2.1pg/mg in non-molting workers to 359.5 and 332.4pg/mg one and two days following defaunation, respectively. There was a second smaller peak two days prior to ecdysis.