Submitted to: Sociobiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 15, 2006
Publication Date: March 20, 2006
Citation: Morales Ramos, J.A., Rojas, M.G., Sittertz-Bhatkar, H. 2006. Effects of diflubenzuron on the peritrophic matrix and fat body of formosan subterranean termite (isoptera: rhinotermitidae) workers. Sociobiology. 47(3):667-676. Interpretive Summary: Chitin synthesis inhibitors are chemicals that are toxic only to insects and other arthropods. The reason for this is because these chemicals interfere with the synthesis of chitin, the main component of insect external skeleton. This type of chemicals has been used with great success to control subterranean termites by delivering them within bait formulations. Because of its mode of action it has been believed that these chemicals affect only those termite stages that are still growing, leaving the developed adults unaffected. This is because insects replace their external skeleton during growth and require a great deal of chitin to replace it. Adult termites, on the other hand do not molt their skeletons because their growth is completed. In insects, however, chitin is not only present in their skeleton but also in the walls of some of their internal organs. These organs include the digestive track and malphigian tubules, which are the equivalent of insect kidneys. The objective of this study was to determine if the most commonly used chitin synthesis inhibitor, diflubenzuron, had any significant effect on the chitinous structures of termite internal organs. Termite specimens treated with diflubenzuron as well as untreated termites were enclosed in resin to make histological sections. These sections were stained with a special procedure designed to color chitinous structures. The sections were inspected under optical microscope and photographed at high magnification (1000X). Observations showed that a structure known as perithrophic matrix was particularly affected by diflubenzuron. This structure is very important in the digestion of food and one of its functions is to protect the digestive epithelium from abrasion produced by food particles. Examination of the fat bode cells of treated termites showed extreme reduction in the accumulation of glycogen. This is an indication of nutritional deficiency possibly induced by deficient food digestion. The implications of this discovery are that chitin synthesis inhibitors can affect adult termites making them sensitive to diseases and possibly reducing their reproductive potential. It is conceivable that these chemicals induce mortality of reproductive caste in termites, contributing to de demise of the colony.
Technical Abstract: The effects of diflubenzuron, a chitin synthesis inhibitor, on the internal chitinous structures of workers of Coptotermes formosanus Shiraki (Isoptera: Rhinotermitidae) were studied. Groups of 1,000 C. formosanus workers were fed with a diet containing 250 ppm of diflubenzuron. A control group was fed with the same diet formulation without diflubenzuron. The 2 groups were kept at 27'C and 98% RH for 30 d. A sample of 20 workers was removed from each of the groups. Termites were decapitated, fixed in a mixture of paraformaldehyde-glutaraldehyde, embedded in epoxy, and sectioned at 1'm thickness. Sections were stained in a methylene blue-azure II, counter-stained in basic fuchsin and inspected in a compound optical microscope. Significant changes in the structure of peritrophic matrix and fat body were observed in termites treated with diflubenzuron. Termites fed on diflubenzuron had peritrophic matrices either damaged or absent. The fat body of treated termites showed large empty spaces and different coloration than that observed on untreated termites. Fat body cells in untreated termites were pink to red in color showing the presence of glycogen stained by basic fuchsin. Fat body cells in treated termites were violet to gray indicating a lack or reduction of glycogen content. Malpighian tubules did not show any noticeable changes but were considerably more fragile during dissection of treated termites. Implications of diflubenzuron effect on internal structures are discussed.