Tenebrio molitor is a major pest of stored grain, although its larvae have potential for use as food. However, little is known about the characteristics of individual larval instars of this species, and the number of instars remains disputed. Therefore, we assessed T. molitor for the average number of instars and its characteristics at different larval stages. The focus of this study was to establish a foundation for further studies on the characteristics of each larval instar. All of the T. molitor larvae showed incubation periods of 7 to 8 d and a period of 3 to 4 d for the 1 st instar. Beyond the 1 st instar, there were relatively large variations in the number of days in each instar period. Before emergence, most of the larvae had typically gone through 15 to 17 instars. The highest rate of pupae formation, 28.32%, was observed in the 17 th instars. The body length gradually increased with each successive instar, reaching its maximum at the 17 th instar. Beyond the 17 th instar, however, the body length decreased. The larvae were white in the first instar, and gradually turned brown after the 2 nd instar.
IntroductionTenebrio molitor is a holometabolous insect that is considered to be a harmful pest of stored grain in South America (Schroeckenstein et al., 1990). However, its larvae, commonly referred to as mealworms, are used as pet food in many countries (Cotton, 1927). Because they are high in protein and fat and consume large amount of fiber, they represent a good food source for humans (Finke, 2002). Furthermore, they are high in oleic acid, which has the ability to decrease low-density lipoprotein (LDL) and increase high-density lipoprotein (HDL) levels in the blood (Yoo et al., 2013). In addition, they are inexpensive and easy to raise, with minimal harmful effects on the environment (Wang et al., 2012). For these reasons, many studies have been conducted on T. molitor to determine its potential uses.The physiological features of T. molitor have been studied in some detail. Several studies on these aspects have found that the age of the parents influences the development of larvae; young parents are associated with the highest egg hatching rates (Ludwig and Fiore, 1960).