Biological Characteristics of <I>Cionus latefasciatus</I> (Coleoptera: Curculionidae) and Effects of Temperature on Its Growth and Development

Abstract

Cionus latefasciatus Voss (Coleoptera: Curculionidae) is one of the most important insect pests on Scrophularia ningpoensis Hemsl. (Scrophulariales: Scrophuhrhceae), which is a well-known traditional Chinese medicine plant in southeast China. The biological characteristics and effects of temperature on the growth and development of C. latefasciatus were studied in nature, in the greenhouse, and in the laboratory. In the area studied, 9-12 generations of this weevil occurred per year depending on climatic conditions. The overwintered adults migrated to the plant-seeding fields in the earlier days of March, and adults of the last generation began to overwinter in early October. Female adults lived for 50-75 d and male adults for 50-65 d at 28 degrees C. Adults fed on leaves, buds, tender stems, and flower stalks during the entire developmental phase of the plant. Female adults began to lay eggs 2-4 d after emergence and laid an average of 330-390 eggs per female at 28 degrees C. The eggs were usually laid on the surface of the leaves or into the leaves. The larvae have four instars judging from the width of the cephalic capsule of the larvae. The larvae fed on leaves and buds of the plant. Under constant temperatures (17, 20, 25, 28, and 30 degrees C) and fixed humidity (75%), the development periods from egg to adult emergence were 36.91, 29.25, 19.11, 17.26, and 15.36 d, respectively, and 346.31 degree-days, in total, above a lower threshold of 7.7 degrees C was required; the survival rates from egg to adult emergence were 49.1, 62.5, 72.0, 78.7, and 50.0%, respectively. Laboratory experiments showed that the optimum temperature for the development from egg to adult emergence was 28 degrees C.