Toshiharu Yoshida

Population biology of the broad-horned flour beetle,Gnathocerus cornutus (F.) II. Crowding effects of larvae on their survival and development

Crowding effects of larvae on survival and development were examined for the broad-horned flour beetle,Gnathocerus cornutus (F.). The larvae matured about 3 weeks after hatching regardless of their densities, but pupation was severely hindered by crowding. There existed an upper limit for the number of the pupae produced and its mechanism was studied by a statistical analysis of the distribution patterns of pupal cells and the experiment in which glass tubes were artificially supplied in addition as pupation site. These studies show thatG. cornutus larvae have a habit to construct cells for pupation and this habit leads to a contest competition for pupation site at high densities. The significance of the contest competition for population regulation was discussed comparing the results onTribolium confusum Jacqueline duVal.

Life History of the Azuki Bean Weevil, Callosobruchus chinensis L., (Coleoptera: Bruchidae), in the Field

The life history of the azuki bean weevil, Callosobruchus chinensis L., was studied in the field. The weevil had two wild leguminous hosts: the annual Vigna angularis var. nipponensis (Ohwi) Ohwi & Ohashi and the perennial Dunbaria villosa (Thumb.) Makino. The adults were observed on the legumes from mid-August to mid-October and oviposited on pods from mid-September to mid-October. This is also true of the biology in the field of their usual host, the azuki bean, V. angularis (Willd.) Ohwi & Ohashi. After hatching, first instar larvae penetrated the developing seeds in the pods and grew to the 2nd instar or pupae by the time of pod dehiscence. The weevils overwintered in the seeds scattered on the ground and emerged from the seeds in late May. By feeding on pollen, water and fungi, the adults prolonged their longevity and oviposition period into late October. The azuki bean weevil had one generation a year in the field.

Historical Review of Bruchid Studies in Japan

In the Meiji era we had two serious Bruchid pests, Callosobruchus chinensis and Bruchus pisorum in Japan. In 1926 B. rufimanus was found in Kyushu. Urgent countermeasures were taken to meet the new pest: biology of and control measures against the weevil were studied extensively especially by Kamito. In 1937 the basis of classification of Bruchids in Japan was established by Chujo. Recently the introduction of C. maculatus was noticed. During and after World War II Ishii started his pioneering study on biochemical resistance to Bruchid attack in legume seeds. Also, Utida was carrying on his continuing study of experimental populations of C. chinensis. The range of his study was enlarged from density effect to interspecific competition, host-parasite relationship and phase dimorphism in Callosobruchus spp. The new pheromones of “opposition marker” and “erectin” were identified and synthesized by Yamamoto and his school in the bean weevils. Some authors took a growing interest in the life history strategy of Bruchids, coevolution between bean and weevil, and evolution or domestication of the bean weevils. Dealing with the increase of imported beans from foreign countries into Japan, the techniques of bean fumigation with methyl bromide and phosphine for quarantine fumigation was developed. In the laboratories of Universities and the private laboratories of agricultural Chemicals Companies many investigations were carried on using the bean weevil as an experimental insect to develop new chemicals without environmental disruption.