イボタロウヒゲナガゾウムシ

Our knowledge on the insect-feeding habit of the family Anthribidae is restricted to those of several species of the genera Brachytarsus and Anthribus, both of which have been reared from Lecaniine scales. In the present paper I gave the results of my studies on the biology of Anthribus niveovariegatus Roelofs which was reared from Ericerus pela Chavannes in Fukuoka, Kyushu, together with the life-cycle of the latter species. As is shown in the Figure 1, the present species has but one generation a year and spends the summer, autumn and winter seasons in the adult stage (Fig. 1). The overwintered adult beetle appears and visits the host scales mainly at the beginning of May for oviposition. After copulation the female deposits her eggs within the chamber of the scales. Oviposition takes place during May, and most of the eggs are deposited until the middle of May. As in the cases of many other parasites and predators already pointed out by Clausen (1940), the feeding of the female beetle at the hole made in the scale by either her mandibles or ovipositor is a closely associated habit with her oviposition. Namely, the female beetle breaks the hardened integument of the scale with her mandibles, feed at the droplet of liquid which comes from the hole. After such performance the beetle turns round herself, thrusts her ovipositor into the hole and through the thin ventral body wall and places her egg eithin the egg chamber of the scale (Fig. 2-B). Observation made in the field shows that among the hosts harbouring beetles eggs 72 per cent of the eggs are deposited by the method mentioned above, ehile 28 per cent are laid by such methods as shown in the Figure 2-A and ?C. The egg is usually found attaching to the body walll of the host at the point of penertration of the ovipositor. Laboratory observation on the oviposition (vide Tables 1 and 2) were divided into two classes, viz. each individual beetle of the first class experiments was provided with 4 host scales per day and that of the second ones with 10. The results are as follows. The beetle deposits usually one to three eggs per day. The total number of eggs deposited by a single female ranges from 10 to 36, and there is no significant difference in the total number of deposited eggs between the two experimental classes mentioned above. The female deposits usually one egg in a single host, but sometimes two or more eggs are laid in one host scale. Only a single individual of the beetle may develop even in the large host scale. Therefore, the number of effective eggs which may give rise to the adult beetles is more significant in the increase of the beetle’s population than the total number of eggs were laid was 15.2 per cent in the first class and 7.5 per cent in the second. From this experiment it may not be difficult to recognize the tendency that the more the host scales are given daily the fewer is the case in which more than two eggs of the beetle are deposited or the more the effective eggs are laid. As is shown in the Table 4(1-2), the number of eggs deposited by a single beetle in the field varies with the host density, and the fact that the frequency of hosts harbouring two or more eggs was lower in the field but higher in confinement may be regarded as having a close connection with the desiccating condition of the tissue of the host scales in the field. Eggs of the scale are necessary to the beetle larvae for their development to the adult stage. Three larval instars are observed. The larval period varies with the date of oviposition, and especially the duration of the third instar depends considerably upon the hatching state of the male scale eggs. Emergence of the adult beetles ranges from the beginning of June to that of the next month, having the peak from the 10th of June to the 22nd of the same month.