Akira Tanaka

Regulation of body size during larval development in the German cockroach, Blattella germanica

Abstract It may be advantageous for insects to attain a certain standard size when they become adult. Recent studies have demonstrated that in some species of insects, a threshold size must be reached in the last instar in order that the adult will attain the standard size. It has been revealed also, however, that there may be another type of regulation of body size during larval development in the German cockroach. Head width and other characteristics were measured in every larval instar up to the adult. Body size is distributed clearly into a small group and a large group in the 5th instar, and even in the 4th instar. This suggests that a larva has already determined the number of following moults by the late 3rd instar. Adult size is almost the same in 5- and 6-instar types. Among individuals which require the same number of instars to reach the adult stage, the coefficient of variation in body size increases until the 3rd instar then decreases to the adult stage. Smaller individuals in a particular instar after the 3rd tend to grow more than larger ones during that instar. These results suggest that a larva regulates its body size after the 3rd instar in order to attain the ‘norm’ for adult size.

Effects of carbon-dioxide anaesthesia on the number of instars, larval duration and adult body size of the German cockroach, Blattella germanica

Abstract Effects of repeated carbon-dioxide anaesthesia during larval development on the number of moults, larval duration, and the body size of resulting adults were investigated. Concentration of carbon dioxide administered was 70%, and each period of anaesthesia lasted for 3 min. Anaesthesia administered twice a week until the 3rd instar increased the number of instars required to reach maturity. However, repeated anaesthesia after the 4th instar scarcely influenced the number of instars. On the other hand, repeated anesthesia prolonged larval duration whenever administered during the early or late instars. It is thus suggested that anaesthesia by carbon dioxide during larval development has two distinct effects: increasing the number of moults and prolonging larval duration. The former is stage specific and effective only during early instars, whereas the latter is effective during any particular instars until the last instar. The body size of resulting adults remained almost the same as for controls even after the repeated carbon-dioxide anaesthesia as many as 14 times. Some further observations concerning correlations between the number of moults, larval duration and adult body size are shown, and differences between the sexes regarding the number of instars and larval duration are also presented.

Studies of the Genetics and Expression of Prowing (Pw) : A Primitive Homeotic Mutant of the German Cockroach, Blattella germanica

Abstract The prowing, T (9; 10)/9; 10 Pw, is a homeotic mutant of the German cockroach, Blattella germanica. Adults are characterized by winglike extensions from the pronotum. This trait is associated with a reciprocal translocation of chromosomes 9 and 10. Translocation heterozygotes express the trait and homozygotes are lethal. The expression of Pw is variable in adults. Individuals with excellent expression show that the pronotal extension is undoubtedly a primitive wing, judging from its venation. We crossed adults with different degrees of expression and found that crosses between parents with excellent expression tended to produced F1 with excellent expression and those with poor expression produced F1 with poor the expression. This suggests that more than one factor is involved in the expression of the trait, and that the different expressions cannot be due to different “expressivity”. We also found that the expression Pw was greatly reduced when prowings were crossed with the Nara wild strain, although this did not happen when they were crossed with individuals with wild-type expression from the Pw strain. This suggests that at least one more factor participates in the expression of Pw. We observed meiosis clearly even in the adult stage. We examined many male adults and confirmed that the reciprocal translocation cause Pw expression without an exception. We also observed the frequencies and stages of embryonic death of F1 from both Pw and Pw × wild type parents. The results agreed well with the ratio between alternate and adjacent disjunction at metaphase I. Pw individuals tended to be delay in nymphal development compared with the wild type.