The Response of a 'Short-Day' Insect to Certain External Factors: the Induction of Diapause in Abraxas miranda BUTLER(Lepidoptera, Geometridae) By Sinzo MASAKI EntomologicalLaboratory, Faculty of Agriculture,Mie University INTRODUCTION is referred to a previous paper (MASAKI, 1957). Among various environmental factors, day- If an adaptation has been evolved in this length is the most precise signal of the particular case in the same direction as in seasons for many creatures, since it undergoes 'summer' insects , it might be expected that a regular and invariable annual rhythm. photoperiod plays an important part in The role of daylength in the seasonal regula- controlling the seasonal activity, probably tion of insects has been nvestigated par- through its effect upon diapause, which is ticularly in relation to the incidence of a most important timing device in insects, diapause, and the studies hitherto performed and that the pattern of the photoperiodic show that many insects fall into the category response involved might be different from of 'long-day' species (cf. LEES, 1955). In that of 'long-day' species. Hence the pos- these forms a long photoperiod prevents sible existence of a 'short-day' species is diapause, and a short one induces it. As a suggested. Standing on this basis, an inves- result, in nature their active period coincides tigation has been undertaken in order to with the warm or hot seasons of the year. determine the influence of photoperiod upon In the warmer parts of temperate regions the incidence of diapause of Abraxas miran- where the winter is mild, there are a few da. The account of this is the main part species having the reversed cycle of activity. of the present paper, and the influence of For instance, Agrotis infusa undergoes a temperature is also discussed to a lesser facultative imaginal diapause in the summer extent. generation, while no arrest of reproduction MATERIAL AND METHODS occurs in the winter generation (COMMON, 1954). Another example is afforded by a Source of material. In the early summer univoltine weevil, Listroderes costirostris, of 1956, several hundred larvae of Abraxas which enters a prolonged period of aestiva- miranda were collected from a hedge of tion in the adult stage (SHIRAGA and ISHII, Euonymus japonica growing on the university 1950). campus at Tsu. Their offspring were succes- The geometrid moth, Abraxas miranda, sively reared from generation to generation is also a member of this latter group. This in the laboratory under uncontrolled con- moth is, however, not a typical 'winter' ditions. No heating device was employed species in that the first generation of the there in winter. Under these conditions, year is active during spring and early sum- the laboratory stock underwent a seasonal mer, and the second generation is partly cycle almost similar to that of the field dormant in winter as a pupa. Yet it displays population; there was a prolonged period of a definite resting stage in summer, and the pupal arrest in summer, and the irregular larva actively feeds and grows in winter. but active growth of the larvae in winter; For details of this seasonal history, the reader the moths emerged in the definite periods (285) 86 Japanese Journal of Applied Entomology and Zoology Vol.2, No.4 of spring and autumn. From moths of this series larvae were exposed to the natural stock, material for the present experiments light conditions in the laboratory, and was obtained at appropriate times. transferred to a dark box at various times Larva. The larvae were reared in groups each day to obtain various regimes of photo- in a breeding jar of 18cm diameter and 13 period. In the third series a 10w fluorescent cm depth, or in a frame cage of 20•~20•~30 daylight tube was employed as a source of cm, both covered with a piece of perforated light in a light-proof wooden box of 60•~80 zink gauze. Twigs of the food plant, Euo- •~ 75cm, and the daily length of illumination nymus japonica, were inserted into a bottle was regulated by means of a time switch. of water placed in the jar or cage. In the Temperature. In most experiments con- younger stages the food plant was renewed cerning the action of photoperiod the larvae every three or four days, but in the later were bred at room temperatures, since no stages this was done every one or two days. suitable constant-temperature room was a- When the larvae became mature, they drop- vailable. The temperature conditions during ped to the bottom of the cage and soon the larval stage were therefore different from after assumed a U-form characteristic of the one series of tests to another according to prepupa. Then they were removed from the season, and this might decrease the the cage and placed in a petri-dish lined reliability of the results. Small constant- with a sheet of paper. temperature cabinets were available for the Pupa. The pupae were kept dry through- experiments on the effect of temperature. out the experiments, since it was found These cabinets were light-proof, and the that contact moisture was not necessary for larvae were exposed to light for less than the growth of the pupae but was sometimes five minutes daily at the time of renewing even harmful, mould growing in the petri- the food plant. dish. They were kept at a temperature of Beside these variable conditions of the 25•Ž except during the latter half of July experimental procedure, the quality of the and the first half of August, when the room food plant could not be standardized. It temperature exceeded this value and the might change according to the season, and thermostat was unable to control it. This its effect upon diapause in Abraxas miranda might influence the length of the pupal was not determined. For these reasons, the stage to a certain extent, but had no sub- results of similar experiments performed in stantial effect upon the incidence of diapause. different seasons are presented in the follow- The emergence of moths was observed daily ing paragraphs. In spite of this the remark- until there was no surviving pupa, and the able effects of photoperiod and temperature length of the pupal stage of each individual during the larval stage upon the incidence was recorded. This record was taken as a of pupal diapause can be recognized. measure indicating the incidence and inten- RESULTS sity of diapause. Photoperiod. The regulation of photo- Experiment a. In this series of experi- period was executed by transferring the insect ments, larvae were constantly kept at 25•Ž. daily from a dark box to an illuminated one Four batches were bred in photoperiods of and vice versa, but later a time switch was 0, 8, 16 or 24 hours per day respectively, available. In the first series of photoperiodic and another batch was reared under uncon- tests, larvae were exposed to light in a trolled conditions in the laboratory. As double-glass-sided box provided with a ther- this experiment was performed in May, 1957, mostat and illuminated by a 60w electric a natural daylength of approximately 14 bulb from outside. During the dark period hours was then prevailing. the larvae were kept in a light-proof con- The results are summarized in table 1a, stant-temperature cabinet. In the second and the weekly totals of moths that emerged November, 1958 MASAKI: The Response of a 'Short-Day' Insect to Certain External Factors 287 Table 1. The effect of photoperiod and temperature during the larval stage upon the incidence and duration of pupal diapause in Abraxas miranda. The pupae were kept at ca 25•Ž throughout. For details of the experimental conditions, see text. *Both diapause and nondiapause pupae transformed into moths at 25•Ž so that the figures in this column indicate the total numbers of pupae that survived throughout the experiments. **The larvae were kept at 5•Ž for 20 days in either the penultimate or last instar. Even at this low temperature larvae were observed to grow. Before chilling they were reared at 25•Ž, and after that at 15-20•Ž. are illustrated in figure 1. In certain batches exerts an apparent effect upon the induction some pupae completed their development in of diapause which is ecologically linked with about two weeks, but the rest did so after the aestivation of this species. Contrary to much longer periods. There was thus a its effect upon the hibernation diapause of clear-cut distinction between the two types certain other insects, long photoperiods of of emergence, nondiapause and diapause. 16 and 24 hours per day, as well as a natural Diapause development in the pupae of Ab- long day of about 14 hours, induced diapause ra xas miranda seemed not to be completely without exception, while a short photoperiod inhibited by the high temperature of 25•Ž. of 8 hours prevented diapause to a consid- The moths eventually emerged from diapaus- erable extent. In continuous darkness, only ing pupae which had been kept constantly a few pupae developed without diapause. at this temperature, so that the length of It should also be pointed out that a few diapause could be directly estimated from pupae raised in 0 or 8 hours of light com- the length of the pupal stage. The number pleted diapause in a relatively short time. of emerging moths shown in table 1 includes On the other hand, the duration of diapause both diapausing and nondiapansing insects. was longer and more uniform in the long- In table 1a and figure 1, it can be seen day treatments. The occurrence of pupae that the photoperiod in the larval stage exhibiting a 'weak' diapause of this kind 288 Japanese Journal of Applied Entomology and Zoology Vol.2, No.4 longer than in the experiments conducted later.