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Effect of photoperiod on development and fecundity in the flour moth, Ephestia kuehniella
J. Insect Physiol.,
1976, Vol. 22, pp. 1213 to 1217. Pergamon
Press. Printed in Great Britain.
EFFECT OF PHOTOPERIOD ON DEVELOPMENT AND FECUNDITY
IN THE FLOUR
MOTH, EPHESTlA KU,?Z~~~~~~
BRONISLAWCYMB~ROWSKIand JADWIGA M. GIEBULTQWICZ Department of Animal Physiology, Zoological Institute. University of Warsaw, Zwirki i Wigury 93 02-089 WARSZAWA, Poland (Received
15 Decemhrr
1975)
Abstract-Examination was made of the effect of alternating light and darkness (LD 12: 12) and constant light (LL) conditions on length of development and fecundity of the moth, Ephrstia kuehniella. It was found the conditions applied cause acceleration of larval development on an average by 3 days in comparison with development under constant darkness conditions (DD). The fecundity of the insects examined decreases considerably under the experimental conditions. When pharate adults are kept in light for 18 hr per 24-hr period on the 6th to 7th day of their development, males incapable of fertilizing females are produced,
INTRODUCTION GROWTH and metamorphosis processes in insects undergo change as the result of the effect exerted by different light conditions applied in laboratory cultures (ORPHANIOLES and GONZALEZ, 1970; KRYSPIN et al., 1974; GIEB~LT~WICZ and CYMBOROWSKI,in press). The fecundity of insects cultured under unnatural photoperiod conditions is also subject to considerabie reduction, as has been shown in the case of Plodia interpunctella (LUM and FLAHERTY, 1969, 1970). The purpose of the present study was to examine the effect of varying light and darkness (LD l2:12) and constant light conditions (LL) on the length of growth and development in the moth. Ephestia kuehniella Zell. an on their fecundity. Examination was also made of the susceptibility of different developmental stages to light. and in addition the critical duration of light affecting the fecundity of the study insects was determined. MATERIAL
AND METHODS
The experiments were carried out on the flour moth, Ephestia kuehniella. The insects were cultured in Petri dishes on food consisting of rye and wheat bran, rye flour, and maize flour, mixed together. The pairs of moths used in the experiments were kept in separate Petri dishes of 5 cm in diameter. The insects were cultured in thermostats with three different sets of light conditions, namely in constant darkness (DD conditions), with a photoperiod of 12 hr light per 24 hr (LD 12:12 conditions) and in constant light (LL conditions). Light intensity during the light phase was approx. 600 lux. A constant temperature of 27 f 0,5”C and relative humidity of 70 + 10% were maintained in all the thermostats.
All experimental insects were taken out from their cocoons except control ones kept in LL conditions. effect
of different
light conditions
on development
In order to investigate the effect of different light conditions on the length of development, 300 freshly ecdysised first instar larvae were taken from the basic culture kept under DD conditions and placed in group of 100 individuals under LL, LD and DD conditions. The various groups of larvae were divided into smaller groups of 25 in each of IOcm dishes. and cultured on a uniform amount of food. The same procedure was applied to freshly ecdysised pupae taken from the DD culture. The number of moths emerging in the different cultures was recorded daily. The insects remained for not longer than 15 min in natural daylight during the time the observations were made. Length of development of the insects under different light conditions was calculated by the weighed average method. Effect
of different
light conditions
on fecundity
The moths emerged from cultures kept under different light conditions were reared further in order to examine their fecundity. The moths were put together in pairs and observations made during the first day to ascertain whether copulation took place. Four days later the moths were removed from the dishes and the number of eggs laid counted. After a further four days the percentage of hatched larvae was determined, examining in the above way at least 20 pairs of moths obtained from development under different lighting conditions. In order to determine which stage of development is most susceptible to the photoperiod used, similar observations were made of the fecundity of moths obtained from experimental cultures, in which only
1214
BRONISLAWCYMBOROWSII AND JADWKA M. GIEBULTOWICZ
larvae, pupae, pharate adults, or emerged adults were subjected to the effect of constant light. After finding that disturbances in the course of reproduction are caused by constant light acting on the pharate adult, further studies were made in order to establish the critical period during the development of the pharate adult. and also the critical duration of lighting causing the maximum effect. For this purpose groups of pharate adults differing in age by 24 hr on each day of their development were transformed from DD to LL conditions (using six pairs of pharate adults for each of the given ages) and from LL to DD conditions (using five pairs of pharate adults for each of the given ages). Observations were also made on fecudity of moths in cases in which the pharate adults were kept under conditions of 2, 4. 6, 9, and 12 hr of darkness per day. There were 10 in each of the groups. Next the moths were put together in pairs under the experimental conditions studied and kept in constant darkness, when copulation readily takes place. Six days later they were examined to establish if larvae had hatched out. In order to discover if males or females are responsible for the reduced fecudity under LL conditions pairs of moths obtained from pharate adults cultured under LL or DD conditions were put together, in the following way: +‘+ from LL x 1; from LL
in Fig. 1. The character of curves of appearance of these stages of development do not in principle undergo any change.
The fecundity of insects obtained by the use of different photoperiods was defined by means of counting eggs laid over 4 days by females originating from different pairs of moths, whereas the percentage of fertilized eggs was established by means of counting the numbers of larvae hatching from that eggs laid by all the paris of moths taken for the experiment, regardless of whether copulation had been observed or not. Table 1 gives the results of the experiment in which pharate adults. and later moths put together in pairs, were cultured under LL, LD or DD conditions. The number of eggs laid by females in a given group varies very greatly. but the average number of eggs laid under LL conditions is far lower than under LD and DD. In the former group seven cases were recorded of no eggs having been laid, even if copulating pairs had previously been observed. In not a single case did larvae hatch from eggs laid under constant lighting conditions. It was next found that males are responsible for the reduced fecundity found under LL conditions and this is illustrated in Table 2. In this experiment the
Ii from LL x ;{ from DD 4’; from DD x ;;
from DD
J + from DD x ;;
from LL.
<“I DD
Each group consisted of not less than 15 pairs of moths. The insects were kept in constant darkness and observations made to see if copulation took place. and a count made of any eggs laid after 4 days. The percentage of larvae hatched from them was examined after 8 days from the date of egg-laying.
RESULTS
Under conditions of constant light and conditions of 12 hr light per day the development of Ephestia kuehniellu (from eggs to the emergence of moths) is accelerated in relation to that of insects cultured in constant darkness. The average length of the whole development process of these insects is respectively: under LL 39.9; under LD 40-5; under DD 42,8 days. Acceleration of development relates only to the larval stage, until the time of spinning larvae are formed; no significant differences being found in the duration of the spinning larva (on an average 3.0 days under different conditions) and the pharate adult stage which lasts respectively: under LL 9,2; under DD 9.4: under LD 9.2 days. The appearance of pupae and moths in parallel cultures under different lighting conditions is illustrated
Days
Fig. 1. Rhythms of pupations (continuous line) and adults emergence (broken line) in Ephrstiu kuehniella kept from eggs in different lighting conditions. DD+onstant darkness, LL--constant light, LD 12hr light and 12hr of darkness per day. Arrows indicate average time of development.
Development and fecundity in the Flour moth
1215
Table 1. Fecundity of moths obtained from pharate adults cultured under different light conditions. Numbers in brackets indicate number of pairs in which copulation was observed
Table 2. Fecundity of females crossed with males from LL or DD conditions. Numbers in brackets indicate number of pairs in which copulation was observed
pairs
examined
moths obtained from pupae cultured under LL or DD conditions were placed in pairs and kept in darkness for a further period. Far smaller average number of eggs was laid while mating males came from LL than in the other cases regardless of the origin of the females. The larvae also appeared only sporadically if males came from LL conditions, but if the. males were taken from DD conditions larvae hatched out in the majority of the cases. Analysis of the different pairs of moths from the two experiments show that the fact that copulation has taken place is not a condition sufficient for normal egg-laying, since in the majority of cases in which a lower than average number of eggs was obtained and from which larvae did not hatch, copulation had previously taken place. It would appear interesting to compare the behaviour of moths cultured with different photoperiods. Table 3 gives the number of copulating pairs, expressed in percentage, observed in the given experimental group. The smallest number of copulating insects was found when both pupae and moths combined in pairs had been subject to constant light. Frequency of copulation was twice as great if the pharate adults and emerged moths had been kept under DD or LD conditions; moths in the first group usually beginning to copulate soon after being placed together in pairs, and in the second group after the onset of the dark phase, i.e. after 1800 hr. Interme-
diate results on copulation were when the pharate adults from which the males were obtained had been kept under LL, and moths under DD conditions. The fact merits attention that in some of the dishes in which copulation was at first observed, on the following day the females endeavoured to attract the males, i.e. behaved in a way characteristic of virgin forms. It was next found that a smaller than average number of eggs and no progeny were obtained in such dishes. Some cases were even found in which no larvae hatched from eggs laid even though copulation had taken place twice. Some females mated with males from LL and DD conditions were checked for presence of spermathophores in their spermatheca. It came out that spermathophores were always present regardless of the origin of males. Table 3. Observed copulations of moths
1216
BRONI~LAW CYMBOROWSKI ANDJADWIGAM. GIEBLJLTOWICZ
Table 4. Sensitivity of pupae to light expressed as the ability or lack of ability to produce the next generation. There were 4 to 5 pairs of moths for each day. The figures in the Table indicate after how many days (counting from formation of pupae) they were transferred from LL condition to DD or from DD to LL respectively
The results of the experiments showing in what period of development of pharate adults light causes disturbance in reproduction processes are given in Table 4. It was found that the period between the 6 and 7th day of life of the pharate adult is critical for normal development of males, whereas the average length of development of pharate adults is slightly over 9 days. A certain amount of darkness is essential during this period. The experiments in which pupae were examined under 2, 4. 6 and 8 hr of darkness per day showed that the period of darkness essential for normal development is about 6 hr per day. Eggs laid by moths obtained from pupae cultured under conditions of 2 and 4 hr darkness per day were not fertilized, despite the fact that copulation has previously been observed, whereas subjecting the moths to more than 6 hr darkness resulted in fertilized eggs being laid from which larvae hatched. DISCUSSION The results presented here suggest that when conditions of alternating light and darkness or constant light are used in cultures of the flour moth this causes shortening of the duration of the larval period by, on an average, 3 days in relation to insects cultured under condition of constant darkness. Different light conditions during culture were not to affect later stages of development, but ORPHANIDESand GONZALEZ (1970) found that continuous light shortened adult longevity in Trichogramma pretiosum. The reverse results were obtained in cultures of the wax moth (Galleria mellonelk) under different light conditions (KRYSPIN et al., 1974). Culturing these insects under LL or LD conditions causes prolongation of the larval period and leads to disturbances in larval-pupal ecdysis in comparison with insects cultured under DD condition. The mechanism of the effect exerted by light on the lifetime of the insects studied has not as yet been discovered. It may be that as the result of applying unnatural light conditions in the culture disturbances of a hormona1 nature arise, manifested in a change in the duration of development of these insects. Preliminary histological examination of the neurosecretory cells of the brain of pharate adults obtained from
LL conditions suggests increased accumulation of neurosecretion in them in comparison with DD pharate adults. Light conditions were, however, observed to exert the most marked effect on fecundity. It is difficult to find an explanation of the fact that light for 18-20 hr/day applied to the pharate adults of Ephrstia kuehniello from 6 to 7 days old, from which male insects are to emerge, renders them incapable of fertilizing females. When females cultured under LD or DD conditions are put together with males from LL no larvae hatch from the eggs laid by these females. It is possible that the cause of this state of affairs is disturbance of the natural circadian rhythm of production and liberation of sperm by LL males. Inhibition in production of spermatocytes and considerable reduction of the numbers of bundles of eupyrene sperm are observed in the gonads of LL pharate adults (in preparation). The results obtained, however, need confirmation and detailed study. On the other hand RIEMANN ct al. (1974) have shown that in this species liberation of sperm takes place in a strictly defined time interval during the 24-hr period. It may be that the cause lies in disturbances of the actual process of sperm transfer despite that spermathophore are always transferred by males cultured under LL, since as LUM and FLAHERTY(1969. 1970) found earlier on, culture under LL conditions of P/o&a irzterpunctella Hiibn.) a species related to Ephestia, greatly affected sperm transfer by the males. Another cause may be disturbances in the production and liberation of sex pheromones by females of the study insects cultured under LL conditions. %iWER of (I/. (1970) found that there is endogenously controlled circadian rhythm of liberation of these substances in female noctuid moths (Trichoplusia ni). It is possible that these is a similar rhythm of production and liberation of sex pheromones in Ephestia. and disturbance of this rhythm by applying LD 20:4, LD 22:2 or LL leads to considerable reduction of the fecundity of these insects (see Table 1). One more possibility is that unnormal lighting conditions cause the disturbance in function of accessory sex glands of Ephestia males. As shown in the review by HINTON (1974) the secretion of male accessory gland plays a major role in reproduction of insects. Recently ADLAKHA and PILLAR(1975) found also that male accessory gland substance is essential for the production of fertile eggs in two species of mosquitoes. Acknowledgements-This work was supported United States Department of Agriculture. FG-PO-333.
in part by Grant No.
REFERENCES ADLAKHAV. and F’ILLAIM. K. K. (1975)
Involvment of male accessory gland substance in the fertility mosquitoes. J. Insect Phjxiol. 21. 1453Sl455. H~NTON H. E. (1974) Accessory function of seminal fluid. J. med. Em. 11. 19-25.
Development and fecundity in the Flour moth KRYSPINI., DUTKOWSKI A. B., and CYMBOROWSKI B. (1974) The influence of illumination conditions on growth and development of Galleria mellonella. Bid/. Acad polar. Sci. (C. II) 22. 803-808. LUM P. T. M. and FLAHERTYB. R. (1969) Effect of mating with males in continuous light or in light-dark cycles on fecundity in Plodia interpunctella Hiibner (Lepidoptera Phycitidae). J. srorrd Prod. Res. 5. 89-94. LUM P. T. M. and FLAHERTYB. R. (1970) Effect of continuous light on the potency of Plod& Interpurvtella males (Leptidoptera: Phycitidae). Ann. ent. Sot. Am. 63. 1470-1471.
1217
ORPHANIDES G. M. and GONZALEZD. (1970) Importance of light in the biology of Trichogramma pretiosum. Ann. ent. Sot. Am. 63, 17341740. RIEMANNJ. G., THORWN B. J.. and RUUD R. L. (1974) Daily cycle of release of sperm from the tests of the mediterranean flour moth. J. Insect Physiol. 20. 195-207. SOWERL. L.. SHOREYH. H.. and GASWN L. K. (1970) Sex pheromones of noctuid moths. XXI. Light: dark cycle regulation and light inhibition of sex pheromone release by females of Trichopfosia ?fi. Ann. wt. Sot. Am. 63. 1090-1092.
1976, Vol. 22, pp. 1213 to 1217. Pergamon
Press. Printed in Great Britain.
EFFECT OF PHOTOPERIOD ON DEVELOPMENT AND FECUNDITY
IN THE FLOUR
MOTH, EPHESTlA KU,?Z~~~~~~
BRONISLAWCYMB~ROWSKIand JADWIGA M. GIEBULTQWICZ Department of Animal Physiology, Zoological Institute. University of Warsaw, Zwirki i Wigury 93 02-089 WARSZAWA, Poland (Received
15 Decemhrr
1975)
Abstract-Examination was made of the effect of alternating light and darkness (LD 12: 12) and constant light (LL) conditions on length of development and fecundity of the moth, Ephrstia kuehniella. It was found the conditions applied cause acceleration of larval development on an average by 3 days in comparison with development under constant darkness conditions (DD). The fecundity of the insects examined decreases considerably under the experimental conditions. When pharate adults are kept in light for 18 hr per 24-hr period on the 6th to 7th day of their development, males incapable of fertilizing females are produced,
INTRODUCTION GROWTH and metamorphosis processes in insects undergo change as the result of the effect exerted by different light conditions applied in laboratory cultures (ORPHANIOLES and GONZALEZ, 1970; KRYSPIN et al., 1974; GIEB~LT~WICZ and CYMBOROWSKI,in press). The fecundity of insects cultured under unnatural photoperiod conditions is also subject to considerabie reduction, as has been shown in the case of Plodia interpunctella (LUM and FLAHERTY, 1969, 1970). The purpose of the present study was to examine the effect of varying light and darkness (LD l2:12) and constant light conditions (LL) on the length of growth and development in the moth. Ephestia kuehniella Zell. an on their fecundity. Examination was also made of the susceptibility of different developmental stages to light. and in addition the critical duration of light affecting the fecundity of the study insects was determined. MATERIAL
AND METHODS
The experiments were carried out on the flour moth, Ephestia kuehniella. The insects were cultured in Petri dishes on food consisting of rye and wheat bran, rye flour, and maize flour, mixed together. The pairs of moths used in the experiments were kept in separate Petri dishes of 5 cm in diameter. The insects were cultured in thermostats with three different sets of light conditions, namely in constant darkness (DD conditions), with a photoperiod of 12 hr light per 24 hr (LD 12:12 conditions) and in constant light (LL conditions). Light intensity during the light phase was approx. 600 lux. A constant temperature of 27 f 0,5”C and relative humidity of 70 + 10% were maintained in all the thermostats.
All experimental insects were taken out from their cocoons except control ones kept in LL conditions. effect
of different
light conditions
on development
In order to investigate the effect of different light conditions on the length of development, 300 freshly ecdysised first instar larvae were taken from the basic culture kept under DD conditions and placed in group of 100 individuals under LL, LD and DD conditions. The various groups of larvae were divided into smaller groups of 25 in each of IOcm dishes. and cultured on a uniform amount of food. The same procedure was applied to freshly ecdysised pupae taken from the DD culture. The number of moths emerging in the different cultures was recorded daily. The insects remained for not longer than 15 min in natural daylight during the time the observations were made. Length of development of the insects under different light conditions was calculated by the weighed average method. Effect
of different
light conditions
on fecundity
The moths emerged from cultures kept under different light conditions were reared further in order to examine their fecundity. The moths were put together in pairs and observations made during the first day to ascertain whether copulation took place. Four days later the moths were removed from the dishes and the number of eggs laid counted. After a further four days the percentage of hatched larvae was determined, examining in the above way at least 20 pairs of moths obtained from development under different lighting conditions. In order to determine which stage of development is most susceptible to the photoperiod used, similar observations were made of the fecundity of moths obtained from experimental cultures, in which only
1214
BRONISLAWCYMBOROWSII AND JADWKA M. GIEBULTOWICZ
larvae, pupae, pharate adults, or emerged adults were subjected to the effect of constant light. After finding that disturbances in the course of reproduction are caused by constant light acting on the pharate adult, further studies were made in order to establish the critical period during the development of the pharate adult. and also the critical duration of lighting causing the maximum effect. For this purpose groups of pharate adults differing in age by 24 hr on each day of their development were transformed from DD to LL conditions (using six pairs of pharate adults for each of the given ages) and from LL to DD conditions (using five pairs of pharate adults for each of the given ages). Observations were also made on fecudity of moths in cases in which the pharate adults were kept under conditions of 2, 4. 6, 9, and 12 hr of darkness per day. There were 10 in each of the groups. Next the moths were put together in pairs under the experimental conditions studied and kept in constant darkness, when copulation readily takes place. Six days later they were examined to establish if larvae had hatched out. In order to discover if males or females are responsible for the reduced fecudity under LL conditions pairs of moths obtained from pharate adults cultured under LL or DD conditions were put together, in the following way: +‘+ from LL x 1; from LL
in Fig. 1. The character of curves of appearance of these stages of development do not in principle undergo any change.
The fecundity of insects obtained by the use of different photoperiods was defined by means of counting eggs laid over 4 days by females originating from different pairs of moths, whereas the percentage of fertilized eggs was established by means of counting the numbers of larvae hatching from that eggs laid by all the paris of moths taken for the experiment, regardless of whether copulation had been observed or not. Table 1 gives the results of the experiment in which pharate adults. and later moths put together in pairs, were cultured under LL, LD or DD conditions. The number of eggs laid by females in a given group varies very greatly. but the average number of eggs laid under LL conditions is far lower than under LD and DD. In the former group seven cases were recorded of no eggs having been laid, even if copulating pairs had previously been observed. In not a single case did larvae hatch from eggs laid under constant lighting conditions. It was next found that males are responsible for the reduced fecundity found under LL conditions and this is illustrated in Table 2. In this experiment the
Ii from LL x ;{ from DD 4’; from DD x ;;
from DD
J + from DD x ;;
from LL.
<“I DD
Each group consisted of not less than 15 pairs of moths. The insects were kept in constant darkness and observations made to see if copulation took place. and a count made of any eggs laid after 4 days. The percentage of larvae hatched from them was examined after 8 days from the date of egg-laying.
RESULTS
Under conditions of constant light and conditions of 12 hr light per day the development of Ephestia kuehniellu (from eggs to the emergence of moths) is accelerated in relation to that of insects cultured in constant darkness. The average length of the whole development process of these insects is respectively: under LL 39.9; under LD 40-5; under DD 42,8 days. Acceleration of development relates only to the larval stage, until the time of spinning larvae are formed; no significant differences being found in the duration of the spinning larva (on an average 3.0 days under different conditions) and the pharate adult stage which lasts respectively: under LL 9,2; under DD 9.4: under LD 9.2 days. The appearance of pupae and moths in parallel cultures under different lighting conditions is illustrated
Days
Fig. 1. Rhythms of pupations (continuous line) and adults emergence (broken line) in Ephrstiu kuehniella kept from eggs in different lighting conditions. DD+onstant darkness, LL--constant light, LD 12hr light and 12hr of darkness per day. Arrows indicate average time of development.
Development and fecundity in the Flour moth
1215
Table 1. Fecundity of moths obtained from pharate adults cultured under different light conditions. Numbers in brackets indicate number of pairs in which copulation was observed
Table 2. Fecundity of females crossed with males from LL or DD conditions. Numbers in brackets indicate number of pairs in which copulation was observed
pairs
examined
moths obtained from pupae cultured under LL or DD conditions were placed in pairs and kept in darkness for a further period. Far smaller average number of eggs was laid while mating males came from LL than in the other cases regardless of the origin of the females. The larvae also appeared only sporadically if males came from LL conditions, but if the. males were taken from DD conditions larvae hatched out in the majority of the cases. Analysis of the different pairs of moths from the two experiments show that the fact that copulation has taken place is not a condition sufficient for normal egg-laying, since in the majority of cases in which a lower than average number of eggs was obtained and from which larvae did not hatch, copulation had previously taken place. It would appear interesting to compare the behaviour of moths cultured with different photoperiods. Table 3 gives the number of copulating pairs, expressed in percentage, observed in the given experimental group. The smallest number of copulating insects was found when both pupae and moths combined in pairs had been subject to constant light. Frequency of copulation was twice as great if the pharate adults and emerged moths had been kept under DD or LD conditions; moths in the first group usually beginning to copulate soon after being placed together in pairs, and in the second group after the onset of the dark phase, i.e. after 1800 hr. Interme-
diate results on copulation were when the pharate adults from which the males were obtained had been kept under LL, and moths under DD conditions. The fact merits attention that in some of the dishes in which copulation was at first observed, on the following day the females endeavoured to attract the males, i.e. behaved in a way characteristic of virgin forms. It was next found that a smaller than average number of eggs and no progeny were obtained in such dishes. Some cases were even found in which no larvae hatched from eggs laid even though copulation had taken place twice. Some females mated with males from LL and DD conditions were checked for presence of spermathophores in their spermatheca. It came out that spermathophores were always present regardless of the origin of males. Table 3. Observed copulations of moths
1216
BRONI~LAW CYMBOROWSKI ANDJADWIGAM. GIEBLJLTOWICZ
Table 4. Sensitivity of pupae to light expressed as the ability or lack of ability to produce the next generation. There were 4 to 5 pairs of moths for each day. The figures in the Table indicate after how many days (counting from formation of pupae) they were transferred from LL condition to DD or from DD to LL respectively
The results of the experiments showing in what period of development of pharate adults light causes disturbance in reproduction processes are given in Table 4. It was found that the period between the 6 and 7th day of life of the pharate adult is critical for normal development of males, whereas the average length of development of pharate adults is slightly over 9 days. A certain amount of darkness is essential during this period. The experiments in which pupae were examined under 2, 4. 6 and 8 hr of darkness per day showed that the period of darkness essential for normal development is about 6 hr per day. Eggs laid by moths obtained from pupae cultured under conditions of 2 and 4 hr darkness per day were not fertilized, despite the fact that copulation has previously been observed, whereas subjecting the moths to more than 6 hr darkness resulted in fertilized eggs being laid from which larvae hatched. DISCUSSION The results presented here suggest that when conditions of alternating light and darkness or constant light are used in cultures of the flour moth this causes shortening of the duration of the larval period by, on an average, 3 days in relation to insects cultured under condition of constant darkness. Different light conditions during culture were not to affect later stages of development, but ORPHANIDESand GONZALEZ (1970) found that continuous light shortened adult longevity in Trichogramma pretiosum. The reverse results were obtained in cultures of the wax moth (Galleria mellonelk) under different light conditions (KRYSPIN et al., 1974). Culturing these insects under LL or LD conditions causes prolongation of the larval period and leads to disturbances in larval-pupal ecdysis in comparison with insects cultured under DD condition. The mechanism of the effect exerted by light on the lifetime of the insects studied has not as yet been discovered. It may be that as the result of applying unnatural light conditions in the culture disturbances of a hormona1 nature arise, manifested in a change in the duration of development of these insects. Preliminary histological examination of the neurosecretory cells of the brain of pharate adults obtained from
LL conditions suggests increased accumulation of neurosecretion in them in comparison with DD pharate adults. Light conditions were, however, observed to exert the most marked effect on fecundity. It is difficult to find an explanation of the fact that light for 18-20 hr/day applied to the pharate adults of Ephrstia kuehniello from 6 to 7 days old, from which male insects are to emerge, renders them incapable of fertilizing females. When females cultured under LD or DD conditions are put together with males from LL no larvae hatch from the eggs laid by these females. It is possible that the cause of this state of affairs is disturbance of the natural circadian rhythm of production and liberation of sperm by LL males. Inhibition in production of spermatocytes and considerable reduction of the numbers of bundles of eupyrene sperm are observed in the gonads of LL pharate adults (in preparation). The results obtained, however, need confirmation and detailed study. On the other hand RIEMANN ct al. (1974) have shown that in this species liberation of sperm takes place in a strictly defined time interval during the 24-hr period. It may be that the cause lies in disturbances of the actual process of sperm transfer despite that spermathophore are always transferred by males cultured under LL, since as LUM and FLAHERTY(1969. 1970) found earlier on, culture under LL conditions of P/o&a irzterpunctella Hiibn.) a species related to Ephestia, greatly affected sperm transfer by the males. Another cause may be disturbances in the production and liberation of sex pheromones by females of the study insects cultured under LL conditions. %iWER of (I/. (1970) found that there is endogenously controlled circadian rhythm of liberation of these substances in female noctuid moths (Trichoplusia ni). It is possible that these is a similar rhythm of production and liberation of sex pheromones in Ephestia. and disturbance of this rhythm by applying LD 20:4, LD 22:2 or LL leads to considerable reduction of the fecundity of these insects (see Table 1). One more possibility is that unnormal lighting conditions cause the disturbance in function of accessory sex glands of Ephestia males. As shown in the review by HINTON (1974) the secretion of male accessory gland plays a major role in reproduction of insects. Recently ADLAKHA and PILLAR(1975) found also that male accessory gland substance is essential for the production of fertile eggs in two species of mosquitoes. Acknowledgements-This work was supported United States Department of Agriculture. FG-PO-333.
in part by Grant No.
REFERENCES ADLAKHAV. and F’ILLAIM. K. K. (1975)
Involvment of male accessory gland substance in the fertility mosquitoes. J. Insect Phjxiol. 21. 1453Sl455. H~NTON H. E. (1974) Accessory function of seminal fluid. J. med. Em. 11. 19-25.
Development and fecundity in the Flour moth KRYSPINI., DUTKOWSKI A. B., and CYMBOROWSKI B. (1974) The influence of illumination conditions on growth and development of Galleria mellonella. Bid/. Acad polar. Sci. (C. II) 22. 803-808. LUM P. T. M. and FLAHERTYB. R. (1969) Effect of mating with males in continuous light or in light-dark cycles on fecundity in Plodia interpunctella Hiibner (Lepidoptera Phycitidae). J. srorrd Prod. Res. 5. 89-94. LUM P. T. M. and FLAHERTYB. R. (1970) Effect of continuous light on the potency of Plod& Interpurvtella males (Leptidoptera: Phycitidae). Ann. ent. Sot. Am. 63. 1470-1471.
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