Ultraviolet light and puparial weight as factors in the autogeny of the fleshfly, Sarcophaga falculata

J. lent

Pkysiol..

1977, Vol. 23. pp. 961 to 964. Pergamon

Press. Printed

in Great

Britaim

ULTRAVIOLET LIGHT AND PUPARIAL WEIGHT AS FACTORS IN THE AUTOGENY OF THE FLESHFLY, SARCOPHAGA FALCULATi YOSEF SCHLEXN Department

of Medical

Entomology.

(Received

The Hebrew University-Hadassah Jerusalem, Israel

21 Jut~uary

1977; rerisd

I

March

Medical

School.

1977)

Abstract-Light

conditions and the puparial weight were assessed as factors that affect autogrny In The frequency and degree of autogeny differed in flies originating from large or small puparia. The limitation of puparial weight range did not prevent the variation in the stage of autogeny. Autogeny was low in flies kept in complete darkness and was very high in uv irradiated flies. Removal of the ocelli before U.V. irradiation prevented most of the increase in autogeny. and it is assumed that the ocelli are the main transmitter of the U.V. effect on oiigenesis. Neurosecretion was found within the cells of the ocellar nerve of adult flies. It is possible that this neurosecretion plays a rnle in the U.V. induced effect on autogeny. Sarcophagu

fulculnta.

INTRODUCTION

AUKKEN\‘, or the capability to mature eggs without a protein meal has been described for several Calypterate Diptera. Records of the phenomenon point out differences between species and also between groups of flies of the same species. Autogeny was found to be highly developed in three species of tropical Sarcocompared to temperate zone fleshflies phqa, (CI-IAIIHA and DENLINGER. 1976). Variations in the expression of autogeny were described in the housefly (ROHBINS and SHORTINO, 1962; LARSEN rt al., 1966) and in S. hullata (DENLINGER, 1971). Differences between batches of the same strain of Sarcophuga hulkm were attributed to the density of larvae during rearing (BAXTER rt crl.. 1973). The small larvae of a dense batch metamorphosed into small adults with a low percentage of autogeny. In this study the degree of autogeny in the fleshfly, S.j&u/atu. is shown to be affected by light conditions and differences of weight of the puparia in the same batch. Irradiation with ultraviolet light caused a marked increase in autogeny and the effect of the U.V. light seems to be entrained mainly via the ocelli. It is suggested that neurosecretion present in ocellar neurons could be one of the mediator agents for the initiation of egg development. MATERIALS

AND

METHODS

Sarcophc~gcr jdcuk~tu Pand. used were from a culture kept in the laboratory, reared on beef, sugar. and water. at a temperature of 24 to 26’C at 60 to X0”,, r.h. with 12 hr illumination per day. Standard fluorescent lamps, Izrom, 40 W, white, 4500 k with

light emission of 400 to 700 nm wave length were used (KAUFMAN, 1966). Samples of puparia were weighed. and batches of medium size (average weight 8&90mg) were used. Very small and very large puparia were discarded. Experimental flies were kept under the same ambient conditions in perspex cages 40 x 40 x 40 cm, with up to I50 flies to a cage. The series, comprising 2/3 females, were reared on a diet of sucrose crystals and water, and their cages were frequently cleaned to avoid accidental feeding on protein. Flies maintained in constant darkness were transferred at the phardte adult stage, 4X hr before the anticipated time of eclosion, to tin boxes of the same dimensions as the perspex cages. These were covered with 6 layers of thick dark cloth. Series that received U.V. irradiation were exposed for 5 hr to a standard Germicidal lamp (15 W. General Electric, G I5 TX) which emits almost exclusively radiation of 253 nm (JAGGER, 1967). Female flies, about 6 hr after eclosion. were irradiated in plastic Petri dishes with a fine mesh top, at a distance of 20 cm from the U.V. source. Afterwards they were transferred to the standard perspcx cages. The ocelli of some fly series were cauterized or dissected at the pharate adult stage. 74 hr before eclosion. A hot pin, gently pressed on the ocelli for one second, was used for cauterization. whereas excision was done by pulling the occlli out with sharpened watchmakers forceps. The wounds were not sealed, and the flies were left to hatch normally. The flies of all experimental series were killed for examination on the tenth day, and the degree of ripening of the eggs was determined. The dcvelopment of the ovaries was scored on a 7-stage scale

961

YOSEt

967 Tahlc

Series

I

, ;

I. Autngcn)

in S.

Puparial Max.

A\ cl-age

133

153

II4 Y2

120 IO’)

SCHLEI>

/~rhrl~rttrfemales separated as puparia to different weight groups

wright Min.

in mg 2

No. fcmalcs

I35 I hi IO

60

IO

x3 50

58.5 7x

Percentage of females 4 3 5 6.6 I6 14.6

26.6 14.6 4

in stages 6

19.0

6.6

7.3 2.4

of development similar to that used by ABASA (1973) for S. tihitrlis. The beginning of vitellogenesis was sometimes dilticult to discern. and doubtful spccimcns were marked as stage 3. whereas the clear cases were marked as stage 4. Flies that showed no traces of autogenic development were grouped in stage ? and females containing eggs of maximal sire or eggs and larvae were classed as stage 7. The ocellar nerves of female ilics were excised fol histological examination. They wcrc pressed under cover slips. fixed in Bouin’s tluid and stained b! EWI u’s (1963) technique for neuroscction. using diffcrent counterstains for the cell nuclei. RESULTS

Autogcnic development in three groups of flies selected from the same batch according to the puparial weight are shown in Table I. This table indicates that the weight of the puparia is a major factor which influences the future autogcnic capacity of the female. 29.9”,, of fern&s with ripe eggs were observed among the flies that hatched from the heavier than average puparia (series I ). whereas only 2.4”,, of the ovaries of series 3. where puparial average weight had been a third lower. devrlopcd to stage 7. Even though there was no puparial weight overlap between series I and 3. all stages of ovarial development were recorded in both. although varied in extent. Furthermore, even in series 2. where the puparial weight range was only IO mg (less than IO”,, of the puparial weight) varied ovarial development was noted. Here. however, 94”,, of the females of this series arc represented in only two of the developmental stages. It seems that a given stage ot autogeny is not determined by the individual weight of any single Hy. though uniformity of limited puparial weight apparTable 2. The ctl’cct of different

Scrles

Constant darknesb (‘on t 1-01 I .v. Irradiated I .v. u-radiated Bies*

light conditions

29.9 2 2.4

ently predisposes to a higher number of females falling within a narrower range of ovarial development.

Complete deprivation of light reduced the autogeny, so that the percentage of undeveloped ovaries in the females that had not been allowed any light was almost 20”; higher than in the control series kept in perspex cages. No ripe eggs were observed in these “darkness” series. A clear cut effect on autogeny was observed in flies that had been exposed to L:.v. light. 89”,, of the females reared in complete darkness were anautogenous and only 2”,, of the females exposed to ~1.v. light remained at this stage. Ninety-six per cent of the U.V. irradiated I’males. of standard size puparia. were autogenous to some degree. and 95.4”,, of the females emerged from large puparia had mature eggs following irradialion. (The differences are highly signifiP < 0.005.) As the random series used in these cant experiments contained puparia of different weights, it seems that the IW light is capable of affecting some degree of autogenic development in almost any S. ,falc,~r/trtc~female.

Cauterization of the ocelli caused an increase in autogeny: XV’,, of these flies were at stages 3 and 4 of ovarial development, compared to the 17.3”,, observed in the controls. The absence of stages 6 and 7 is not significant as the series is small and only (XX”,,were in these stages in the controls. The I .v. irradiation of previously cauterized females caused ;I I’urthcr incrcasc in autogeny (stages 2. 3 41.5”,,). In the series where the ocelli had been surgically removed. the percentage of females at stages 2 and 3 did not differ from the control series. But. on the autogeny

in S. ,firkulur~c females

Percentage of females 3 4 5

No. females

2

IIX II6 100

XY 71.4 2

4.2 7.7 2

1.1

I.1

5.9 9.5 I4

0.8 X.6 19

in stages 6

I

0.8 20

0.X 33

2.5

95.4

heavy-puparia XY

7

Ultraviolet Table

3. Autogeny

in ocelli-deprived

light and puparial

U.V. irradiated

weight

S. ,falculata

963

in comparison

to control

series

Percentage of females in stages Series Control Aies Ocelli excised flies Ocelli cauterized flies t.v. irradiated control Ocelli cauterized U.V. irradiated flies Ocelli excised U.V. irradiated flies

No. females

2

116 47 50 100

12.4 65.9 50 2

60 80

as in the ocelli-cauterized flies, the exposure to U.V. irradiation caused a significant increase (P < 0.005) in autogeny and also in the series of operated females: 557; of the Ries were in the initial stages (2 and 3) of ovarian development, compared to the 80.1% found in the control series. Autogeny in both cauterized and operated flies that had been U.V. irradiated was much lower than in irradiated untreated flies, where only 4”” were below stage 4 (P < 0.005 for the ocelli operated flies). The normal function of oogenesis in ocelli-cauterized females was found by giving a protein meal to 20 females, all of which were at stage 7 of egg development 10 days later. About 2/3 of the pharate adults, in which the ocelli had been excised. died following the operation. Mortality in all treated flies except this series. did not exceed that of the controls. ~j,,,,.o,st,,.,.f~tiorl iri t/Iv ocellar

rzerl!e

Neurosecretory cells in the ocellar nerve of the pharate adult 5. fulcrllatu had previously been described (SCHLEIPU’. 1972). These cells were found to secrete during the late pharate adult stage and to be empty at the time of eclosion of the flies. Histological examination of the ocellar nerve that had been excised at eclosion and 1, 2, and 3 days later. showed that neurosecretion was present in this nerve in the emerged adult female fly also. The cells contained little paraldehyde fuchsin (P.A.F.) positive material in the nerves at eclosion. In nerve preparations of females 2 days after eclosion, only 4 to 5 cells were deeply stained, whereas in 3 day flies, all the cells (about 12) were thus stained. (Although the technique used for the preparation of the ocellar nerve was the same, the preparations were somewhat uneven because of the different pressures that had been applied to the nerves during the fixation). DISCUSSION Two factors that seem to play the main role in influencing autogeny in Sarcophaga are considered in this study: the weight of the puparia and the lighting conditions. The effect of the weight of the puparia of a given batch on the autogeny, as described here, is appar-

3

4

5

6

7

7.7 17 22 2

9.5 10.63 16 14

8.6 2.1 12 19

0.8 2.1

0.8 2.1

24.9

16.6

41.6

40

15

12.5

9.9 10

20 3.3 15

43 3.3 7.5

ently the same as the phenomenon recorded by BAXTER et al. (1973). They ascribed the differences in the average weight of whole batches of puparia and the differences in the level of their autogeny to the density of the larvae in a population of 5. hullatu. The level of autogeny in both cases is probably an expression of the quantity of available nutrients. Such dependence on nutrients was recorded for i2luscc1 domestica that were autogenous when reared on a larval diet containing cholesterol (ROBBINS and SHORTINO, 1962) and similar examples were described for mosquitos (LEA, 1964; THOMASand LENG, 1972, etc.). The attribution of low autogeny in the small pupae of 5. bulluta to the crowding effect of a dense larval population (BAXTER et ~1.. 1973) has not been confirmed. The 5. ,falculuta reported here were all from a common batch and autogeny was correlated with differences in their puparial weight. Light conditions are the second factor that influences autogeny. The lowest degree of autogeny in the experimental series was observed in flies that had been kept in constant darkness, whereas almost a 100% autogeny was found in the U.V. irradiated heavypuparia females. It seems that the combined effect of low puparial weight and absolute darkness could completely suppress the autogeny of 5. ,~/culatu. The experiments described here were carried out with a short wave U.V. source, but series exposed to a “Sunlamp” (Philips HP, 3202) with an emission of waves longer than 300nm also showed an increase in autogeny. This “Sunlamp” has the disadvantage of emitting heat as well as U.V. light. and was therefore not used in the experiments. It is. however, possible that the U.V. of sunlight induces autogeny in Surcopl~ay~~ Ries in nature. Ultraviolet in sunlight reaching the earth’s surface is longer than 292nm (HODGMAN. 1958). Cauterization of the ocelli caused an increase in autogeny in comparison with control series and with flies in which the ocelli had been excised. The probable mode of action in this case is through heat stimulation of the median group of neurosecretory cells of the brain (MNC). This was the only observed effect of the destruction of the ocelli. Cauterization did not alter normal egg development in flies given meat in their diet, and autogeny in sucrose fed flies, in which

YO~EFSCHLEIN

964

the occlli had been excised. was the same as in the control series. The effect of U.V. irradiation on ocellideprived flies was significantly lower than that on normal (irradiated) flies. On this evidence it seems that the ocelli are the main channel through which the U.V. light exerts its effect on the process of autogeny. But the increase in autogeny in the ocellideprived irradiated flies. when compared to normal control series. indicates that the ocelli are not the only U.V. sensitive tissue and that other factors are also involved. Egg maturation in S. hu/I~t~ is initiated by the neurosecretion secreted from the MNC after a protein meal (WILKENS, 1968) and the corpus allatum is apparently involved in the process as a regulator of protein metabolism (WILKENS, 1969). The removal of this gland prevents about 30”;, of egg maturation in S. hullutcl (WILKENS, 1969) and in S. in5 (CHADAH and DENLINGER,1976). The effect of the U.V. excitation of the ocelli on the oiigenesis could be transmitted either by a neural stimulus or by the release of the neurosecretion seen in the ocellar nerve. Both the MNC and the corpus allatum are possible targets for this effect. It was shown in this study that the U.V. light caused an increase of autogeny in most of the flies. This U.V. effect when combined with a high puparial weight caused the formation of ripe eggs in 95.4”,, of the flies. The puparial weight and the amount of U.V. absorbed by the flies are therefore determining factors in autogeny of S. ,fti/c&ta.

BAX~~KJ. A., MJENI A. M., and MOKKIWNP. E. (1973) Expression of autogeny in relation to larval population density of Surcophayu hullata Parker (Diptera: Sarcophagidae). Ca/l. J. Zonk. 51. I I X9-I 193. CHADHAG. K. and DENLINGERD. L. (1976) Autogeny and endocrine involvement in the reproduction of tropical fleshflies (Diptera: Sarcophagidae). B~tornologitr. r\-p. trppl. 20. ?I 3x. DINLINGER D. L. (1971) Autogeny in the flesh fly Sarco/‘hu+r ~lr
LIA A. 0. (1964) Studies on the dietary and endocrine regulation of autogcnous reproduction in .-Lcdrs tuwiorI7wcl7~s (Wied.) J. u&. Eu~. I. J&44. ROHIJI~SW. E. and SHOKTIW T. J. (1961) Effect of cholesterol in the larval diet on ovarian development adult housefly. Nutuw. Lord. 194. 503~503.

lar nerve. Nutwc.

Lad.

236. 217-219.

THO~~AS U. and LENGY. P. (1972) The inheritance of autogcny in .AN/c.s (Fir7luycr) to&@ (Theobald) from Malaysia and some aspects of its biology. Sourht~st .4siu~ J. trap. Pddic

H/t/7 3. I63

173.

W~~.rtrnsJ. L. (196X) The endocrine and nutritional of egg maturation

ABASAR. 0. (1971) Reproductive biology of Sarcophu~a tihiulis (Diptera: Sarcophagidae). 11. Morphology of external and internal reproductive organs. .417r1.mt. Sock. .4m 65. 40&405.

in the

ScHLt IN Y. (1972) Postemergence growth in the fly Sarcophqu /u/cdrrtu initiated by neurosecretion from the occl-

hid.

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