Food quality and quantity in relation to egg production in Locusta migratoria migratorioides

J. Insect Physiol., 1975, Vol. 21, pp. 1551 to 1558. Pergamon Press. Printed in Great Britain.

FOOD QUALITY AND QUANTITY IN RELATION TO EGG PRODUCTION IN

LOCUSTA

MIGRATORIA

MIGRATORIOIDES

A. R. MCCAFFERY Centre for Overseas Pest Research, College House, Wrights Lane, London W8 5SJ, England (Received 15 January 1975) Abstract-OBcyte development is not initiated when female Locusta migratoria migratorioides are fed on poor, low-protein Agropyron repens. Survival on this diet is improved by the provision of water and small quantities of lush A. repens. When maturing female locusts (with developing ogcytes), previously fed on lush grass, are provided with the poor-quality grass the rate of egg pod production is reduced and terminal oiicyte resorption is increased. The final percentage resorption and the possibility of oviposition is determined by the total quality of food during vitellogenesis. In poorgrass fed locusts the levels of ingestion and utilization are low and suggest that quantitative factors are likely to be critical. Quantitative studies show that the provision of gradually decreasing amounts of A. repens produces corresponding decreases in the rate of egg pod production and increases in terminal oiicyte resorption. When the quantity of food ingested is reduced, the rate of oijcyte development is first reduced, followed at lower levels of feeding by an increase in terminal oijcyte resorption. Ingestion of less than 80 mg (dry weight) of grass/female per day is insufficient to initiate oijcyte development in locusts whose somatic growth period is normal. The significance of these results is discussed. INTRODUCTION THE RESORPTIVE breakdown of developing terminal oocytes is one of the major factors limiting the egg production and consequently the population size of Locusta migratoria in the Middle Niger outbreak area (FARROW, 1972). During vitellogenesis the fat body produces specific proteins which are released into the haemolymph and are subsequently taken up by the developing oiicytes (HILL, 1965). This process is hormonally controlled (HIGHNAM et al., 1963a; MINKS, 1967). It is thought that shortages of yolk proteins and of a gonadotrophic hormone from the corpora a.llata cause the resorptive breakdown of a proportion of the terminal oijcytes (HIGHNAM et al., 1963b). The nutritional state of the locust is therefore likely to have profound effects on yolk synthesis and oScyte development. Furthermore, feeding may affect the activity of the neuroendocrine system which may in turn affect egg development (HIGHNAM et al., 1966; HIGHXAM and MORDUE(LUNTZ), 1974). As part of a study of the nutritional and endocrine control of normal and resorptive egg development, the experiments described in the present paper examine the extent to which feeding is a factor in the initiation and maintenance of oijcyte development. MATERIALS

AND MJZHODS

Adult female Locusta migratoria migratorioides were used as experimental animals in this study.

Locusts were bred at the Centre for Overseas Pest Research and reared under crowded conditions in glass-fronted cages (HUNTER-JONES, 1961). Groups of 10 experimental females were removed from stock cages on emergence and placed in 12 1. cylindrical Perspex cages with an equal number of males of the same age. Control and experimental cages were then kept in constant environmental cabinets providing day and night temperatures of 35 and 25°C respectively, with relative humidities of 25 and 30% respectively. Stock and control animals were given excess (ad lib.) amounts of fresh Agropyron repens daily. Old grass was removed prior to daily feeding. Feeding treatments were carried out as described below and administered daily. Qualitative

feeding studies

The amounts of grass eaten during qualitative feeding studies were measured since it was considered that effects on reproductive performance apparently due to qualitative grass differences might in fact be due to quantitative differences in ingestion and utilization. (1) Poor and lush grass diets. In the first series of experiments, groups of 10 newly emerged females were given excess known quantities of lush green Agropyron (dry matter, 12% ; water content, 88% ; crude protein content (see below), 22.4% of dry weight) or similar known amounts of poor-quality Agropyron (dry matter, 40% ; water content, 60% ; crude protein content, 10.7% of dry weight) which

1551

A. R. MCCAFFERY

1552

had moist green central stems and browning leaf blades. Grass remaining in the cages and faeces produced were removed at 2 or 3 day intervals and dried to constant weight. The dry matter food intake and faeces production was thus measured for each treatment. Since oijgenesis is affected by the presence of males (HIGHNAM and LUSIS, 1962), the females were caged with 10 males of the same age which had their mouths sealed with wax so they were unable to eat. The males were starved for 48 hr before the experiment so that they produced no faeces and were replaced by fresh, similarly treated males, after 48 hr with the females. (2) Supplemented poor diet. In a second series of experiments, cages of 10 Locusta females were set up with non-eating males as described above. One group of females was given 1.5 g of lush Agropyronl female per day (water content, 81%) equivalent to 280 mg dry weight/female per day). A second group was fed on poor-quality Agropyron at a rate of 0.5 g/female per day (water content 43%, equivalent to 280 mg dry weight/female per day) together with a lush grass supplement of 0.2 g/ female per day (dry weight equivalent, 40 mg/ female per day). All cages were provided with fresh tap water daily in Petri dishes. In this way, any possible effects due to a lack of water or trace substances could be investigated. (3) Successive diet changes. To reduce the adverse effects of poor feeding during somatic growth, one group of 10 females was fed in a further experiment on the lush green diet until at least the end of somatic growth when yolk synthesis and sexual activity begin (day 22). From day 23 the poor diet was provided. A second group of 10 females was given the reverse feeding regimes in which the poor diet was provided up to day 21 followed by the lush diet from day 22. Total dry food intake and faeces production in these two groups was measured as before.

Quantitative

feeding studies

Using standard lush green Agropyron, a series of quantitative feeding studies was carried out as described below. (1) Group-fedfemales. In the first series of experiments, groups of 10 Locusta females were fed ad lib., until day 15. From day 16 groups of females were fed on various amounts of lush grass from 40 to 240 mg dry weight/female per day. Controls were continuously fed ad lib. on lush grass. Experimental females were caged with males of the same age and all groups ate all the grass provided. All the cages were provided with a source of water. (2) Individually fed females. Two further groups of females were fed individually for 5 hr in glass jars of 1 1. capacity. After feeding, the females were returned to the cages in which normal fed

males were present but in which no further food was provided. In this way the stimulus resulting from moderate crowding and the presence of males was maintained whilst individual feeding levels of the females were precisely monitored. The two groups of females were fed ad lib. on lush Agropyron from fledging to day 16. From day 17 restricted amounts of lush Agropyron were placed in the individual feeding jars such that the amounts of grass consumed by the locusts were calculated to be 35 rt 3 and 77 + 15 mg dry weight/female per day for the two groups. A third group was fed ad lib. throughout the experiment as a control.

Crude protein content of grass The total nitrogen content of 0.1 g samples of dried Agropyron was determined by the Kjeldahl method (VOGEL, 1961), and the result termed the crude protein content (M.A.F.F., 1971). The determinations were repeated several times. Mean values obtained for the crude protein content were: lush quality A. repens-mean crude protein content 22.4 rt 1.0% (n = 5) ; poor quality A. repens-mean crude protein content 10.7 + 0.9% (n = 4).

Estimation

of egg production and resorption

Egg pods were collected daily and the number of eggs in each pod counted. At the end of the experiment the females were killed and the number of ovarioles in each female determined, thus giving the percentage of terminal oiicyte resorption. The resorption bodies at the base of each ovariole were observed and the percentage resorption correlated with that obtained above. In all cases the percentage resorption quoted refers to that found at oviposition.

Estimation

of haemolymph protein and blood volume

The total protein concentration of the haemolymph was measured by the method of LAYNE (1957) using a bovine serum albumin standard. From measurements of blood volume (MORDUE and GOLDSWORTHY, 1969)and the protein concentration obtained above, the total haemolymph protein was determined. RESULTS

Qualitative

studies

(1) Poor and lush grass diets. Two groups of 10 females were fed from emergence on qualitatively differing samples of Agropyron as described earlier. The females ate and utilized less of the poor grass, on a dry weight basis, at all stages of somatic and reproductive development (Fig. lc), and no marked increase in ingestion occurred at any stage compared with lush-grass fed females. Poor diet females gained weight normallv during the first part of

Food quality and quantity

ExperftWtt

b

in relation to egg production

in Locusta

1553

Experiment B

A

3.0

10

20

Da-after

Days after ecdysis

30

40

ecdysis

Fig. 1. (a) The mean level of terminal oijcyte resorption ( + S.E.M.). (b) The mean live body weight (+ S.E.M.). (c) The levels of food intake (upper line) and faeces production (lower line) (shaded area represents quantity of food utilized) of adult female L. migvatovia fed on lush or poorquality Agropyron. Table

Feeding

1. The clutch size and rate of terminal oijcyte resorption various diets

regime

Pods laid/ female per day (mean)

Mean clutch size + S.E.M. -

a. Poor quality Agropyron Lush quality Agropyron

Nil 0.13

b. Poor quality Agropyron (supplemented) Lush quality Agropywm

Nil

54.5 + 1.5 (20) -

of adult female L. migratovia

Mean ovariole no. + S.E.M. so.4* 1.7 (8) 82.4k2.1 (10) 77.2k2.1

(10)

Mean ye resorption

fed on

Comments

33.93 -

0.15

46.1 f 2.2 (21)

74.3 + 2.3 (10)

37.93

c. Poor quality Agropyron up to day 21 + Lush quality Agropyron day 22 on

0.06

38.3 k4.6

76*4&l-3

(10)

49-86

Laying rate increasing with time. Rate of resorption tending to 35 per cent approx.

d. Lush quality Agropyron up to day 23 + Poor quality Agropyron day 24 on

0.02

30.8 + 2.4 (4)

76.3 + 2.0 (10)

59.65

Laying rate decreasing to zero. Rate of resorption tending to 100 per cent

(12)

somatic growth but subsequently lost weight gradually and some late mortality occurred. The live body weight of lush-grass fed females was significantly higher than that of the poor-grass fed females from day 12 after ecdysis (P< 0.001) (Fig. lb). Mating behaviour was seen on day 21 in the lushgrass fed females, followed by copulation on day 22 and the first oviposition on day 25. Subsequently egg pods were produced continuously and the level

of oiicyte resorption was maintained at about 33.9 per cent (Table la). In contrast, the poor-grass fed females exhibited no sexual activity and no egg pods were laid. Dissection of these females showed that the oiicytes had developed to a length of 1.5 mm during somatic growth, but no vitellogenesis had taken place. The blood protein concentration of the poor-grass fed females fell from day 13 whilst that of the lushgrass fed females rose (Table 2). The blood volume

1554

A. R. MCCAFFERY

Table 2. Blood volume, haemolymph tration,

and total haemolymph

protein concenprotein of adult female

L. migratoria fed on lush and poor diets of A. repens (n = 5)

Age after ecdysis (days) 4 13 20 22 29

days days days days days

Age after ecdysis (days) 4 13 20 22 29

days days days days days

Mean blood volume (~1) rt S.E.M.

Exfaeriment A

Lush-grass fed

Poor-grass fed

t

P

231.5 rf:5.07 256.8 f 20.1 301.4+22.6 329.6 +48*2 324.4+ 57.1

236.2+ 16.72 250.8 + 16.8 342.Ok25.4 372.0 + 60.2 165.0 + 3.8

0.27 0.23 1.20 0.55 2.09

NS NS NS NS NS

b

Experiment B

-I

Mean haemolyrnph protein cont. (g/l00 ml) f S.E.M. Lush-grass fed

Poor-grass fed

t

P

3.91 f 0.29 4.56 rl:0.29 4.74kO.13 4.63 f 0.60 5.80 f 0.46

3+X4+0.14 4.31+ 0.16 2.88 + 0.38 2.51 *O.lS 1*60?0.38

0.22 0.76 4.67 3.35 6.23

NS NS < 0.005
Mean total haemolymph protein (mg) f S.E.M.

Age after ecdysis (days)

Lush-grass fed

Poor-grass fed

t

P

4 13 20 22 29

9.06+0.19 10.86 + 0.39 18.85 + 1.44 20.68 + 5.37 23.86 + 5.22

9.06+0.13 IO.822 0.66 12.54+1.15 12.08+1*90 3.52 2 0.92

0 0.05 3.42 1.51 5.22

NS NS
days days days days days

earlier. Before the change of diet the lush-grass fed females ate large amounts of food and the quantities utilized were similar to those observed during the first experiment although the absolute amounts ingested were higher (Fig. 2~). Despite a

NS, not significant. of poor-grass fed females was maintained until about day 24 after which it fell to a level below that of the lush-diet group. As a result, the total blood protein of the poor-grass fed females fell sharply during the last week of the experiment (Table 2). (2) Supplemented poor diet. In these experiments poor diets of Agropyron were supplemented with small quantities of lush green grass as described earlier and all experimental cages were provided with a source of fresh water. No mortality occurred in the poor-diet females as in the previous experiments. Egg production and oiicyte resorption in the lush-grass fed group of females was similar to that observed in the previous experiment (Table lb) but poor-grass fed females given lush grass supplements and water showed neither sexual activity nor vitellogenesis. (3) Successive diet changes. Experiments in which the diet quality was changed at particular times during development were carried out as described

ti

30’

40

Days after ecdysis

50

10

:

Days after ecdysis

Fig. 2. Effects of changes in Agropyron diet quality on: (a) The level of terminal oijcyte resorption. (b) The mean live body weight (+S.E.M.). (c) The levels of food intake (upper line) and faeces production (lower line) (shaded area represents quantity of food utilized) of adult female L. migratoria. fairly high intake, the rate of food utilization in the initially poor-grass fed females decreased until faeces production virtually equalled food intake. Correlated with this, the lush-grass fed locusts gained weight steadily whereas the initially poorgrass fed females managed only to maintain their emergence weight (Fig. 2b). Following the reversal of diet on day 23 the initially lush-grass fed females maintained a fairly high level of ingestion and utilization of food for 10 days. After this time the intake and utilization of food fell markedly (Fig. 2~). When initially poorgrass fed females were fed on a lush diet, the overall food intake, although similar to that just prior to the change of diet, resulted in a much increased level of food utilization (Fig. 2~). The former animals maintained their body weight at the time the diet was changed, whilst the latter gained weight following the change of diet at a rate of 0.065 g/day (lush-grass fed controls gained weight from emergence at a rate of O-048 g/day) (Fig. 2b). Sexual activity in the initially lush-grass fed females began on day 22, copulation occurred on day 25, and the first egg pods were laid on day 26. Initially poor-grass fed females showed sexual

. Food quality and quantity in relation to egg production in Locusta activity 5 days after the change of diet on day 26, copulation occurred on day 29, and the first egg pods were laid on day 30. The latter females then laid pods continually until the experiment was terminated (Table lc). The rate of egg pod production was initially low but increased during the period of the experiment. The whole group of 10 females fed initially on lush grass followed by poor grass laid only four pods in total (Table Id). The later these pods were laid, the higher was the observed level of oijcyte resorption (Fig. 2a). Since the development of these clutches was not synchronous, the rate of oijcyte resorption and resultant clutch size varied according to the length of time that the female was able to eat lush grass. Three females showed no signs of vitellogenic activity, whilst a further three showed 100 per cent resorption. Egg production subsequently ceased in this group of females. Females fed first on poor grass followed by lush grass laid their first egg pods 9 days after the change of diet. High rates of terminal oocyte resorption were associated with the development of these first pods but later egg pods had higher clutch sizes as a result of decreased resorption of oScytes (Fig. 2a). This level of oticyte resorption took 2 weeks to fall to a control level of about 30 per cent. Since the intake of the different qualities of grass was not equal, a series of quantitative feeding experiments was carried out.

1555

from the time of the first oviposition continuous egg production occurred in all groups except those fed 40 mg dry weight/female per day. In this latter group only two egg pods were produced during the experiment, both by the same female. Of the remaining females all but one showed signs of vitellogenic activity accompanied by small single resorption bodies in all the ovarioles due to total resorption of all oiicytes. No further initiation of gonotrophic cycles took place. The single female able to produce two egg pods must be considered as atypical. Since group feeding was adopted, it may well have been possible for such a female to obtain sufficient food to initiate egg development at the expense of other individuals. Females fed ad lib. had the highest rate of egg pod production, whilst females fed 200 and 240 mg dry weight/day had somewhat lower rates (Fig. 3). Further decreases in the quantity of food

q Eggpodsbi q ReMrptial

:1:: : :. -80

.70

-60

5 g 8

-50

“E

-40

= r 5

-30

;

-20

E %

?!

8

Quantitative

studies

(1) Group-fed females. Groups of 10 Locusta females were fed with various amounts of lush Agropyron. Females given 240 mg dry weight/ female per day of lush grass gained weight in a similar fashion to the ad lib. fed controls. The provision of smaller quantities of food had a correspondingly greater effect on the reduction in fresh body weight (Table 3). Copulation took place on days 18 to 19 in all groups. First egg pods were laid on day 19. There was no apparent, correlation between the amount of food available and the time of oviposition in these experimental groups and

1 :

Starved

40

80

Q

120

Dry wt.(mg) of

grass eater&!/day

‘Ad lil i

Fig. 3. The rate of egg pod production and level of terminal oiicyte resorption of adult female L. migratoria fed on various quantities of lush Agropyron.

Table 3. Fresh body weight of adult female L. migratoria fed on various amounts of Agropyron from day 16 Feeding regime (mg dry wt./female per day after day 16) 40 80 120 160 200 240 Ad lib.

Mean live body weight (g) ( f S.E.M.) Day 5

-10

Day 14

Day19

Day 26

1.49&0.07 l-65+0.06 l-72+0.03 1*77*0.06 1.73kO.04 l-74&0.04

2.21kO.05 2.46kO.07 2-33kO.06 2.38-+0*07 2*21+0.06 2.27+0-05

2.01*0.09 2.32kO.07 2.32+0-06 2-46&O-06 2.34kO.05 2*37+0'06

1-90~0~08 2.22kO.07 2.48+0-07 2.60+0*10 2.70+0.09 2*99+0.12

1.75 * 0.04

2.29 f o-07

2.55 f 0.05

3.04+0.08

1556

A. R.

MCCAFFERY

supplied resulted in corresponding reductions in the rate of egg pod production (Fig. 3). The number of ovarioles in the ovary was similar in all the groups, and females given 240 mg dry weight of grass/day produced mean clutches of 62-13 + 2.41 eggs which was not significantly different (P> O-2) from the mean clutch size of 65.30 z!zl-23 found in ad lib. fed controls. Signitlcant reductions in clutch size and increases in terminal oijcyte resorption (Fig. 3) were found as the food provided was decreased. Using the results shown in Fig. 3 for the rate of egg pod production and percentage terminal oiicyte resorption, the total number of eggs produced per female per unit time can be calculated (Fig. 4). An approximate straight line relationship between the level of feeding and the total egg production is obtained.

Week

123

35mg

1

week

2

3

1 week9: 2 3 Ad lib

77mg

.

l-l

week

123

~~%Gng>

weeks:

123

l?i

77mg Ad lib of grass eaten&hay

Fig. 5. The rate of egg pod production and terminal oijcyte resorption of adult female L. migratoria at various times after the beginning of sub-optimal feeding. &3edj

40

80

120

160

200

240

‘tilib’

Dry wtlmg) ofgrass eaten/$/day

.30-

Fig. 4. The total egg production per unit time of adult female L. migmtoria fed on various quantities of lush Agropyron.

(2) Individually fed females. To confirm these results, three groups of Locusta females were fed individually in glass jars as described earlier. The two groups of females eating reduced amounts of food laid their first egg pods on days 15 and 16. In the first week after the change of diet, the females given 35 mg dry weight/day laid a few more egg pods (Fig. 5), then their egg production stopped during the second week as a result of total otjcyte resorption (100 per cent) or the lack of initiation of further vitellogenesis (Fig. 5). The females given 77 mg dry weight/day continued to lay egg pods but the level of oiicyte resorption was higher than that seen in the group of females fed ad lib. Examination of rates of egg pod production and levels of terminal oocyte resorption found in these experiments reveals that initial reductions in food ingestion result in decreased rates of egg pod production. Further reductions in ingestion cause increases in the level of oocyte resorption (Fig. 6).

.25-

.20-

resorption

_

Fig. 6. The rate of egg pod production found in adult female L. migratoriushowing various levels of terminal oScyte resorption when fed on various diets (each point represents a mean from 10 animals).

Food quality and quantity in relation to egg production in Locusta DISCUSSION Failure to produce mature oijcytes may arise in one of two ways: there may be a total failure to initiate vitellogenesis, or developing oBcytes may be resorbed. In the current experiments the failure to initiate vitellogenesis could be due to one of three causes: (a) the composition of the protein in the grass is incorrect for the production of specific vitellogenins, (b) the quantity of nutrient materials for the construction of vitellogenic proteins is too low, or (c) ingestion of food materials is low causing a reduction in the activity of the cerebral neurosecretory system, and a consequent inhibition of the corpora allata (GIRARDIE,1964) and egg development. The last possibility seems to be precluded by the experiments in which small quantities of lush food and water were added to poor grass since it is generally supposed that activity within the endocrine system is generated by the stimulation of foregut stretch receptors during increased feeding (HIGHNAMet al., 1966; HILL et al., 1966). It remains a possibility that correct nutrient levels for oiicyte development trigger activity within the endocrine system. Grasses of differing quality appear to be ingested in differing amounts. Great care must therefore be taken in the interpretation of these results. Effects which appear to be due to the intake of particular grasses may in fact be due to a difference in the absolute amount of grass ingested. The quantitative feeding studies presented here support this view and attempt to define the minimum levels of ingestion of Agropyron required for the initiation of egg development in Locusta. Lack of water does not appear to be a significant factor in the failure to initiate egg development in poor-grass fed females. The blood volume of these females is maintained until after the normal beginning of vitellogenesis (about day 18). It is only in the final stages of the experiments with poor grass alone that water shortages probably affect survival. This effect is most likely due to the reduced intake of food. Hence it may be concluded that the failure to initiate vitellogenesis arises from the poor quality or quantity of the food itself. Vitellogenesis, once initiated, continues provided adequate food is available. The final level of oijcyte resorption is a measure of the nutritional status of the female during the process. Transfer of females to a poor diet (either qualitatively or quantitatively sub-optimal) results in oijcyte resorption. Following a change from poor- to lush-grass feeding, fairly rapid oviposition occurs although the initially high level of terminal oocyte resorption and low rate of egg pod production suggest that fat body metabolism does not fully recover for some weeks. It is most probable that during somatic

15.57

growth fairly large amounts of food are ingested in order that the fat body may develop to a point at which vitellogenic protein synthesis can begin (MORWE (LUNTZ) and HILL, 1970; HILL et al., 1968). Poor-grass feeding during this period may reduce the availability of necessary nutrients and retard or abolish fat body development. This will therefore have to be completed before the level of egg development is comparable to that of the controls. Continuous egg pod production requires the ingestion of at least 75 to 80 mg (dry weight) of lush green Agropyron per female per day. This level appears to allow the initiation of successive vitellogenie cycles but the rate of egg pod production is low and the level of terminal oi+zyte resorption is high. Quantities of at least 240 mg/day are required for a rate of development and a level of resorption which approach those seen in control ad lib. fed animals. Oiicyte resorption may not be the critical factor limiting fecundity since the first effect of reduced food intake is to reduce the rate of oijcyte development rather than the number of eggs resorbed. Using Locusta migratoria cinerascens and artificial diets, PETAVY (1966) quotes similar effects. The process of vitellogenesis is horn-tonally controlled (HIGHNAMet al., 1963a) and feeding may a#ect the release of hormonal factors from the corpora cardiaca (HIGHNAM et al., 1966; HIGHNAM and MORDUE (LUNTZ), 1974) in turn influencing the corpora allata (MCCAFFERY and HIGHNAM, 1975). Since resorption of terminal oijcytes is considered to be a result of competition between developing oiicytes for yolk protein and corpus allatum hormone (HIGHNAMet al., 1963b), it is clear that feeding may affect the vitellogenic process by altering the concentration of nutrients in the haemolymph and/or by affecting the hormonal balance of the insect. The effects of feeding on egg development may therefore occur at one or more of several. stages. Feeding may affect the development of the fat body during somatic growth. This will have later effects on vitellogenesis. Initiation of vitellogenesis fails when the quantity of usable food ingested falls below certain levels. Both resorption and the rate of egg development are affected, to differing degrees, when the quantity of utilizable food ingested is low. The degree to which the neuroendocrine system is responsible for failure of egg development in particular conditions is uncertain. The profound effects of feeding on the reproductive processes in the female locust are being further investigated in the light of known and possible .mechanisms of endocrine control. Acknowledgements-My thanks are due to Dr. R. F. CHAPMANfor helpful discussions and for reviewing the manuscript and to Dr. E. A. BERNAYS for useful suggestions and advice.

A. R. MCCAFFERY

1558 REFERENCES

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HILL L., MORDUEW., and HIGHNAM K. C. (1966) The endocrine system, frontal ganglion, and feeding during maturation in the female desert locust. r. Insect Physiol. 12, 1197-1208. HUNTER-JONES P. (1961) Rearing and Breeding Locusts in the Laboratory. Anti-Locust Research Centre, London. _ LAYNE E. (1957) Soectroohotometric and turbidometric methods‘ for ‘measuring proteins. Meth. Enzym. 3, 448. MCCAFFERY A. R. and HIGHNAMK. C. (1975) Effects of corpora allata on the activity of the cerebral neurosecretory system of Locusta -migratoria migratorioides R. & F. Gen. coma. Endocr. 25. 358-372. MINISTRY OF AGRI&JX.TURE,FISHERIES AND FOOD (1971) Grassland Practice No. 7; Grass as a Feed. M.A.F.F. leaflet 134. MINKS A. K. (1967) Biochemical aspects of juvenile hormone action in the adult Locusta migratoria. Arch. nt!erl. Zool. 17, 175-257. MORDUE(LUNTZ) A. J. and HILL L. (1970) The utilization of food by the adult female desert locust, Schistocwca gregaria. Entomologia exp. appl. 13, 352-358. MORDUE W. and GOLDSWORTHY G. J. (1969) The physiological effects of corpus cardiacurn extracts in locusts. Gen. camp. Endow. 12, 360-369. PETAVY G. (1966) Rannorts entre alimentation et physiologie ’ chez un- -insecte: Locusta migratwia cinerascens Fab. (Orthoptera, Acrididae)-I. Utilisation de milieux nutritifs artificiels. Ann. N&r. Aliment. 20, 279-299. VOGEL A. I, (1966) A Text-book of Quantitative Inorganic Analysis. Longman, London.