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Influence of diet composition and crowding on wing production by the aphid Myzus persicae
r. Insect Physiol., 1971,Vol. 17,pp. 321to 328.Pergamon Press. Printed in Great Britain
INFLUENCE OF DIET COMPOSITION AND CROWDING ON WING PRODUCTION BY THE APHID MYZUS PERSICAE 0. R. W. SUTHERLAND* Division of Entomology,
and T. E. MITTLER
University of California, Berkeley, California 94720 (Received 13 June 1970)
Abstract-Two factors have been shown to affect alata-production in a Californian strain of Myzus persicae. Contact between adult apterous females increases the proportion of alatae in their progenies as, to a lesser extent, does contact between the larvae themselves. In the absence of behavioural interactions between the aphids, the relative proportions of apterae and alatae can be influenced by the diet the mothers and their larvae receive. By suitable dietary adjustments, it is therefore possible to increase or decrease the proportions of alatae among the progeny of isolated as well as of grouped aphids. In neither case is it necessary to isolate the larvae directly after their birth in order to observe the influence of diet composition on their wing dimorphism. INTRODUCTION
As AN INSECT of considerable economic importance, Mazes persicae has been the subject of numerous studies, which recently have been reviewed by VANEMDEN et al. (1969). It is clear that although interest in the polymorphism of this aphid is widespread, the question of what factors are involved in the production of alate virginoparae, and at what point in the life cycle they exert their influence has been relatively neglected. As has been found to be the case with Aphis craccivora (JOHNSON, 1965, 1966) and Acyrthosiphon pisum (SUTHERLAND, 1969a, b), at least two factors, crowding and the composition of the diet, are directly involved in the control of wing dimorphism in M. per&z. In an investigation of the effects of crowding, BONNEMAISON (1951) found that interactions between new-born larvae (less than 24 hr old) of his French strain of M. persicae induced many of these to become alatae. Since Bonnemaison failed to obtain a convincing response by crowding adult apterae, he concluded that tactile contact between first instar larvae was of over-riding significance in the production of the alate morph. However, the results of AWRAM(1968) with an English strain of M. persicae indicated that prenatal effects of crowding may be at least as important as post-natal effects. Evidence that pre-natal crowding is highly effective in inducing alata-production in a Californian strain of the species was previously obtained by Mittler
and Kunkel (unpublished). * Present address: Entomology Division, D.S.I.R., 321
Nelson, New Zealand.
322
0.
R. W. SUTHERLAND AND T. E.
MITTLER
That nutritional factors may have a pronounced effect on wing dimorphism has been demonstrated for M. persicae using artificial diets and host plants (MITTLER and SUTHERLAND, 1970). In these studies the greatest numbers of alatae were typically produced on ‘complete’ artificial diets, while on nutritionally imbalanced diets the proportions of apterae generally increased, sometimes spectacularly. Apterous adults and larvae were maintained in approximately constant numbers on these diets, on the assumption that interactions would be similar on the different diets. This may not have been justified, since it, is known that the crowding response is not necessarily a function of the numbers of aphids present per unit area but of the numbers of contacts that occur among them (JOHNSON, 1965 ; LEES, 1966, 1967; SUTHERLAND,1969a). Although MITTLER and KLEINJAN(1970) provided a partial defence to this objection by pointing out that the greatest restlessness (and presumably maximum interaction) occurred on imbalanced diets on which alata-production was minimal, the question of the relative influences of tactile stimulation and of diet composition remained open. The present study was, therefore, undertaken in order to elucidate the status of these two factors in the control of wing dimorphism in this species, and to determine whether the composition of the diet could, in the absence of any crowding stimulus, affect significantly the proportions of winged and wingless virginoparae. To this end, four diets differing from the standard diet were tested. As MITTLER and KLEINJAN(1970) had found that a diet incorporating half the routine concentration of all the amino acids increased the proportion of apterae, while one lacking ascorbic acid favoured an increase in alata-production by grouped aphids, these two diets were among the four tested. A diet lacking valine on which a slight increase in alata-production was previously observed (DADD, 1968), was also offered to isolated aphids. The fourth diet was one containing three times the routine amount of proline and half that of glutamine. It is known that increased alata-production is sometimes associated with physiological stress of the host plant (LEES, 1966). BARNETT and NAYLOR (1966) had found that wilting plants (Bermuda grass) contained increased amounts of proline (other amino acids showing a concomitant decrease in concentration) and it seemed possible that an artificial diet reproducing to some extent this situation might also have some influence on form determination. MATERIALS AND METHODS Groups of 10 to 20 apterous virginoparae were reared on individual radish seedlings (mostly still in the cotyledon stage) in a controlled-environment chamber at 20 _+1°C and in a photoperiodic regime of 16 hr light, 8 hr dark, per day. All experiments were carried out under these conditions. The basal composition of the artificial diets used in this study incorporated the modifications by MITTLER et al. (1970b) of the diet developed by DADDand MITTLER (1966). The diets were aseptically encapsulated in sachets and presented to the aphids in the manner previously described (DADD et al., 1967). The aphids were given fresh sachets every 3 days. Apteriform larvae in the fourth instar were removed from the radish seedling
INFLUENCE
OF DIRT COMPOSITION
AND CROWDING ON MYZUS
PERSICAE
323
culture and caged thereafter in isolation or in groups of 10 on sachets of the various diets tested. On each of 7 days, the youngest (smallest looking) daughter produced in each previous 24 hr period by each isolated aptera was caged singly on another sachet of the same diet as that given to the mother. The remaining progeny of all the isolated apterae were pooled and caged in groups of 25, also on fresh sachets of the maternal diet. Of the larvae produced daily by each group of 10 apterae, 25 of the youngest were placed in isolation and the remainder caged in groups of 25 on sachets of the maternal diet. Where apterae and their daughters were reared exclusively on radish seedlings the former were placed in isolation on the seedlings as first instar larvae. Each day, the youngest daughters deposited in the previous 24 hr were isolated on separate seedlings. The youngest larvae, probably between 1 and 6 hr in age, were chosen for isolation because they were least likely to have been influenced by post-natal tactile stimulation. RESULTS
Standard diet The importance of post-natal crowding in M. persicae is clearly confirmed by the data presented in Fig. 1. When the new-born offspring of isolated mothers were themselves isolated, the number of alatae that appeared was small: it was maximal 100 90
80
I 1
I
1
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2
3
4
I
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6
7
DAY OF LARVIPOSITION FIG. 1. Per cent of apteriform individuals among the progeny of isolated (A, B, and S) and grouped (C and D) apterae of M. penicae. Larvae deposited on each of 7 successive days on standard diet (A-D) were raised on the diet in isolation (A and C) or in groups of 25 (B and D). Larvae deposited on radish seedlings were raised in isolation on similar seedlings (S).
324
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at the onset of parturition (28 per cent of the day 1 larvae) but declined rapidly (Fig. 1, A). A substantial increase in the percentage of alatae was found when the progeny of isolated parents were reared in groups of 25 individuals (Fig. lB), the difference of 20 to 25 per cent between the two treatments being surprisingly constant throughout the experiment. The progeny of grouped mothers, whether isolated or grouped mostly became alatae (Fig. 1, C and D). Although there was some difference between the isolated and grouped daughters born on the first day of larviposition, the proportions of apterae and alatae hardly differed subsequently. In view of the low proportion of apterae in the progenies of grouped mothers in comparison with those of isolated females, it must be concluded that there is a pre-natal maternal response to tactile stimulation. The possibility exists that (given the numbers in which larvae are deposited within a 24 hr period by the grouped mothers) mutual interactions between the larvae and between the adults and their larvae in the first 6 to 8 hr of larval life are as (or more) effective in inducing alate development as are interactions subsequent to this period. Hence, the high proportions of alatiforms among larvae isolated subsequent to having been born under crowded conditions could be due to such interactions as well as the interactions between the adults (Mittler and Kunkel, unpublished). Before testing diets differing from the standard diet it was desirable to establish whether the results were biased by choosing for isolation the youngest of the daughters of isolated mothers. An experiment was therefore performed in which both first- and last-born larvae were removed daily from their mothers and isolated (Fig. 2). The results do not indicate a significant difference between the two lots 100
80
1
I
I
2
3
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4
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1
5
6
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7
DAY OF LARVIPOSITION FIG. 2. Of the 4 to 7 larvae deposited by each of 20 to 25 isolated apterae of M. persicae on each of 7 successive days on standard diet, the youngest and oldest were raised in isolation on the diet; values for the proportions of apteriforms among these are joined by solid and broken lines, respectively.
INFLUENCE
OF DIET
COMPOSITION
AND
CROWDING
ON
MYZUS
PERSICAE
325
of larvae. Apparently behavioural interactions within the daily batches of progeny (5-8 larvae) were not numerous enough to induce a crowding response. Radish seedlings Although the highest proportions of apterae developed among larvae deposited and reared in isolation on standard diet (Fig. 1, A), a small proportion of alatae continued to be produced throughout the 7 days of the experiment. No alatae developed among larvae deposited and reared in isolation on radish seedlings (Fig. 1, S). Whereas the standard artificial diet might induce the production of some winged individuals, previous studies (MITTLER and SUTHERLAND, 1970; MITTLER, et al., 1970a) indicate that it lacks a factor present in the seedlings which, acting either pre- or post-natally, can cause larvae born and reared on such host plants to become apterae. Non-standard
diets
When the standard diet was replaced with diets lacking various components or containing increased amounts of others, some changes in the relative proportions of apterae and alatae were found. In these tests only isolated mothers were employed, but their larvae were either isolated (Fig. 3) or grouped (Fig. 4) as before. 100 90 80 w
a 5
70 60
l-
% 8
50 40
1
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3
4
5
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7
DAY OF LARVIPOSITION FIG. 3. Per cent of apteriform individuals among the progeny of 20 to 25 isolated apterae of M. persicae deposited on each of 7 days on five different diets. Each day a single larva from each aptera was raised in isolation on the diet on which it was born. A, standard diet; @, diet with no ascorbic acid; x , diet with half routine level of all amino acids ; 0, diet with no valine ; 0, diet with three times the routine level of proline and half that of glutamine.
O.R. W. SUTHERLAND AND T.E.MITTLER
326
While in general fewer alatae were found among isolated than among grouped larvae, a comparison of the data indicates that in both cases each diet influenced the form of the offspring in the same sense. The proportion of alatae increased considerably when the insects were fed on a diet lacking ascorbic acid regardless of whether or not the larvae were grouped. When a diet containing three times the standard amount of proline and one-half the standard amount of glutamine was 100 90
80 %
70
Ei
60
k a
50
30 20
i
i
i
i
4
k
t
DAY OF LARVIPOSITION FIG. 4. As in Fig. 3 but larvae deposited each day were raised on the diets in groups of 25 to 30.
offered the proportion of alatae was also increased, but only among the larvae born on the first day. The diet lacking valine had little influence on alata-production here. On the other hand, the proportion of apterae increased when the insects were fed on a diet containing half the normal concentration of all the amino acids. This was particularly noticeable in the case of the grouped larvae indicating that the influence of the dietary composition was strong enough to overcome almost entirely the response to tactile stimulation. As the proportions of apterae among the isolated offspring of isolated mothers reared on standard diet were already high (Fig. 3), a convincing increase in the numbers of apterae could not be demonstrated by this treatment. DISCUSSION
The important role of tactile stimulation in the production of alatae is clearly established by the data presented in Fig. 1, from which it can be seen that both
INFLUENCE
OF
DIETCOMPOSITION ANDCROWDING ONMYZUS
PERSICAE
327
pre- and post-natal crowding increase the proportion of alatae produced on standard diet. Since in several instances all of even the first few larvae produced on the first day that their mothers were grouped developed into alatae, it seems certain that interactions between the adult apterae resulted in the production of alatae without the necessity of larval stimulation of the mothers. This does not, however, rule out the possibility that tactile stimulation of the mothers by their progeny (suggested by BONNEMAISON (195 l)), or of the larvae by their mothers may enhance alataproduction. The occurrence of a small proportion of alatae among the progeny of isolated mothers may attest to either or both these possibilities. However the relative effectiveness of such interactions remains to be investigated, as does the influence of higher larval densities on mutual interactions between larvae. The morph responses to changes in diet composition found by DADD (1968) and MITTLER and KLEINJAN (1970) may in part have been influenced by differences in adult and larval interactions on the different diets. However, by maintaining mothers and their larvae in isolation such influences were eliminated or kept to a minimum in the present investigation. Under these circumstances, therefore, the differences in the ratios of apterae to alatae that occurred on the experimental diets clearly demonstrate that the composition of the food imbibed does play a part in the control of wing dimorphism in M. persicae. However, the extent to which the composition of the food exerts its influence depends on the overall level of alateness. It may be concluded from the data presented in this paper that larval M. persicae interact with each other to enhance alata-production. However, it is not possible to ascribe the different responses to diets solely to influences of the diets on the larvae, since their mothers had been feeding on the same diet for some days. In previous studies in which a maternal response to diet composition was demonstrated (DADD, 1968; MITTLER and KLEINJAN, 1970) the experiments were initiated with plant-reared apterous adults and the responses appeared only after 1 or 2 days of maternal feeding on the diets. In the present studies, however, the reproducing apterae had received the diets from the fourth instar and appreciable differences on the proportions of apteriforms and alatiforms occurred already on the first day of larviposition. A comparison of the data presented in Figs. 3 and 4 indicates that valid inferences can probably be drawn concerning the positive effect of certain diets on aptera-production, and of others on alata-production, regardless of whether the The proportions of apterae will be greater when the larvae are grouped or not. insects are isolated than when they are grouped, but it should still be possible to increase or decrease these figures by exposing the aphids to appropriate diets. The possibility that larvae may be more restless on one diet than on another, a contingency that could have considerable effect on alata-production, cannot be overlooked. There was no indication of this in the present study where progeny were grouped on the same diet as that upon which they had been born. Since adult aphids settle more readily on some diets than on others (MITTLER and KLEINJAN, 1970), it seems wiser at this juncture to maintain at least the adult insects in
328
0. R. W. SUTHERLAND ANDT. E. MITTLER
isolation when studying dietary influences on the control of wing dimorphism in this species. AcknomZedgements-This study was supported in part by a grant (GB-5398X) from the National Science Foundation. We thank Miss JOYCE E. KLEINJANfor technical assistance, in particular for making up the thousands of sachets of sterile diet used in this study. REFERENCES AWRAMW. J. (1968) Effects of crowding and wing morphogenesis in Myzus persicae Sulz. (Aphididae; Homoptera). Quaestiones entomologicae 4, 3-29. BARNETTN. M. and NAYLORA. W. (1966) Amino acid and protein metabolism in Bermuda grass during water stress. Plant Physiol. 41, 1222-1230. BONNEMAISON L. (1951) Contribution a l’etude des facteurs provoquant l’apparition des formes ailees et sexuees chez les Aphidinae. Ann. Epiphyt. 2, l-380. DADD R. H. (1968) Dietary amino acids and wing determination in the aphid Myzus persicae. Ann. ent. Sot. Am. 61,1201-1210. DADD R. H., KRIEGERD. L., and MITTLERT. E. (1967) Studies on the artificial feeding of the aphid Myzus persicae (Sulzer)-IV. Requirements for water-soluble vitamins and ascorbic acid. J. Insect Physiol. 13, 249-272. DADDR. H. and MITTLER T. E. (1966) Permanent culture of an aphid on a totally synthetic diet. Experientia 22, 832. VAN EMDEN H. F., EASTOPV. F., HUGHESR. D., and WAY M. J. (1969) The ecology of Myzuspersicae. A. Rev. Ent. 14,197-270. JOHNSON B. (1965) Wing polymorphism in aphids-II. Interaction between aphids. Entomologia exp. appl. 8,49-64. JOHNSONB. (1966) Wing polymorphism in aphids-III. The influence of the host plant. Entomologia exp. appl. 9,213-222. LEES A. D. (1966) The control of polymorphism in aphids. Adw. Insect Physiol. 3,207-277. LEES A. D. (1967) The production of the apterous and alate forms in the aphid Megoura viciae Buckton, with special reference to the r61e of crowding. I. Insect Physiol. 13, 289-318. MITTLER T. E. and KLEINJAN J. E. (1970) Effect of artificial diet composition on wingproduction by the aphid Myzus persicae. J. Insect Physiol. 16, 833-850. MITTLERT. E. and SUTHERLAND 0. R. W. (1970) Dietary influences on aphid polymorphism. Entomologia exp. appl. 12, 703-713. MITTLER T. E., KLEINJANJ. E., and KUNKELH. (1970a) Apteriform development induced by radish seedlings in larvae of the aphid Myzus persicae reared on artifiical diet. J. Insect Physiol. 16,2119-2125. MITTLER T. E., TSIT~IPIS J. A., and KLEINJANJ. E. (1970b) Utilization of dehydroascorbic acid and some related compounds by the aphid Myzus persicae feeding on an improved diet. r. Insect Physiol. 16,2315-2326. SUTHERLAND 0. R. W. (1969a) The rBle of crowding in the production of winged forms by two strains of the pea aphid, Acyrthosiphonpisum. J. Insect Physiol. 15,1385-1410. SUTHERLAND 0. R. W. (1969b) Th e role of the host plant in the production of winged forms by two strains of the pea aphid, Acyrthosiphon pisum. J. Insect Physiol. 15, 2179-2201.
INFLUENCE OF DIET COMPOSITION AND CROWDING ON WING PRODUCTION BY THE APHID MYZUS PERSICAE 0. R. W. SUTHERLAND* Division of Entomology,
and T. E. MITTLER
University of California, Berkeley, California 94720 (Received 13 June 1970)
Abstract-Two factors have been shown to affect alata-production in a Californian strain of Myzus persicae. Contact between adult apterous females increases the proportion of alatae in their progenies as, to a lesser extent, does contact between the larvae themselves. In the absence of behavioural interactions between the aphids, the relative proportions of apterae and alatae can be influenced by the diet the mothers and their larvae receive. By suitable dietary adjustments, it is therefore possible to increase or decrease the proportions of alatae among the progeny of isolated as well as of grouped aphids. In neither case is it necessary to isolate the larvae directly after their birth in order to observe the influence of diet composition on their wing dimorphism. INTRODUCTION
As AN INSECT of considerable economic importance, Mazes persicae has been the subject of numerous studies, which recently have been reviewed by VANEMDEN et al. (1969). It is clear that although interest in the polymorphism of this aphid is widespread, the question of what factors are involved in the production of alate virginoparae, and at what point in the life cycle they exert their influence has been relatively neglected. As has been found to be the case with Aphis craccivora (JOHNSON, 1965, 1966) and Acyrthosiphon pisum (SUTHERLAND, 1969a, b), at least two factors, crowding and the composition of the diet, are directly involved in the control of wing dimorphism in M. per&z. In an investigation of the effects of crowding, BONNEMAISON (1951) found that interactions between new-born larvae (less than 24 hr old) of his French strain of M. persicae induced many of these to become alatae. Since Bonnemaison failed to obtain a convincing response by crowding adult apterae, he concluded that tactile contact between first instar larvae was of over-riding significance in the production of the alate morph. However, the results of AWRAM(1968) with an English strain of M. persicae indicated that prenatal effects of crowding may be at least as important as post-natal effects. Evidence that pre-natal crowding is highly effective in inducing alata-production in a Californian strain of the species was previously obtained by Mittler
and Kunkel (unpublished). * Present address: Entomology Division, D.S.I.R., 321
Nelson, New Zealand.
322
0.
R. W. SUTHERLAND AND T. E.
MITTLER
That nutritional factors may have a pronounced effect on wing dimorphism has been demonstrated for M. persicae using artificial diets and host plants (MITTLER and SUTHERLAND, 1970). In these studies the greatest numbers of alatae were typically produced on ‘complete’ artificial diets, while on nutritionally imbalanced diets the proportions of apterae generally increased, sometimes spectacularly. Apterous adults and larvae were maintained in approximately constant numbers on these diets, on the assumption that interactions would be similar on the different diets. This may not have been justified, since it, is known that the crowding response is not necessarily a function of the numbers of aphids present per unit area but of the numbers of contacts that occur among them (JOHNSON, 1965 ; LEES, 1966, 1967; SUTHERLAND,1969a). Although MITTLER and KLEINJAN(1970) provided a partial defence to this objection by pointing out that the greatest restlessness (and presumably maximum interaction) occurred on imbalanced diets on which alata-production was minimal, the question of the relative influences of tactile stimulation and of diet composition remained open. The present study was, therefore, undertaken in order to elucidate the status of these two factors in the control of wing dimorphism in this species, and to determine whether the composition of the diet could, in the absence of any crowding stimulus, affect significantly the proportions of winged and wingless virginoparae. To this end, four diets differing from the standard diet were tested. As MITTLER and KLEINJAN(1970) had found that a diet incorporating half the routine concentration of all the amino acids increased the proportion of apterae, while one lacking ascorbic acid favoured an increase in alata-production by grouped aphids, these two diets were among the four tested. A diet lacking valine on which a slight increase in alata-production was previously observed (DADD, 1968), was also offered to isolated aphids. The fourth diet was one containing three times the routine amount of proline and half that of glutamine. It is known that increased alata-production is sometimes associated with physiological stress of the host plant (LEES, 1966). BARNETT and NAYLOR (1966) had found that wilting plants (Bermuda grass) contained increased amounts of proline (other amino acids showing a concomitant decrease in concentration) and it seemed possible that an artificial diet reproducing to some extent this situation might also have some influence on form determination. MATERIALS AND METHODS Groups of 10 to 20 apterous virginoparae were reared on individual radish seedlings (mostly still in the cotyledon stage) in a controlled-environment chamber at 20 _+1°C and in a photoperiodic regime of 16 hr light, 8 hr dark, per day. All experiments were carried out under these conditions. The basal composition of the artificial diets used in this study incorporated the modifications by MITTLER et al. (1970b) of the diet developed by DADDand MITTLER (1966). The diets were aseptically encapsulated in sachets and presented to the aphids in the manner previously described (DADD et al., 1967). The aphids were given fresh sachets every 3 days. Apteriform larvae in the fourth instar were removed from the radish seedling
INFLUENCE
OF DIRT COMPOSITION
AND CROWDING ON MYZUS
PERSICAE
323
culture and caged thereafter in isolation or in groups of 10 on sachets of the various diets tested. On each of 7 days, the youngest (smallest looking) daughter produced in each previous 24 hr period by each isolated aptera was caged singly on another sachet of the same diet as that given to the mother. The remaining progeny of all the isolated apterae were pooled and caged in groups of 25, also on fresh sachets of the maternal diet. Of the larvae produced daily by each group of 10 apterae, 25 of the youngest were placed in isolation and the remainder caged in groups of 25 on sachets of the maternal diet. Where apterae and their daughters were reared exclusively on radish seedlings the former were placed in isolation on the seedlings as first instar larvae. Each day, the youngest daughters deposited in the previous 24 hr were isolated on separate seedlings. The youngest larvae, probably between 1 and 6 hr in age, were chosen for isolation because they were least likely to have been influenced by post-natal tactile stimulation. RESULTS
Standard diet The importance of post-natal crowding in M. persicae is clearly confirmed by the data presented in Fig. 1. When the new-born offspring of isolated mothers were themselves isolated, the number of alatae that appeared was small: it was maximal 100 90
80
I 1
I
1
I
I
2
3
4
I
I
I
5
6
7
DAY OF LARVIPOSITION FIG. 1. Per cent of apteriform individuals among the progeny of isolated (A, B, and S) and grouped (C and D) apterae of M. penicae. Larvae deposited on each of 7 successive days on standard diet (A-D) were raised on the diet in isolation (A and C) or in groups of 25 (B and D). Larvae deposited on radish seedlings were raised in isolation on similar seedlings (S).
324
0. R. W. SUTHERLAND ANDT. E. MITTLER
at the onset of parturition (28 per cent of the day 1 larvae) but declined rapidly (Fig. 1, A). A substantial increase in the percentage of alatae was found when the progeny of isolated parents were reared in groups of 25 individuals (Fig. lB), the difference of 20 to 25 per cent between the two treatments being surprisingly constant throughout the experiment. The progeny of grouped mothers, whether isolated or grouped mostly became alatae (Fig. 1, C and D). Although there was some difference between the isolated and grouped daughters born on the first day of larviposition, the proportions of apterae and alatae hardly differed subsequently. In view of the low proportion of apterae in the progenies of grouped mothers in comparison with those of isolated females, it must be concluded that there is a pre-natal maternal response to tactile stimulation. The possibility exists that (given the numbers in which larvae are deposited within a 24 hr period by the grouped mothers) mutual interactions between the larvae and between the adults and their larvae in the first 6 to 8 hr of larval life are as (or more) effective in inducing alate development as are interactions subsequent to this period. Hence, the high proportions of alatiforms among larvae isolated subsequent to having been born under crowded conditions could be due to such interactions as well as the interactions between the adults (Mittler and Kunkel, unpublished). Before testing diets differing from the standard diet it was desirable to establish whether the results were biased by choosing for isolation the youngest of the daughters of isolated mothers. An experiment was therefore performed in which both first- and last-born larvae were removed daily from their mothers and isolated (Fig. 2). The results do not indicate a significant difference between the two lots 100
80
1
I
I
2
3
I
4
I
1
5
6
1
7
DAY OF LARVIPOSITION FIG. 2. Of the 4 to 7 larvae deposited by each of 20 to 25 isolated apterae of M. persicae on each of 7 successive days on standard diet, the youngest and oldest were raised in isolation on the diet; values for the proportions of apteriforms among these are joined by solid and broken lines, respectively.
INFLUENCE
OF DIET
COMPOSITION
AND
CROWDING
ON
MYZUS
PERSICAE
325
of larvae. Apparently behavioural interactions within the daily batches of progeny (5-8 larvae) were not numerous enough to induce a crowding response. Radish seedlings Although the highest proportions of apterae developed among larvae deposited and reared in isolation on standard diet (Fig. 1, A), a small proportion of alatae continued to be produced throughout the 7 days of the experiment. No alatae developed among larvae deposited and reared in isolation on radish seedlings (Fig. 1, S). Whereas the standard artificial diet might induce the production of some winged individuals, previous studies (MITTLER and SUTHERLAND, 1970; MITTLER, et al., 1970a) indicate that it lacks a factor present in the seedlings which, acting either pre- or post-natally, can cause larvae born and reared on such host plants to become apterae. Non-standard
diets
When the standard diet was replaced with diets lacking various components or containing increased amounts of others, some changes in the relative proportions of apterae and alatae were found. In these tests only isolated mothers were employed, but their larvae were either isolated (Fig. 3) or grouped (Fig. 4) as before. 100 90 80 w
a 5
70 60
l-
% 8
50 40
1
I
I
I
I
I
I
I
2
3
4
5
6
7
DAY OF LARVIPOSITION FIG. 3. Per cent of apteriform individuals among the progeny of 20 to 25 isolated apterae of M. persicae deposited on each of 7 days on five different diets. Each day a single larva from each aptera was raised in isolation on the diet on which it was born. A, standard diet; @, diet with no ascorbic acid; x , diet with half routine level of all amino acids ; 0, diet with no valine ; 0, diet with three times the routine level of proline and half that of glutamine.
O.R. W. SUTHERLAND AND T.E.MITTLER
326
While in general fewer alatae were found among isolated than among grouped larvae, a comparison of the data indicates that in both cases each diet influenced the form of the offspring in the same sense. The proportion of alatae increased considerably when the insects were fed on a diet lacking ascorbic acid regardless of whether or not the larvae were grouped. When a diet containing three times the standard amount of proline and one-half the standard amount of glutamine was 100 90
80 %
70
Ei
60
k a
50
30 20
i
i
i
i
4
k
t
DAY OF LARVIPOSITION FIG. 4. As in Fig. 3 but larvae deposited each day were raised on the diets in groups of 25 to 30.
offered the proportion of alatae was also increased, but only among the larvae born on the first day. The diet lacking valine had little influence on alata-production here. On the other hand, the proportion of apterae increased when the insects were fed on a diet containing half the normal concentration of all the amino acids. This was particularly noticeable in the case of the grouped larvae indicating that the influence of the dietary composition was strong enough to overcome almost entirely the response to tactile stimulation. As the proportions of apterae among the isolated offspring of isolated mothers reared on standard diet were already high (Fig. 3), a convincing increase in the numbers of apterae could not be demonstrated by this treatment. DISCUSSION
The important role of tactile stimulation in the production of alatae is clearly established by the data presented in Fig. 1, from which it can be seen that both
INFLUENCE
OF
DIETCOMPOSITION ANDCROWDING ONMYZUS
PERSICAE
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pre- and post-natal crowding increase the proportion of alatae produced on standard diet. Since in several instances all of even the first few larvae produced on the first day that their mothers were grouped developed into alatae, it seems certain that interactions between the adult apterae resulted in the production of alatae without the necessity of larval stimulation of the mothers. This does not, however, rule out the possibility that tactile stimulation of the mothers by their progeny (suggested by BONNEMAISON (195 l)), or of the larvae by their mothers may enhance alataproduction. The occurrence of a small proportion of alatae among the progeny of isolated mothers may attest to either or both these possibilities. However the relative effectiveness of such interactions remains to be investigated, as does the influence of higher larval densities on mutual interactions between larvae. The morph responses to changes in diet composition found by DADD (1968) and MITTLER and KLEINJAN (1970) may in part have been influenced by differences in adult and larval interactions on the different diets. However, by maintaining mothers and their larvae in isolation such influences were eliminated or kept to a minimum in the present investigation. Under these circumstances, therefore, the differences in the ratios of apterae to alatae that occurred on the experimental diets clearly demonstrate that the composition of the food imbibed does play a part in the control of wing dimorphism in M. persicae. However, the extent to which the composition of the food exerts its influence depends on the overall level of alateness. It may be concluded from the data presented in this paper that larval M. persicae interact with each other to enhance alata-production. However, it is not possible to ascribe the different responses to diets solely to influences of the diets on the larvae, since their mothers had been feeding on the same diet for some days. In previous studies in which a maternal response to diet composition was demonstrated (DADD, 1968; MITTLER and KLEINJAN, 1970) the experiments were initiated with plant-reared apterous adults and the responses appeared only after 1 or 2 days of maternal feeding on the diets. In the present studies, however, the reproducing apterae had received the diets from the fourth instar and appreciable differences on the proportions of apteriforms and alatiforms occurred already on the first day of larviposition. A comparison of the data presented in Figs. 3 and 4 indicates that valid inferences can probably be drawn concerning the positive effect of certain diets on aptera-production, and of others on alata-production, regardless of whether the The proportions of apterae will be greater when the larvae are grouped or not. insects are isolated than when they are grouped, but it should still be possible to increase or decrease these figures by exposing the aphids to appropriate diets. The possibility that larvae may be more restless on one diet than on another, a contingency that could have considerable effect on alata-production, cannot be overlooked. There was no indication of this in the present study where progeny were grouped on the same diet as that upon which they had been born. Since adult aphids settle more readily on some diets than on others (MITTLER and KLEINJAN, 1970), it seems wiser at this juncture to maintain at least the adult insects in
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isolation when studying dietary influences on the control of wing dimorphism in this species. AcknomZedgements-This study was supported in part by a grant (GB-5398X) from the National Science Foundation. We thank Miss JOYCE E. KLEINJANfor technical assistance, in particular for making up the thousands of sachets of sterile diet used in this study. REFERENCES AWRAMW. J. (1968) Effects of crowding and wing morphogenesis in Myzus persicae Sulz. (Aphididae; Homoptera). Quaestiones entomologicae 4, 3-29. BARNETTN. M. and NAYLORA. W. (1966) Amino acid and protein metabolism in Bermuda grass during water stress. Plant Physiol. 41, 1222-1230. BONNEMAISON L. (1951) Contribution a l’etude des facteurs provoquant l’apparition des formes ailees et sexuees chez les Aphidinae. Ann. Epiphyt. 2, l-380. DADD R. H. (1968) Dietary amino acids and wing determination in the aphid Myzus persicae. Ann. ent. Sot. Am. 61,1201-1210. DADD R. H., KRIEGERD. L., and MITTLERT. E. (1967) Studies on the artificial feeding of the aphid Myzus persicae (Sulzer)-IV. Requirements for water-soluble vitamins and ascorbic acid. J. Insect Physiol. 13, 249-272. DADDR. H. and MITTLER T. E. (1966) Permanent culture of an aphid on a totally synthetic diet. Experientia 22, 832. VAN EMDEN H. F., EASTOPV. F., HUGHESR. D., and WAY M. J. (1969) The ecology of Myzuspersicae. A. Rev. Ent. 14,197-270. JOHNSON B. (1965) Wing polymorphism in aphids-II. Interaction between aphids. Entomologia exp. appl. 8,49-64. JOHNSONB. (1966) Wing polymorphism in aphids-III. The influence of the host plant. Entomologia exp. appl. 9,213-222. LEES A. D. (1966) The control of polymorphism in aphids. Adw. Insect Physiol. 3,207-277. LEES A. D. (1967) The production of the apterous and alate forms in the aphid Megoura viciae Buckton, with special reference to the r61e of crowding. I. Insect Physiol. 13, 289-318. MITTLER T. E. and KLEINJAN J. E. (1970) Effect of artificial diet composition on wingproduction by the aphid Myzus persicae. J. Insect Physiol. 16, 833-850. MITTLERT. E. and SUTHERLAND 0. R. W. (1970) Dietary influences on aphid polymorphism. Entomologia exp. appl. 12, 703-713. MITTLER T. E., KLEINJANJ. E., and KUNKELH. (1970a) Apteriform development induced by radish seedlings in larvae of the aphid Myzus persicae reared on artifiical diet. J. Insect Physiol. 16,2119-2125. MITTLER T. E., TSIT~IPIS J. A., and KLEINJANJ. E. (1970b) Utilization of dehydroascorbic acid and some related compounds by the aphid Myzus persicae feeding on an improved diet. r. Insect Physiol. 16,2315-2326. SUTHERLAND 0. R. W. (1969a) The rBle of crowding in the production of winged forms by two strains of the pea aphid, Acyrthosiphonpisum. J. Insect Physiol. 15,1385-1410. SUTHERLAND 0. R. W. (1969b) Th e role of the host plant in the production of winged forms by two strains of the pea aphid, Acyrthosiphon pisum. J. Insect Physiol. 15, 2179-2201.