Cu~np. Blochun. Phgslol.. 1977. Vol 56A, pp. 203 to 205. Pergnmon Press. Prtnted m Crept Britain

QUANTITATIVE REQUIREMENTS FOR TYROSINE, PHENYLALANINE AND TRYPTOPHAN BY THE COTTON APHID, APHIS GOSSYPII (GLOVER)*

RALPH B. TURNER

Department of Botany and Entomology, New Mexico State University, Las Cruces, NM 88003, U.S.A.

(Received 9 April 1976)

Abstract-l. The cotton aphid, Aphis gossypii (Glover) requires a dietary source of tryptophan and phenylalanine.

2. Optimum concentrations are: tryptophan 4 mg/ml and phenylalanine 2 mg/ml, but higher concen- trations of both are tolerated quite well.

3. Tyrosine is not required.

INTRODUCTION

With the development of suitable holiclic diets for the aphid, Aphis gossypii (Auclair, 1967a, b), it is possible to evaluate dietary requirements for this species by the definitive deletion technique. Our previous studies of the sulfur-containing amino acids revealed the in- dispensable nature of both cysteine and methionine and established quantitative requirements for maxi- mum growth and survival (Turner, 1971). This report describes the quantitative dietary requirement for phenylalanine and tryptophan and the non-essential character of tyrosine in the holidic diet of A. gossypii.

MATERIALS AND METHODS

Stock cultures of aphids were maintained and the holidic diet was prepared as previously described (Turner, 1971) except the composition of the standard diet was as shown in Table 1. The procedure for testing and evaluation [growth index (G.I.) = No. of survivors x av wt after 6 days/No. of initial x initial av wt] of the diets has been used previously (Turner, 1971).

RESULTS

Results of this investigation reveal a dietary require- ment for phenylalanine and tryptophan. Tyrosine is non-essential.

Analysis of variance revealed significant differences among growth indices (G.I.) with various concen- trations of phenylalanine in the standard diet. The G.I. obtained with each concentration of phenyl- alanine was compared to that of the standard diet and significance of any difference was determined with a protected “t” test, or a Fisher significant differ- ence (Carmer & Swanson, 1973). Although omission of phenylalanine from the standard diet did not signi- ficantly reduce the G.I., increasing the concentration

* Journal Article No. 577-Agricultural Experiment Station, New Mexico State University.

of phenylalanine caused a significant increase in G.I. (Table 2). This tends to confirm a previous observa- tion that the standard diet is probably suboptimal in its nutritive value (Auclair, personal communica- tion; Turner, 1971). Comparison then of the G.I. obtained with the diet lacking phenylalanine to that obtained with the diet having increased (2 x ) phenyl- alanine, clearly reveals a requirement for this amino acid. Higher concentrations of phenylalanine failed to further increase the G.I. of the standard diet, but had no detrimental effect.

Omission of tryptophan from the standard diet caused a significant (1% level) decrease in G.I. (Table 3), indicating the essential character of tryptophan. It was also noted that increased concentration of tryptophan (4-fold) in the standard ‘diet caused a sig- nificant (5% level) increase in the G.I., further indicat- ing the suboptimal value of the standard diet.

As shown in Table 4, the omission of tyrosine caused no significant decrease in G.I., and increased concentration of tyrosine had no effect on G.I. These data indicate that the aphid not only does not need tyrosine, but will tolerate tyrosine at saturation in the holidic diet.

DISCUSSION

It thus appears that the maximum value of the holidic diet is realized when the concentration of phenylalanine is 2mg/ml, and that of tryptophan is 4mg/ml. Omission of tyrosine does not significantly lower the growth index, indicating it is not essential in this holidic diet of Aphis gossypii. Tyrosine is generally considered non-essential as long as its essen- tial precursor, phenylalanine is present in adequate quantities. The possible sparing effect of tyrosine on the phenylalanine requirement in the aphid diet is under investigation. Phenylalanine and tryptophan are both generally considered as essential. Trypto- phan is utilized in cuticle melanization (along with tyrosine) and in formation of ommochrones, e.g. xan- thommatin (Bursell, 1970). A significant biochemical

203

204 RALPH B. TURNER

Table 1. Composition of the standard diet

Sucrose Maltose MgClz.6Hz0 Mixture of ~-amino acids (see below) Vitamins

Biotin Ca Panthothenate Choline chloride Folic acid i-Inositol Nicotinic acid p-Aminobenzoic acid Pyridoxine.HCl Riboflavin Thiamine. HCl Ascorbic acid

USP salts NBC No. 2

K,P% Cholesterol benzoate H,O (glass redistilled from KMnO,) to make lOOm1

pH adjusted to 7.4-7.8 with H3P04 and KOH L-Amino acid mixture

Alanine Arginine Asparagine Aspartic acid Cysteine y-Aminobutyric acid Glutamic acid Glutamine Glycine Histidine Homoserine Isoleucine Leucine Lysine’HCl Methionine Phenylalanine Proline Serine Threonine Tryptophan Tyrosine Valine

2og 10 0.2 5.01

0.1 mg 5

50 1

50 10 10 2.5 5 2.5

10

5mg 500

2.5

1OOmg 400 300 100 750

20 200 600

20 200 800 200 200 200 100 100 100 100 200 100 20

200 Amino acid mix total 5010 mg

Table 2. Effect of concentration of phenylalanine on growth index of A. gassypii

Diet Composition Mean G.I. Replicates

Standard (Phenylalanine 1 mg/ml) 3.65 154 Minus Phenylalanine 4.02 106 Phenylalanine 2 mg/ml 4.93 69 Phenylalanine 4 mg/ml 4.23 31 Phenylalanine 8 mg/ml 4.35 28

* Significant at 5% level. ** Significant at 1% level.

Table 3. Effect of concentration of tryptophan on G.I. of A. gossypii

t

1.6086 N.S. 4.96** 1.65 N.S. 2.16*

Diet Composition Mean G.I. Replicates t

Standard (Tryptophan 1 mg/ml) 3.65 154 Minus Tryptophan 2.11 44 5.920** Tryptophan 2 mg/ml 4.20 19 1.486 N.S. Tryptophan 4 mg/ml 4.45 20 2.240* Tryptophan 8 mg/ml 4.05 29 1.30 N.S.

* Significant at 5% level. **Significant at 1% level

Quantitative requirements for tyrosine 205

Table 4. Effect of concentration of tyrosine on G.I. of A. gossypii

Diet Composition Mean G.I. Replicates

Standard (Tyrosine 0.2 mg/ml) 3.65 154 Minus Tyrosine 3.16 56 Tyrosine 0.4 mg/ml 3.13 26

Analysis of variance revealed no significant difference among these diets.

function of phenylalanine in insects appears to be to supply tyrosine as noted above.

Demonstration that the cotton aphid tolerates such a wide range of concentrations of amino acids, e.g. phenylalanine, 6mM to 48mM and tryptophan, 5 mM to 40 mM, support the interpretation that reduced G.I., in response to deletion of an amino acid indicates a specific need rather than creation of a general nitrogen deficiency.

It is recognized that the young aphid may acquire sufficient quantities of some amino acids transovari- ally from the parent, or by its early feeding on the cotton plant. Thus, some amino acid requirements may be masked Also, interconversion among amino acids may obscure some requirements. However, posi- tive results, where omission of an amino acid signifi- cantly reduced the G.I., are unequivocal.

Acknowledgements-The competent technical assistance of Roberta Swanson and Steve Judd is gratefully acknow- ledged.

REFERENCES

AUCLA~R J. L. (1967a) Effects of pH and sucrose on rearing the cotton aphid, Aphid gossypii, on a germ-free and holi- die diet, J. Insect Physiol. 13, 431446.

AUCLAIII J. L. (1967b) Effects of light and sugars on rearing the cotton aphid, Aphis gossypii on a germ-free and holi- die diet. J. Insect Physiol. 13, 1247-1268.

BUR~ELL E. (1970) An Introduction to Insect Physiology. pp. 28-30. Academic Press, New York.

CAKVIEII S. G. & SWANSON M. R. (1973) An evaluation of ten pairwise multiple comparison procedures by Monte Carlo methods. J. Am. Stat. Assoc. 68, 6674.

TURNER R. B. (1971) Dietary amino acid requirements of the cotton aphid, Aphis gossypii: The sulphur-containing amino acids. J. Insect Physiol. 17, 2451-2456.

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