No. 4B7G April 13, 1963 NATURE 209

The name protarrhenotoky has been suggested for this Qualitative as well as quantitative differences in cyto­ condition by Prof. J. B. S. Haldane. Kohl2 uses the word plasmic wax contents might also be of some importance. 'proterandry' for the fact that males emerge before females. Chibnall and Piper1 found B. oleracea varieties and B. This could, of course, be due to their developing more napus to contain either 15-nonacosanone (C 2.H580) or rapidly. It may be desirable to coin a word meaning that 15-nonacosanol, the ketone and alcohol from n-nonacosan. male-producing eggs are laid before female-producing eggs. While both were present in brussels sprouts, neither were The evolutionary consequences are interesting. An identified in white mustard (Sinapis alba L.), which is abnormal sex-ratio is essential for the kind of socializa­ known to be fairly resistant to . tion that the Hymenoptera have achieved. If protar­ It would thus appear that, although may be a rhenotoky is primitive, the process of socialization must specific stimulus for host selection by the cabbage , have involved a change over to the condition where a large resistance to the aphid can be determined by the waxy or number of fertilized eggs are laid before any unfertilized non-waxy nature of plants. eggs are laid, though, so far as I know, complete proto­ K. F. THOMPSON thelytoky (where all female-producing eggs precede all the Plant Breeding Institute, male-producing) has not been observed to be the rule in Maris Lane, any hymenopteran. Trumpington, s. D. JAYAKAR Cambridge. 1 Chibnall, A. C., and Piper, S. H., Biochem. J., 28, 2209 (1934). Genetics and Biometry Laboratory, 'Wensler, R. J. D., Nature, 195, 830 (1962). Government of Orissa, 'Heathcote, G. D., thesis, Univ. London (1955) cited in Broadbent, L., Bhubaneswar-3 Investigation of Virus Diseases of Brassica Crops (Camb. Univ. Press). • Lamb, K. P., N.Z. J. Auric. Res., 3, 320 (1960). Orissa, India. 'Spurway, H., Dronamraju, K. R., and Jayakar, S. D., Atti Quarto Gong. Intern. U.I.E.I.S., Pavia (in the press). 'Kohl, F. F., Ann. Naturhist. Hofmuseums, 32, 1 (1918). Differential Utilization of Amino-acids by 'Olberg, G., Das Verhalten der Solitliren Wespen Mitteleuropas (Berlin, Myzus persicae (Sulzer) fed on Artificial Diets 1959). IN a recent report by Mittler and Dadd1 on the artificial feeding of Myzus persicae (Sulzer) through membranes of Resistance to the Cabbage Aphid ( stretched 'Parafilm' it was noted that the aphids excreted brassicae) in Brassica Plants numerous honeydew droplets when feeding on an 18 per cent sucrose solution with or without amino-acids, A MARROW-STEM kale (Brassica oleracea var. acephala) vitamins and salts. selection segregated on selfing for plants with and without Spot tests failed to detect amino-acids in the honeyde·w cuticular wax on their leaves, and it was observed in a excreted by M. persicae feeding on solutions of sucrose natural field infestation that the non-waxy plants were only, but indicated a high level of amino-compounds in not colonized by the cabbage aphid (Brevicoryne brassicae the honeydew excreted by aphids feeding on a diet con­ L.), whereas the normal, waxy plants had large colonies. taining the 20 L-amino-acids previously listed1• The rosistance of non-waxy plants was confirmed in a In to test whether some of these dietary amino­ field plot, artificially infested. In a severe attack of acids are differentially utilized by the aphids, 20 per cent cabbage white fly (Aleuroides brassicae Walk.), which sucrose solutions containing only 3 or 6 of the 20 amino­ developed later in the year than the aphid attack, no acids, at the concentrations indicated in Table I, were fed larvre or pupre, and only occasional adult flies, were found to several groups of 40-90 apterous adult M. persicae for on the non-waxy plants, whereas the lower sides of the periods of 6 days and the honeydew excreted by each group leaves of the waxy plants were covered with white fly at analysed chromatographically. Five of the amino-acids all stages of their life-cycle. were selected from those considered to be essential in the The non-waxy plants were thus resistant to both nutrition of several • and hence likely to be required cabbage aphid and white fly. Both insects secrete a white, in specific amounts also by aphids, whereas asparagine mealy covering of wax over their bodies, and it therefore was included as it is frequently a major component of seems possible that the absence of wax or its immediate plant sap. A butanol-methyl ethyl ketone-water precursors in the plants may be the cause of the resistance. solvent• was found to give good and rapid resolution on In brussels sprouts (var. gemmifera) and in other botanical strip chromatograms of the 6 amino-acids. From diet varieties of B. oleracea, waxes and related substances are honeydew comparisons the relative amounts of the present as an integral part of the cell cytoplasm as well as excreted amino-acids were semi-quantitatively evaluated forming cuticular wax1 • (Table 1). Other factors, besides non-waxiness, may be involved in resistance to cabbage aphids. Thus W ensler2 found that Table 1. RELATIVE AMOUNTS* OF AMINO-ACIDS FOUND IN THE HONEYDEW the glucoside, sinigrin, is a specific stimulus for OF Myzus persicae FED ON VARIOUS AMINO-ACID SUCROSE DIETS No. of amino-acids and concentration of each in diets host selection by B. brassicae. Also lines ofkalo, with some 3 at 3 at 0·7% 6 at 6 at 0·5% resistance to aphids but not with waxless leaves, can be 0·5% (2 replicates) 0·1% (3 replicates) bred. It may be that such lines have a low sinigrin Threonine + + + + + + tr tr Valine tr + + + tr content. Methionine tr tr + tr Differences in waxiness of plants also occur between J,ysine tr + + + + + Leucine tr + + + + species in the Brassica and may be correlated with Asparagine + + + + + + + + + + relative susceptibility to cabbage aphids. Heathcote• • Relative amounts indicated as follows: - - , not present in the diet found the aphid to flourish best on brussels sprouts with nor detected in the honeydew; -, not detected in the honeydew; tr, trace amounts detected; + , + + , + + +, amounts on an increasing but not (B. oleracea var. botryt,is) and cabbage (B. proportional scale. oleracea var. capitata) as other good hosts, and Lamb4 f01md dwarf Essex rape (B. napus L.) to be very suscep­ It is evident that the 6 amino-acids were not excreted tible, marrow-stem kale to be fairly susceptible and in the same proportions as they occurred in the diets. turnips (B. rapa L.) to be resistant. Both the B. oleracea The amino-acids could be arranged in the following order varieties (brussels sprouts, cauliflower, cabbage and kale) in which they were found to occur in progressively decreas­ and B. napus have waxy, blue green leaves, whereas ing amounts in the honoydew: asparagine, lysine, leucine, turnips (B. rapa) have light green leaves with less wax. threonine, valine and methionine. The chromatograms Also it is known that turnips contain sinigrin because also indicated that as the amino-acid concentrations in their leaves were attractive in Wensler's experiments. the diets are increased the number and concentration

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