Population Growth, Longevity and Fecundity of maidis FITCH (Homoptera: ), on and Seedlings Grown under Different Nutritional Conditions

By Yosiaki ITO and Chisato HIRANO NationalInstitute of AgriculturalSciences, Nishigahara, Kita-ku, Tokyo

Insect: The stocks used for the INTRODUCTION experiments were progenies of the original The corn leaf aphid, Rhopalosiphum stocks collected at the beginning of maidis FITCH, a well-known of respective seasons from barley fields of corn and grain in the United the National Institute of Agricultural Sci- States (PAINTER, 1951), is a serious pest ences at Nishigahara, Tokyo. of winter barley in Japan. The Cultural conditions of host plants: Three do not attack any variety of wheat with cultural conditions were provided for a few exceptional cases (WILDERMUTH and wheat and barley seedlings: on soil with WALTER, 1932; IIJIMA, TANAKA, MATSUSHIMA manure (termed as soil-planted), on sand and HORI, 1953; ITO, 1960), despite of their with culture solution high in nitrogen aptitude to maintain their colonies on (high-N), and on sand with culture solu- caged wheat plants over several gene- tion deprived of nitrogen (low-N). In soil rations. ITO (1960) demonstrated ex- culture, seedlings were planted on soil perimentally that non-preference and filled in pots or iron boxes and watered antibiosis were responsible for the aphid- when necessary. In sand culture, seed- resistance of wheat, while certain ecologi- lings were planted on sand filled in pots cal factors such as grouping of host or or iron boxes which were placed in non-host plants might affect the degree of enameled basin containing nutrient solu- the resistance under field conditions. The tions (Table 1). The low-N plants were physiological mechanism of the aphid- distinctly more yellowish in colour and resistance of the wheat, however, has smaller in size than the high-N and the remained to be studied. soil-planted plants, in both barley and In the present paper, results of the wheat. The soil-planted plants appeared studies on survival rate and fecundity of to be in the best nutritional condition. apterous viviparae, and also population The results of chemical analyses of the growth, on wheat and barley seedlings seedlings grown under these different growing under different nutritional condi- conditions are given in Table 2, in order tions are reported. Table 1. Composition of nutrient solutions MATERIALS AND METHODS used in sand culture of plants

All the rearing experiments were con- ducted in a greenhouse, where tempera- tures ranged from 20•‹to 27•Ž, except for the experiment conducted in spring of 1959 when the temperature often exceeded 30•Ž.

(Received for publication, March 25, 1963) -132- June, 1963 ITO & HIRANO: Rhopalosiphum maidis on and Barleys 133

Table 2. Chemical composition of wheat and or had become alate were excluded from barley seedlings grown under different the result. Throughout the experiment, nutritional conditions (Percentage on dry however, alate individuals emerged at a weight basis). rate of less than 1 per cent. Usually six replications were provided for each ex- perimental series.

RESULTS Population growth: Population growth

to show the relative difference of nutri- tional and physiological conditions among these plants. Experiments on population growth: Each host seedling was planted in a pot, 6cm in diameter and 7cm depth, and covered with a glass cylinder, 10cm in diameter and 30cm in height (ITO, 1960). The upper opening of the glass cylinder was covered with silk gauze. In the first, the second and the third experiments, two or three apterous newly born aphids, from alate viviparae of 2 to 4 days after the fi nal ecdysis, were settled on top leaf of a host seedling, when the second or the third leaf had emerged. Only in the fourth experiment five apterous young- lings were settled on each seedling. Number of individuals on each leaf level and on stem of the plant was thereafter Fig.1. Population growth of Rhopalosiphum counted on alternate days. maidis on wheat and barley seedlings Experiments on longevity and fecundity: grown under different nutritional condi- tions (First experiment, conducted in Twelve apterous younglings born of alate April, 1959). Curves for the respective viviparae within 48 hours were caged series indicate average of four repli- with plastic leaf-cage on a wheat or barley cations. leaf of different nutritional conditions1. Symbols stand for following items: Hollow squares•c•chigh-N barley, Number of surviving individuals and Solid squares•c•clow-N barley, number of younglings laid per 48 hours Squares with oblique lines•c•csoil-planted were recorded every other day. Whenever barley, the counting was made, the caged leaves Hollow circles•c•chigh-N wheat, Solid circles•c•clow-N wheat, were renewed, and the younglings were Circles with oblique lines•c•csoil-planted eliminated. Individuals lost by accident wheat.

For details of the plastic leaf-cage used, see the previous paper (ITO, 1960). 134 Japanese Journal of Applied Entomology and Zoology Vol.7, No.2 of Rhopalosiphum maidis on wheat and which the aphid population remained on barley seedlings grown under different lower level than on barley, the population nutritional conditions was examined. growth on the high-N plants was slower According to the result of the first ex- than on the low-N plants (Fig.1). periment conducted in April, 1959, the In the third experiment conducted in aphid population on barley reached higher December, 1959, the growth rate of the asymptote on the high-N plants than on the aphid population was highest on the low-N plants; while, on wheat plants in barley, lower on the low-N wheat and on the high-N wheat, and lowest on the soil-planted wheat. The low-N wheat gave a better population growth than the high-N wheat, specially in early period of the plant growth (Fig.2). Fig.3, the result of the fourth experiment conducted in May, 1961, shows that, among wheats, the growth rate of the population was highest on the low-N wheat, lower on the high-N wheat and lowest on the soil-planted wheat. No difference was observed in the population growth on barley plants grow- ing under different conditions up until the 11th day, but here- after the population growth on the low-N barley was remarkably suppressed. Dif- ference between the high-N and the soil-planted barley was not statistically signi- fi cant (P>0.05). Aphids on the wheat plants of all the nutritional series often became extinct in the fi rst few days after they were settled. In such cases, one or two fresh younglings were again settled on the top leaf. Fig.2. Population growth of Rhopalosiphum maidis on wheat After 21st day, however, plants and barley seedlings grown under different nutritional on which the aphid became conditions (Third experiment, conducted in December, extinct were discarded. Fre- 1959). Curves represent averages of six replications in respective series, and vertical bars show confidence quency of such extinction is intervals at 95% level of t (SNEDECOR, 1940). Points given in Table 3. without vertical bar stand for replications less than four. Such a situation is represent- For symbols see explanation of Fig.1. ed more precisely in Fig.4, June, 1963 ITO & HIRANO: Rhopalosiphum maidis on Wheats and Barleys 135

Fig.4. Initial phase of the Rhopalosiphum maidis-population growth on wheat seed- lings grown under different nutritional Fig.3. Population growth of Rhopalosiphum conditions. Each line represents res- maidis on wheat and barley seedlings pective seedlings. •~-Marks mean die off of all the settled grown under different nutritional condi- tions (Fourth experiment, conducted in aphids. May, 1961). Left top: Soil-planted wheat, For symbols see explanation of Fig.1. Left bottom: High-N wheat, Right: Low-N wheat. Table 3. Number of plants on which the once settled aphids became extinct (the planted wheats. third experiment). The results of the second experiment are not given because they were essentially similar to the above-mentioned experi- ments. Generally speaking, increase of aphids was slower on wheats than on barleys, specially on the high-N and soil-

planted plants. Even on the low-N wheat, the highest aphid population attained was far below than that on the barley plant. Note: When aphids became extinct, one or two Suitability of wheat seedlings grown under new individuals were again settled. different nutritional conditions, for in- Six plants were used for each series. creasing aphid population, seems to be in which results of the fourth experiment correlated positively with sugar content are given. It is clear that the low-N and/or negatively with nitrogen content wheat provides a better condition for the (Table 2). Fig.5 shows accumulated establishment of Rhopalosiphum maidis population densities of Rhopalosiphum population than the high-N and the soil- maidis up until the 14th day on wheat 136 Japanese Journal of Applied Entomology and Zoology Vol.7, No.2

Fig.5. Relationship between accumulated population density of Rhopalosiphum maidis on wheat seedlings till the 14th day and Fig.6. Survival rate (top) and number of the total nitrogen contents of the seedling younglings laid within 48 hours per sur- grown under different conditions. viving apterous female (bottom) of Rhopalosiphum maidis on middle leaves plants growing under different conditions. of barley plants grown under different It seems that the rate of increase inversely conditions (Fourth experiment). correlated with the nitrogen content of For symbols see explanation of Fig.1. the seedlings. Difference between the low-N and the high-N wheats was stati- of wheat is given in Figs.6 (top) and 7. No stically significant (P<0.05), whereas difference was recorded among survival difference between the high-N and the rates of Rhopalosiphum maidis on barley soil-planted wheats was not significant. plants growing under different conditions. It was found that a notable increase of Differences in survival rates are highly sig- aphid population occurred occasionally on nificant (P<0.01) between the high-N the high-N and soil-planted wheats (see barley and both the soil-planted and the dotted line of Fig.2 and some lines of high-N wheat, and between the low-N wheat Fig.4). In these cases, aphid density and the soil-planted wheat. Examining later reached as high level as that on the Fig.7 in which results of the third ex- barley. According to another experiment, periment were given, it is apparent that the resistance of the wheat plant to Rho- the low-N wheat gave better survival rate palosiphum maidis became low as the plant than the high-N and the soil-planted wheats. grew (HIRANO and ITO, unpublished). One Fecundity: Number of younglings laid by of the reasons for the increase in the caged females within each 48 hours are aphid population on wheat plant may be given in Figs.6 (bottom) and 8. Fig.8 attributed to this point. shows that the fecundity of apterae reared Longevity: Longevity of apterous indivi- on barley leaves is significantly greater duals caged on middle leaves of barley and than that on wheats grown under all the June, 1963 ITO & HIRANO: Rhopalosiphum maidis on Wheats and Barleys 137

Fig.8. Number of younglings laid within 48 hours per surviving apterous female of Rhopalosiphum maidis on middle leaves of the high-N barley and wheat plants Fig.7. Survival rate of apterous Rhopalosi- grown under different nutritional condi- tion (Third experiment). phum maidis on middle leaves of the high- For symbols see explanation of Fig.1. N barley and wheat plants grown under different nutritional conditions (Third experiment). HOWITT and PAINTER, 1956). For sorghum, For symbols see explanation of Fig.1. CARTIER and PAINTER (1956) reported that preference (or non-preference) and anti- nutritional conditions tested. The aphids biosis were the cause of such differences in reared on the high-N barley temporarily resistance. Chemical and morphological produced more younglings than those aspects of this antibiosis have, however, reared on the low-N barley (Fig.6, bottom), remained unstudied, except for some while total number of younglings laid attempts to connect the sugar (HABER and throughout the adult stage on the low-N GAESSLER, 1942) and carotene contents barley was about equal to that on the (COON, MILLER and AURAND, 1948) in tassel high-N barley. This is probably due to a and grains of corn with the resistance to longer reproductive period of the aphid Rhopalosiphum maidis which gave rather on the low-N barley. The aphids reared obscure results. on the soil-planted wheat gave a lower ITO (1960) demonstrated that relative fecundity than those reared on the low-N non-preference (low preference) was con- and the high-N wheat, while the difference cerned with the resistance of wheat to was not statistically significant. this aphid. The present experiments showed that DISCUSSION the aphid reared on wheat plants gave a It has been reported that there are higher mortality and a lower fecundity remarkable intraspecific differences in Rho- than that on barley plant. Increasing rate, palosiphum maidis-resistance of gramineous mortality and fecundity of Rhopalosiphum (e.g. WALTER and BRUNSON, 1940; maidis on the low-N barley were not SNELLING, BLANCHARD and BIGGER, 1940; different from those on the high-N and 138 Japanese Journal of Applied Entomology and Zoology Vol.7, No.2 the soil-planted barley, but saturation since the aphids reared on the high-N density of the population was remarkably wheat did not show any significant dif- low on the low-N barley. The experiment ference in the fecundity as compared with also showed that the physiological condi- the low-N wheat, and since the high-N tions of the wheat plant would affect the barley gave a higher saturation density of resistance to Rhopalosiphum maidis. The aphid population than the low-N barley. low-N wheat provided a significantly better MULLER (1958) observed that the difference establishment of the aphid population than in fecundity of Aphis fabae on resistant on the high-N and the soil-planted wheat, and susceptible fieldbean plants became particularly in early stages of the plant obscure when detached leaves were used growth. Survival and reproductive rates in place of rooted plants. As the result of the aphid on the low-N wheat were described herein seems to be in line with also significantly higher than those on the that of MULLER, the authors incline to soil-planted wheat. Although difference adopt the second hypothesis. in the survival rate and the fecundity Mechanical factors such as hardness of between the low-N and the high-N wheat the leaf epidermis or morphological incon- was not demonstrated, it is reasonable to formity of the leaf tissues for penetrating assume that the high-N wheat is in an mouth-parts of the aphids may also affect intermediate position between the more the resistance. Analysis along this line resistant soil-planted wheat and the less will be reported elsewhere. resistant low-N wheat. Since the high- N wheat contains nitrogen and sugars in SUMMARY an intermediate level between the soil- Population growth, survival rate and planted and the low-N wheat, degree of fecundity of apterous Rhopalosiphum maidis the resistance of wheat plants to Rhopalo- were examined on wheat and barley seed- siphum maidis seems to be correlated with lings growing under different nutritional these chemical characters of the seedlings. conditions. Barley plants grown under all These results may lead to the following the cultural conditions tested always gave two hypotheses: (1) Production of chemi- more rapid population growth, higher sur- cal substances, which is indispensable for vival rate and greater fecundity of the the growth and development of this aphid, aphid than wheat plants. On wheats, the may be accelerated highly in the low-N aphid increased its population more rapid- wheat than in the soil-planted and proba- ly on seedlings cultured in low-nitrogen bly in the high-N wheat; and (2) produc- solution (termed as low-N wheat) than on tion and/or action of certain antibiotic seedlings grown in high nitrogen solution substances in wheat plant may be sup- (high-N wheat) and in manured soil (soil- pressed under conditions such as nitrogen planted wheat). Survival rate and fecun- deficiency. dity of the aphid were highest on the low- Although ARANT and JONES (1951) repor- N wheat, lower on the high-N wheat and ted a reverse case for Toxoptera graminum, lowest on the soil-planted wheat. The most papers dealing with the influence of suitability of barley and wheat seedlings nutrient levels of the host plant on aphid grown under different nutritional condi- reproduction show a promoting effect of tions as a host plant are arranged as an increased nitrogen level on population follows: soil-planted barley=high-N barley growth and survival rate (DAVIDSON, 1922, low-N barley>low-N wheat>high-N 1925; EVANS, 1938; HASEMAN,1946; MALTAIS, wheat>soil-planted wheat. 1951; MALTAIS and AUCLAIR, 1957). In case The suitability of wheat seedlings as a of Rhopalosiphum maidis reported here, the host plant seems to correlate positively fi rst hypothesis seemed to be inadequate with sugar content and negatively with June, 1963 ITO & HIRANO: Rhopalosiphum maidis on Wheats and Barleys 139

nitrogen content of the seedlings. The DAVIDSON, J. (1925) Ann. appl. Biol. 12: 472•`507. wheat seedlings may contain an antibiotic EVANS, A.C. (1938) Ann. appl. Biol. 25: 558•`572. HABER, E.S. & W.G. GAESSLER (1942) Amer. substance against Rhopalosiphum maidis, Soc. hort. Sci., Proc. 40: 429•`431. synthesis and/or acitivity of which reduced HASEMAN, L. (1946) J. econ. Ent. 39: 8•`11. under such conditions as nitrogen defici- HOWITT, A.J. & R.H. PAINTER (1956) Kansas ency. agr. exp. Sta., Tech. Bull. 82: 1•`38. ACKNOWLEDGEMENTS IIJIMA, K., T. TANAKA, K. MATSUSHIMA & H. HORI (1953) Bull. Nat. Inst. agr. Sci., C3: 1•`41. The authors' thanks are due to Dr. ITO, Y. (1960) Bull. Nat. Inst. agr. Sci., C11: Shoziro ISHII and Dr. T.T. IIDA for their 45•`130. kind abvice in the preparation of this MALTAIS, J.B. (1951) Can. Ent. 83; 29•`33. manuscript, and to Mrs. Yasuko IWATA for MALTAIS, J.B. & J.L. AUCLAIR (1957) Can. Ent. her help in carrying the experiments. 89: 365•`370.

MULLER, H.J. (1958) Ent. exp. & appl. 1: 181 REFERENCES •` 190. PAINTER, R.H. (1951) Insect resistance in ARANT, F.S. & C.M. JONES (1951) J. econ. Ent. plants. New York. 44: 121•`122. SNEDECOR, G. (1940) Statistical methods. Ames. CARTIER, J.J. & R.H. PAINTER (1956) J. econ. SNELLING, R.O., R.A. BLANCHARD & J.H. BIGGER Ent. 49: 498•`508. (1940) J. amer. Soc. Agron. 32: 371•`381. COON, B.F., R.G. MILLER & L.W. AURAND WALTER, E.V. & A.M. BRUNSON (1940) J. (1948) Penn. agr. exp. Sta. Dept. Zool. & econ. Ent. 33: 623•`628. Ent. Multilith Rpt. 8p. (Cited from PAINTER, WILDERMUTH, V.L. & E.V. WALTER (1932) U. 1951). S.D.A., Tech. Bull. 306: 1•`21. DAVIDSON, J. (1922) Ann. appl. Biol. 9: 135•`145.

摘 要

寄主の栄養条件 とトウモロコシアブラムシの増殖

伊 藤 嘉 昭 ・平 野 千 里 農林省農業技術研究所

トウモ ロ コ シア ブ ラ ム シは オ オ ムギ,ト ウ モ ロ コ シ な 群 を増 加 したが,高 窒 素 区 や施 肥 土壤 区 で は ほ とん ど増 どイ ネ科 植 物 の害 虫 と して 知 られ て い るが,コ ム ギに は 加 せ ず 大 部 分 は絶 滅 した。 また リー フ ・ケー ジ で生 存 日 ほ とん ど寄生 しな い 。栄 養 条 件 の 異 な る3区 の コ ムギ お 数 や 産 仔 数 を し らべ た と ころ,無 窒 素 区が 最 も高 く,以 よ び オ オ ム ギ 苗(無 窒 素 砂 耕 区,高 窒 素 砂 耕 区,施 肥 土 下 高 窒 素 区,施 肥 土壤 区 の順 で あ った。 壤 区)に お け る個体 群 増 殖,生 存 日数 お よび 産 仔 数 を調 4. 以 上 の結 果 を総 合 す る と,ト ウ モ ロ コシ ア ブ ラ ム 査 した。 シ の寄 主 と して の好 適 性 は次 の順 とな る:施 肥 土 壤 区 オ 1. どの よ うな栄 養 条 件 下 で も,オ オ ムギ 区 の アブ ラ オ ム ギ=高 窒 素 区 オ オ ム ギ 無 窒 素 区 オオ ム ギ>無 窒 素 ム シは コム ギ 区 の ア ブ ラ ム シに く らべ て 速 か に 個 体 群 を 区 コ ム ギ>高 窒 素 区 コム ギ>施 肥 土 壤 区 コ ム ギ。 増 し,生 存 日数 は長 く,ま た 産 仔 数 も多 か った 。 5. コム ギ苗 の寄 主 と して の好 適 性 は苗 体 中 の糖 分 と 2. オ オ ム ギ 区 の 間 で は,無 窒 素 区 で の個 体 群 増 殖 が 正 の相 関 を も ち,窒 素 含 量 と負 の相 関 を も つ よ うで あ る. 高 窒 素 区や 施 肥 土 壤 区 に く らべ て や や 劣 って い るが,生 6. コム ギ 苗 は トウモ ロ コ シア ブ ラ ム シ に対 して抗 生 存 日数や 全 産 仔数 は寄 主 の栄 養 状 態 に よ って ほ とん ど影 的 に作 用 す る物質 を 含有 して い る可 能性 が示 唆 され る。 響 を うけ てい ない 。 そ の 物質 の合 成 能 あ るい は 活性 は,窒 素 欠 乏 条件 下 で は 3. コム ギ 区 の 間 で は,無 窒 素 区 で は ゆ っ く りと個 体 抑 制 され るの で は な い で あ ろ うか 。