Population Growth, Longevity and Fecundity of Rhopalosiphum maidis FITCH (Homoptera: Aphididae), on Wheat and Barley Seedlings Grown under Different Nutritional Conditions By Yosiaki ITO and Chisato HIRANO NationalInstitute of AgriculturalSciences, Nishigahara, Kita-ku, Tokyo Insect: The aphid 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 pest insect of respective seasons from barley fields of corn and grain sorghum 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 aphids 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 Wheats 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.