Sitobion avenae F. multiplies at a higher rate on winter wheat than Rhopalosiphum padi L. and Metopolophium dirhodum Wlk. Unlike the other two species S. avenae prefers the ear, where it multiplies twice as quickly as on the flag leaf. Infestation of the ear rather than of the leaves leads to reduction of the average grain weight. These results suggest that S. avenae is the most injurious. In 3 field trials with this aphid fungal growth on honeydew caused about half of the damage. After correction for the fungus effect, the loss in yield caused by S. avenae feeding on the ear did not differ much from that calculated from its energy budget. Therefore, it is concluded that stylet insertion and saliva injection have no important influence on the growth of grains. From results with long living and highly productive crops it seems that honeydew can cause a more serious loss in yield if the crop does not prematurely ripen under the influence of various other yield-reducing factors.

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Feeding and multiplication of three cereal aphid species and their effect on yield of winter wheat

(1984). The biology of aphids. Journal of Biological Education: Vol. 18, No. 2, pp. 119-131.

The biology of aphids

Living organisms maintain a thermodynamic steady state that is far from equilibrium and thus they require a constant source of free energy. A part of this energy may be transformed or stored for short or long periods of time, but most is degraded to heat through the performance of the internal work necessary for life. The direct connection between life and the produc­ tion of heat was first convincingly demonstrated in the late eighteenth century by Lavoisier & Laplace using a simple ice calorimeter [see discus­ sion in Lusk (61), p. 33ff.]. Since then, the study of energetics (molecular, cellular, and organismal) has interested generations of biochemists and physiologists. Energetics tells us much about the conditions and mecha­ nisms responsible for vital processes and transformations within organisms. Energy considerations also have an important effect on the behavior and interaction ofindividuals and populations. But not until well into the twen­ tieth century, following the development of ecology as a rigorous discipline, was this common knowledge subjected to scientific scrutiny. The relative ignorance that exists concerning the energetics of insects is surprising, especially if one considers their numerical dominance and diver­ sity. This lack of attention at the physiological level persisted until well into the twentieth century. Researchers were more concerned with investigating human energy needs and those of domesticated animals which, with a few notable exceptions, e.g. the honey bee, are all mammals. Then too, mam­ mals, like all homoiotherms, degrade a much larger proportion of as­ similated energy to heat than do poikilotherms, so measurements of respiratory heat loss dominated the early energetics scene. .

Energy Transfer in Insects

In plant growth room (PGR) and open-air pot (OAP) experiments, potato cvs King Edward and Maris Piper were grown under two nitrogen levels or two different nitrogen release patterns. Plants were subjected to infestation by peach potato aphids Myzus persicae (Homoptera: Aphididae). Total glycoalkaloid (GA) levels were measured in the foliage of both infested and non-infested plants, before, during and after aphid infestation. In the PGR experiment, aphid infestation reduced the amounts of total GAs in both cultivars. This reduction is attributed to the sugar deficiency induced in the plants owing to the dense aphid colonization. Results from the OAP experiment showed a temporal increase of GAs produced by potato cv. King Edward plants subjected to aphid infestation. Elevated amounts of nitrogen in the nutrient solutions (PGR experiment) reduced total GAs, while no differences were observed between manure and fertilizer treated plants (OAP experiment). It is concluded that the source of available nitrogen does not affect foliar GA synthesis in potatoes, and as a consequence, does not affect its endogenous chemical defense against insect herbivory. The case for insect-induced chemical defense mechanisms as triggered by low rates of aphid infestation is discussed.

Interactions of aphid herbivory and nitrogen availability on the total foliar glycoalkaloid content of potato plants.

This study investigates the thermal requirements, nymphal development rates and the fecundity of both alate and apterous adults of the giant willow aphid, Tuberolachnus salignus (Gmelin) at several temperatures. Nymphal development rate increased linearly with temperature. It was estimated that 196 ± 4 degree-days above a threshold temperature of 5.5 ± 0.3°C were required for apterae to complete development from birth to final ecdysis. The alate morph was significantly less fecund than the apterous morph and its fecundity did not vary with temperature. The apterous morph displayed highest fecundity at 20°C. Survival to reproduction was lower in the alate morph, but temperature had no effect on the proportion reproducing in either morph.

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M. Llewellyn

Papers

The Ecological Energetics of the Willow Aphid Tuberolachnus salignus (Gmelin); Honeydew Production