Effect of temperature on the cereal aphids Metopolophium dirhodum (Wlk.), Rhopalosiphum padi (L.) and Macrosiphum avenue (F.) (Hem., Aphididae) AbstractThe effect of temperature within the range 10-30°C on Metopolophium dirhodum (Wlk.), Rhopalosiphum padi (L.) and Macrosiphum avenae (F.) was measured in controlled environment cabinets. Development rates increased with temperature to a maximum at 20°C for Metopolophium dirhodum, 22-5°C for Macrosiphum avenae and 25°C for R. padi, decreasing thereafter to zero by 30 °C when all the nymphs died. The fourth instar and pre-reproductive adult appeared to be affected at temperatures below those for the younger instars. Mortalities of immature M. avenae were similar between 10° and 25°C, but more immature Metopolophium dirhodum died at high, and R. padi at low, temperatures. Survival rates decreased with increase of temperature, and fecundity was largest at 20°C. Rates of increase became largest at 20°C for M. dirhodum and Macrosiphum avenae and at 25°C for it. padi. Above 15°C, R. padi had a 4-16 times larger capacity for increase than the other two species because it developed faster and achieved its rate of maximum fecundity sooner.

In a study of aphids and their parasites, hyperparasites and predators in a field of cereals at Rothamsted Experimental Station in 1970-71, samples were taken by counting specimens in 0-3-m lengths of row and by means of a suction trap set 12-2 m above ground and 0-5 km away from the field. Migrant aphids (Metopolophium dirhodum (Wlk.) and Macrosiphum avenae (F.)) and Braconid parasites (Aphidius spp., Ephedrus plagiator (Nees) and Praon volucre (Hal.)) were caught from April-May to August-September, with most from mid-June to August, whereas hyperparasites (Phaenoglyphis sp., Lygocerus aphidivorus Kieff., Asaphes vulgaris Wlk., Coruna clavata Wlk. and Alloxysta sp.) occurred for more of the year. Of the six parasite species attacking aphids on cereals in 1970-71, three Aphidius spp. were more common than E. plagiator and Praon volucre. Parasitism was higher and aphids were fewer in 1971 than in 1970. In the field, more than 80% of the mummies were of old nymphs; parasitism of live old nymphs and apterae was similar, larger than for alatae, and larger for Metopolophium dirhodum than for Macrosiphum avenae. Hyperparasitism by five species affected parasitism, especially in 1970. Migrant Coccinellids were trapped at the start and end of aphid infestations on cereals, Syrphids mainly in July and August, and other predators for longer. The commonest predators were Coccinella septempunctata L. and Propylea quatuordecimpunctata L. in 1970 and Syrphus balteatus (Deg.) in 1971; the others were scarce. July populations of aphids were primarily reduced by the Syrphids.

In controlled temperature, light and relative humidity, Metopolophiurn dirhodum and Sitobion avenue multiplied more on young Proctor barley than on Blenda oats, and less on Cappelle wheat. Rhopalosiphum padi increased in number fastest on barley and slowest on oats. More survived, and generation lengths seemed shorter, on barley for M . dirhodum and S. avenue and on wheat for R. pa&.Tests with young cereals outdoors generally agreed with those in controlled conditions. On mature plants, there were more M . dirhodum on barley, more R. padi on wheat and more S. avenue on oats than on the other cereals.Given a free choice in large cages outdoors, most aphids were found on barley. When allowed to choose between grasses, more M. dirhodum were on Dactylis glomerata, Poa pratensis and Festuca pratensis, more R. padi on Lolium perenne and F. pratensis, and more S . avenue on D. ylomerata and L. perenne. Most aphids of all species combined were on F. pratensis, Loliumand Phleum, and fewest on Festuca rubra and Holcus mollis.The host plants of the English grain aphid (Sitobion avenue F.) and the oat birdcherry aphid (Rhopalosiphum padi L.) outside Britain include several dozen species for both aphids (Patch

S U M M A R YCereal crops were examined weekly for aphids during 1969. Plants in twenty samples of row 0.3 m long were examined in a sheltered perimeter of a crop and along a transect 36.6 m into the crop. Aphids were usually first found within 1-4 weeks of the first alatae caught in a suction trap operating 12.2 m above ground. When first found from 10 to 27 % of the 0.3 m lengths sampled contained aphids.Rhopalosiphum padi, first found late in May, were scarce ( < 0*53/0*3 m) throughout June and July. Sitobium spp. and Metapolophium dirhodum, which appeared in mid-June, were more numerous than R . padi; most occurred during the second half of July, and populations decreased just before harvest in early August. Sitobium avenue was more abundant (max. 19*3/ sample) than either S. fragariae (0.91) or M. dirhodum (2.5 I).More aphids occurred in oats (max. 52/0.3 m) during July than in wheat (45), and barley had fewer (6.8). S. avanae was-more abundant than M . dirhodum in sheltered areas of barley and wheat, and in exposed areas of the same crop M. dirhodum was commonest. Along sheltered perimeters, the ratio of S. avenue to M. dirhodum was largest in barley ( I I : I), intermediate in oats (6:1) and smallest in wheat (3*7:1). Sitobium spp. were most numerous on the ears, when most M. dirhodum were on the leaves.Regression analyses of log. S2 on log. m suggested that S. avenue was more evenly distributed within (36.6 m) the field (b = 1.056 f 0.109) than along the sheltered perimeter (b == 1-432 0.132), though it seemed similarly distributed along perimeters of barley, oats and wheat. The distributions of M. dirhodum and Sitobiurn spp. along sheltered perimeters of all crops were apparently similar.

For most of this century, aphids have been known to infest cereals, but their potential importance does not seem to have been fully appreciated until the early 1950s when they were found to be vectors of barley yellow dwarf virus (Bruehl, 1961). Although this discovery initiated a great deal of research in many countries, especially in North America, very little was done, or thought necessary to be done, in Britain. In 1968, however, some of this complacency was lost when the large numbers of aphids found on the cereals in this country indicated how little was known about them and their effects. Aphids are part of a complex four‐dimensional continuum of time and space, and this paper briefly describes some of the results obtained since 1969.