Migration of alate morphs of the bird cherry aphid (Rhopalosiphum padi) and implications for the epidemiology of barley yellow dwarf virus

Abstract

Suction trapping data indicate three periods of migration of Rhopalosiphumpadi in spring, summer and autumn. Four alate morphs are present at different times during the year. A comparison of data from suction traps operating at 12.2 and 1.5 m suggests a different behaviour of females in autumn with more being recorded at 12.2 than 1.5 m. Males, which are only present in autumn, were also more numerous at 12.2 m. During tests to measure barley yellow dwarf virus (BYDV) infectivity, only 9% of female R. padi reproduced on oat seedlings in autumn compared with 74% in summer. Tests on alate female R. padi trapped alive showed that in summer all were exules, but during the first half of September these were largely replaced by gynoparae so that in autumn only 5% of all R. pad; trapped at 12.2 m were alate exules. The aerial densities of gynoparae and males were 10 times greater at 12.2 than 1.5 m while densities of alate exules were similar at both heights. It is suggested that gynoparae and males fly higher to increase the chance of finding a taller dispersed host plant.The implications for BYDV epidemiology of the behaviour and presence of the various R. padi alate morphs indicate that autumn-sown cereals emerging before mid-September are particularly at risk from colonisation by alate exules before the transition to a mainly sexual migrant population is complete. Alate exules introduce BYDV from comparatively local sources. The ratio of total R. padi to Sitobion auenae in suction trap samples in autumn usually exceeds 100 : I , but on crops it was only 10 : I . The ratio of alate exule R. padi to S . avenue in suction traps in autumn was only 12 : I , similar to that observed on crops.

Pattern and rate of within-field dispersal and bionomics of the cowpea aphid, Aphis craccivora (Aphididae), on selected cowpea cultivars

“…Since wind direction at MPFS was generally north-westerly, it was apparent that the pattern and rate of spread of localised aphid infestations or within-field dispersal, was aided by wind currents. It is also well known that winds aid the long distance movement of alates (Johnson, 1954;Tatchell et al, 1988;Tatchell and Woiwod, 1989).…”

Cereal aphid flights and barley yellow dwarf virus infection of cereals in Canterbury, New Zealand

“…Similarly, in eastern Germany, R. padicomprised over 99% of aphids trapped in autumn, but all were males and gynoparae and the main vector of BYDV was S. avenae (Geissler & Karl 1989). In southern England, gynoparae and males comprised c. 90% of R. padi trapped in autumn whereas the remainder were parthenogenetic exules (following an anholocyclic life cycle) flying between cereal crops (Tatchell et al 1988;Kendall & Chinn 1990). In the same area, Kendall & Chinn (1990) found no statistical relationship between total aphid trap catches in autumn, and spring BYDV intensity in nearby cereal crops.…”

Genetic diversity and mode of reproduction in French populations of the aphid Rhopalosiphum padi L.

“…The latter consist of a large number of Gramineae, Juncaceae and Cyperaceae (Rautapaa, 1970) on which parthenogenetic populations develop during the summer (Dixon & Glen, 1971). Where winters are mild and the primary host is scarce, R. padi sustains parthenogenesis all the year round on its secondary hosts, displaying an incomplete life cycle or anholocycle (Dedryver & Gellé, 1982;Tatchell et al, 1988;Simon et al, 1991a). Laboratory experiments have shown that this variation in mode of reproduction is under genetic control (Simon et a!., 1991a(Simon et a!., , 1994.…”