132
a. R. POTTS AND 0. P. VICKERMAN
this was particularly noticeable in 1970 due t o the build up of aphid
apterae in the crops. By 27 June 1970 the average density of field-layer
arthropods in cereals was 1850/m2 but 70% of these were aphids.
Arthropod numbers then declined as crops senesced.
B. H E M I P T E R A
The vacuum insect net samples from cereal crops in 1970 contained
62 species of Hemiptera. The samples included 36 species of Aphididae,
two species of Delphacidae, five species of Cicadellidae and 16 species
of Heteroptera.
In 1970 less than 1 % of the individuals of the immature Homoptera
(i.e. excluding migratory aphids temporarily present in crops) were of
species which dwell on dicotyledonous weeds. These were mainly
Myzzcs ascaloniczcs Doncaster on Stellaria media (L.) Vill. Although the
figure increased to 4% in 1971 it was still a marked contrast with the
Heteroptera in which 87% of the nymphs were weed dwellers. Indeed,
the Heteroptera reflect weed abundance more clearly than any group
except the Chrysomelidae (see p. 161).
Only 5% of the Heteroptera were predatory, these being the only
secondary consumers among the cereal Hemiptera.
1. Aphids; introduction
Approximately 45 species of aphid feed on Gramineae in Britain
(V. F. Eastop, Natural History Museum, London). About 15 species
occur on the roots but only six of the remaining species are important
cereal pests. Only three genera are involved-Sitobion ( = Macrosiphum),
Rhopalosiphum and Hetopolophiurn.
Certain of these aphids have been sufficiently numerous to be
classed as outbreak pests for many years. Marsham (1798) mentioned
an outbreak in 1797 and Curtis (1802) said that aphids were highly
detrimental to corn in some years. There was an important outbreak in
northern France in 1830 (Macquart, 1831).
There is little information on long-term changes in cereal aphid
density in Britain, but data concerning trapped migrants from 1951
to 1969 at Rothamsted suggest a five-fold increase starting in the mid
1950’s (Heathcote, 1970). In 1968 very large numbers of cereal aphids
occurred in the eastern counties (Dean and Luuring, 1970) and again
in both 1970 and early 1972. In Canada a similar increase appears
to have taken place (Adams and Drew, 1965). There have recently
been several important outbreaks of cereal aphids in Denmark and
Germany (Kolbe, 1969) and in the southern Netherlands (D. Hille Ris
Lambers, Bladlwisondenoek T. N. 0.).
a. R. POTTS AND 0. P. VICKERMAN
this was particularly noticeable in 1970 due t o the build up of aphid
apterae in the crops. By 27 June 1970 the average density of field-layer
arthropods in cereals was 1850/m2 but 70% of these were aphids.
Arthropod numbers then declined as crops senesced.
B. H E M I P T E R A
The vacuum insect net samples from cereal crops in 1970 contained
62 species of Hemiptera. The samples included 36 species of Aphididae,
two species of Delphacidae, five species of Cicadellidae and 16 species
of Heteroptera.
In 1970 less than 1 % of the individuals of the immature Homoptera
(i.e. excluding migratory aphids temporarily present in crops) were of
species which dwell on dicotyledonous weeds. These were mainly
Myzzcs ascaloniczcs Doncaster on Stellaria media (L.) Vill. Although the
figure increased to 4% in 1971 it was still a marked contrast with the
Heteroptera in which 87% of the nymphs were weed dwellers. Indeed,
the Heteroptera reflect weed abundance more clearly than any group
except the Chrysomelidae (see p. 161).
Only 5% of the Heteroptera were predatory, these being the only
secondary consumers among the cereal Hemiptera.
1. Aphids; introduction
Approximately 45 species of aphid feed on Gramineae in Britain
(V. F. Eastop, Natural History Museum, London). About 15 species
occur on the roots but only six of the remaining species are important
cereal pests. Only three genera are involved-Sitobion ( = Macrosiphum),
Rhopalosiphum and Hetopolophiurn.
Certain of these aphids have been sufficiently numerous to be
classed as outbreak pests for many years. Marsham (1798) mentioned
an outbreak in 1797 and Curtis (1802) said that aphids were highly
detrimental to corn in some years. There was an important outbreak in
northern France in 1830 (Macquart, 1831).
There is little information on long-term changes in cereal aphid
density in Britain, but data concerning trapped migrants from 1951
to 1969 at Rothamsted suggest a five-fold increase starting in the mid
1950’s (Heathcote, 1970). In 1968 very large numbers of cereal aphids
occurred in the eastern counties (Dean and Luuring, 1970) and again
in both 1970 and early 1972. In Canada a similar increase appears
to have taken place (Adams and Drew, 1965). There have recently
been several important outbreaks of cereal aphids in Denmark and
Germany (Kolbe, 1969) and in the southern Netherlands (D. Hille Ris
Lambers, Bladlwisondenoek T. N. 0.).