STUDIES ON THE CEREAL ECOSYSTEM
141
Larval Tipulidae damage most arable crops, but attention is generally
focused on the damage they cause to spring cereals (French, 1969).
In years of high populations, losses may be widespread and severe.
It has been estimated (Potter et al., 1965) that in an average year
approximately 106 000 ha of wheat and barley may be affected to some
extent by leatherjackets. They are not important in the relatively
dry soils of the study area.
The wheat blossom midges Contarinia tritici and Sitodiplosis msellana
are important outbreak species throughout the wheat lands of North
America, Europe, Russia and Asia. Although wheat is usually attacked,
crops of rye and barley may also suffer damage. Barnes (1956) investigated the biology of these species on the Broadbalk continuous
wheat field at Rothamsted Experimental Station for a number of years:
in bad years more than 10% of the grain was lost. In the early 1950’s
an outbreak of C. tritici resulted in heavy grain losses in Eire. There is,
however, a lack of information on the current importance of these
pests in commercial crops in this country.
Although both species were scarce in 1967 and 1968 some outbreaks
were noted in the study area in 1969, and in an A.D.A.S. survey of 20
fields throughout West Sussex the average density of the larvae was
about 4000/m2. I n 1970 the average density of emerging wheat blossom
midge adults was approximately 1000/m2 over an area of 50 ha, an
infestation which clearly must be considered an important outbreak.
Unfortunately it was not possible to estimate the effect on yield
because the midge invasion was accompanied by a severe attack of
glume blotch, Septoria nodorum, which has a similar effect on the grain.
I n 1971 the midges were back to their background level of abundance
although there was some carry-over from the wheat of 1970.
In both 1970 and 1971 most adults were found in those fields which
followed winter wheat (see Table VIII). This suggested that adult
dispersal, a t least in 1970 and 1971, was limited, and supported the
suggestion of Jones and Jones (1964) that these midges can be controlled by avoiding successive wheat crops. In fact, in the study area,
successive wheat crops are avoided wherever practicable because of the
build-up of the root fungus, Ophiobolus graminis, in the fist three
successive crops.
Although for the 20 years prior to 1953 few attacks by cereal leaf
miner (either Agromyza or Domomyxa) were recorded in the Monthly
Summaries of Insect Pests issued by the Plant Pathology Laboratory,
Harpenden, since that date there have been numerous reports of widespread damage. Three species appear to be common in BritainAgromyza ambigua Fall., A . nigrella Rond. and the Ephydrid Hydrellia
griseola Fall. Damage appears to be sporadic and in a three-year
141
Larval Tipulidae damage most arable crops, but attention is generally
focused on the damage they cause to spring cereals (French, 1969).
In years of high populations, losses may be widespread and severe.
It has been estimated (Potter et al., 1965) that in an average year
approximately 106 000 ha of wheat and barley may be affected to some
extent by leatherjackets. They are not important in the relatively
dry soils of the study area.
The wheat blossom midges Contarinia tritici and Sitodiplosis msellana
are important outbreak species throughout the wheat lands of North
America, Europe, Russia and Asia. Although wheat is usually attacked,
crops of rye and barley may also suffer damage. Barnes (1956) investigated the biology of these species on the Broadbalk continuous
wheat field at Rothamsted Experimental Station for a number of years:
in bad years more than 10% of the grain was lost. In the early 1950’s
an outbreak of C. tritici resulted in heavy grain losses in Eire. There is,
however, a lack of information on the current importance of these
pests in commercial crops in this country.
Although both species were scarce in 1967 and 1968 some outbreaks
were noted in the study area in 1969, and in an A.D.A.S. survey of 20
fields throughout West Sussex the average density of the larvae was
about 4000/m2. I n 1970 the average density of emerging wheat blossom
midge adults was approximately 1000/m2 over an area of 50 ha, an
infestation which clearly must be considered an important outbreak.
Unfortunately it was not possible to estimate the effect on yield
because the midge invasion was accompanied by a severe attack of
glume blotch, Septoria nodorum, which has a similar effect on the grain.
I n 1971 the midges were back to their background level of abundance
although there was some carry-over from the wheat of 1970.
In both 1970 and 1971 most adults were found in those fields which
followed winter wheat (see Table VIII). This suggested that adult
dispersal, a t least in 1970 and 1971, was limited, and supported the
suggestion of Jones and Jones (1964) that these midges can be controlled by avoiding successive wheat crops. In fact, in the study area,
successive wheat crops are avoided wherever practicable because of the
build-up of the root fungus, Ophiobolus graminis, in the fist three
successive crops.
Although for the 20 years prior to 1953 few attacks by cereal leaf
miner (either Agromyza or Domomyxa) were recorded in the Monthly
Summaries of Insect Pests issued by the Plant Pathology Laboratory,
Harpenden, since that date there have been numerous reports of widespread damage. Three species appear to be common in BritainAgromyza ambigua Fall., A . nigrella Rond. and the Ephydrid Hydrellia
griseola Fall. Damage appears to be sporadic and in a three-year