126
Q. R. POTTS AND a. P. VICKERMAN
dispersal would be a clear disadvantage. Many species have rather
limited dispersal powers. For example, among Coleoptera, Crepidodera
transversa Mm. (Co1eoptera:Chrysomelidae) and Tytthaspis 16-punctata
(L.) (Co1eoptera:Coccinellidae) had a markedly local distribution in
what appeared to be a comparatively uniform habitat (Figs. 8 and 9).
I n the case of Tytthaspis the distribution was centred on areas in which
piles of wood commonly contained large numbers of hibernating
individuals. The precise ecological requirements of these two species
were not investigated; however, another species, Gastrophysa polygoni
(L.) (Coleoptera:Chrysomelidae), was found to feed preferentially on
Polygonurn awiculare L. Although G . polygoni can be found on other
Polygonum spp. and fed on them in a laboratory trial, it can breed
successfully only on P . awiculare and P . convolvulus L. But even on
P . convolvulus the egg production is very limited in the laboratory
(Tischler, 1966) and we never found larvae on this species in the
laboratory or in the field.
TABLE V
West Swam study area, 1968-1971
Changes in the atatw, of Polygonum aviculare L. on atubblea in the
No. times present in 10 rnz random quadrats*
Fieldsexamined 0 1 2 3 4 6
6 7 8 9 10
Meam
1968
36
12 6
3
1
6
3
1
4 - - - 2.6
-(34%)
61 %
14%
1971
20
14 2
1 - 1 1 - - - 1 -
1.1
-(70%)
26%
6%
* The quadrats were placed in October.
P . aviculare varied in abundance from year to year, but there has
been a steady decline of post spray populations over the period 19681971 (Table V). Although G . polygoni waa never found on any plant
other than P . awiculare in the field, there were many fields containing
the weed but not the animal. It appears that G. polygoni has poor
powers of dispersal, and that it therefore occurs mainly where P .
aviculare is permanent. At least this seems to be the reason for its
extraordinary distribution in cereal fields (Fig. 10).
Q. R. POTTS AND a. P. VICKERMAN
dispersal would be a clear disadvantage. Many species have rather
limited dispersal powers. For example, among Coleoptera, Crepidodera
transversa Mm. (Co1eoptera:Chrysomelidae) and Tytthaspis 16-punctata
(L.) (Co1eoptera:Coccinellidae) had a markedly local distribution in
what appeared to be a comparatively uniform habitat (Figs. 8 and 9).
I n the case of Tytthaspis the distribution was centred on areas in which
piles of wood commonly contained large numbers of hibernating
individuals. The precise ecological requirements of these two species
were not investigated; however, another species, Gastrophysa polygoni
(L.) (Coleoptera:Chrysomelidae), was found to feed preferentially on
Polygonurn awiculare L. Although G . polygoni can be found on other
Polygonum spp. and fed on them in a laboratory trial, it can breed
successfully only on P . awiculare and P . convolvulus L. But even on
P . convolvulus the egg production is very limited in the laboratory
(Tischler, 1966) and we never found larvae on this species in the
laboratory or in the field.
TABLE V
West Swam study area, 1968-1971
Changes in the atatw, of Polygonum aviculare L. on atubblea in the
No. times present in 10 rnz random quadrats*
Fieldsexamined 0 1 2 3 4 6
6 7 8 9 10
Meam
1968
36
12 6
3
1
6
3
1
4 - - - 2.6
-(34%)
61 %
14%
1971
20
14 2
1 - 1 1 - - - 1 -
1.1
-(70%)
26%
6%
* The quadrats were placed in October.
P . aviculare varied in abundance from year to year, but there has
been a steady decline of post spray populations over the period 19681971 (Table V). Although G . polygoni waa never found on any plant
other than P . awiculare in the field, there were many fields containing
the weed but not the animal. It appears that G. polygoni has poor
powers of dispersal, and that it therefore occurs mainly where P .
aviculare is permanent. At least this seems to be the reason for its
extraordinary distribution in cereal fields (Fig. 10).