I94
N. WALOFF
in thiriking that diqwxnal of Phytodectu olivacecc is a slow proccss, mainly
hy walking (Richard8 and Waloff, 1961). A large number of Phylodecta
were collected on the small broom trap plants outsidc Area 4, both after
the spring and autumn adult emergence and nearly all the dispersing
females were immature. Very few individuals were caught in the suction
traps and it seems probable that the beetles tend to fty only a few feet
above the ground level. No alary dimorphism was noted in Phytodecta,
but it occurred in two curculionid beetles, rSitona regensteinensis and
Apion immune.
Williams (1966) examined and analysed the catches of a number of
Apion species in the suction and light traps at Silwood and amongst
them the two that live on broom, namely A. fuscimstre and A . immune.
A. fuscinostre overwinters in the adult stage in broom litter (Parnell,
1966) and does not disperse in the autumn. A . immune has several
overlapping generations and overwinters in all stages of its life history.
The dispersing beetles of both species were caught in spring and in early
summer and none after June. “Flitting” within the plantation, usually
1.5 to 2 m above ground level, was seen in both species up to midsummer and occasionally an adult was seen to alight on a plant from a
height of over 3 m. The emigrating females of A . immune were all
immature. No alary dimorphism was seen in A. fuscinostre and all
beetles collected on broom were alate, whereas in the A . immune population there was a great preponderance of brachypterous forms End out
of the 308 beetles carefully examined, only 13.6% were alate. The ratio
of alate to brachypterous forms w w greater in the females than males
(9 1 alate:3-9 brachypterous; cf 1:12.4), but as they copulate on emergence all the emigrating females were fertilieed.
Only 9% of the Sitona regensteinensb population studied by Danthanarqana (1965) were alate (Table LX). There are two types of
movements that lead to dispersal in Sitona regensteineneie. One is walking by brachypterous forms at the time of emergence from hibernation.
the other is by flight, a few weeks later by the macropterous forms,
Dispersal by walking was assessed by sampling broom trap plants,
placed on a logarithmic scaie away from the study area. The density
of dispersing individuals waa inversely proportional to the distance from
the source and could be expressed by the linear regression equation
y = 2.272-1.285 2 (p =. = 0.01), where y is the logarithm of the number
of Sitona on a trap plant and x the log. of distance from the atudy area.
Danthanarayana considers that it is very unlikely that walking could
lead to dispersal over large distanceR, but is a means of finding young
plants in a natural broomland where bushes of various ages and state
are found and where expansion of the habitat itself takes place by
growth of new plants at the boundaries.
N. WALOFF
in thiriking that diqwxnal of Phytodectu olivacecc is a slow proccss, mainly
hy walking (Richard8 and Waloff, 1961). A large number of Phylodecta
were collected on the small broom trap plants outsidc Area 4, both after
the spring and autumn adult emergence and nearly all the dispersing
females were immature. Very few individuals were caught in the suction
traps and it seems probable that the beetles tend to fty only a few feet
above the ground level. No alary dimorphism was noted in Phytodecta,
but it occurred in two curculionid beetles, rSitona regensteinensis and
Apion immune.
Williams (1966) examined and analysed the catches of a number of
Apion species in the suction and light traps at Silwood and amongst
them the two that live on broom, namely A. fuscimstre and A . immune.
A. fuscinostre overwinters in the adult stage in broom litter (Parnell,
1966) and does not disperse in the autumn. A . immune has several
overlapping generations and overwinters in all stages of its life history.
The dispersing beetles of both species were caught in spring and in early
summer and none after June. “Flitting” within the plantation, usually
1.5 to 2 m above ground level, was seen in both species up to midsummer and occasionally an adult was seen to alight on a plant from a
height of over 3 m. The emigrating females of A . immune were all
immature. No alary dimorphism was seen in A. fuscinostre and all
beetles collected on broom were alate, whereas in the A . immune population there was a great preponderance of brachypterous forms End out
of the 308 beetles carefully examined, only 13.6% were alate. The ratio
of alate to brachypterous forms w w greater in the females than males
(9 1 alate:3-9 brachypterous; cf 1:12.4), but as they copulate on emergence all the emigrating females were fertilieed.
Only 9% of the Sitona regensteinensb population studied by Danthanarqana (1965) were alate (Table LX). There are two types of
movements that lead to dispersal in Sitona regensteineneie. One is walking by brachypterous forms at the time of emergence from hibernation.
the other is by flight, a few weeks later by the macropterous forms,
Dispersal by walking was assessed by sampling broom trap plants,
placed on a logarithmic scaie away from the study area. The density
of dispersing individuals waa inversely proportional to the distance from
the source and could be expressed by the linear regression equation
y = 2.272-1.285 2 (p =. = 0.01), where y is the logarithm of the number
of Sitona on a trap plant and x the log. of distance from the atudy area.
Danthanarayana considers that it is very unlikely that walking could
lead to dispersal over large distanceR, but is a means of finding young
plants in a natural broomland where bushes of various ages and state
are found and where expansion of the habitat itself takes place by
growth of new plants at the boundaries.