168
N. WALOFF
males and 31 females from Hylaetinaccr. In both instances more females
emerged from the larger host.
(b) Predat0t.S.
(i) The cucujid beetle Laenwpldoew, ater (Ol.), was commonly found
in the galleries of both species of scolytida. Both the larvae and adults
of this predator suck the juices of prey and then enter it and eat out
the contents. L. ater is univoltine, although the early adults give rise
to a second generation which is not completed. This predator thus overwinters as an adult or as an immobile final instar larva. The numbers of
L. ater larvae, pupae and adults reach a peak in June and July and then
decline in August. The beginning of the decline coincides with the
attack by birds on scolytid galleries. Only about 4% (9 out of 203)
L. atep larvae were paxaaitid by Platygerrhw th&wus, Diaaprsia sp.
and by BioqAaccr ephippium.
It waa estimated that about 16.6% of P h b e o p t h were'killed by
Laemophloeua in 1957. No estimate waa made of the proportion of
H y b t i n u s population killed by this predator, but it commonly
occurred in the galleries of this beetle.
(ii) Birds feeding on scolytids. M. R. Smith (1958) considers that predation by birds is the most important single factor in affecting changes
in the po2ulation of P. r-luu.
From his sampling data he estimated that about 40% of the overwintering population of this beetle
was destroyed by birds principally by the Blue Tits ( P a m cae&
L.).
The other birds frequently seen in the area were the Robin, Whitethroat and the Bullfinch. In contrast, only a small number of H. ObSCUrmS
were removed from the galleries by the Blue Tit (P. cueruleaccr) and the
Great Tit (Parus major L.).
Bird damage became apparent in the last week of August and galleries
were attacked throughout the autumn and winter when other insects
which live on the surface of the plants became scarue. The birds changed
their feeding habits through the season. From January to April they
searched leaf buds, from May to August leaves and frsm September to
December dead branches and twigs. The last period corresponded with
the bird attack on mining larvae a t Silwood, which extended from late
August to mid-January.
M. R. Smith compared the ratios of paragiteS and Phbeop?&rw, on
broom stems damaged by birds and on undamaged stems of the same
age and came to the conclusion that a higher proportion of available
parmites than of hosts were eaten, This is mainly because most parasites lie in the parent galleries which are more acceesible (see Table XLI).
The relationship between the density of galleries and bird attack was
also investigated. Stems densely attacked by P M a r v p & h were liable
to be completely stripped of beetles by the end of winter, whereas Borne
N. WALOFF
males and 31 females from Hylaetinaccr. In both instances more females
emerged from the larger host.
(b) Predat0t.S.
(i) The cucujid beetle Laenwpldoew, ater (Ol.), was commonly found
in the galleries of both species of scolytida. Both the larvae and adults
of this predator suck the juices of prey and then enter it and eat out
the contents. L. ater is univoltine, although the early adults give rise
to a second generation which is not completed. This predator thus overwinters as an adult or as an immobile final instar larva. The numbers of
L. ater larvae, pupae and adults reach a peak in June and July and then
decline in August. The beginning of the decline coincides with the
attack by birds on scolytid galleries. Only about 4% (9 out of 203)
L. atep larvae were paxaaitid by Platygerrhw th&wus, Diaaprsia sp.
and by BioqAaccr ephippium.
It waa estimated that about 16.6% of P h b e o p t h were'killed by
Laemophloeua in 1957. No estimate waa made of the proportion of
H y b t i n u s population killed by this predator, but it commonly
occurred in the galleries of this beetle.
(ii) Birds feeding on scolytids. M. R. Smith (1958) considers that predation by birds is the most important single factor in affecting changes
in the po2ulation of P. r-luu.
From his sampling data he estimated that about 40% of the overwintering population of this beetle
was destroyed by birds principally by the Blue Tits ( P a m cae&
L.).
The other birds frequently seen in the area were the Robin, Whitethroat and the Bullfinch. In contrast, only a small number of H. ObSCUrmS
were removed from the galleries by the Blue Tit (P. cueruleaccr) and the
Great Tit (Parus major L.).
Bird damage became apparent in the last week of August and galleries
were attacked throughout the autumn and winter when other insects
which live on the surface of the plants became scarue. The birds changed
their feeding habits through the season. From January to April they
searched leaf buds, from May to August leaves and frsm September to
December dead branches and twigs. The last period corresponded with
the bird attack on mining larvae a t Silwood, which extended from late
August to mid-January.
M. R. Smith compared the ratios of paragiteS and Phbeop?&rw, on
broom stems damaged by birds and on undamaged stems of the same
age and came to the conclusion that a higher proportion of available
parmites than of hosts were eaten, This is mainly because most parasites lie in the parent galleries which are more acceesible (see Table XLI).
The relationship between the density of galleries and bird attack was
also investigated. Stems densely attacked by P M a r v p & h were liable
to be completely stripped of beetles by the end of winter, whereas Borne