120
N. WALOFF
the host plant contributed to these differences in fecundity. Waloff and
Richards (1968) and Donia (1968) have shown in Phytolivacea
that beetles fed on young broom shoots laid more eggs than those fed
on old shoots. The effects of the ageing hoet planta may have thus
effected fecundity in the field populations of Sijona and possibly of
Phybdmta where the decline in the 5 years WBB also by a factor
of 2.4.
(b) Motzaldy. The muses of mortality of adult beetles strongly
paralleled those of Phyt&cta. A section of the adult population was
killed by a hymenopterous parasite C e n t b k excrucian8 Haliday
[ =Leiolphron Zituratus Hal.] (Braconidae). The parasite is a parthenogenetic, thelytokous, bivoltine species with a facultative diapause in
the first instar larval stage within the haemomle of the hibernating
host. The first generation of Centistes emerges in MayJune, the second
in September-October.
Some adult mortality waa caused by fungal diseases, mainly by
Beauveria bassiana. Another pathogenic fungus Paecilomycas sp. waa
isolated from Sitana and identified by Dr M. F. Madelin, but this
occurred in one year only and attacked less than 1 % of the population.
A large proportion of the beetles disappeared in winter. One of the
reawns for “winter disappearance” is the tendency shown by some
brachypterous forms to emigrate (walk) from the habitat, and by
macropterous forms to fly out of the habitat in early spring (see Section IX). It is not considered that Sitona adults died by exposure to
lethal temperatures. J. Smith (verbal communication) studied the “cold
death point” of 5. regensteineneis and she found that whereas some
individuals were killed by exposures ranging between -0.1”C and
-lO.S”C, most of the weevils were able to withstand temperatures of
2 to 3°C below zero. Throughout this study Denthanarayana recorded
temperatures in the broom litter and these did not fall below zero at
any stage and even in the severe winter of 1962-63, the lowest temperature recorded was 0.5”C. It is possible that, as in Phytodecta, much
unexplained “winter disappearance” wae caused by greater effects
of fungi than were detected and also by the predators. The causes
of mortality according to Danthanarayana are summarised in
Table XVII.
The causes of mortality in the egg stage were identified as sterility,
paraitism by the mymarid Patasson diam (Girault) (det. R. L. Doutt)
and to predation by the carabid and staphylinid beetles and by mites.
Initial laboratory observations involved confining the eggs with suspected predators, and these were confirmed by precipitin tests, which
are diacussed in a later section (see p. 178). Dsnthanarayana EWE up
mortality in the egg stage in Table XVIII.
N. WALOFF
the host plant contributed to these differences in fecundity. Waloff and
Richards (1968) and Donia (1968) have shown in Phytolivacea
that beetles fed on young broom shoots laid more eggs than those fed
on old shoots. The effects of the ageing hoet planta may have thus
effected fecundity in the field populations of Sijona and possibly of
Phybdmta where the decline in the 5 years WBB also by a factor
of 2.4.
(b) Motzaldy. The muses of mortality of adult beetles strongly
paralleled those of Phyt&cta. A section of the adult population was
killed by a hymenopterous parasite C e n t b k excrucian8 Haliday
[ =Leiolphron Zituratus Hal.] (Braconidae). The parasite is a parthenogenetic, thelytokous, bivoltine species with a facultative diapause in
the first instar larval stage within the haemomle of the hibernating
host. The first generation of Centistes emerges in MayJune, the second
in September-October.
Some adult mortality waa caused by fungal diseases, mainly by
Beauveria bassiana. Another pathogenic fungus Paecilomycas sp. waa
isolated from Sitana and identified by Dr M. F. Madelin, but this
occurred in one year only and attacked less than 1 % of the population.
A large proportion of the beetles disappeared in winter. One of the
reawns for “winter disappearance” is the tendency shown by some
brachypterous forms to emigrate (walk) from the habitat, and by
macropterous forms to fly out of the habitat in early spring (see Section IX). It is not considered that Sitona adults died by exposure to
lethal temperatures. J. Smith (verbal communication) studied the “cold
death point” of 5. regensteineneis and she found that whereas some
individuals were killed by exposures ranging between -0.1”C and
-lO.S”C, most of the weevils were able to withstand temperatures of
2 to 3°C below zero. Throughout this study Denthanarayana recorded
temperatures in the broom litter and these did not fall below zero at
any stage and even in the severe winter of 1962-63, the lowest temperature recorded was 0.5”C. It is possible that, as in Phytodecta, much
unexplained “winter disappearance” wae caused by greater effects
of fungi than were detected and also by the predators. The causes
of mortality according to Danthanarayana are summarised in
Table XVII.
The causes of mortality in the egg stage were identified as sterility,
paraitism by the mymarid Patasson diam (Girault) (det. R. L. Doutt)
and to predation by the carabid and staphylinid beetles and by mites.
Initial laboratory observations involved confining the eggs with suspected predators, and these were confirmed by precipitin tests, which
are diacussed in a later section (see p. 178). Dsnthanarayana EWE up
mortality in the egg stage in Table XVIII.