200
N. WALOFF
adults of two species of beetles, Phyt&cta and Sitonu died from the
effects of the parasitic fungus Beauveria bamianu, and Leucoptera larvae
from a disease which, as far as could be ascertained, was bacterial.
In those phytophagus species where the females do not ovipost
directly on the feeding sitea, the first instar larvae are exposed to new
hazards. Thus Bruchidiua eggs are laid on the outside of the pod, in no
relation to the position of the seeds, i.e. to the feeding sites. The first
instar larvae are primarily locomotary and have to tunnel through the
pericarp, and many of them die in the tunnels before reaching the seeds.
Again, the most vulnerable stage in the life of Sikma is the first instar
larva. In 2 successive years over 86% of the recruited population died
in this stage, probably because the minute larvae failed to reach the
root nodules inside which they feed. Parallel effects in other instars have
been shown by Dethier (1959), in the caterpillars of Melitaea hurrisii
where mortality may be as great as 80% diiring dispersal, owing to the
failure to find new feeding sites.
In the closely knit fauna on the same hoe: plant, it would have been
surprising to find no evidence of intra - or interspecific competition,
but it seems to be more usual than is generally supposed, although its
effects are difficult to prove conclusively. Competition is here understood in Milne’s (1961) sense as “. . . the endeavour of two (or more)
animals to gain some particular thing, or to gain the measure each
wants from the supply of the thing, when the supply is not sufficient
for both (or all)”. As most of the instances of competition have already
been described they are only briefly mentioned here.
Both Brwhidius ater and Apion fusciroatre feed and grow within
broom seeds and only one larva completes development in a aeed
(Parnell, 1966). Sharp frosts which occurred in late May 1961 killed
62% of all pods in Area 4. Many Brmehidiug eggs were then laid on the
remaining pods and between 29-37% of the overcrowded larvae that
entered the pods died as a result of intraspecific competition. Although
it was not proved, probably interspecific competition between Apion
and Bruchidiua larvae also occu.rred, aa Apkm hatched first and had
“the first choice” of the seeds, Parnell (lQ64b) ale0 found evidence of
interspecific competition within the pod galls formed by the midge
Asphndylia sarotiaamni. Here competition waa mainly for space and
occurred between the single larva of A s p M y l i a and the inquiline
larvae of the midge Trotteria, as well as between Trotteria and the larvae
of Aprostocetus brev&.mniis, a hymenopterous parasite of Aspkmd$ia.
M. R. Smith (1968) also found that a small proportion of the population of the bark beetle PhEoeopMurus died from intraspecific competition for food and space (see Fig. 8). Locally, where the galleries were
dense they iatercroseed and then the larger Pkhopibthorus larvae killed
N. WALOFF
adults of two species of beetles, Phyt&cta and Sitonu died from the
effects of the parasitic fungus Beauveria bamianu, and Leucoptera larvae
from a disease which, as far as could be ascertained, was bacterial.
In those phytophagus species where the females do not ovipost
directly on the feeding sitea, the first instar larvae are exposed to new
hazards. Thus Bruchidiua eggs are laid on the outside of the pod, in no
relation to the position of the seeds, i.e. to the feeding sites. The first
instar larvae are primarily locomotary and have to tunnel through the
pericarp, and many of them die in the tunnels before reaching the seeds.
Again, the most vulnerable stage in the life of Sikma is the first instar
larva. In 2 successive years over 86% of the recruited population died
in this stage, probably because the minute larvae failed to reach the
root nodules inside which they feed. Parallel effects in other instars have
been shown by Dethier (1959), in the caterpillars of Melitaea hurrisii
where mortality may be as great as 80% diiring dispersal, owing to the
failure to find new feeding sites.
In the closely knit fauna on the same hoe: plant, it would have been
surprising to find no evidence of intra - or interspecific competition,
but it seems to be more usual than is generally supposed, although its
effects are difficult to prove conclusively. Competition is here understood in Milne’s (1961) sense as “. . . the endeavour of two (or more)
animals to gain some particular thing, or to gain the measure each
wants from the supply of the thing, when the supply is not sufficient
for both (or all)”. As most of the instances of competition have already
been described they are only briefly mentioned here.
Both Brwhidius ater and Apion fusciroatre feed and grow within
broom seeds and only one larva completes development in a aeed
(Parnell, 1966). Sharp frosts which occurred in late May 1961 killed
62% of all pods in Area 4. Many Brmehidiug eggs were then laid on the
remaining pods and between 29-37% of the overcrowded larvae that
entered the pods died as a result of intraspecific competition. Although
it was not proved, probably interspecific competition between Apion
and Bruchidiua larvae also occu.rred, aa Apkm hatched first and had
“the first choice” of the seeds, Parnell (lQ64b) ale0 found evidence of
interspecific competition within the pod galls formed by the midge
Asphndylia sarotiaamni. Here competition waa mainly for space and
occurred between the single larva of A s p M y l i a and the inquiline
larvae of the midge Trotteria, as well as between Trotteria and the larvae
of Aprostocetus brev&.mniis, a hymenopterous parasite of Aspkmd$ia.
M. R. Smith (1968) also found that a small proportion of the population of the bark beetle PhEoeopMurus died from intraspecific competition for food and space (see Fig. 8). Locally, where the galleries were
dense they iatercroseed and then the larger Pkhopibthorus larvae killed