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Journal of Mosquito Research, 2013, Vol.3, No.5, 33
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36
ieved by
H. indica
and 3~4 times the mortality values
achieved by
S. feltiae
and
S. carpocapsae
, respectively.
When using
Steinernema
species, nematode individuals
were melanized and were obviously seen through the
host cuticle (Figure 2). In contrast,
Heterorhabditis
species successfully completed their life cycle within
the host larvae till adult stage (Figure 3) and infective
juvenile emergence. For this reason, only
Heterorhab-
ditis
species were used to estimate their role in contr-
olling the mosquito larvae.
Figure 2
Culex quinquefasciatus
larvae showing the melanized
Steinernema carpocapsae
nematode in thorax and abdomen
Figure 3
Culex quinquefasciatus
larvae showing the adult stage
of
Heterorhabditis bacteriophora
in head and thorax (showed
by an arrow)
3.2 Exposure period assay
Increasing the exposure period from 3~12 hr resulted
in a significant increase in nematode entry to the host
in both
H. bacteriophora
and
H. indica
(r=0.97, P
≤
0.01), (Figure 4), but the difference between numbers
of
H. bacteriophora
juveniles and those of
H. indica
was not quite significant during the first 3 hr of incub-
ation (P
≥
0.05). The difference between them becomes
more pronounced as the duration of exposure increased
from 6~12 hr (P
≤
0.01) ; where the number of the inf-
ective juveniles that entered the hosts was doubled.
Considering host mortalities, it was found that, increa-
sing the exposure period resulted in a significant
increase in host mortality (r=0.9, P
≤
0.01). Also, it is
worthy to mention that, at all of the tested exposure
periods,
H. bacteriophora
caused significantly higher
host mortalities than those obtained by using
H. indica
(Figure 5). After 6 hr, the recorded host mortality
values due to
H. bacteriophora
infection were nearly
double the mortality levels recorded due to
H. indica
infection. By increasing the exposure time from 6 to
24 hr, the increase in host mortality became gradual in
both nematode species. Maximum mortality (96.0%,
80.0%) was achieved when insects were exposed to
nematodes from the species
H. bacteriophora
and
H.
indica
for 48 hr, respectively (Figure 5).
Figure 4 The effect of the exposure of
C. quinquefasciatus
larvae to 300 ijs of
H. bacteriophora
(=HB) and
H. indica
(=HI)
per larva for different time periods on the average number of
nematodes found in the insect cadaver (=N)
Figure 5 The effect of the exposure of
C. quinquefasciatus
larvae to 300 ijs of
H. bacteriophora
(=HB) and
H. indica
(=HI)
per larva for different time periods on percentage host larval
mortality in the exposure period assay
Considering lethal time, it was found that
H. bacteri-
ophora
was proved to be a faster killer than
H. indica
,
where the Probit analysis showed a deduced LT
90