Basic HTML Version
Journal of Mosquito Research, 2013, Vol.3, No.5, 33
-
44
http://jmr.sophiapublisher.com
34
host insect dies rapidly within 2~3 days (Poinar, 1990;
Wang and Bedding, 1996). Upon death of the insect,
the bacteria digest the host tissues, providing nourish-
ment needed for the nematode to successfully repro-
duce and provide conditions for the nematode multipl-
ication (Burnell and Stock, 2000; Park et al., 2004). In
addition, the bacterial cells produce antibiotics that
protect the host cadaver from saprophytes and scaven-
gers (Boemare, 2002; Hazir, 2004). The infective juve-
niles of the next generations leave the cadaver and
enter the environment seeking for infecting new host
(Kaya and Gaugler, 1993).
Studies on the potential of the entomopathogenic
nematodes for the control of mosquitoes are rare.
Welch & Bronskill (1962), Dadd (1971) and Poinar &
Kaul (1982) were the first to study the potentiality of
the rhabditoid nematode and its associative bacterium
against mosquitoes. Recently, a laboratory colony of
the mosquito,
C. apicinus
was parasitized by the
nematode
S. rarum
(Cagnolo & Walter, 2010).
The fitness of a parasite can be adversely affected by
increasing population density within the host. This has
been noted in vertebrate intestinal helminthes, and
mermithid nematodes in mosquito larvae. Density
dependent effects on parasite include reduced fecund-
dity, increased mortality, change in sex ratio, reduction
in adult size, increased generation time and reduced
oviposition (Selvan & Muthukrishnan, 1988). Although
all entomopathogenic nematodes have the same general
life histories, species difference in host utilization
(Selvan & Blackshaw, 1990) and reproductive strategies
(Poinar, 1990) may influence the nematode response
to increasing density.
The present investigation aimed to evaluate and com-
pare virulence of four nematode species belonging to
the genera,
Heterorhabditis
and
Steinernema
against
Culex quinquefasciatus
larvae and to estimate the
different factors that can improve the beneficial traits
of the infective juveniles.
2 Materials & Methods
2.1 Insects
The mosquitoes,
Culex quinquefasciatus
were kindly
supplied by Prof. Dr. Fatma Kamel Adham, Faculty of
Science, Cairo University, Giza, Egypt.
2.2 Nematode isolates
The nematode isolates representing four species,
Hete-
rorhabditis bacteriophora
(HB),
Heterorhabditis indica
(HI),
Steinernema carpocapsae
(SC),
Steinernema feltiae
(SF) were supplied by Prof. Dr. Muhammed Mostafa
Shamseldean, Zoology and Nematology Department,
Applied Center of Entomonematode, (ACE), Faculty
of Agriculture, Cairo University, Giza, Egypt. They
were mass reared according to Bedding & Akhurst
(1975) using last instar larvae of the greater wax moth,
Galleria mellonella
.
2.3 Susceptibility to EPN
The one-on-one assay according to Miller (1989) was
used with some modifications related to the water
habitat of the mosquito larvae.
C. quinquefasciatus
4
th
instar larvae were placed individually in a 1.5 cm dia-
meter plates (24-well plates). Each well contained only
one infective juvenile of the four tested nematode
species in distilled water. Each treatment consisted of
20 replicates and repeated 3 times (n=60). The plates
were incubated at 25
℃
in the darkness. Mortality
records were taken after 72 h and corrected according
to Abbot’s formula (Abbott, 1925) versus a control tre-
atment contained only
Culex
larvae in distilled water.
2.4 Infective juvenile virulence
The virulence of the infective juveniles of
H. bacter-
iophora
and
H. indica
was estimated in relation to:
a- The exposure period.
b- Concentration of the infective juveniles (Dose res-
ponse).
2.5 Exposure period assay
In this assay, both of nematode invasion ability and
host larval mortality were evaluated in response to
varying exposure periods. Fifty 4
th
instar mosquito
larvae were exposed to infective juveniles of the diffe-
rent nematode species in 9 cm diameter Petri-dish half
filled with distilled water containing the desired infective
juvenile concentration. There were three replicates per
treatment. Different batches of nematodes and insects
were used for each replicate. Controls contained only
mosquito larvae in distilled water. 1500 infective juv-
eniles of
H. bacteriophora
and
H. indica
nematode
were incubated at 25
℃
in the dark with host larvae
for 6,9,12,24 and 48 hr. After each exposure time, the