A Review of Biopesticides and Their Mode of Action Against Insect Pests - Environmental Sustainability: Role of Green Technologies - page 53

Release of
bacteria

Host finding

Infection

Infective juvenile

Host Killed

Development

Infective Juvenile Emergence

Heterorhabditidae
Adult stage

Steinernematidae
Adult stage

[Inside Egg]

Reproduction

Fig. 4 Mode of action of entomopathogenic nematodes against lepidopteran insects

6 Protozoa

host tissues. Almost two to three generations of
the nematodes are fi nished within the host
cadaver (Pomar and Leutenegger 1968 ; Bird and
Akhurst 1983 ).
In previous research studies, it has been
clearly indicated that entomopathogenic nema-
todes can be effective biocontrol agents against
some of the major insect pest families found in
stored goods like Pyralidae (Shannag and
Capinera 2000 ) and Curculionidae (Duncan and
McCoy 1996 ; Shapiro and McCoy 2000 ). Earlier,
Morris ( 1985 ) had demonstrated the susceptibil-
ity of insect pests found in stored products,
including Ephestia kuehniella Zeller and
Tenebrio molitor L., to an increased concentra-
tion of nematodes. Georgis ( 1990 ) had also advo-
cated a fi eld concentration of >2.5 billion
nematodes/ha against some of the major insect
pests of row crops, but concentrations few times
higher (7-15 billion/ha) are demanded to accom-
plish the control of pest population (Loya and
Hower 2002 ).

6.1 Nosema

In previous studies, protozoan diseases of
insects are ubiquitous in nature and constitute
an essential regulatory role in insect populations
(Maddox 1987 ; Brooks 1988 ). Microsporidia,
such as Nosema spp., are generally host specifi c
and slow acting, most frequently producing
chronic infections. The biological activities of
most entomopathogenic protozoa are complex.
They grow only in living hosts and some spe-
cies necessitate an intermediate host.
Microsporidia species are among the most
commonly observed, and their main benefi ts
are persistence and recycling in host popula-
tions and their debilitating effect on reproduc-
tion and overall fi tness of target insects. As
inundatively utilized microbial control agents,
some species have been moderately successful
(Solter and Becnel 2000 ).