A Review of Biopesticides and Their Mode of Action Against Insect Pests - Environmental Sustainability: Role of Green Technologies - page 54

7.1 Neem

Some protozoan species are pathogenic like
Nosema locustae for grasshoppers, which is the
only species that has been registered and estab-
lished commercially (Henry and Oma 1981 ). N.
bombycis , the fi rst reported microsporidium, is a
pathogen of silkworm pébrine, which persisted in
Europe, North America, and Asia during the
mid-nineteenth century (Becnel and Andreadis
1999 ). Pébrine is still an epidemic and causes
heavy economic losses in silk-producing coun-
tries such as China (Cai et al. 2012 ).
Almost 1,000 protozoan species, mainly micro-
sporidia, attack invertebrates, including numerous
insect species like grasshoppers and heliothine
moths. Virtually renowned insect-pathogenic pro-
tozoan species are Nosema spp. and Vairimorpha
necatrix . Protozoans produce spores, which are
the infectious phase in several susceptible insects.
Nosema spp. spores are assimilated by the host
and develop in the midgut. Germinating spores are
released from the sporoplasm and invade host tar-
get cells, inducing massive infection and demol-
ishing organs and tissues. Sporulation process
begins again from the infected tissues and, upon
expulsion and ingestion by a susceptible host,
induces an epizootic infection. Naturally, parasit-
oids and insect predators commonly act as vectors
distributing the disease (Brooks 1988 ).

In Asia, neem has an extensive history of use
mainly against household and storage pests and,
to some extent, against insect pests of crops.
Nevertheless, a breakthrough in the insecticidal
application of neem was attained by Pradhan
et al. ( 1962 ) who successfully protected the crops
from insects by applying them with low concen-
tration of 0.1 % neem seed kernel suspension
during a locust invasion. The Indian neem tree
( Azadirachta indica ) is one of the most important
limonoid-producing plants from the Meliaceae
family. Several components of its leaves and
seeds show marked insect control potential, and
due to their relative selectivity, neem products
can be recommended for many programs on crop
pest management (Schmutterer 1990 ). Neem
product activity has been assessed against 450-
500 insect pest species in different countries
around the world, and from that, 413 insect pest
species are reportedly susceptible at various con-
centrations (Schmutterer and Singh 1995 ).
In India alone, neem activity has been assessed
against 103 species of insect pests, 12 nematodes,
and several pathogenic fungi (Singh and Kataria
1991 ; Arora and Dhaliwal 1994 ). Some recent
reviews on the potential of neem in pest manage-
ment include those of Singh ( 1996 , 2000 ), Singh
and Raheja ( 1996 ), Naqvi ( 1996 ), Saxena ( 1998 ),
and Dhaliwal and Arora ( 2001 ). Most works have
focused on azadirachtin (Fig. 5 ) richly from neem
seed extracts which act as both strong antifeed-
ants and insect growth regulators. Azadirachtin
affects the physiological activities of insects
(Mordue (Luntz) and Blackwell 1993 ) and does
not affect other biocontrol agents. Further, neem
products are biodegradable and nontoxic to non-
target organisms (Senthil-Nathan 2013 ).
In several Asian countries, numerous studies
have measured neem activity alone or in combi-
nation with established insecticides and other
biocontrol agents of damaging insect pests in
agricultural crop system (Abdul Kareem et al.
1987 ; Senthil-Nathan et al. 2005a , 2006 ). In
Indian fi eld trials carried out, neem treatments
were determined to be effective against some
insect species like green leafhopper, yellow stem

7 Botanical Insecticides

Since ancient times, natural compounds from
plants were used, more or less effi caciously to
give security from insect pests. In the nineteenth
century, these compounds became scientifi cally
established and widely utilized in the earlier
period of the twentieth century (Morgan 2004 ).
Plants and some insects have coexisted on the
earth for almost three and a half million years,
which has allowed lots of time for both to develop
offensive and defensive strategies. Plants have
developed many strategies to assist themselves
from being assaulted by predators. An example
of such plant strategy is developing compounds
that are highly toxic to insects (Warthen and
Morgan 1985 ; Arnason et al. 1989 ; Morgan and
Wilson 1999 ; Nisha et al. 2012 ).