Contents - Faperta

164 Biotechnological Approaches for Pest Management and Ecological Sustainability
Acetone extracts of pods of pigeonpea and its wild relative, Cajanus platycarpus (Benth.)
Maesen, have a signifi cant feeding stimulant effect on H. armigera larvae, whereas the
extracts from C. scarabaeoides pods have no such effect (Shanower, Yoshida, and Peter, 1997).
Quercetin, quercetrin, and guercetin-3-methyl ether (present in pod surface exudates) play
an important role in food selection behavior of H. armigera larvae in pigeonpea (Green
et al., 2002, 2003). Sterols and soybean leaf extractables in combination with sucrose are
phagostimulant to the larvae of the cabbage looper, T. ni (Sharma and Norris, 1994a).
Antifeedants
Chemicals that inhibit feeding are called phagodeterrents. High acidity in the leaf exudates
of chickpea is associated with resistance to H. armigera (Srivastava and Srivastava,
1989; Bhagwat et al., 1995). Chickpea exudates have malate and oxalate as the main components,
and there are characteristic differences among genotypes depending on diurnal
cycles and growth stage. Varieties with the highest amounts of malic acid are resistant to
H. armigera (Rembold, 1981; Rembold et al., 1990). Malic acid acts as an antifeedant to the
H. armigera larvae (Bhagwat et al., 1995). Oxalic acid inhibits the growth of H. armigera
larvae when incorporated into artifi cial diet, while malic acid shows no growth inhibition
(Yoshida, Cowgill, and Wightman, 1995, 1997). The chickpea fl avonoids judaicin 7-O- -
glucoside, 2 methoxy judaicin, judaicin, and maakiain present in wild relatives of chickpea
(Cicer bijugum Rech. and C. judaicum Boiss.) have shown antifeedant activity towards the
larvae of H. armigera (Simmonds and Stevenson, 2001). Stilbene, a phytoalexin, occurs at high
concentrations in pigeonpea cultivars with resistance to H. armigera (Green et al., 2003).
Growth Inhibitors
Alkaloids, ketones, terpenoids, fl avonoids, and organic acids produced by the plants are
toxic to insects. Gossypol, heliocide 1, heliocide 2, gossypolone, hemigossypolone, lactone,
condensed tannins, and volatile terpenes in cotton confer resistance to bollworms (Hedin
et al., 1983; Sharma, 1982; Sharma and Agarwal, 1982a, 1982b; Tang and Wang, 1996). High
density of gossypol glands on squares rather than leaves, calyxes, and bracts contributes to
H. armigera resistance in cotton (Rajarajeswari and Subba Rao, 1997). Tannins and terpenoid
aldehydes gradually increase from the cotyledon stage to the late-bloom stage of cotton
(Zummo, Segers, and Benedict, 1984). However, there is a sudden drop in tannins at the
one-third growth stage, which provides a window of increased vulnerability to H. zea.
Phenolics have also been reported to impart resistance to bollworms. Catechin, chrysanthemin,
isoquercitrin, quercetin, condensed tannins, cyanidin, and delphinidin have been
tested in laboratory bioassays against H. armigera, and found to exert a weight inhibition
of 50% at variable concentrations. The polar solvent extractables of the soybean genotype
PI 227687, resistant to the cabbage looper, T. ni, contains diadzien, coumesterol, sojagol, and
glyceollins. These compounds reduce feeding, survival, and development of T. ni (Sharma
and Norris, 1991, 1994b).
In tomato, L-tomatine, 2-tridecanone, and phenolics are responsible for antibiosis to
H. zea (Ferry and Cuthbert, 1975; Dimock and Kennedy, 1983; Farrar and Kennedy, 1988,
1990). The allelochemical 2- tridecanone is highly toxic to H. zea (Kennedy and Yamamoto,
1979). High phenol content has also been reported to be associated with resistance to
H. armigera (Banerjee and Kalloo, 1989). Acylglucoses exuded by trichomes of the wild
tomato species, Lycopersicon pennellii (Corr.) D’Arcy act as feeding or oviposition deterrents
or both. Exposure to these compounds in artifi cial diet or as sprays on cultivated tomato