Contents - Faperta

160 Biotechnological Approaches for Pest Management and Ecological Sustainability
FIGURE 6.3 Glandular (A) and nonglandular (B) trichomes in pigeonpea, Cajanus cajan, and its wild relative,
Cajanus scarabaeoides, are associated with susceptibility and resistance, respectively, to Helicoverpa armigera.
Trichomes
Trichomes are hair-like glandular outgrowths on the epidermis of plants. These are found
on leaves, shoots, and roots, and occur in several shapes and sizes (Jeffree, 1986). They
affect locomotion, attachment, shelter, feeding, and survival of insects. The glandular
trichomes in dicotyledons produce sticky exudates that may contain chemicals acting as
phagostimulants (Figure 6.3), antifeedants, and/or repellents (Figure 6.4), and disrupt
development and survival of insects (Peter, Shanower, and Romeis, 1995; Romeis, Shanower,
and Peter, 1999; Rupakala et al., 2005). Trichomes act as a defense mechanism of plants to
insects, although in some instances, they also provide a suitable substrate for egg laying
and attachment, or interfere with the activity of natural enemies (Kauffman and Kennedy,
1989; Sharma, Pampapathy, and Sullivan, 2003). Some insect species have also developed
adaptations to neutralize the effect of trichomes or their exudates (Gregory et al., 1986;
Kennedy et al., 1987).
Hooked trichomes on bean, Phaseolus vulgaris L., impair the movement of the aphid, Aphis
craccivora Koch ( Johnson, 1953) and potato leafhopper, E. fabae (Pillemer and Tingey, 1978).
Glandular exudates in Solanum neocardenasii Hawkes and Hjerting provide resistance
FIGURE 6.4 Acid exudates on the leaf surface of chickpea which act as antifeedants to pod borer, Helicoverpa
armigera.