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FARHA-REHMAN ET AL.
tobacco plant released volatiles that repelled nocturnal pregnant moths looking for
the site of oviposition. In the day, tobacco plants under attack by herbivores released
blends attracting parasitic or predatory insects (De Moraes et al., 2001). These
responses were beneficial for tobacco plants and the herbivorous insect involved
(De Moraes et al., 2001). These findings indicate that host plant on one hand
attracted predators of herbivorous caterpillars during day time and female moth coevolved
to avoid such plants for oviposition using some exclusive night time blends
to avoid predators of larvae. This co-evolution between tobacco and pregnant female
moth maintained ecosystem functioning.
A co-evolutive adaptation was observed as the result of plant-insect interactions
(Wittstock et al., 2004). For example, maize rapidly mobilizes the accumulation of a
33-kDa cysteine protease in response to feeding of caterpillars, thereby posing
resistance to herbivory. The accumulation of the 33-kDa cystein protease in the maize
midwhorl significantly reduced caterpillar growth due to impaired nutrient utilization
(Pechan, Cohen, Williams, & Luthe, 2002). The larvae of the specialist insect, Pieris
rapae (cabbage white butterfly, Lepidoptera) also appear adapted to the glucosinolatemyrosinase
system, a defensive chemical arsenal of the host plants.
Trotter, Cobb, and Whitham (2002) studied herbivory, plant resistance and
climate in the tree ring records and noted that interactions distorted climatic
reconstructions. The resistance or susceptibility of pines to herbivore and climate
interaction in the tree ring record were detectable, due to hereditary characteristics.
These authors found that herbivory reduced tree rings growth by 25–35% and
distorted climate reconstruction on growth rings. Herbivory-induced changes also
reduced preference and performance of a variety of insects for a diverse group of
plants and ultimately increased their fitness in natural environments, as shown from
studies on wild radish (Raphanus raphanistrum) (Agrawal, 1999).
4.5. Herbivore Strategies
Several factors affect herbivores feeding, including the type of available food and
the biochemical products released during feeding. For example, the lubber
grasshopper (Romalea guttata) feeds on a wide range of plant species and produces
a metathoracic defensive secretion containing primarily phenolics and quinones
(Jones, Hess, Whitman, Silk, & Blum, 1987). When reared on onion (Allium
canadense) and an artificial diet, it secreted volatiles with fewer compounds, in
altered proportions as compared to a set of insects reared on diets from a diverse
group of 26 plant species, including onion. The diet diversity appeared to have a
major impact on the quality and quantity of the autogenous defensive secretions of
this generalist herbivore, possibly due to changes in precursors availability, owing to
a diverse diet and/or to diet restrictions, leading to a physiological stress caused by
partitioning of resources to defensive chemicals (Jones et al., 1987).
Larvae of Spodoptera eridania preferred for its diet proteins of Lotus
corniculatus, as compared to tannins (Briggs, 1990). The larvae were given a choice
of L. corniculatus plants whose chemical profiles were altered by feeding on plants
grown with nutrient fertilization, or with symbiotic nitrogen fixation as their only