ABSTRACT
Several stresses can be involved during the life of plants. One of the major stresses is caused by tissue damage. Tissue damage in plants is most often associated with insect herbivore infestation. The insect uses the plant as a source of food but the plant tissue consists of dilute nutrients in a matrix of indigestible structural compounds, such as cellulose and lignin, and a variety of allelochemicals. The insect differs from other animals in that it lacks the capacity to synthesize sterols. The insect, in fact, must extract sterol together with several other essential nutrients (amino acids, carbohydrates, lipids, fatty acid, vitamins, trace element) from their food (Behmer and Nes, 2003). Optimal insect growth, survival, and fecundity require certain proteins: carbohydrate ratios, which may vary considerably among species and developmental stages (Schoonhoven et al., 2005). The food is not totally converted to insect biomass but follow the decrease line from food ingested to growth and
29.1 Introduction .......................................................................................................................... 747 29.2Plant Interactions with Insect Herbivores ............................................................................. 749
29.2.1How Insect Herbivores Find a Host Plant ................................................................. 749 29.2.2Damage to Plants Caused by Insect Herbivores ....................................................... 750
29.2.2.1Herbivory in Aboveground and Belowground Plant Tissues ..................... 750 29.2.2.2 Plant Compensation to Insect Herbivores Damage ................................... 751
29.3Plant Responses to Insect Herbivores Attack ....................................................................... 752 29.3.1Early Events in Plant-Insect Interactions ................................................................. 753 29.3.2Plant Defense Signaling Pathways ............................................................................ 754 29.3.3Direct Defense Responses ........................................................................................ 755 29.3.4 Chemical Communication during Herbivory ........................................................... 756
29.4Detrimental Effects of Insect Herbivores to Plants .............................................................. 757 29.4.1Effects on Photosynthesis ......................................................................................... 757
29.4.1.1Direct Reduction of Photosynthetic Capacity ............................................ 757 29.4.1.2Indirect Reduction of Photosynthetic Capacity ......................................... 758
29.4.2 Effects on Yield ........................................................................................................ 759 29.4.2.1The Yield Loss ........................................................................................... 759 29.4.2.2Yield Losses Assessment ........................................................................... 760 29.4.2.3Economic Injury Level and Economic Threshold ..................................... 760 29.4.2.4Damage in Natural and Agricultural Environments .................................. 760
29.5 Molecular Approaches to Insect Resistance ......................................................................... 761 29.6Conclusions ........................................................................................................................... 762 References ...................................................................................................................................... 763
reproduction. The performance (the extent to which an insect herbivore is able to realize maximum growth and reproduction) is preferentially expressed in rate parameter, and when looking at performance and utilization value, large differences appear to exist between different feeding guilds, such a mandibulate feeders of herbs and forbs versus woody plants or mandibulate versus haustellate (piercing-sucking) species (Table 29.1). Estimates of crop production removed by foliage-feeding insects typically ranges from 5% to 30% (Mattson and Addy, 1975), and insect outbreaks can reduce net primary productivity by more than 70% in some terrestrial ecosystems (Cyr and Pace, 1993; Agarwal et al., 2006). The loss of productivity to herbivory traditionally has been estimated as the amount of leaf tissue removed (Ohmart et al., 1983; Lowman, 1985). It is estimated that insects (mandibulates) consume in the order of 10% of all annually produced plant biomass, these data varies considerably with vegetation type, time, and locality (Barbosa and Schultz, 1987; Damman, 1993; Coupe and Cahill, 2003). Losses to sap-feeding insect (haustellate mouth parts) are more difcult to measure, but are estimated to be around 5% of the net primary production (Schoonhoven et al.,
TABLE 29.1 Average Value of Performance and Indices of Nutritional Utilization by Mandibulate and Haustellate Herbivorous Insects (Range in Parentheses)
TABLE 29.2 Numbers of Herbivorous Species in Some Insect Order
2005). Measuring the intensity of insects herbivory is often difcult and estimate of losses can differ two-to vefold among the methods used (Coley and Barone, 1996; Schowalter, 2000; Peterson and Higley, 2001). Insects often in…ict much more damage in agro-ecosystems than in natural settings (Peterson and Higley, 2001). Conspicuous among herbivores are the Lepidoptera (butter…y and moth), Hemiptera (bugs, leafhoppers, aphids, etc), and Orthoptera (grasshoppers and locust), but large parts of Coleoptera, Hymenoptera, and Diptera (Schoonhoven et al., 2005) (Table 29.2) are also present. Tissue damage usually induces local osmotic stress responses that are often found to be a key component in the response to mechanical wounding (Reymond et al., 2000; Deneckamp and Smeekens, 2003). In this chapter, we analyze in depth how the insect herbivores nd host plants and arrive in a patch, how damaging the plant tissue causes stress, how the plant responds to damage, and the effects of this stress on growth and reproduction of the plant.
