Repellent allelochemics

The above results point to qualitative and quantitative differences between the allelochemics of SSB-susceptible and resistant varieties. The insect s greater preference for egglaying on Rexoro can be attributed to the presence of attractant factor(s) and ovipo-sition inducer(s) in the acid fraction and absence of repellents and oviposition inhibitors in the basic and neutral fractions. In contrast, whatever little oviposition inducer(s) the TKM6 acid fraction has, its effect is masked by the inhibitors in the neutral and basic fractions. It also explains the total reversal in ovipositional behavior of SSB moths on TKM6 plants treated with Rexoro extracts and vice versa. It may become possible to use these chemicals for interrupting SSB moth s oviposition on a rice crop, or alternatively make a trap crop so attractive that SSB moths lay all eggss on it. 

Saxena and Pathak (3) made systematic studies of BPH-rice plant interactions, particularly behavioral and physiological responses involved in BPH establishment on rice plants. They found that resistant plants were as suitable as susceptible plants in eliciting some responses. The interaction of all the responses determined the overall susceptibility or resistance to the pest. Saxena and Pathak (3) Saxena and Puma (30), and Saxena and Okech (31) also determined the biochemical basis of suitability of rice varieties to BPH. They found that allelochemics and nutritive balance of rice varieties were important in eliciting optimal or suboptimal responses, thereby affecting BPH ability to establish on rice plants. The steam distillate extracts of resistant varieties and of the barnyard grass were repellent and, when applied topically, caused high mortalities even at low doses. In contrast, extracts of susceptible varieties possessed moderate to high attractance and were relatively nontoxic to the insect. Recently, Obata et al. (32) isolated and identified constituents of BPH attractant in the Japanese rice cultivar Nihonbare . 

The interactions between rates and efficiencies are complex, involving homeostatic mechanisms that influence an insect s behavior, physiology, growth and reproduction. These interactions are influenced by starvation, induction of preference, nutrients, allelochemics and various environmental (climatic) factors. Classification of a chemical as a repellent, deterrent, feeding suppressant, toxin or digestibility-reducer may be situation-dependent, dose-dependent, and involve chemicals, behavioral and physiological feedback systems (Blau et al., 1978 Duffey, 1977,1980 Reese, 1979 Grabstein and Scriber, 1981). 

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