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The hypothesis that cyanogenic potential in cassava is a defense mechanism against arthropod pests is one of the crucial questions relevant to current efforts to reduce or eliminate cyanogenic potential (CNP) in cassava. The generalist arthropod Cyrtomenus bergi, which attacks cassava roots, was used in a bioassay relating oviposition and survival to CNP, concentration of nonglycosidic cyanogens, and linamarase (beta-glycosidase) activity in twelve selfed cassava siblings and their parental clone, which has segregated for different levels of cyanogenesis. Electron microscopic evaluation revealed an intracellular pathway of the stylet of C. bergi in the cassava root tissue to rupture cell walls. This feeding behavior causes cyanogenesis and increased linamarin content in the hemolymph of C. bergi while feeding on a cyanogenic diet. This diet resulted in a significant reduction in oviposition, especially at levels of CNP above 150 ppm (expressed as hydrogen cyanide) on fresh weight basis (or 400 ppm on dry weight basis) in cassava roots. An exponential decline in oviposition was observed with increasing levels of CNP, beginning 12 d after exposure to the cyanogenic diet. Cyanogenic potential and dry matter content showed a positive effect on survival. No relationship was found between concentrations of nonglycosidic cyanogens or linamarase activity in the cassava root and either oviposition or survival. According to our results, there is a significant difference between potentially noncyanogen and high cyanogen clones, but there may not be a significant difference between potentially noncyanogen and low cyanogen clones. Consequently, more frequent outbreaks or higher levels of damage might not be anticipated in potentially noncyanogen cassava clones than that anticipated in low cyanogenic clones. The negative effect of cyanogenesis on oviposition concurrent with a positive effect on survival of this pest is most likely the result of a physiological trade-off between survival and oviposition. The question of whether ovipositional rates could be recovered after a long-term exposure to cyanide remains unanswered.

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The hypothesis that cyanogenic potential in cassava is a defense mechanism against arthropod pests is one of the crucial questions relevant to current efforts to reduce or eliminate cyanogenic potential (CNP) in cassava. The generalist arthropod Cyrtomenus bergi, which attacks cassava roots, was used in a bioassay relating oviposition and survival to CNP, concentration of nonglycosidic cyanogens, and linamarase (beta-glycosidase) activity in twelve selfed cassava siblings and their parental clone, which has segregated for different levels of cyanogenesis. Electron microscopic evaluation revealed an intracellular pathway of the stylet of C. bergi in the cassava root tissue to rupture cell walls. This feeding behavior causes cyanogenesis and increased linamarin content in the hemolymph of C. bergi while feeding on a cyanogenic diet. This diet resulted in a significant reduction in oviposition, especially at levels of CNP above 150 ppm (expressed as hydrogen cyanide) on fresh weight basis (or 400 ppm on dry weight basis) in cassava roots. An exponential decline in oviposition was observed with increasing levels of CNP, beginning 12 d after exposure to the cyanogenic diet. Cyanogenic potential and dry matter content showed a positive effect on survival. No relationship was found between concentrations of nonglycosidic cyanogens or linamarase activity in the cassava root and either oviposition or survival. According to our results, there is a significant difference between potentially noncyanogen and high cyanogen clones, but there may not be a significant difference between potentially noncyanogen and low cyanogen clones. Consequently, more frequent outbreaks or higher levels of damage might not be anticipated in potentially noncyanogen cassava clones than that anticipated in low cyanogenic clones. The negative effect of cyanogenesis on oviposition concurrent with a positive effect on survival of this pest is most likely the result of a physiological trade-off between survival and oviposition. The question of whether ovipositional rates could be recovered after a long-term exposure to cyanide remains unanswered.

The hypothesis that cyanogenic potential in cassava roots deters polyphagous insects in the field is relevant to current efforts to reduce or eliminate the cyanogenic potential in cassava. To test this hypothesis, experiments were conducted in the field under natural selection pressure of the polyphagous root feeder Cyrtomenus bergi Froeschner (Hemiptera: Cydnidae). A number of cassava varieties (33) as well as 13 cassava siblings and their parental clone, each representing a determined level of cyanogenic potential (CNP), were scored for damage caused by C. bergi and related to CNP and nonglycosidic cyanogens, measured as hydrogen cyanide. Additionally, 161 low-CNP varieties (< 50 ppm hydrogen cyanide, fresh weight) from the cassava germplasm core collection at Centro Internacional de Agricultura Tropical (CIAT) were screened for resistance/tolerance to C. bergi. Low root damage scores were registered at all levels of CNP. Nevertheless, CNP and yield (or root size) partly explained the damage in cassava siblings (r2 = 0.82) and different cassava varieties (r2 = 0.42), but only when mean values of damage scores were used. This relation was only significant in one of two crop cycles. A logistic model describes the underlying negative relation between CNP and damage. An exponential model describes the underlying negative relation between root size and damage. Damage, caused by C. bergi feeding, released nonglycosidic cyanogens, and an exponential model fits the underlying positive relation. Fifteen low-CNP clones were selected for potential resistance/tolerance against C. bergi.