Olfactory responses of 72- to 96-hr-old, 24-hr starved adult male, female, or mixed-sex groups of the red flour beetle,Tribolium castaneum (Herbst), to volatiles from wheat and millet kernels, certain milled fractions, and solvent extracts were recorded by using a lightsensitive apparatus. Wheat-germ volatiles from intact germ or solvent extracts were generally more attractive than volatiles of wheat endosperm or wheat bran. Volatiles of whole wheat kernels were the least attractive among test materials of wheat origin, whereas there were no significant differences among whole wheat flour, germ, and endosperm. Wheat-germ extracts, however, were more attractive than were extracts of the other fractions. Whole millet flour or fermented millet flour volatiles were more attractive than those from whole millet kernels or millet starch. Beetles reached maximum responsiveness to grain volatiles by 72-96 hr after adult ecdysis. Groups of virgin female beetles generally were more responsive than male or mixed-sex groups to volatiles of substances tested.
The resistance of Phaseolus vulgaris to infestation by the bruchid Callosobruchus maculatus (F.) was investigated and the roles contributed by its physical or chemical characteristics were examined. The haricot bean seed coat was not the thickest and its seeds were not the least preferred for oviposition by the bruchid beetles. The tiny shallow depressions underneath the dead larvae indicated that the larvae had initiated feeding after completion of the embryonic development, but none of them has successfully developed or survived to adulthood. Thus, the physical characteristics of the haricot bean were probably not the major factors causing the observed premature death of the bruchid larvae. Asparagine, an amino acid usually exists in association with its toxic substrate of Beta‐cyanoalanine and Alpha‐diaminobutyric acid, was found only in haricot bean among the tested grain legumes. Pellets made of a blend of cowpea seed powder with haricot bean seed powder or with a synthetic asparagine both suppressed C. maculatus infestation and caused premature mortality. This suggests that the resistance in haricot bean is of chemical nature and that it is related to the presence of asparagine.
Zusammenfassung
Zur Bedeutung von Asparagin und Samenschalendicke für die Resistenz von Phaseolus vulgaris gegenüber Callosobruchus maculatus (F.) (Col., Bruchidae)
Es wurden physikalische und chemische Faktoren hinsichtlich ihrer Bedeutung für die Resistenz von Phaseolus vulgaris gegenüber Callosobruchus maculatus untersucht. Die Samenschale von P. vulgaris gehört weder zu den härtesten, noch zu den für die Eiablage von Samenkäfern am wenigsten bevorzugte. Eine kleine Vertiefung unterhalb der toten Larven zeigte, daß die Larven nach der Embryonalentwicklung mit dem Fraß begonnen hatten, jedoch keine der Larven konnte sich erfolgreich weiter entwickeln oder gar bis zum Imaginalstadium überleben. Daraus folgt, daß physikalische Faktoren nicht der Hauptgrund für die Larvenmortalität sind. Asparagin, eine Aminosäure, die gewöhnlich zusammen mit den toxischen Substanzen Beta‐cyanoalanin und Alpha‐diaminobuttersäure auftritt, wurde nur in P. vulgaris nicht aber in den anderen Samen gefunden. Pellets, die aus “Cowpea”‐ und P. vulgari‐Samenpulver oder mit synthetischem Asparagin hergestellt wurden, wiesen einen reduzierten C. maculatus‐Befall auf und bewirkten eine frühzeitige Mortalität der Larven. Daraus ist zu schließen, daß die Resistenz von P. vulgaris auf chemischen Faktoren beruht, und zwar auf den Inhaltsstoff Asparagin.
The orientation responses of the rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae) as influenced by the olfactory stimulants emanating from either resistant or susceptible pearl millet, Pennisetum americanum, kernels were studied using a Y‐tube olfactometer. The rice weevils were more attracted towards odours from millet grains than to blank controls and to susceptible entries more than to resistant entries, in general. However, there were exceptions. Odours from some resistant entries caused statistically the same, or even more positive orientations than those from some susceptible entries, and this suggests that the relative resistance of an entry and its olfactory attractiveness may not be strongly related, or that the resistance to infestation might be influenced by factors other than attractiveness. The partial damage of the millet kernel pericarp by abrasion slightly increased the orientational response of the weevils to odours from some susceptible and some resistant entries alike.
The relative resistance of 71 sorghum, Sorghum bicolor (L) Moench entries to the American bollworm, Helicoverpa armigera (Hüb.) (Lepidoptera: Noctuidae) was evaluated under natural field infestation condition in two locations in the eastern Sudan. The number of larvae per five heads (HL/5 heads) and the magnitude of damage (HOR), measured on a rating scale of 0-9, were used to measure resistance. The grand mean for the 71 entries was 7.80 and 1.95 in the first location, and 2.45 and 1.96 in the second location for HL/5 heads and HDR, respectively. The entries Tetron, Zanebelshah, P.988*, Silca and Trokash were the least susceptible to H. armigera expressed as lowest larval counts and lowest damage ratings across both trials. The entries IS.7349*, Feterita Iriana, Super Feterita, Culum, Wadelfahel, Fererita Bafta. Wad Yabis, White Aker and IS.7271* were the next most resistant as measured by the same parameters. None of these 14 entries, of which 11 were indigenous and three exotic, had mean HL/5 heads higher than 4.50 (<1 larva per head) or mean HDR of more than 1.0 in either trial.
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