The mustard oil glucosides, sinigrin, sinalbin, and glucocheirolin and the musard oil, allyl isothiocyanate, as well as the enzyme myrosin, were prepared from the seeds of cruciferous plants. Pieris brassicae (L.) and Plutella maculipennis (Curt.) were induced to feed on leaves of plant species which they normally refuse by painting the leaves with a solution of sinigrin or sinalbin but would not feed on such leaves treated with allyl mustard oil. Feeding responses of P. maculipennis larvae were tested on agar gels containing the powdered, dehydrated leaves of various plants alone and in combinations with glucosides, mustard oil, and myrosin. The amount of feeding was estimated by counts of frass pellets produced by the larvae during the test period. It was shown that sinigrin, sinalbin, and glucocheirolin are feeding stimulants for P. maculipennis larvae. Since the larvae feed readily on at least 40 plant species which are reported to contain mustard oil glucosides it was concluded that the mustard oil glucosides are specific feeding stimulants for this insect. The threshold concentrations for P. maculipennis of gustatory perception of sinigrin under these conditions are of the order of 2 p.p.m. for sinigrin and about 20 p.p.m. for sinalbin. Optimum feeding responses were obtained only when the glucoside is offered in a medium containing other nutrients in the form of powdered, dehydrated leaves or artificial mixtures. In some experiments the addition of allyl mustard oils slightly increased feeding on media containing sinigrin. The addition of viable myrosin to diets containing sinigrin decreased the feeding responses. Since heat-killed myrosin has no repellent effect, it appears that the action of myrosin is due to the depletion by hydrolysis of the quantity of sinigrin in the medium. Apparently the fission products of the hydrolysis including mustard oil are less attractive than the parent glucosides. Since hydrolysis of glucoside will release only minute amounts of mustard oil in the short space of time intervening between biting and swallowing it is unlikely that the gustatory receptors will be exposed to appreciable concentrations of mustard oil as compared with glucoside. On the other hand it is possible that infinitesimal amounts of mustard oil vapor emanating from leaves may stimulate the olfactory sense which is characteristically extremely sensitive in insects. While hunger induces sustained feeding in the absence of mustard oil provided a gustatory stimulant is present, such an olfactory stimulus might conceivably initiate feeding more promptly. This would account for observations in some experiments that larvae produced more frass when feeding on media containing a little mustard oil as well as sinigrin. The power of sinigrin to induce P. maculipennis to feed on nutrient media makes possible the development of an artificial medium for studies of the nutrition of this phytophagous insect.
Oviposition responses to natural and artificial substrates were investigated. More eggs were deposited on plants that contain isothiocyanates (natural hosts). Depletion of isothiocyanate content by sulfur-deficient plant nutrition appears to reduce attractiveness of host plants as egg substrates. Eggs are laid preferentially in concavities of leaves or stems. Significantly more eggs are laid on dimpled than smooth polyvinyl plastic surfaces. On both types of plastic substrate more eggs are laid if allyl isothiocynate or mustard leaf juice is added. Mustard leaf juice contains allyl isothiocyanate but is more stimulating to oviposition indicating that other factors contribute to the total effect.Although the coumarin in Melilotus sp. tends to inhibit oviposition, Plutella may be induced to increase egg deposition on such plants by treating them with allyl isothiocyanate. Unknown inhibitory constituents in tomato leaves prevent egg laying even in the presence of allyl isothiocyanate. It was concluded that oviposition is regulated significantly by external stimuli and that inhibitory chemical influences as well as positive chemical stimuli and texture of the surface are all significant factors.The chemical influence of plant constituents on acceptance or rejection of plants as food by the larva of the diamond-back moth, Plutella maculiDennis (Curt.) has been considered previously (GuPTA & THORSTEINSON, 1960; THOR-STEINSON, 1953). The mechanisms of food plant specificity as expressed by this insect in nature must also take into account the regulation of oviposition behaviour of the adult female inasmuch as this determines what plant the newly hatched larva must accept or reject. The object of this study is, therefore, to determine what attributes of the plant are most significant as oviposition stimulants and to investigate interactions among these influences. MATERIALS AND METHODSAdults for the experiments were taken from a culture that had been maintained in our laboratory for three years. Newly emerged adults were isolated in new wooden cages or paper cartons provided with brass wire net for ventilation. The insects were fed on sugar solution. Plants of Brassica juncea (Mustard), Lycopersicon esculentum (Tomato), Pisum sativum (Garden Pea), Melilotus officinalis (Sweet Clover) and Melilotus alba (var. Coumino) used in various experiments were grown in the green house. Allyl isothiocyanate (Eastman Organic Chemicals) *) On visit from the University of Lucknow, India.
The attractiveness of colored spheres was compared in the field for several tabanid species. Black and red spheres were highly attractive to all the species. Tabanus illotus was attracted nearly equally to black, gray, and white silhouettes. The attractiveness of gray and white spheres for the other species decreased rapidly with increasing reflectance. Green and yellow spheres were unattractive for all species. Two-dimensional black silhouettes attracted only a small number of tabanids. Three-dimensional black silhouettes with plane surfaces attracted larger numbers of flies. Glossy black silhouettes with convex curvature in the vertical plane were much more attractive than other silhouettes. Interpretations of these results are presented.
Samples of nine crystalline mustard oil glucosides including sinigrin were isolated from plant tissues of species in the families Cruciferae and Tropaeolaceae. The isolations were achieved by the use of column chromatography on neutral alumina, cellulose powder, activated carbon: by paper and thin-layer chromatography; and by crystallization from methanol-water mixtures.Feeding responses of fifth instar larvae of Plutella maculipennis (Curtis) were tested on agar-cellulose diets containing individual glucosides a t various concentrations in the presence or absence of 0.1 M glucose. The amount of feeding was measured by counts of frass pellets produced by the larvae during the test period. All the above-mentioned ~lucosides were found to act as feeding stimulants for the larvae of P. nzaculipennis. However, the relative palatability of these glucosides a t the same concentration (20 mg per 10 rnl of water in the diet) was found to be in the following order: progoitrin >glucocheirolin = glucoconringiin = glucoerucin >glucotropaeolin = sinigrin = sinalbin >gluconasturtiin = gluconapin. Higher concentrations of the glucosides, gluconasturtiin, and gluconapin were toxic to the larvae. Can. J. Zool. Downloaded from www.nrcresearchpress.com by Vancouver Island University on 11/21/14 For personal use only. SCIKLTZ, 0. E. and WAGNER, n'. 1956. Trennun~: dcr Senfolplrtcosidc durch absteigende Pnpierhromatngraphie. Z. Natrirforsch. 11B, 13-78. STEPANOJA, L. A. 1Ubl. The role of the foud factor in the mass rrpmduction of pests on Crucifcrae. EntomoI. Kev. USSR (English Trans.), 4R, 512-5 17. T A o n s~e t~~o~, A. J. 1953. The chernorartic responses that determine host specificity in an otigophagous insert (PIutdla na~culipcnnis Curt.). Can. J. Zool. 31, 51-72. VERSCHAEFFELT, E. 191n. The cause rletcrrniniril: the seleciion of lood in some herbivorous i n w t s . I'roc. Acad. Sci. (Aii~sterdnn~ ), 13, 536-542. YOGEL, 11;. G.. DOIZAKI, !I{. M., anrI Zrrrm, L. 1962. Rapid thin-layer chromatographic separation of phospholipids and neiltral lipid5 of serum. J. Lipirl Res. 3, 138-140. Y A M A M O~, R T. and FIUENKEL, G. 1960. -4ssay n l the principal guslatory stimulant for the tobacco hurnwol-nt, Pro!oparce sextcla (Johan.), from ~Ianaceons plants. Ann. EntomoI, %c. Am. 53, 499-503.Can. J. Zool. Downloaded from www.nrcresearchpress.com by Vancouver Island University on 11/21/14For personal use only.
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