No abstract

The overall interest in environmentally safe pest control methods and the rise of insecticide resistance in pest populations have prompted medical and agricultural entomology research on insect repellents in recent years. However, conducting research on repellent is challenging for several reasons: (1) the different repellent phenomena are not well defined; (2) it is difficult to test for and quantify repellent; (3) the physiological mechanisms are poorly known; (4) the field efficacy appears to be highly variable. Here, we identified five different types of repellent: expellency, irritancy, deterrency, odor masking and visual masking, and described behavioral bioassays to differentiate between them. Although these categories are currently defined by their behavioral response to different stimuli, we suggest new definitions based on their mechanism of action. We put forward three main hypotheses on the physiological mechanism: (1) a dose effect that modifies the behavior, (2) a repellent mechanism with specific receptors, or (3) inhibition of the transduction of neural information

No abstract

No abstract

A comparison was made among 16 native North American Vitis species and Vitis vinifera L. ('Carignane') grown in the San Joaquin Valley of California with or without irrigation over 2 years. Predawn water potential (ΨPD), predawn leaf osmotic potential (Ψπ), midday leaf (Ψl), and stem water potential (Ψstem), stomatal conductance (gs), net CO2 assimilation rate (A), and intrinsic water use efficiency (WUE) were measured on five dates during the growing season the first year of the study and pruning weights were evaluated both years. Net gas exchange and water potential components taken on the last measurement date in 1992 and pruning weights of the nonirrigated species were less (or more negative for Ψ components) than those of the irrigated vines. The 17 Vitis species were ranked according to their relative drought tolerance based upon their performance without irrigation and when compared to their irrigated cohort. The Vitis species considered most drought tolerant were V. californica, V. champinii, V. doaniana, V. longii, V. girdiana, and V. arizonica. Those six species generally had high values of A, gs, and pruning weights and more favorable vine water status at the end of the study than the other species when grown without irrigation. The drought-induced reductions in the measured parameters also were less for those species when compared to their irrigated cohorts. The least drought tolerant species were, V. berlandieri, V. cinerea, V. lincecumii, V. riparia, and V. solonis. The drought-tolerant rankings were generally associated with the species' native habitat and probable soil water availability.

fusiform, rhizome-like or corm-like roots. Leaves entire, linear to cordate, sessile or petiolate, alternate. Stems one to many from each root, decumbent to erect, usually unbranched below the inflorescence, 0.3-17 dm. tall. Inflorescence a lax or congested, ebnicteate, unilateral, modified scorpioid cyme, or with the lowest flowers often single and subtended by leaves, often becoming panicled in age. Calyx 5-parted, occasionally campanulate, often accrescent. Corolla tubular, infundibuliform or campanulate, the expanded limb 1 exceeding or exceeded by the tube, with or rarely without fornices in the throat alternating with the stamens, blue, occasionally white or pink. Filaments attached below the throat, the anthers exserted or included. Style shorter or longer than the corolla, in some dior trimorphic, the base often dilated slightly; the stigma entire or obscurely lobed. Ovary 2-celled, each cell 2-lobed. Nutlets 4, or by abortion few <>r, attached laterally to the gynobase from one-fourth to one-half the distance above the base to the apex of the nutlet, the point of attachment usually elevated and twisted lo one side, open or closed, usually rugose or pectinately rugose, coriaceous or in M. maritima smooth and shining, utricle-like. Gynobase 2 subtending the nutlets of 2 unequal pairs of lobes alternate with the nutlets and of leu intruding between them.Type* species: Mertensia virginica (L.) Pers. (Mertensia piUmoitarioides Roth, Cat. Bot. 1: 34. 1797). KEY TO THE SECTIONS A. Nutlets smooth, utricle-like; procumbent plants of the sea-shore and salt marshes Section 1. Steenhammera. A A. Nutlets rugose, not utricle-like; mostly erect or ascending inland plants. ¥>. Corolla not divided into a tube and a limb, campanulate, 10 mm. or less long Section 2. N euranthia. BIS. Corolla divided into a tube and a limb, not campanulate, usually 10 mm. or more long or if shorter then the division into tube and limb well pronounced Section 3. EUMERTENSIA. Section 1. Steenhammera (Reichb.) Gray in Proc. Am. Acad. N. S. 2: [whole series 10:] 52. 1874, as section. (Changed to Stenhammaria.) 1 l e footnole on p. 20. *cf. Moore, J, A. Morphology of the gynobase in Mertensia. Am. Midi. Nat. 17: 749-752. L936. 1937] WILLIAMS MONOGRAPH OF MERTENSIA 29 Steenhammera Reichb., Fl. Germ. Excurs. p. 337. 1831, as genus. Nutlets smooth, utricle-like; leaves thick and fleshy; procumbent plants of the sea-shore and salt marshes. A single species 1. M. maritima Section 2. Neuranthia, n. sec. 1 Nutlets rugose ; corolla not divided into a tube and a limb, campanulate, 10 mm. long or less; roots conn-like, usually rounded, small ; cauline leaves with lateral veins. A single species 2. M. bella Section 3. Eumertensia Gray, I.e. Nutlets rugose; corolla divided into a tube and limb, not campanulate, usually more than 10 mm. long, if less then definitely divided into a tube and limb ; cauline leaves with or without lateral veins. KEY TO SPECIES AND VARIETIES OF SECTION EUMERTENSIA X. Plants usually with prominent lateral veins in the cauline lea...

Apolygus lucorum (Hemiptera: Miridae) is an important insect pest of cotton and fruit trees in China. The adults prefer host plants at the flowering stage, and their populations track flowering plants both spatially and temporally. In this study, we examine whether flower preference of its adults is mediated by plant volatiles, and which volatile compositions play an important role in attracting them. In olfactometer tests with 18 key host species, the adults preferred flowering plants over non-flowering plants of each species. Coupled gas chromatography-electroantennography revealed the presence of seven electrophysiologically active compounds from flowering plants. Although the adults responded to all seven synthetic plant volatiles in electroantennography tests, only four (m-xylene, butyl acrylate, butyl propionate and butyl butyrate) elicited positive behavioral responses in Y-tube olfactometer bioassays. The adults were strongly attracted to these four active volatiles in multi-year laboratory and field trials. Our results suggest that these four fragrant volatiles, which are emitted in greater amounts once plants begin to flower, mediate A. lucorum’s preference to flowering host plants. We proved that the use of commonly occurring plant volatiles to recognize a large range of plant species can facilitate host selection and preference of polyphagous insect herbivore.

Plant volatiles induced by herbivory are often used as olfactory cues by foraging herbivores and their natural enemies, and thus have potential for control of agricultural pests. Compared to chewing insects and mites, little is known about plant volatile production following herbivory by insects with piercing-sucking mouthparts. Here, we studied factors (insect life stage, gender, the role of salivary glands, and type of bioassay used for volatile induction) that influence the induction of plant volatiles by two agriculturally important hemipterans, Lygus hesperus and Nezara viridula. Feeding on intact cotton by virgin females of L. hesperus induced 2.6-fold greater volatile response compared to that induced by mated females, possibly due to increased feeding activity by virgin females. This plant volatile response was associated with elicitors present in the insect's salivary glands as well as to the degree of mechanical injury. Feeding injury by N. viridula females also increased volatile emissions in intact maize by approximately 2-fold compared to control plants. Maize seedlings injured by N. viridula emitted higher amounts of the monoterpene linalool, the sesquiterpenes (E)-beta-caryophyllene, alpha-trans-bergamotene, and (E,E)-beta-farnesene, and the homoterpene (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene, but not amounts of green leaf volatiles, compared to uninjured plants. Emissions from intact maize injured by adult males were lower than those emitted by adult females of the same age and did not differ from those emitted by uninjured plants. Similarly, feeding by virgin female N. viridula followed by excision led to 64% higher quantities of volatiles compared to untreated plants. Volatile emission in excised plants, however, was considerably greater than in intact plants, suggesting that careful consideration must be given to bioassay design in studies of herbivore-induced plant volatiles. Salivary gland extracts of N. viridula led to sesquiterpene emissions approximately 2.5-fold higher than for controls, although no significant differences were observed for green leaf volatiles, monoterpenes, and homoterpenes. These results indicate that L. hesperus and female N. viridula feeding induce volatile production in plants, and that volatile production is affected by gender and life stage of the bug. Although oviposition and mechanical injury by stylets may increase release of volatiles, elicitors from salivary glands of L. hesperus and N. viridula also seem to play a role in the emission of plant volatiles.