Gustatory responses of a specialist and a generalist grasshopper to terpenoids of Artemisia ludoviciana

Abstract

Hypochlora alba (Dodge) is a specialist grasshopper that lives and feeds almost exclusively on the sage brush Artemisia ludoviciana Nutt., a plant mostly avoided by the generalist grasshopper Melanoplus sanguinipes (Fabr.). Analysis of leaves, seed heads, and glandular trichomes by gas chromatography-mass spectrometry revealed 1,8-cineole, camphor and borneol to be the major monoterpenes and achillin the major sesquiterpene lactone. These terpenoids increased over the growing season and were two to five times more concentrated in the seed heads than in the leaves. Gustatory choice tests showed a feeding stimulant(s) for H. alba to be present in extracts of A. ludoviciana and A. carruthii Wood, a closely related species that H. alba will feed upon, but not in a non-host species, A. filifolia Torr. This stimulant activity was found in a fraction containing primarily monoterpene hydrocarbons. Other fractions containing sesquiterpene lactones had antifeedant activity against M. sanguinipes. Tests with achillin showed the average foliar levels (ca. 2~ dry weight) to be above the rejection threshold of the generalist (0.5~ but below that of the specialist (4~ Reproductive tissue contained average levels greater (ca. 7~ than the rejection threshold of either species.

Olfactory responses of two species of grasshoppers to plant odours

“…However, both sexes of adult O. d. asiaticus have the same feeding habits, yet the males possess more antennal sensilla sensitive to plant odour than the females. A similar phenomenon was also observed in Hypochlora alba (Blust & Hopkins, 1987). Therefore, in addition to the two explanations mentioned, we suggest that sex differences might also relate to many other factors relevant to morphology and behaviour.…”

“…Electroantennogram (EAG) studies on the role of olfaction in host-plant location, although limited, exhibited some specificity of grasshoppers to host-plant odours at the antennal level. EAG responses to plant odours in grasshoppers with different feeding habits have been investigated in several grasshopper species (White & Chapman, 1990;Blust & Hopkins, 1987). However, study indicating the possible importance of host-plant odour in relation to feeding behaviour of grasshoppers is relatively scarce.…”

Feeding patterns of a specialist and a generalist grasshopper: electronic monitoring on their host plants

“…, 1969;Knutson, 1982;Joern, 1983). This sage species is defended by both glandular and non-glandular trichomes (Smith & Kreitner, 1983;Blust & Hopkins, 1987a) and is fed upon very little by polyphagous grasshoppers, such as the related Melamplus satzguitzipes (Fabr.) (Mulkern et al, 1969).…”

Measurements of areas consumed from leaf discs by chewing phytophagous insects: Description of a new method involving image processing

“…In most cases the amounts consumed from leaf discs have been estimated visually (Arnason et al, 1987;De Boer & Hanson, 1987;Lewis & van Emden, 1986;Nielsen, 1987;Risch, 1985). Electronic area meters have only been used in a few cases for measuring consumption of leaf discs (Raffa & Frazier, 1988), but they have been widely used for measuring consumption of inert materials (Adams & Bernays, 1978;Blust & Hopkins, 1987). Normal electronic area meters are very fast, but they are not accurate enough, because individual leaf discs may shrink or expand during the 24 h experiments.…”

“…A change of 0.1 mm in diameter causes a change in area of the leaf disc (d = 14.5 mm) of more than 2 mmL Especially in studies of feeding deterrents, it is very important to be able to detect such small consumed areas. Electronic area meters have only been used in a few cases for measuring consumption of leaf discs (Raffa & Frazier, 1988), but they have been widely used for measuring consumption of inert materials (Adams & Bernays, 1978;Blust & Hopkins, 1987).…”