Orientation to a host (or to aggregation pheromones) must inevitably be in opposition to dispersal behavior. The behavioral transition involved has been investigated for aphids (Kennedy and Booth 1963... Orientation to a host (or to aggregation pheromones) must inevitably be in opposition to dispersal behavior. The behavioral transition involved has been investigated for aphids (Kennedy and Booth 1963a, b) and can be explained in terms of «hitting stimulus threshold levels (Johnson 1969). At the beginning of the dispersal phase, the insect has a very low threshold for dispersal stimuli, but a very high concentration. The threshold for host-positive stimuli. In other words, it would require an extremely intense host stimulus to divert it from dispersal to host orientation. However, after a given ight period, the insect becomes able to respond to a normal stimulus from its host according to http://swankyseven.com/pheromone-perfume-sexual-excitement/ Such a ight-dependent, behavioral reversal was discovered by Graham (1959, 1962) for Dypodendron lineatum. Subsequently, other researchers unsuccessfully searched for similar mechanisms in other scolytids, e.g.Ips paraconfusus (Gara 1963; Borden 1967). However, Graham’s (1959, 1962) hypothesis of release from photo- positive domination by ight has recently been veried in the laboratory for two scolytids. Female Dendroctonus pseudotsugae which were host-negative became host-positive after varying amounts of ight exercise (Atkins 1966b). In addition, Bennett and Borden (1971) found that only after 30 and 90 min of ight on a ight mill would Tkypodendron lineatum and Dendroctonus pseudotsugae, respec- tively, respond to the odor of pheromone-laden frass by ceasing ight. Graham (1961) hypothesized that Trjypodendrorz lineatum swallowed air in ight and developed a large ventricular air bubble, which could provide an internal feedback indication of ight duration. However, ventricular air bubbles have been found in T. lineatum which were denied ight (C. E. Fockler and J. H. Borden unpublished results), and stationary Dendroctonus pseudotsugae were observed to swallow air on exposure to temperatures conducive to ight (Bennett and Borden 1971). An alternative threshold determination system may occur in the lipid metabolism of scolytid beetles. Atkins ( 1966b) found that D. pseudotsugae with more than 20% total lipid (per dry weight) were ight-positive and host-negative. Beetles with less than 20% lipid could still y, but were host-positive if given the appropriate stimuli. Thus, beetles with great energy reserves could afford the luxury of extended dispersal, while beetles with minimal reserves would respond to the first new host and/or pheromone encountered and would conserve their energy reserves for reproduction. In support of the lipid metabolism hypothesis Thompson and Ben- nett (1971) showed that there was selective oxidation of mono-unsaturated fatty acids (C 16:1 and C 18:1) by male D. pseudotsugae in ight. Thus Atkins’ (1969) hypothesis that behavioral changes may be stimulated through the accumulation of selective metabolic by-products may be correct. Cessation of ight: Once a beetle is in the proximity of a host, ight must be inhibited. There is evidence that cessation of ight occurs in response to olfactory stimuli (Borden and Bennett 1969; Bennett and Borden 1971). Preown D. females (the first-attacking sex) on ight mills ceased ight on exposure to the odor of Douglas-fir phloem tissue, but not to the odor of pheromone-laden frass. Such a selective response could inhibit female beetles from landing on heavily attacked hosts, thus avoiding overcrowding and partially explaining the ‘switching phenomenon’ by which the center of Dendroctonus frontalis Zimmerman aggregation is shifted to unattacked trees (Gara and Coster 1968). Source: Free Articles from ArticlesFactory.com Alexander P is a blogger who studies pheromones. He is from Los Angeles, CA.