Posted on: 02 March, 2017
Author: Alexander P
Although the use of different top pheromone attractants is the most obvious method of achieving reproductive isolation, many species apparently employ the same attractant system. In these cases rate o... Although the use of different top pheromone attractants is the most obvious method of achieving reproductive isolation, many species apparently employ the same attractant system. In these cases rate of pheromone release from the female may be a species-specific cue. Particular pheromone concentrations may be required to elicit male attraction, close-range searching behavior and copulatory attempts. Hierarchies of behavioral responses (antennal movement, wing uttering, anemotaxis, etc.) in which each successive step necessitates a specic concentration have been demonstrated in laboratory assays with several Lepidoptera (Schwinck 1955; Tray- nier 1968; Bartell and Shorey 1969). In the Tortricidae attraction response to synthetic pheromone often requires a specic release rate. The larch bud moth, Zeiraphera diniana was found to be attracted to very low concentrations of trans- 11-tetradecenyl acetate (l0'3 to 10'6 mg per lure as compared to 10 mg per lure for redbanded leafroller attractancy); high release rates were completely unattractive (Roelofs et al. 1971a). In a similar case, the grape berry moth, Paralobesia viteana (Clemens) was best lured to 10“ to 10‘2 mg of attractant per dispenser while 1 and l0’3 mg treatments were largely ineffective (Roelofs et al. 1974). In Iowa, Klun and Robinson (1972) have reported another apparent example of male discrimination among various top pheromones. Cis-ll-tetradecenyl acetate was found to be most attractive to males of the obliquebanded leafroller, Choristoneura rosaceana (Harris), at high release rates, such as 10" mg per lure, whereas the pyralid European corn borer, Ostrinia nubilalis (Hubner), was most attracted to dispensers containing about 10“ mg of this chemical and not attracted at all to the high release rates, such as one mg according to http://webstyletalk.net/how-pheromones-really-work-update/ Kaae et al. (l973a) demonstrated the importance of pheromone concentration on a reproductive isolating mechanism between two closely allied noctuids, THcho- plusia m’ (Hiibner) (the cabbage looper) and Autographa californica (Speyer) (the alfalfa looper), both of which overlap widely in geographical distributions, seasonal cycles and die] mating rhythms. These species apparently use the same male attrac- tant, cis-7-dodecenyl acetate (c7-12 : Ac). This chemical was identied as a sex pheromone for Tchoplusia ni (Berger 1966) and based on gas chromatography. hioassays and electroantennogram responses, Aurographa californica also appears to employ the same top pheromone (Kaae et al. 1973a). Observations in a heterogeneous population of both species showed that Trichoplusia ni males tended to be attract- ed to release rates of c7-l2 : Ac that were 10 to 100 times greater than the most attractive release rates for Autographa californica (see g. 6.1). These high relem rates were essentially unattractive to A. californica males. Such ndings indicate that one important isolating mechanism is differing rates of pheromone release from the female. Field trapping tests utilizing virgin females support this hypo- thesis: Trichoplusia ni females attract only conspecic males, whereas Autographa valifornica females lure males of both species, but are less attractive to Trichoplusla ni males than are conspecic females. Presumably the Autographa califomlca females would not release sufficient c7-12 : Ac to elicit copulatory attempts from ’I‘ricIzoplusia ni males. Although the discriminatory powers of the males to detect different release rates can play a role in the isolation of species, it is possible that other differences exist in their use of pheromones to help reduce fruitless. Source: Free Articles from ArticlesFactory.com Mark Alexander is a blogger that studies pheromones. He is from Los Angeles, CA.