Posted on: 02 March, 2017
Author: Alexander P
The emergent beetle is exposed to new environmental conditions such as sunlight, uctuating relative humidity, wind and heat. At this point in their life cycle, scolytids are characteristically ight ... The emergent beetle is exposed to new environmental conditions such as sunlight, uctuating relative humidity, wind and heat. At this point in their life cycle, scolytids are characteristically ight positive. Many of the physiological criteria governing emergence must also govern readiness to y. In addition, emergence periodicity is apparently reected in the diet ight rhythms of many scolytids (Daterman et al. 1965; Gara 1963; Vité et al. 1964). The environmental conditions most known to determine ight initiation are temperature, light and humidity (Henson 1962; Perttunen and Boman 1965; Borden 1967). For Conophthorus coniperda (Schwarz) Henson (1962) observed that ‘. . .the preight conditions which lead to the most extensive ight are high humidity in the period between emergence and ight. Maximum ight will take place between 27 and 35 °C and after about 9 hr of flight’. He concluded that‘ . . .the peak of ight may be expected in the early afternoon on bright, dry days following a period of weather which would permit drying of the litter’. Thus, the beetle is under quite precise control by us. Pheromones are part of an external environment and can presumably most readily initiate ight in environmental conditions favoring dispersal, host selection and response to pheromones. Pheromone Selection and concentration As a general rule, if the scolytid species is monogamous, as in the genus Dendroctonus, females are the first-attacking sex. In polygamous genera such as Ips, males initiate the attack. There are some exceptions. For example, it is monogamous, but males initiate the attack. Characteristically, a very few beetles of the first-attacking sex make the initial attack on a new host. These are commonly referred to as ‘pioneer’ beetles. The remaining beetles of the rst—attacking sex face a different behavioral task since they orient to a host already attacked by pioneer beetles, which by then may possibly have been joined by their prospective mates. However, for such phenomena as physiological release of host-positive response, cessation of ight, initiation and establishment of galleries, and pheromone production, all beetles of the first-attacking sex are apparently similar according to http://swankyseven.com/pheromones-signals-sexual-attraction/ Early research, primarily on the western pine beetle, Dendroctonus brevicomis, resulted in considerable (still unresolved) controversy as to whether the pioneer attack is directed to selected hosts due to a primary (host) attraction, or occurs at random. The various arguments have recently been reviewed by Wood (I072). The D. brevicomis controversy has stimulated research on many other scolytids and for the majority of species investigated, primary attraction is a fact. Orientation to a host (or to aggregation pheromones) must inevitably be in opposition to dispersal behavior. The behavioral transition involved has been inves- ligated 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 chance of success. For example, these pheromones orients to silhouettes following an initial photopositive ight (Henson 1962) and Dendroctonus ponderosae Hopkins orients most readily to horizontally placed ‘log’ configuration olfactometers (Pitman and Vite’ 1969). Source: Free Articles from ArticlesFactory.com Alexander P is a blogger that studies pheromones. He lives in Los Angeles.