Posted on: 02 March, 2017
Author: Alexander P
It is the intent of this article to describe the essential biological role of aggregation pheromones in the processes of scolytid host selection and mass attack. In addition, the role of scolytid pher... It is the intent of this article to describe the essential biological role of aggregation pheromones in the processes of scolytid host selection and mass attack. In addition, the role of scolytid pheromones in guiding associated insects to scolytid-attacked hosts will be examined as outlined in g. 8.2. Specic examples are taken from well researched species to illustrate each step. It is not the intent of this chapter to explore the chemical nature of aggregating pheromones, chemical methodology or the practical use of pheromones. The conditions under which beetles emerge and take ight determine the availability of insects, the occurrence of the rst attack on a new host, and the environment in which beetles must produce and respond to aggregating pheromones, ultimately leading to a mass attack. Emergence and ight are apparently very similar for scolytids of both sexes. Most bark and timber beetles emerge from the host in which they have matured, either directly following maturation, or after an overwintering period. Some species emerge from a second (overwintering) host to which they migrated following maturation in the brood host. A third group emerges after spending the winter in a non-host substrate such as litter and duff on the forest oor. Precise seasonal timing is important. The beetles must emerge into a hospitable environment. Generally, temperature must be favorable and rainfall absent so that ight may occur. The new host must be in an acceptable state. For example, new cones must be available for Conophthorus spp., winter snow-break and wind-throw trees must be available for ambrosia beetles, or host tree carbohydrate content and composition must be optimal (Pitman 1966). Diel timing is also important, e.g. a crepuscular emergence may serve to avoid adversely high mid-day temperature, or may coincide with maximum activity and pheromone production by prospective mates (Borden 1967). There are two important internal factors which inuence emergence: general physiological readiness and biological rhythms according to http://thongchaimedical.org/top-pheromones-review-updated/ Physiological readiness may require a maturation feeding. For example, development of ight muscles in Ips para- confusus Lanier* must occur prior to emergence (Borden and Slater 1969a). Diapause must also be terminated, enabling beetles to respond to environmental stimuli. Flight muscles of Dendroctonus pseudotsugae Hopkins do not mature while the insect is in diapause (Ryan 1959) and Trypodendrort lineatum (Olivier), while appearing normal, will not mate while in a winter reproductive diapause (Fockler and Borden 1972). Only for Xyleborus fermgineus (F .) is there extensive evidence that emergence and subsequent ight are under control of a true circadian rhythm (Saunders 1967). However, emergence and ight rhythms often show distinct, pre- dictable diel periodicity (Gara and Vité 1962; Cameron and Borden 1967; Daterman et al. 1965), which may, in fact, reect endogenous circadian rhythms. 9 A" beetle which has received all the necessary internal feedback information is ready to emerge. Its ight muscles are functional, energy reserves adequate, sensory systems operational, and the alarm bell is ringing on its internal clock. Temperature is apparently the most important environmental factor regulating emergence, possibly because the majority of sites from which the beetles emerge are continually dark and humid. If all internal and external conditions are favorable the beetle will emerge by chewing and/or crawling its way to the surface of a given substrate. Source: Free Articles from ArticlesFactory.com Alexander P is a blogger from Los Angeles who studies pheromones.