Silk pheromones

Evans, T. A. and Main, B. Y. (1993). Attraction between social crab spiders silk pheromones in Diaea socialis. Behavioral Ecology 4 99-105. 

The silk pheromones of female Lycosa tristani and L. longitarsis are unaffected by water (Lizotte and Rovner, 1989). 

Bombykol (50), pheromone of the silk moth and the first whose structure was elucidated, can be made by two successive Wittig reactions, each giving the right geometry. Can you find this route ... 

Unlike parasitoids of other insect orders that have host-seeking larvae, most parasitic hymenoptera lay their eggs on, in, or very close to a host individual [11]. This requires the adult female to find a suitable host, often with the aid of chemical cues from host frass, pheromones, plant volatiles emitted upon host feeding or egg-deposition, silk, honeydew and other secretions. She may then chemically mark the host following oviposition to reduce superparasitism by herself or intra- and inter-specific insects [11]. 

One additional factor that comes into play in the overall chemistry of the communication system relates to chemical signals from host plants that can override the photoperiodic control of phermone production. With the com earworm, it was found that a volatile chemical signal from com silk, probably ethylene, was required by wild insects for stimulation of pheromone production (33). This signal probably interacts with controls on the photoperiodic release of PBAN. 

Fig. 2.6 Structures of the pheromone binding protein (form A) from the silk moth Bombyx mori [96] obtained in six iterative cycles of combined...

Pheromones, especially insect pheromones, have become common news stories in the popular press and hence are well known to most people. For instance, most elementary schools in the USA now include coverage of pheromones in general science and biology courses. Concomitant with this widespread coverage and inclusion in elementary school curricula is ongoing basic and applied research, which leads to important practical uses and beneficial applications. Since Butenandt s initial report on the pheromone of the silk worm moth, there have been many reviews of pheromones and recent ones are cited here. This review of the chemistry of insect pheromones will cover the isolation and identification of new pheromones and the synthesis of these compounds as well as other recently reported syntheses of important pheromones. 

Sphodros abboti Probable female contact sex pheromone silk bound Coyle and Shear, 1981... 

Metellina segmentata Male mate guarding released by pheromone on the silk of females Prenter el al 1994... 

Cupiennius salei I 3 Female silk-bound sex pheromone elicits courtship behavior of males Rovner and Barth, 1981 Papke et al., 2000 Tichy et al., 2001... 

Diaea socialis 108 Salticidae E Social spider volatile silk bound pheromone attracts conspeciflcs Evans and Main, 1993... 

Trite planiceps s Males respond selectively to female silk, probably a bound pheromone Jackson, 1987 Taylor, 1998... 

To exclude the possibility of response toward tactile cues delivered from silk, silk has been extracted with various solvents and then retested in behavioral experiments (marked W in Table 4.1). This procedure implies pheromone usage but is not conclusive. The experimentum crucis, abehavioral test of the extract for pheromonal activity, often was not performed, particularly in older studies. A complicated issue is that solvent extraction of silk can alter its physical characteristics, as shown in... 

Purse-web spiders (Atypidae) capture their prey through the walls of a silk tube, thus hiding from the environment. Males stopped wandering around on sites from which female silk tubes had been removed (Coyle and Shear, 1981), suggesting a contact sex pheromone. However, the response could have been evoked by remnants of the silk tube. In the Hexathelidae, male Atrax infensus were attracted by volatiles from females, and this behavior was exploited to trap males, using traps with hidden females (Hickman, 1964). 

Courtship behavior of Dysdera crocata, a specialized feeder on woodlice (Pso-coptera), is released by contact with nest silk or the cuticle of a live or even dead female. Washing with ether rendered these substrates inactive, suggesting the presence of a lipophilic contact pheromone (Pollard et al., 1987). 

Only one species in this large family has been investigated. Female Clubiona cam-bridgei silk induces courtship by males. The silk is active even in the absence of the female, but loses its activity upon extraction with ether (Pollard et al, 1987), suggesting the presence of a lipid-soluble pheromone. 

The only evidence to date for a male pheromone in spiders was presented by Ayyagari and Tietjen (1986), who obtained an extract from male S. ocreata silk that mediated agonistic encounters between males. The pheromone was not identified, but the authors concluded that two different components must be present, one apolar and the other of medium polarity. 

The wandering spider Cupiennius salei (Ctenidae) deposits a pheromone on its silk. This cue triggers vibrational signaling by males, to which a receptive female... 

The behavior of the males was used in a bioassay-guided identification of the pheromone, which was extractable by polar solvents such as water or methanol. The bioassay apparatus consisted of a cardboard channel with silk samples treated with different extracts. A positive response consisted of a male producing a typical drumming behavior upon contact with a stimulus. Because males responded to some extent to silk without pheromone, individual spiders were tested first with inactive silk, followed by extract-treated silk (Tichy et al, 2001). GC-MS analyses of the active silk extracts were not successful, even using several derivatization procedures. However, the pheromone structure was deduced by NMR spectroscopy... 

The extracts contained almost pure pheromone, with only minor amounts of other components. By comparison with synthetic samples, derivatization, and gas chromatography on a chiral cyclodextrin phase, the pheromone was identified as a 95 5 mixture of (5)- and (/ )-enantiomers of dimethyl citrate (cupilure (3), Fig. 4.2). Only the (5)-enantiomer was active (Tichy et al., 2001). Cupilure is probably present in ionized form on the silk (pK 3.5), because solvent extracts were neutral. The ionized carboxyl group may be conjugated to basic amino acids of the silk proteins. This would also explain why the pheromone is not volatile, despite its relatively low molecular weight, and is easily washed from the silk by water, including rain. In the tropical habitat of C. salei this would ensure the presence of cupilure only on freshly laid silk. 

Dolomedes triton males live mainly on water surfaces and can follow female draglines, even on water. Males also respond to water that has been in contact with female integument with announcement displays, which are enhanced in the presence of silk (Roland and Rovner, 1983). Earlier experiments had suggested the presence of an ether-soluble pheromone on the integument of the congener Dolomedes scriptus that released courtship in males, as did the silk of females (Kaston, 1936). 

As can be seen from the examples discussed so far, pheromones present on spider cuticle or silk frequently play an important role in spider communication, but limited information is available about their composition. Lipids, whose primary function is regulation of water content, also may have important roles in communication. 

Many studies have provided evidence that pheromones on the silk and/or the cuticle of females stimulate courtship or related behaviors in males, as do the few pheromones that have been fully identified to date. Contact with the pheromone and with silk or cuticle is usually necessary to evoke the proper courtship responses. Olfactory cues, such as those in A. aperta, may release courtship when the male is in contact with silk. There are insufficient data to draw conclusions about which classes and types of chemical might typically be used for the various kinds of pheromone, particularly as the few identified pheromone structures vary widely in polarity, volatility, and other chemical characteristics. 

A particularly thorny problem that remains to be resolved is the species-recognition process that is mediated by physical or tactile cues associated with silk or the cuticle, as well as pheromones on these two substrates. To date, the lipid mixtures associated with silk or cuticle seem to display the most variable structures and blends, making them good candidates for species recognition. In contrast, the more polar components appear to be less species specific and so are less likely to be the key factors in intraspecific recognition. 

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