Spider pheromone

Table 4.1. Studies on spider pheromones listing reports from a variety of sources, ranging from anecdotal observations to detailed behavioral studies...

From our limited knowledge of spider pheromones, at least three different categories of releaser pheromones can be identified those associated with triggering courtship... 

Finally, volatile attractants that act over a distance, analogous to many insect sex attractant pheromones, have been identified from several spider species. To date, this class of spider pheromones has received very limited study, and there is no doubt that many more volatile attractants remain to be discovered. 

The predators discussed up to this point search for prey by using their ability to perceive certain chemical clues. Some unusual predators have evolved the ability to attract their prey with scents that mimic the odor of a valuable resource (see reviews of chemical mimicry in refs. 9 and 39). Several groups of spiders lure male insect prey with scents that mimic the sex pheromone scents of females of the prey species (see reviews in refs. 9,13,40, and 41). To the best of our knowledge, these spiders are the only predators that mimic sex pheromones. However, the spiders share some similarities with the diverse orchids which mimic insect sex pheromones to lure pollinators (9, 42, 43) and with the predatory fireflies, which practice elaborate mimicry of visual sexual signals to lure their prey heterospecific male fireflies (44). 

FIGURE 3 Pairwise combinations of moths caught by a population of spiders (M. cornigera) at one site in California (Winchester, CA) and the number of spider individuals catching both species in a pair [from a study of six spiders whose prey was recorded for up to 1.5 years over a span of 5 years (M.K.S. and W. Icenogle, unpublished data)]. Cells surrounded by a border indicate pairs of moths that seem to be pheromonally incompatible—i.e., compounds that are necessary components in attractive blends for one moth species make blends unattractive for the other species (47). 

Cupilure or (S j-TT-dimethyl citrate was identified as the contact sex pheromone of the female spider, Cupiennius salei. Chemical analysis, electrophysiology and behavioral assay demonstrated that it was indeed the contact sex pheromone." ... 

An example of chemical mimicry of pheromones involves the female bolas spider, Mastophora hutchinsoni it feeds exclusively on male moths of a... 

Dicke, M. (1986). Volatile spider-mite pheromone and host-plant kairomone, involved in spaced-out gregariousness in the spider-mite Tetranychus urticae. Physiological Entomology 11 251-262. 

Spiders are an important order of carnivorous arachnids having a great impact on many ecosystems. Because most of their prey consists of insects, they can play an important role in controlling pest insects in agricultural crops. There are currently about 36000 described species, out of an estimated overall number of 60000-80000 species (Platnick, 1999). Unlike the situation with insects (Francke and Schulz, 1999), pheromones and other semiochemicals of arachnids, and especially spiders, have received little attention from researchers. What information is available on the use of semiochemicals by spiders will be reviewed and discussed in this chapter. 

One of the earliest records of pheromones in spiders was made by Lendl (1887— 88), who described an odor emanating from female Geolycosa vultuosa (as Trochosa infemalis) (Lycosidae), which attracted males. Subsequent work by Bristowe and Locket (1926) described male lycosid courtship displays (in the absence of the females) in response to contact chemical stimuli. Kaston (1936) demonstrated that female appendages released courtship in males, and that the activity was lost after extraction with ether. These observations were confirmed for several other species by various authors (reviews Leborgne, 1981 Tietjen and Rovner, 1982 Pollard etal., 1987 Stewart, 1988). 

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

Proof of the existence of a volatile pheromone is more straightforward, but experimental separation of olfactory from visual, vibrational, and acoustic cues remains essential. Mate location may be mediated by pheromones in many spider species, because spiders, like insects, often face the task of locating a mate at some distance. 

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). 

These jumping spiders are known for their excellent vision, but there is evidence from several species that they also use pheromones for communication, as suggested by Crane (1949). More than 30 species now have been investigated, making this the most thoroughly studied family. The earlier work has been reviewed and will not be discussed in detail here (see Table 4.1 for list of species Pollard et al., 1987 Jackson, 1987). In addition, the variability of response to pheromones by individual males has been addressed (Jackson and Cooper, 1990). 

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. 

Females of the desert spider Agenelopsis aperta emit a volatile pheromone that attracts conspecihc males (Riechert and Singer, 1995). This pheromone was identified as 8-methyl-2-nonanone (1 Fig. 4.1), a previously unknown arthropod semio-chemical. It was found by headspace analysis and abdominal washings of females 2 weeks after their hnal molt, when they become sexually receptive it was absent in females of other age classes. The pheromone attracted males in a three-choice arena system at doses as low as 500 ng (Papke et al., 2001). Another female-specific ketone, 6-methyl-3-heptanone (2), was not attractive. Very low doses of 1 (10-9 mg/ml applied to a hlter paper placed in empty juvenile female webs) also induced courtship behavior in males (Papke et al., 2001). The normal behavioral sequence was followed, except for phases which required input from the female. The ED50 value (mean effective dose) of 1 was 5.5x 10-4 mg/ml hexane. In contrast, ketone 2 only induced a response in some males at unnaturally high concentrations... 

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