Selectivity in Chemical Communication Systems of Arthropods
245
(Z)-9-tetradecenyl acetate ( 4), (Z)-7 -dodecenyl acetate (23), and (Z)-5-decenyl acetate (24) (Lofstedt et al. 1986).
In general, every species has its own characteristic blend. Thus, the need for the
development of unique chemical structures is reduced. Selectivity can be achieved
by using extant biosynthetic routes to known compounds or by slight modifications thereof. For example, the specific ~11-desaturase may have evolved from the
ubiquitous ~9-desaturase. Within a species, variations in the blends between populations (see e.g., Lofstedt 1993) and even individuals have been observed (see
e.g., Barrer et al. 1987). The specific blends will become less defined with distance from the source, because of dilution, whereas minor components will fall
below the threshold level of the receiver. Nevertheless, some males will still respond to nonoptimized blends. This allows bolas spiders to use incomplete moth sex
pheromone blends for prey attraction (Yeargan 1994). In some cases, blends are not
enough for ensuring a unique signal; this suggests the existence of antagonists. The
oblique-banded leafroller, Choristoneura rosaceana, uses a sex pheromone consisting of a 100:2: I : I mixture of 20, 21, 19, and (E)-11-tetradecenyl acetate. The
sex pheromone of the sympatric leafroller Pandemis limitata is made up of a 91 : 9
mixture of the two positional isomers 20 and 4. If as little as 1% of the minor Pandemis component 4 is added to the complete blend of C. rosaceana, trap catches
of this species are completely inhibited. Specialized receptor cells probing for this
antagonist are present in C. rosaceana (Evenden et al. 1999).
Sometimes, the elaboration of a biosynthetic pathway leads to unique compounds,
which obliterate the need to use mixtures. This is exemplified in the processionary
moth, Thaumetopoea pityocampa, which is unlike other lepidopteran genera in being able to synthesize triple bonds. Its pheromone is (Z)-13-hexadecen-11-ynyl acetate (25; see Fig. 8), which is unaccompanied by other components. Nevertheless,
this species has receptors for antagonists that are used by related Thaumetopoea spp.
as pheromone components (Quero et al. 1997).
0
OA_
25
Fig.S. Chemical structure of the single sex pheromone component 25 of Thaumetopoea pityocampa
The compounds discussed so far in this section are all acetogenins, being made
up of acetate (Cz) units, and are directly linked to the primary fatty acid metabolism
and katabolism. A common deviation from the pure acetogenins is to employ starter
units other than acetyl-CoA. The desert funnel web spider, Agenelopsis aperta, attracts males by using the ketone 8-methylnonan-2-one (26, Papke, Riechert, and
Schulz, subm.). The biosynthesis of this compound can be rationalized as starting from 3-methylbutyrate (derived from the amino acid leucine by transamination
and decarboxylation), which in tum is elongated by acetate units to form 9-methyl3-oxodecanoate (27). The loss of the terminal carboxyl group would then lead to
26 (see Fig. 9). Amino acid derivatives are used as starters in the biosynthesis of
branched lepidopteran pheromones (Charlton and Roelofs 1991 ).
245
(Z)-9-tetradecenyl acetate ( 4), (Z)-7 -dodecenyl acetate (23), and (Z)-5-decenyl acetate (24) (Lofstedt et al. 1986).
In general, every species has its own characteristic blend. Thus, the need for the
development of unique chemical structures is reduced. Selectivity can be achieved
by using extant biosynthetic routes to known compounds or by slight modifications thereof. For example, the specific ~11-desaturase may have evolved from the
ubiquitous ~9-desaturase. Within a species, variations in the blends between populations (see e.g., Lofstedt 1993) and even individuals have been observed (see
e.g., Barrer et al. 1987). The specific blends will become less defined with distance from the source, because of dilution, whereas minor components will fall
below the threshold level of the receiver. Nevertheless, some males will still respond to nonoptimized blends. This allows bolas spiders to use incomplete moth sex
pheromone blends for prey attraction (Yeargan 1994). In some cases, blends are not
enough for ensuring a unique signal; this suggests the existence of antagonists. The
oblique-banded leafroller, Choristoneura rosaceana, uses a sex pheromone consisting of a 100:2: I : I mixture of 20, 21, 19, and (E)-11-tetradecenyl acetate. The
sex pheromone of the sympatric leafroller Pandemis limitata is made up of a 91 : 9
mixture of the two positional isomers 20 and 4. If as little as 1% of the minor Pandemis component 4 is added to the complete blend of C. rosaceana, trap catches
of this species are completely inhibited. Specialized receptor cells probing for this
antagonist are present in C. rosaceana (Evenden et al. 1999).
Sometimes, the elaboration of a biosynthetic pathway leads to unique compounds,
which obliterate the need to use mixtures. This is exemplified in the processionary
moth, Thaumetopoea pityocampa, which is unlike other lepidopteran genera in being able to synthesize triple bonds. Its pheromone is (Z)-13-hexadecen-11-ynyl acetate (25; see Fig. 8), which is unaccompanied by other components. Nevertheless,
this species has receptors for antagonists that are used by related Thaumetopoea spp.
as pheromone components (Quero et al. 1997).
0
OA_
25
Fig.S. Chemical structure of the single sex pheromone component 25 of Thaumetopoea pityocampa
The compounds discussed so far in this section are all acetogenins, being made
up of acetate (Cz) units, and are directly linked to the primary fatty acid metabolism
and katabolism. A common deviation from the pure acetogenins is to employ starter
units other than acetyl-CoA. The desert funnel web spider, Agenelopsis aperta, attracts males by using the ketone 8-methylnonan-2-one (26, Papke, Riechert, and
Schulz, subm.). The biosynthesis of this compound can be rationalized as starting from 3-methylbutyrate (derived from the amino acid leucine by transamination
and decarboxylation), which in tum is elongated by acetate units to form 9-methyl3-oxodecanoate (27). The loss of the terminal carboxyl group would then lead to
26 (see Fig. 9). Amino acid derivatives are used as starters in the biosynthesis of
branched lepidopteran pheromones (Charlton and Roelofs 1991 ).