Parasitoids attraction

Mattiacci, L., Dicke, M. and Posthumus, M. A. (1994). Induction of parasitoid attracting synomone in brussels-sprouts plants by feeding of Pieris brassicae larvae role of mechanical damage and herbivore elicitor. Journal of Chemical Ecology 20 2229-2247. 

Interestingly, plants treated with the plant activators did not show any consistent increase in volatile emissions. On the contrary, treated plants released less herbivore-induced volatiles such as indole, which has been reported to interfere with parasitoid attraction. The results support the yet undetectable and unidentified phenomena that plant activators are major factors for parasitoid attraction, and these attractants may be masked by some of the major compounds in the volatile blends. This study confirms that activators of pathogen resistance are compatible with the biological control of insect pests and may even help to improve it. 

Several long-range attractant sex pheromones have been identified (Table 3) or evidence for such a pheromone has been obtained in the past 13 years. The parasitoid Ascogaster reticulatus produces (9Z)-hexadec-9-enal 9 in a tibial gland [47]. The pheromone is spread by the females much like a trail on the substrate, and the males follow the mark to the source by close antennal contact with the substrate [48]. EAG studies have revealed that the males respond much more strongly to (9Z)-hexadec-9-enal than the females and that the response to the... 

Indication of a sex attractant has also been obtained for the noctuid pupal parasitoid Diapetimorpha introita (Ichneumonidae). Antennae from D. introita males gave EAG responses to diethyl ether extracts of female head, thorax or abdomen. Antennae from females did not respond to this chemical signal and male extracts elicited no activity. This suggested the presence of an extractable female-produced pheromone, to which the males respond. While live females were able to attract males, extracts were not active. This may be due to very low levels of biologically active material in the extracts [57]. 

Synergy between polar and nonpolar components is indicated for sex attraction in the larval parasitoid Eriborus terebrans (Ichneumonidae) [58]. Males show several behaviors when exposed to a polar component with chemical... 

In Alloxysta victrix, 6-methylhept-5-en-2-one 16, which is produced by both males and females, was identified as potentially attractive to the males and slightly repellent to the females in Y-tube olfactometer assays [60]. In this study, the activity was also dependent on prior exposure of the insects to the compound. Naive insects responded more strongly than previously exposed ones. This underscores a second difficulty in the bioassay-guided identification of parasitoid hymenopteran pheromones the responses are very dependent on the context and on prior exposure. Learning has been demonstrated in several species of parasitic hymenoptera [61-65]. 

Parasitic hymenoptera often eavesdrop on the pheromone communication of their host species. The type of host pheromone recognized depends on the host stage parasitized. Phoretic egg parasitoids are often attracted by the host sex pheromone, while species that parasitize later stages (larval, pupal) often do not respond to host sex pheromone components [ 11,42]. Larval parasitoids often recognize volatiles from the damaged host plant and/or host larval frass volatiles. Parasitoids of forest beetles respond to the beetle aggregation pheromones [42]. 

An example of a larval parasitoid that responds to the host sex pheromone is seen with Cotesiaplutellae (Braconidae), also a parasitoid of the diamondback moth. These insects were attracted equally to the pheromone blend (31,32,33, see above), the acetate 32, or aldehyde 31 components [80]. This larval parasitoid, however, was also strongly attracted to host frass volatiles, in particular, dipropyl disulfide 34, dimethyl disulfide 35, allyl isothiocyanate 36, and dimethyl trisulfide 37. In contrast, the egg parasitoid Trichogramma chilonis was only weakly attracted to 36. In both, T. chilonis and C. plutellae, plant volatiles, in particular (3Z)-hex-3-en-l-yl acetate 38, significantly enhanced attraction by the pheromone [80]. 

Several other examples of host plant recognition by hymenopteran parasitoids have been described recently. Six species of aphid parasitoids, Aphidius ervi, Trioxys sp., Praon sp., Aphelinus flavus, Lysiphlebus fabarum, and Aphidius rophalosiphi were most strongly attracted to their host aphid in combination with the damaged host plant [62]. For A. rhopalosiphi, three wheat volatiles were... 

Egg-deposition also can induce the host plant to emit volatiles that attract egg parasitoids. For example, egg deposition by the elm leaf beetle (Xantho-galeruca luteola) causes its host plant, the field elm (Ulmus minor), to release a blend of mostly terpenoids that attract the egg parasitoid Oomyzus galleru-cae (Eulophidae) [ 86]. Although the specific compounds that initiate the volatile emission and that attract the egg parasitoid are unknown, the host plant response can be induced with jasmonic acid. 

One recent study addressed the response of a parasitoid to the host s spacing pheromone. Aphidius rhopalosiphi did not respond to the spacing pheromone of one host, the cherry-oat aphid Rhopalosiphum padi, which consists of 6-methylhept-5-en-2-one 16,6-methylhept-5-en-2-ol, tridecan-2-one and methyl salicylate. These compounds did not attract or repel the parasitoid. Because the aphid spacing pheromone can potentially be used to cause aphids to disperse, the failure of the parasitoid to respond to the spacing pheromone makes simultaneous use of the spacing pheromone and the parasitoid possible in aphid management [87]. 

Alarm signals produced by stressed hosts also attract parasitoids. For example, stressed aphids (Aphidius sp.) were attractive to female parasitoids of two... 

All of the long-range kairomones attractive to parasitoids that have been identified thus far are sex pheromones of the hosts. However, we are probably aware of only a small fraction of the predators and parasites that are eavesdropping on the pheromonal communications of their prey or hosts. While the evolution of individuals that are as inconspicuous as possible to their enemies is favored, it is impossible for a species to completely avoid emitting chemical signals. Thus, pheromones that are important to reproduction or other vital functions, and are good indicators of the presence of a species, are available for predators or parasitoids to exploit. 

Poelman EH, Oduor AMO, Broekgaarden C, Hordijk CA, Jansen JJ, van Loon JJA, Van Dam NM, Vet LEM, Dicke M (2009) Field parasitism rates of caterpillars on Brassica oler-acea plants are reliably predicted by differential attraction of Cotesia parasitoids. Funct Ecol 23 951-962... 

Lou YG, Ma B, Cheng JA (2005) Attraction of the parasitoid Anagrus nilaparvatae to lice volatiles induced by the rice brown planthopper Nilaparvata lugens. J Chem Ecol 31 2357-2372... 

Van Poecke RMP, Posthumus MA, Dicke M (2001) Herbivore-induced volatile production by Arabidopsis thaliana leads to attraction of the parasitoid Cotesia rubecula Chemical, behavioral, and gene-expression analysis. J Chem Ecol 27 1911-1928... 

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