Click beetles and pheromones – an overview Miklós Tóth Plant Protection Institute, HAS, Budapest, Hungary Wireworms, the larvae of click beetles (Coleoptera: Elateridae) are important soil-dwelling polyphagous pests all over the world. www.photoshelter.com www.naturamediterraneo.com Traditional forecast and monitoring involves labour-intensive soil sampling methods, Photo L. Furlan and to obtain wireworms from soil samples collected is time-consuming (several days or more). Photo L. Furlan Pheromone-baited traps are much easier and simpler to use. However, the pheromone composition should be identified first! Photo M. Tóth On the picture: the YF trap design specifically developed for pheromone trapping of click beetles (Furlan Inform. Fitopat. 10:49. (2004) Pheromone structures - first identifications The very first chemical structures elucidated from click beetles (female- produced pheromone) were organic acids O O OH OH valeric acid (pentanoic caproic acid (hexanoic acid) acid) Limonius californicus Limonius canus Jacobson Science 159:208 Butler Environ. Entomol. 4:229 (1968) (1975) Limonius californicus www.bugguide.net Pheromone structures - geranyl/farnesyl esters Starting from the eighties, a number of geranyl and farnesyl esters were identified mainly by scientists from the Soviet Union. Example structures: O O O O geranyl butyrate (E,E)-farnesyl acetate [(E)-3,7)-dimethyl-2,6- [(E)-3,7,11)-trimethyl-2,6,10- octadienyl butyrate] dodecatrienyl acetate] i.e. A. sputator i.e. A. ustulatus First report on similar structures from: Oleschenko, 1979, cited in Kamm, Coleopt. Bull. 37:16 (1983) Pheromone structures - geranyl/farnesyl esters Permutations and combinations of such compounds are present in the pheromones of several Agriotes spp. ger.hex. farn.acet. ger.oct. ger.i-val. farn.but. ger.but. IS ustulatus IS obscurus IS sordidus IS litigiosus IS lineatus brevis IS sputator 46 81012141618202224 min GC analysis of pheromone gland extracts of Agriotes spp. (after Tóth J. Chem. Ecol.. 28:1641 (2002) and Pest Manag. Sci. 59:1 (2003) Pheromone structures - geranyl/farnesyl esters Structures for many spp. were reported, however, a great part of these compounds showed no behavioral activity. I = compound identified but no behavioral activity shown I P = compound identified, P found attractive A A = synthetic compound attractive, but not known Total: 24 spp. whether present in female Data from <www.pherobase.com> and my own files Pheromone structures - geranyl/farnesyl esters One reason for this may be that most early identifications were accessory based on direct gland extracts, gland which may not necessarily represent composition emitted bursa into the air by the females. oviduct ovary (After Ivaschenko Zool. Zh. 59: 225 supposed (1980). pheromone glands / reservoirs Gland extract vs. volatile collection (example No. 1) In A. sordidus, in gland extracts large amounts of (E,E)-farnesyl hexanoate were present,Agriotes with only sordidus traces in volatile collections. glands E,E-farnesyl ratio ger:farn =1:1 hexanoate geranyl hexanoate int. std. volatiles ratio ger:farn =1:<0.1 A. sordidus ? Photo J. Vuts 15 20 25 30 35 40 45 50 50 min Gland extract vs. volatile collection (example No. 1) In field tests on A. sordidus, no influence of the addition of the farnesyl compoundAgriotes could sordidusbe observed. glands E,E-farnesyl ratio ger:farn =1:1 hexanoate geranyl Eraclea, Italy, 20 hexanoate 1998 int. std. Total caught in test: 10 535 beetles volatiles ratio a ger:farn =1:<0.1 a bbb average catch/trap/inspection 0 -- 3 30 30 30 geran. hex. ? 30 30 30 3 -- E,E-farn. hex. (mg) 15 20 25 30 35 40 45 50 50 min (after Tóth M, et al., unpublished) Gland extract vs. volatile collection (example No. 1) Consequently, by definition, only geranyl hexanoate can be termed a pheromoneAgriotes component sordidus in this species. glands E,E-farnesyl ratio ger:farn =1:1 hexanoate geranyl Eraclea, Italy, 20 hexanoate 1998 int. std. Total caught in test: 10 535 beetles volatiles ratio a ger:farn =1:<0.1 a bbb average catch/trap/inspection 0 -- 3 30 30 30 geran. hex. ? 30 30 30 3 -- E,E-farn. hex. (mg) 15 20 25 30 35 40 45 50 50 min (after Tóth M, et al., unpublished) Gland extract vs. volatile collection (example No. 2) Gland extracts of A. lineatus were dominated by a single very large peak of geranyl octanoate, geranyl butyrate was hardly detectable (ratio of octanoate:butyrate = 100:<0.01) geranyl octanoate retention region of int. std. geranyl butyrate 4681012 14 16 18 20 22 24 min Gland extract vs. volatile collection (example No. 2) In volatile collections the butyrate was well visible (ratio of mV octanoate:butyrate = 100:10) 10 geranyl- octanoate 5 int. std. geranyl- butyrate 0 24681012 14 16 18 20 22 24 min (After Vuts J. et al., in preparation) Gland extract vs. volatile collection (example No. 2) In the field the presence of the butyrate was absolutely necessary for attraction. Total caught in test: 279 beetles A.lineatus Geranyl hexanoate Geraniol Geranyl butanoate Neryl isovalerate Geranyl octanoate E,E-farnesyl acetate 10 - - - - - 0 30 - - - - - 2 100 - - - - - 0 10 1 - - - - 273 Rümlang, 10 - 1 - - - 2 May 23 - 10 - - 1 - - 1 August 14, 10 - - - 1 - 0 1997 10 - - - - 1 1 (After Tóth Pest Manag. Sci. 59:417 (2003) Gland extract vs. volatile collection (example No. 2) It appears that volatile collections reflect better the true pheromone composition of a given species than gland extracts do. Total caught in test: 279 beetles A.lineatus Geranyl hexanoate Geraniol Geranyl butanoate Neryl isovalerate Geranyl octanoate E,E-farnesyl acetate 10 - - - - - 0 30 - - - - - 2 100 - - - - - 0 10 1 - - - - 273 Rümlang, 10 - 1 - - - 2 May 23 - 10 - - 1 - - 1 August 14, 10 - - - 1 - 0 1997 10 - - - - 1 1 (After Tóth Pest Manag. Sci. 59:417 (2003) Geometrical isomers Another reason for inactivity of identified structures may be that in some cases geometrical purity of synthetic compounds is crucial - as commonly found also in moth pheromones. It is well known that Agriotes ustulatus responds only to synthetic (E,E)- O farnesyl acetate batches which have >95% (E,E) O geometric purity. Presence of higher (E,E)-farnesyl acetate percentages of the other isomers inhibits catches. Agriotes ustulatus www.elateridae.com (After Tóth et al., unpublished) Geometrical isomers A recent report described the first neryl ester (nerol is the geometrical isomer of geraniol) as a pheromone component in Agriotes acuminatus also suggesting the importance of geometrical isomerism in click beetles. “Good” isomer “Wrong” isomer O O O O neryl butyrate geranyl butyrate [(Z)-3,7)-dimethyl-2,6- [(E)-3,7)-dimethyl-2,6- octadienyl butyrate] octadienyl butyrate] After Tolasch J. Chem. Ecol. 36:314 (2010) Geometrical isomers The full pheromone composition in A. acuminatus contained also another ester with an unusual structure, which was necessary for field activity. “Good” isomer second component O O O O O O neryl butyrate (Z,E)-2,6-dimethyl- [(Z)-3,7)-dimethyl-2,6- 2,6-octadien-1,8-diyl octadienyl butyrate] dihexanoate] After Tolasch J. Chem. Ecol. 36:314 (2010) Other structures Some Melanotus spp. from the far east appear to use dodecenyl compounds (structurally similar to moth pheromones) O O O O dodecyl acetate (E)-9,11-dodecadienyl acetate Melanotus okinawensis Melanotus sakishimensis, M. tamsuyensis Tamaki Jpn KokaiTokyo Koho JP 61:12601 (1986) Iwanaga, Appl. Ent. Zool. 35:283 (2000) Yen, Syn. Comm. 28:4561 (1998) Other structures As new structure, a methyloctanolAmi ester kell) has been identified from the non- pest Ectinus aterrimus click beetle. O O 7-methyloctyl 9- methyldecanoate Ectinus aterrimus www.biolib.cz Tolasch Chemoecology 18:177 (2008) Other structures Four similar esters were recentlyAmi shown kell) out from E. ferrugineus, an endangered click beetle. O O O O O 7-methyloctyl 5- 7-methyloctyl O methylhexanoate octanoate 7-methyloctyl 7- methyloctanoate Elater ferrugineus O Tolasch J. Chem. Ecol. O 33:2156 (2007) 7-methyloctyl www.nhmus.hu (Z)-4-decenoate Other structures Kairomonal effect: www.hvlfoto.cz E. ferrugineus also is attracted to the pheromone of its prey, Osmoderma eremita (Scarabaeidae). Osmoderma eremita Elater ferrugineus O O (R)-gamma-decalactone www.nhmus.hu Svensson J. Chem. Ecol. 30:353 (2004) Pheromone information in click beetle genera At present we have some information on chemical structures in 34 spp. Information on the genus Agriotes predominates. Agriotes Athous Cidnopus Ectinus Elater Limonius Melanotus Synaptus Total: 33 spp. Data from <www.pherobase.com> and my own files Females responding to the pheromone Traditionally it was thought that in click beetles only males respond to the pheromone (as in the case of “classical” sex pheromones). 2.5 (total caught: 2 109 beetles) 1.5 1 Catches of male and female mean / trap (+SE) 0.5 A. sordidus in traps baited abcc with different doses of the 01030100 mg pheromone (Italy, Veneto, May 1 - 26, 2001, Furlan et abbcc 2 al., unpubl.) 4 6 8 10 mean / trap (+SE) 12 (total caught: 14 709 beetles) Females responding to the pheromone However, L. Furlan observed that in traps of A. sordidus baited with synthetic pheromone, sizeable catches of females (besides large catches of males) were recorded 2.5 (total caught: 2 109 beetles) 1.5 1 Catches of male and female mean / trap (+SE) 0.5 A. sordidus in traps baited abcc with different doses of the 01030100 mg pheromone (Italy, Veneto, May 1 - 26, 2001, Furlan et abbcc 2 al., unpubl.) 4 6 8 10 mean / trap (+SE) 12 (total caught: 14 709 beetles) Females responding to the pheromone Female catches also showed a dose response, suggesting that the pheromone showed true attraction in female A. sordidus. 2.5 (total caught: 2 109 beetles) 1.5 1 Catches of male and female mean / trap (+SE) 0.5 A.