Recruitment trails

Although insect pheromone structures represent a myriad of chemical functionalities [6], the composite pheromones can be classified into six behaviourally functional groups sex, aggregation, dispersal (spacing or epideictic), alarm, recruitment (trail), and maturation. 

One recent study has indicated that trails can be colony-specific, and may thereby form part of territorial marking. Recruitment trails of Lasius neoniger, which originate in the hindgut, consist of an ephemeral stimulatory component and a more durable orientation cue. It is the latter which is colony-specific, but apart from workers showing a preference for their nestmates trails, no overt behavior is observed when workers encounter foreign trails no aggressive or aversive reaction is evident (Traniello, 1980). 

Within Hymenoptera, pheromones produced by workers in social colonies are the best studied across many genera, principally in ants [6], with those eliciting trail following most extensively studied. The distinct behavior and the relative ease of the bioassay have resulted in chemical identifications in many species [ 113,114]. Those that have been recently identified are listed in Table 5. In addition, several alarm and recruitment signals have recently been identified. Many of the compounds recently identified in ants have previously been reported as trail or alarm pheromones in other ant species. For example, methyl 4-methylpyrrole-2-carboxylate 64, 3-ethyl-2,5-dimethylpyrazine 65, (9Z)-hexadec-9-enal 66,4-methylheptan-3-ol 67, and methyl 6-methylsalicy-late 68 have been identified as trail pheromone components, and heptan-2-one 69,4-methylheptan-3-one 70, formic acid 71, undecane 61,4-methylheptan-3-ol 67, methyl 6-methylsalicylate 68, and citronellal 72 have been identified as alarm pheromone components [6]. The use of the same chemicals across genera, with some used for very different functions, is an interesting phenomenon. 

Reinhard J. and Kaib M. (2001) Trail communication during foraging and recruitment in the subterranean termite Reticulitermes santonensis De Feytaud (Isoptera Rhinotermitidae). J. Insect Behav. 14, 157-171. 

Dictyoptera. Notwithstanding the economic importance of termites and cockroaches, relatively few pheromones have been identified in species in this order. In the case of termites, most of the chemical research has been undertaken on trail pheromones, which are utilized for a variety of critical social functions, such as emigration and recruitment to nest breaks or food finds. 

An alternative pathway involves the adaptor protein RAIDD (RIP-associated ICH/CED-3-homologous protein with a death domain), which is recruited by the Fas receptor via its C-terminal DD. At its N-terminus RAIDD contains a caspase recruitment domain (CARD) that is also present in procaspase-2. The adaptor protein TRADD (TNFR-associated death domain), most effectively bound following ligation of TNFR-1, functions as a platform that recruits several signalling molecules, such as TRAF-2 (the TNFR-associated factor-2), RIP (the receptor-interacting protein), both of which stimulate activation of NF-kB (the nuclear factor k B) and also FADD, which mediates activation of apoptosis (Ashkenazi and Dixit, 1998). TRAMP has been reported to bind TRADD, TRAF-2, FADD and caspase-8. TRAIL can bind either to a TRAIL-Rl trimer or to a TRAIL-R2 trimer, which recruit FADD and caspase-8 or caspase-10 (Schneider et al., 1997). 

Caspase-8 is recruited to FADD via interaction between death effector domains. We found that ORF E8 of the equine herpes virus-2 encoded a protein with two predicted death effector domains. This protein, called v-FLIP, is also present in several other viruses including human herpes virus-8. It interferes with the apoptotic pathway of FasL by binding to FADD and potently inhibits TRAIL-mediated cell death (Thome et al., 1997). The sequence information from v-FLIP led to the discovery of a mammalian homo-logue, cellular FLIP (c-FLIP, also called CASPER/I-... 

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