# Bacterial Semichemicals and Transkingdom Interactions with Insets and Plants
## 1 Introduction
### Bacteria and Interspecies Insect Communication  
As described before, microorganisms may influence chemical signaling with BVOC emission or CHC metabolism in insect communities. In a number of mutualistic symbioses, as well as in some parasitic interactions between insect species, the acquisition and exchange of microbial strains can induce a phenomenon of chemical camouflage that reduces the aggressiveness between non-nestamate insects [61]. In literature, many reported observations of mutualist relationships were focused on ants for different reasons: (I) Simple feeding and growth, and easy management under laboratory conditions; (II) direct impact on agriculture by increasing soil quality and nutrients; (III) indirect impact in biocontrol of pest insects. The most well-known example of microbial-mediated mutualism in ants is that which is established between ants and aphids (Rhynchota, Aphidae). Ants establish a long-termmutualistic interaction with aphids, managing the aphid nest and protecting them from natural aphid predators and parasites. In turn, by feeding on plant sap, aphids produce honeybee for the ants [62]. In a well-characterized ant-aphid interaction model, BVOCs produced by _Acyrtlosiphon pisum_ (Rhynchota, Aphidae)-associated _Staphylococcus sciuri_ and _Staphylococcus xylosus_ living in the honeybee produced by aphid mediate mutualistic interaction with _Lasius niger_ (Hymenoptera, Formicidae) [29; 30]. Bacteria produce a blend of semiochemicals (including limonene, butanoic acid, 3-methyl-1-butanol, 3-methyl-2-butenal, 2-methyl-2-buten-1-ol, 3-methyl-3-buten-1-ol, 2-methylbutanal, 3-methylbutanal, 2-methylbutanoic acid, 3-methylbutanoic acid, 2,3-butanedione, propanone-propane, 2,5-dimethylpyrazine) that attract ant scouts (Figure 2). However, at the same time, some semiochemicals produced in this system by _S. sciuri_ and _Acinetobacter calcoaceticus_ (butanoic acid, 3-methyl-2-butenal, 2-methylbutanoic acid) act as attractants and oviposition stimulants for the natural enemy of _A. pisum_, _Episurplus balteatus_ (Diptera, Syrphidae). This is one of the most efficient, abundant, and highly specialized aphidophagous predators [63]. Another type of insect-insect mutualistic interaction is that between ants and butterflies during their larval stages. Interactions can be facultative or obligate, mutualistic or parasitic. In the interaction between _Myrmica_ (Hymenoptera, Formicidae) and _Maculinaa_ (=_Phengaris_) (Lepidoptera, Lycaenidae), ants defend instars from natural enemies (usually staying on top of instars). In turn, they are rewarded with nutrition secretions from specialized exocrine glands [64]. On the other hand, this relationship can be parasitic. Caterpillars of some _Maculinaa_ species are adopted by certain _Myrmica_ species, transported into their nest, and fed on either ant regurgitations (trophallaxis) or directly on ant brood [65]. The central role of CHCs and acoustic signals in the crosstalk between butterflies and ants is well-known [66]. The possibility that symbiotic microorganisms living on butterflies and ants may  
Figure 2: Aphids mutualism and predation. In aphids, _S. xylosus_ and _S. sciuri_ produces BVOCs that acts as an attractant for ants. Mutualistic ants manage and protect aphid nests. On the other hand, _S. sciuri_ and _A. calcoaceticus_ produce some BVOCs that help _E. blateatus_ larvae to find the aphids (the prey). influence this host-parasite interaction by either CHC metabolism or MVOC production has recently brought the study of the butterfly and ant microbiota to attention [67; 68]. The gut microbiomes of the endangered butterfly _Maculinea alcon_ at different life stages and that of its adopting ant _Myrmica scabrinodis_ were characterized in a recent study case [67]. On the Alpine Arc, the life cycle of _Maculinea alcon_ begins in August when eggs are deposited on both flower buds and leaves of _Gentiana asclepiadea_ or _Gentiana pneumonanthe_.