# Bacterial Semichemicals and Transkingdom Interactions with Insets and Plants
## 1 Introduction
### Bacteria and Interspecies Insect Communication
Early lurves (EL) hatches through the base of the egg into the flower ovary, where they spend two to three weeks eating the flower tissue and developing seed. Phytophagous EL moulds three times. Then, they chew a hole in the flower, through which they let themselves fall into the soil. Here, intermediate larvae (IL) wait until they are adopted by the ants that collect the IL and carry them to their nest. Late larvae (LL) are fed by worker ants and become carnivorous. They spend the whole autumn, winter, and spring in the ant nest. Then, in the early summer, they turn into pupae. A month later, adult butterflies emerge from pupae, which leave the ant nest and fly to flowers in July for a one-month duration [69] (Figure 3). As demonstrated by 16S rRNA-guided metabarcoding, the _M. alcon_ larval development is associated with significant changes in the structure and predicted functions of the butterfly microbiota [67]. Alphaproteobacteria dominated _M. alcon_ microbiota during EL and IL stages, while gamma-proteobacteria were predominant in LL. The PICRUSt functional prediction from DNA metabarcoding data suggested changes in predominant biochemical pathways during larval development, which are consistent with a different ability to digest carbohydrates (herbivorous EL) or proteins (carnivorous LL) and to metabolize CHCs (Figure 3). A characteristic pattern was  
Figure 3: Mirmecophilus butterfly. _P. alcon (Maculinea)_ is a lepidoptera that is adopted by ants (_M. scabrinodis_) in, intermediate larvae (IL) stage when the larvae fall on soil (after the early phytophagous phase). The attraction mechanism and chemical camouflage strategy is related to gut microbiota, which produces BVOCs. The genera _Staphylococcus_ and _Serratia_ shows a consistent distribution with camouflage skills. PICRUST prediction of genetic content shows as digestion of carbohydrate and proteins are consistent with the development of larvae and validate the system. represented by an increase, among the intracellular obligate bacterial endosymbionts, in _Ricketsiella_ (Gammaproteobacteriaabacteria) abundance during larval development and a parallel decrease in _Wolbachia_ (Alphaproteobacteria) abundance. This shift may be associated with larval color shift from red (EL) to green/yellow (LL). Indeed, _Ricketsiella_ is known to be responsible for a red to green color shift in pea aphids, which makes the aphids less visible to predators and parasites [70]. A similar red to green/yellow color shift may facilitate the integration of _M. alcon_ larvae in the host ant colonies considering that ant species have a dichromatic color vision system that is insensitive to red light [71]. Another characteristic pattern was represented by dynamics of BVOC-producing _Serratia_ spp., _Staphylococcus_ spp., and actinomycetes in _M. alcon_ larvae. In particular, _Serratia marcescens_ and _Serratia entomophila_ were largely abundant in EL, while their abundance progressively declined in IL and LL. Microorganisms belonging to the genus _Serratia_ are very common in plants, where they act as plant growth-promoting bacteria, as well as in the gut of arthropods as symbiotic bacteria. Intriguingly, these bacteria produce volatile pyrazines used as trail pheromones by insects. Particularly, 2,5-dimethylpyrazine and 3-ethyl-2,5-dimethylpyrazine are trailmarkers in ants. Thus, the abundance of _S. marcescens_ and _S. entomophila_ in EL and IL may play a specific role in the production of deceptive pyrazines that facilitate recognition of the _M. alcon_ larvae by adopting ants.