Symbiont‐mediated chemical defense in the invasive ladybird Harmonia axyridis

Abstract

The volatile alkylpyrazines methyl‐ and methoxypyrazines (MPs) present in the reflex bleeds of coccinellid beetles such as the harlequin ladybird beetle Harmonia axyridis are important semiochemicals that function in antipredatory defense behavior. Pyrazines have also been coadapted from a primarily defensive role into pheromones that function in intraspecific communication, attraction, and aggregation behavior. However, the biosynthesis of MPs in ladybird beetles is poorly understood. Here, we tested the hypothesis that MPs could be produced by microbial symbionts in H. axyridis , which generates four different MPs. The evaluation of tissue‐specific MP production showed that MP concentrations were highest in the gut tissue and hemolymph of the beetles rather than the fat body tissue as the presumed site of MP biosynthesis. Furthermore, manipulation of gut microbiota by antibiotic‐containing diets resulted in a lower MP content in adult beetles. The analysis of the bacterial community of the digestive tract revealed the presence of bacteria of the genera Serratia and Lactococcus which are reportedly able to produce MPs. In line with the known diet‐dependent production of MP in H. axyridis, we determined that the presence or relative abundance of some of the potential MP producers ( Enterococcus and Staphylococcus ) is also diet‐dependent. We hypothesize a potential role of the microbiota in MP production in H. axyridis as a possible example for outsourcing the synthesis of ecologically important semiochemicals to its gut bacteria.

Volatile Organic Compounds From Lysobacter capsici AZ78 as Potential Candidates for Biological Control of Soilborne Plant Pathogens

“…The monoalkyl-methoxypyrazines (6, 9, 10, 13, and 14) identified in the profile, are widely distributed metabolites of plants, insects, fungi and bacteria. For instance, they are known semiochemicals of ladybird beetle ( Harmonia axyridis ) and their occurrence in insects can be related to bacterial metabolism ( Schmidtberg et al, 2019 ). Their biosynthesis in bacteria is proposed to originate from condensation of amino acids like valine or isoleucine with glycine ( Cheng et al, 1991 ; Bungert et al, 2001 ) and their production has been already described in Chondromyces crocatus , Halomonas venusta , and P. perolens ( Cheng et al, 1991 ; Bungert et al, 2001 ; Schulz et al, 2004 ).…”

Evaluation of the Expression and Function of the TRE2-like and TRE2 Genes in Ecdysis of Harmonia axyridis

“…The typical breeding strategy of H. axyridis involves multiple mating and thus increasing its population (Awad et al, 2017; Du et al, 2019). When faced with various natural threats, H. axyridis adapts with different strategies, such as gathering in winter to protect against cold (Durieux et al, 2015) and releasing harmful exudates to expel natural enemies (Schmidtberg et al, 2019). As an immediate source of energy, trehalose plays a vital role in the energy storage of the H. axyridis , in the oxidative function of various physiological activities, and in the growth and development (Ge et al, 2011; Xie et al, 2013; Kojić et al, 2018; Pathak et al, 2018; Zhao et al, 2018).…”

Microbially Mediated Chemical Ecology of Animals: A Review of Its Role in Conspecific Communication, Parasitism and Predation

“…Until very recently, microbial production of chemical signals had been mainly described in mammals and insects [ 6 ]. However, solid evidence for the role of bacterial symbionts in producing volatile metabolites that contribute to the host odor profile is rapidly being accumulated for a wider range of animal taxa, including not only mammals [ 15 , 16 ] and insects [ 14 , 26 , 27 ], but also amphibians [ 28 ] and especially birds [ 17 , 29 , 30 ].…”

“…Other insects benefit from the production of toxins or antibiotics by microbial symbionts that reduce palatability or prevent pathogenic infections. For instance, the gut microbiota of coccinellid beetles produces antipredatory volatiles (i.e., methoxypyrazines) [ 27 ]. Similarly, endosymbionts of some species of rove beetles of the genus Paederus produce toxins that deter wolf spiders [ 133 ].…”