Influence of Symbionts in Insect Invasions
Authors: Satyapriya Singh
Division of Entomology, ICAR-Indian Agricultural Research Institute, New Delhi - 12, India.

A growing number of insects are transported and established in non-native regions and become invasive and these invasive insects are impacting both the environment and local or regional economies (Snyder and Evans, 2006). They also exert evolutionary pressures and can threaten biological diversity as well as the fundamental structure and function of ecosystems. So research highlighted several cases of insect invasions that were facilitated by microbes. It proposes a conceptual framework for assessing the role of symbiotic microbes in insect invasions that promises improved risk analyses, spread and impact modelling and management of invasive insects.


Symbiotic microbes colonize insects on the insect exoskeleton, in the insect gut and within insect cells. As plant tissues are generally low in essential amino acids, nitrogen, vitamins, and sterols, so in some cases symbiotic microbes can synthesize these compounds for insects having nutritional contribution. Symbioses, especially mutualisms, enhance invasions of many alien species leading to population declines, reduced biodiversity, and altered ecosystem functioning. The red imported fire ant (Solenopsis invicta) ranks as one of the world’s most destructive invasive species because of its ability to affect human health and to disrupt natural and agricultural systems (Tschinkel, 2006). To enhance their transmission, symbiotic microbes have evolved mechanisms, including embryonic male-killing, larval male-killing, feminization, parthenogenesis induction and cytoplasmic incompatibility, to manipulate their hosts on a large scale. Symbiotic microbes benefiting their host insects by manipulating plant physiology and also by the degradation of plant cell wall material and detoxification of plant materials in insects. In multispecific Interactions, these microbes are known to protect their insect hosts against pathogens and carnivores by multiple mechanisms, including competition for nutrients or space, production of toxins and activation of the insect’s immune system.

Cases demonstrating the role of symbiotic microbes in pest invasions

Invasive pest Introduced ranges Symbiotic microbes Functions
Bemisia tabaci United States Rickettsia sp. near bellii Fitness benefits
B. tabaci China Tobacco curly shoot virus and Tomato yellow leaf curl China virus Fitness benefits
Harmonia axyridis Europe Microsporidia closely related to Nosema thompsoni Suppressing native competitors
Xyleborus glabratus United States Raffaelea lauricola Host tree pathogen and nutrition provision


The integration of current models of biological invasions with data sets on the role of symbiotic microbes and use high-throughput approaches to assay microbial symbionts across many taxa and regions, the role of symbiotic microbes in invasive insects will be much clearer, so ultimately it helps the plant protection strategies by exploring the thoughts in new dimensions. The more we understand the role of symbiotic microbes during insect invasions, the better we will be able to predict the ecological trajectories of future introductions.


Snyder, W.E. and Evans, E.W. 2006. Ecological effects of invasive arthropod generalist predators. Annu. Rev. Ecol. Evol. Syst. 37:95–122.

Tschinkel, W.R. 2006. The Fire Ants. Cambridge, MA: Harvard Univ. Press

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