An integrative approach combining molecular analyses and experiments to investigate predation of insect eggs by a mite

Authors: DESURMONT, GAYLORD - European Biological Control Laboratory (EBCL); BON, MARIE-CLAUDE - European Biological Control Laboratory (EBCL); KERDELLANT, ELVEN - European Biological Control Laboratory (EBCL); GUERMACHE, FATIHA - European Biological Control Laboratory (EBCL); PFINGSTL, TOBIAS - Universitat Graz; TIXIER, MARIE-STEPHANE - Institut National De La Recherche Agronomique (INRA)

Submitted to: Ecosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/7/2020
Publication Date: 3/2/2020
Citation: Desurmont, G., Bon, M., Kerdellant, E., Guermache, F., Pfingstl, T., Tixier, M. 2020. An integrative approach combining molecular analyses and experiments to investigate predation of insect eggs by a mite. Ecosphere. 11(3). https://doi.org/10.1002/ecs2.3065.
DOI: https://doi.org/10.1002/ecs2.3065

Interpretive Summary: Mites can be used as biological control agents against many targets, including insect pests. Here we tested the mite Trichoribates trimaculatus against eggs of the viburnum leaf beetle, an invasive insect pest in North America where it destroys wild and cultivated viburnum shrubs. Results showed that mites do not have an impact on insect eggs under laboratory conditions: eggs survived just as well with and without mites. However, traces of DNA of viburnum leaf beetle were still found inside the body of several T. trimaculatus mites, showing that they did consume something containing viburnum leaf beetle DNA. In addition, mites decreased the growth of fungi surrounding viburnum leaf beetle eggs but did increase the growth of algae. In conclusion, our study shows that T. trimaculatus is not a predator of viburnum leaf beetle eggs and should not be considered as a possible biological control agent against this pest.

Technical Abstract: The oribatid mite Trichoribates trimaculatus can be found within egg masses of the viburnum leaf beetle Pyrrhalta viburni in nature. To test the hypothesis that T. trimaculatus poses a predation threat to P. viburni eggs and assess its potential as a biological control agent, laboratory experiments were conducted, exposing P. viburni eggs to mites and comparing their integrity and survivorship to unexposed eggs. Gut content analyses using quantitative PCR (qPCR) were conducted with T. trimaculatus individuals from one of these experiments to detect traces of consumed P. viburni egg DNA. Finally, fungal and algal growth were measured in petri dishes containing eggs exposed and unexposed to mites. Results showed that egg integrity and survivorship were totally unaffected by the presence of mites. However, traces of P. viburni egg DNA were still detected in the gut of some mites that had been exposed to P. viburni eggs, indicating that they consumed either fragments of the chorion or fragments of the “egg cap” secreted by the P. viburni females, which protects the eggs. Interestingly, fungal growth was consistently reduced and algal growth consistently increased in petri dishes exposed to mites. Trichoribates trimaculatus is considered to be mainly an algae feeder and it may be able to promote algal dispersal and growth in its environment. In conclusion, T. trimaculatus does not directly impact P. viburni eggs and does not have value for biological control. The fact that mites did not directly predate eggs but still retained traces of P. viburni DNA in their gut shows that consumption does not necessarily equals predation and that gut molecular analyses should be used with caution in studies attempting to reconstruct trophic interactions and putative food webs.