Biology and ecology of Cryptonevra nigritarsis, a potential biological control agent against the giant reed Arundo donax

Authors: ESCOBAR, YAEL - European Biological Control Laboratory (EBCL); GUERMACHE, FATIHA - European Biological Control Laboratory (EBCL); BON, MARIE-CLAUDE - European Biological Control Laboratory (EBCL); KERDELLANT, ELVEN - European Biological Control Laboratory (EBCL); PETOUX, LOUIS - Universite De Lille; DESURMONT, GAYLORD - European Biological Control Laboratory (EBCL)

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/23/2020
Publication Date: 4/25/2020
Citation: Escobar, Y., Guermache, F., Bon, M., Kerdellant, E., Petoux, L., Desurmont, G. 2020. Biology and ecology of Cryptonevra nigritarsis, a potential biological control agent against the giant reed Arundo donax. Biological Control. 147:104287. https://doi.org/10.1016/j.biocontrol.2020.104287.
DOI: https://doi.org/10.1016/j.biocontrol.2020.104287

Interpretive Summary: The giant reed Arundo donax is a highly invasive plant in the southern United States. It grows in dense populations near bodies of water, reduces water availability and has negative effects on the native flora and fauna. The fly Cryptonevra nigritarsis has been observed in the native range of A. donax attacking young shoots of the plant, quickly killing them. The present study was conducted to explore the life cycle of C. nigritarsis and measure its impact on A. donax populations. Results showed that C. nigritarsis is most abundant in the field in July, has several generations per year and overwinters as pupa. Its impact on populations of A. donax was low, and we evaluated a 6.3% shoot mortality possibly associated with this fly under field conditions. Under laboratoy conditions, shoot mortality when exposed to C. nigritarsis was higher when soil humidity was low, indicating that stressed plants are more susceptible to the insect. Further research is needed to evaluate the specificity of C. nigritarsis and its overall potential as a biological control agent.

Technical Abstract: Arundo donax (L.), commonly known as giant reed, is an invasive weed in the southern United States where it invades riparian habitats. The chloropid fly Cryptonevra nigritarsis is often found infesting young shoots of A. donax in its native range and may have potential as a biological control agent. The current study was designed to investigate the life cycle and ecology of C. nigritarsis in the field and document its impact on native A. donax populations. Populations of A. donax were monitored in ten sites in the south of France for a full year and sticky traps were used to assess C. nigritarsis abundance. Young A. donax shoots were monitored and shoots showing symptoms of C. nigritarsis infestation were dissected monthly. A metabarcoding diagnosis method was developed to assess the prevalence of C. nigritarsis among the dipteran pupae and larvae found in the shoots dissected. Finally, a manipulative experiment was performed under laboratory conditions to evaluate the impact of water stress on A. donax vulnerability to C. nigritarsis. Sticky traps showed that C. nigritarsis adults were present on all sites, had a peak of abundance in July and were absent between November and February. Overall, 6.3% of the shoots monitored in the 10 sites were infested with dipteran larvae and/or pupae, which represents the maximum potential impact of C. nigritarsis on these populations. Dissections of Arundo shoots and molecular analyses revealed that the overall prevalence of C. nigritarsis among the dipteran larvae and pupae found in A. donax shoots was 54.3%. Importantly, C. nigritarsis larvae were found every month of the year, strongly suggesting that this species is multivoltine, and pupae were found to be the main overwintering stage. Lastly, C. nigritarsis larvae and pupae were found in shoots of all diameters, including very thin shoots. Results of the manipulative experiment showed higher mortality of A. donax shoots under water stress conditions (=10% soil moisture), but C. nigritarsis larvae were not found in most of the shoots that died, casting uncertainty on the cause of mortality of the shoots. Overall, these results shed light on some important aspects on the biology, ecology, and impact of C. nigritarsis. Further research should be conducted to determine whether C. nigritarsis actively kills its host plant or merely develops in dying or decaying shoots.