Effect of shade and eutrophication on the biological control of Salvinia molesta by the weevil Cyrtobagous salviniae
Salvinia molesta (Salviniaceae: EPPO A2 List) is a floating aquatic plant species native to Brazil and introduced to Africa, Asia, Australia, New Zealand and North and Central America. The species has been also introduced into the EPPO region where it is considered transient. The biological control agent, Cyrtobagous salviniae (Coleoptera: Erirhinidae) has been utilised against the aquatic plant in many regions of the world where it has shown to be an effective biological control agent. However, in some areas, where S. molesta grows in shaded waterbodies the biocontrol agent has been less effective. The current study assessed the effect of three shade regimes (80 %, 40 % and full light) on C. salviniae in a series of replicated greenhouse experiments where plants were grown in water containing two nutrient levels (high and low) under each shade regime. Half of the plants for each nutrient level and each shade regime were subjected to herbivory by C. salviniae. Plants grown under shade and in high nutrient levels were of higher quality (expressed as carbon: nitrogen ratio) compared to plants exposed to full sunlight. The plants grown under shade incurred less damage by the biocontrol agent than those grown under full sunlight. The authors suggest the reason for this may be due to higher insoluble nitrogen concentrations in plants grown under shade which may act to deter herbivory from the weevil.
Sources
Maseko Z, Coetzee JA, Hill MP (2018) Effect of shade and eutrophication on the biological control of Salvinia molesta (Salviniaceae) by the weevil Cyrtobagous salviniae (Coleoptera: Erirhinidae). Austral Entomology https://doi.org/10.1111/aen.12370