Impacts of a sub-lethal dose of glyphosate on water hyacinth nutrients and its indirect effects onNeochetinaweevils

Abstract

A sub-lethal dose of a herbicide under field conditions was applied to determine if it stimulates an increase in water hyacinth nutrients, thereby increasing feeding intensity by Neochetina spp. weevils used as biocontrol agents of the weed. Nitrogen (N) and carbon (C) were measured and compared between sprayed plants and control plants. At one site (Delta Park), N levels were lower in the sprayed plants compared to the control plants both in the leaves and the crown. At the second site (Farm Dam), leaf N was also lower in the sprayed plants than in the control plants, while no difference was found in crown N. Mean number of feeding scars per cm 2 at Delta Park was significantly higher on the sprayed plants compared to the control plants, while no significant difference was found at Farm Dam. At Delta Park, there was no correlation, however, between the number of weevil feeding scars and leaf N or C:N ratio in sprayed plants. In conclusion, the sub-lethal dose of glyphosate did not directly result in an increase in weevil feeding intensity but it can be recommended in an integrated control system to retard water hyacinth growth while conserving the weevil population.

Glyphosate residues in soil can modify plant resistance to herbivores through changes in leaf quality.

“…(2021) observed no difference in the amount of chewing insect herbivore damage between glyphosate‐exposed and control plants in two strawberry ( Fragaria ) species. Likewise, a sublethal dose of glyphosate‐based herbicide did not dramatically affect leaf damage by biocontrol weevils in water hyacinth, Eichhornia crassipes (Katembo et al ., 2013). Overall, the strongest predictor of both herbivore damage and herbivore intensity in the present study was time; leaf herbivory increased during the growing season in all groups.…”