Sitona lineatus (Coleoptera: Curculionidae) Larval Feeding on Pisum sativum L. Affects Soil and Plant Nitrogen

Citation

Cárcamo, H.A., Herle, C.E., Lupwayi, N.Z., Weintraub, P. (2015). Sitona lineatus (Coleoptera: Curculionidae) Larval Feeding on Pisum sativum L. Affects Soil and Plant Nitrogen. Journal of Insect Science, [online] 15(1), http://dx.doi.org/10.1093/jisesa/iev055

Plain language summary

Adults of pea leaf weevil feed on foliage of several plants in the bean family. Their larvae destroy nodules of peas and faba bean, which can reduce yields. Soils with high levels of nitrogen can tolerate adult and larval feeding because they no longer rely on nitrogen fixation by bacteria. In this study we demonstrated that the effects of the weevil on nitrogen content are more pronounced during early flower and that an insecticide seed treatment (thiamethoxam neonicotinoid) increased nitrogen content at late flower when weevils were attacking the plant. These results are important to understand how this insect pest damages the plant and how farmers may protect crop yields. Pea or faba bean crops planted on land amended with manure may not suffer severe damage from this pest.

Abstract

Adults of Sitona lineatus (pea leaf weevil, PLW) feed on foliage of several Fabaceae species but larvae prefer to feed on nodules of Pisum sativum L. and Vicia faba L. Indirectly, through their feeding on rhizobia, weevils can reduce soil and plant available nitrogen (N). However, initial soil N can reduce nodulation and damage by the weevil and reduce control requirements. Understanding these interactions is necessary to make integrated pest management recommendations for PLW. We conducted a greenhouse study to quantify nodulation, soil and plant N content, and nodule damage by weevil larvae in relation to soil N amendment with urea, thiame-thoxam insecticide seed coating and crop stage. PLWs reduced the number of older tumescent (multilobed) nodules and thiamethoxam addition increased them regardless of other factors. Nitrogen amendment significantly increased soil available N (>99% nitrate) as expected and PLW presence was associated with significantly lower levels of soil N. PLW decreased plant N content at early flower and thiamethoxam increased it, particularly at late flower. The study illustrated the complexity of interactions that determine insect herbiv-ory effects on plant and soil nutrition for invertebrates that feed on N-fixing root nodules. We conclude that effects of PLW on nodulation and subsequent effects on plant nitrogen are more pronounced during the early growth stages of the plant. This suggests the importance of timing of PLW infestation and may explain the lack of yield depression in relation to this pest observed in many field studies. Also, pea crops in soils with high levels of soil N are unlikely to be affected by this herbivore and should not require insecticide inputs.

Publication date

2015-01-01