Nitrogen fertilizer decreases survival and reproduction of female locusts by increasing plant protein to carbohydrate ratio

1. Nitrogen limitation theory predicts that terrestrial plants should benefit from nitrogen inputs and that herbivores should benefit from subsequent higher plant protein contents. While this pattern has generally been supported, some herbivorous insects have shown preference and higher performance on low protein (p), high carbohydrate (c) diets as juveniles.

2. However, little is known about the effects on reproduction in adults. Using nitrogen fertilizer, we demonstrate that high plant p:c has negative effects on Senegalese locust (Orthoptera: Oedaeleus senegalensis) reproduction and survival in an agroecological setting.

3. For this, we measured p:c in millet plants (Pennisetum glaucum) that received two levels of fertilizer (high and moderate) and a control, then we caged locusts on these plants for two weeks. In the laboratory, we gave locusts the choice between untreated millet leaves and leaves that received one of the two fertilization treatment.

4. We found that fertil...