March 14, 2019
This post was written by Marion Le Gall, a postdoctoral researcher in Arizona State University's Cease Lab.
Last summer, with Master of Science in sustainability student Mira Word having brilliantly defended her thesis and Arianne Cease in writing jail, I (Marion Le Gall) found myself the sole member of the Arizona State University Senegal field team. With that in mind, I decided that the reasonable thing to do was to craft not one, but two field seasons for myself.
At the end of July, I thus packed the material I needed and took the long flight to Senegal. What didn’t take long was being reacquainted with the local rhythm. By that I mean that five hours before landing I still didn’t know where and who my Airbnb host was… Not to worry, in a country that prizes itself for its sense of hospitality, the famous Senegalese “teranga,” everything always seems to work out.
A couple days later I was on my way to the phytosanitary station of Nganda. The station belongs to the Direction de la Protection des Végétaux (DPV), a branch of the Senegalese agricultural department, whose mission is to monitor and control crop pests. The DPV has been collaborating with Arianne since 2015, and they let us stay at the station to do field work and provide amazing local support and experience.
My first time in Senegal was in 2017 and I became instantly fascinated by the dynamic Sahel environment. The country goes from brown to green as soon as the rain arrives (the rainy season roughly lasts from July to October) and life seems to be exploding during that time. It is also during that crucial period that crops are grown, as most of the agriculture in Senegal is rain-fed. Alas, this is also when my current favorite grasshopper, Oedaleus senegalensis, can become a very serious problem for millet, an essential subsistence crop in Senegal.
Thanks to the work conducted by the Cease lab in 2016 (1), and 2017 (2), as well as several studies by local experts (see Touré et al. 2013 (3) who studied the effect of cultural techniques and Maiga et al. 2008 (4), for a review on the ecology and management of O. senegalensis), we now have a fair understanding of what nutritional needs O. senegalensis has at the beginning of the rainy season. Interestingly even though it’s the most important pest of millet, it doesn’t really care for millet. It prefers some weed species present in the neighboring fallow fields. Nevertheless, when the density of grasshoppers gets high, the insects spill on the millet fields and will feed on the seedlings, sometimes causing farmers to have to replant entire fields.
We think that this host plant choice may be partially nutrient driven and that at the beginning of the rainy season O. senegalensis is essentially a sugar-fiend. What we don’t know is what’s happening at the end of the rainy season. O. senegalensis produces three generations per year, the third and last one attacks millet seeds when they are still soft (this is called the milky stage of millet), causing direct yield damage. It is important to note that seeds are typically rich in protein not sugars. What happens to our sugar-fiend?
I tried to figure that out by heading to Senegal for a second time mid-September, after a month of respite in the United States, and conducted several experiments with millet seeds this time. I can’t really discuss the results for now as they are top secret (meaning not fully analyzed yet), but what I can tell you is that two field seasons abroad alone is hard work!
- Word, M. L., S. J. Hall, B. E. Robinson, B. Manneh, A. Beye and A. J. Cease (2019). "Soil-targeted interventions could alleviate locust and grasshopper pest pressure in West Africa." Science of The Total Environment 663: 632-643.
- Le Gall, Marion, et al. “Linking land use and the nutritional ecology of herbivores: a case study with the Senegalese locust (Oedaleus senegalensis).” Submitted.
- Toure, M, Ndiaye, M. and Diongue, A., 2013. Effect of cultural techniques: Rotation and fallow on the distribution of Oedaleus senegalensis (Krauss, 1877)(Orthoptera: Acrididae) in Senegal. African Journal of Agricultural Research, 8(45), pp.5634-5638.
- Maiga, I. H., M. Lecoq and C. Kooyman (2008). Ecology and management of the Senegalese grasshopper Oedaleus senegalensis (Krauss 1877) (Orthoptera: Acrididae) in West Africa: review and prospects. Annales De La Societe Entomologique De France 44(3): 271-288.