Quantitative analysis of behaviour phase difference in locusts with the examination of spatial distribution patterns

The use of cameras to analyze locust activity, attraction / repulsion is an innovation that is increasingly used in behavioral studies. It allows to simultaneously collect information without interacting with the locusts and to observe more discrete behaviors which are not visually noticeable. Although the technique is complementary to the one focused on the analysis of the individual response to a group of stimuli, it offers an improvement in the observation methods of groups of individuals through the application of spatial statistics. In our present study, we did laboratory analysis of locust spatial distribution patterns in a circular arena for characterizing phase status. With spatial statistics, we examined the temporal variations of nearest neighbor distances as a criterion of attraction / repulsion between individuals raised either in isolation or in groups in order to induce phase behavior. Also, the successive changes of position of the individuals because of their activity in the circular arena were interpreted as criterion of differentiation between solitarious and gregarious locust phases. Tests were carried out, first with the sequences of photographs taken at regular intervals on 3rd instar hoppers of Desert Locust, Schistocerca gregaria, and secondly with the help of video tracking on 3rd instar hoppers of the Migratory Locust, Locusta migratoria. Making inferences on the underlying process that generates the temporal variations of the positions of the hoppers in the arena, we found that there was a larger nearest neighbor distance between isolated-rearedhoppers (indicating repulsion) in contrast to crowd-rearedhoppers, which showed an attraction with their conspecifics. From the analysis of walked distances in both tests, we found a greater activity of crowd-rearedhoppers compared to isolated-rearedhoppers. This method of quantitative analysis of locust phase differences appears to be more effective in saving time and providing more insight into as yet unclear aspects of behavioral phase studies

SMOS based high resolution soil moisture estimates for Desert locust preventive management

This paper presents the first attempt to include soil moisture information from remote sensing in the tools available to desert locust managers. The soil moisture requirements were first assessed with the users. The main objectives of this paper are: i) to describe and validate the algorithms used to produce a soil moisture dataset at 1 km resolution relevant to desert locust management based on DisPATCh methodology applied to SMOS and ii) the development of an innovative approach to derive high-resolution (100 m) soil moisture products from Sentinel-1 in synergy with SMOS data. For the purpose of soil moisture validation, 4 soil moisture stations where installed in desert areas (one in each user country). The soil moisture 1 km product was thoroughly validated and its accuracy is amongst the best available soil moisture products. Current comparison with in-situ soil moisture stations shows good values of correlation (R>0.7R>0.7) and low RMSE (below 0.04 m3 m−3). The low number of acquisitions on wet dates has limited the development of the soil moisture 100 m product over the Users Areas. The Soil Moisture product at 1 km will be integrated into the national and global Desert Locust early warning systems in national locust centres and at DLIS-FAO, respectively

Allocation of more reproductive resource to egg size rather than clutch size of gregarious desert locust (Schistocerca gregaria) through increasing oogenesis period and oosorption rate

International audienceThe desert locust, Schistocerca gregaria, shows a density-dependent reproductive trade-off by laying fewer but larger eggs in crowded conditions (gregarious phase) than in isolated conditions (solitarious phase). However, the physiological mechanisms controlling reproductive resource allocation remain unclear. We examined how egg production processes, including ovulation timing (i.e., oogenesis period), oocyte and ovarian growth rates, and oosorption rate (resorbing developing terminal oocytes), regulate reproductive outputs (egg biomass per clutch, egg size, and clutch size) during a reproductive cycle in S. gregaria by rearing them either under isolated or crowded conditions. We observed a common density-dependent negative correlation between egg size and clutch size, with no significant difference in egg biomass between the two rearing conditions. Dissection of female locusts after different days of oviposition revealed that the daily oocyte growth rate was almost similar between the two rearing conditions, but crowd-reared females ovulated later than isolated-reared ones, resulting in further oocyte growth in the former. Terminal oocytes were renewed by previous penultimate oocytes at the onset of a new reproductive cycle, and oosorption mainly occurred at an early stage in both rearing conditions; however, crowd-reared locusts displayed higher levels of oosorption compared to their isolated-reared counterparts. Crowding induced a high oosorption rate, resulting in a reduced clutch size and a prolonged oogenesis period, which in turn allowed oocytes to intake more yolk, which was probably recycled via oosorption. These results suggest that the length of the oogenesis period and oosorption rate are manipulated by maternal density, and these physiological modifications interactively regulate reproductive trade-off in S. gregaria

Forecasts of desert locust presence in Morocco coupling remote sensing imagery and field surveys

International audienceWith the objective of improving preventive management of desert locust, an operational system was developed to help in the planning of field surveys in Morocco. This operational system produce regularly some presence probability maps of solitarious or transiens desert locust. The spatial resolution is 25km over the Moroccan territory and the temporal horizon of the forecasts are 40 days. The forecasts are based on statistical models coupling historical data of field surveys with several layers of remote sensing imagery. These images are proxy of environmental variables important for desert locust: temperature, rainfall and vegetation availability. The statistical coupling was realised with random forest models. These models were assessed with a splitting of the data to evaluate the forecast errors and validate the approach. An automatic process was also developed to transform new remote sensing imagery into probability maps in order to operationalize the system. As the system has been running for over 3 years, another level of evaluation can be presented: the correspondence between the forecasts of probability of locust presence and the actual observations of field survey teams of the national anti-locust centre of Morocco since 2015

Effects of starvation and Vegetation Distribution on Locust Collective Motion

International audienceLocusts are able to migrate over long distances across areas with different vegetation structures. This work investigates how the spatial arrangement of vegetation might affect locust collective motion. The behavior of groups of third instar Schistocerca gregaria hoppers that had been fed or starved for 24 h was studied experimentally. Food patches were introduced into a circular arena where locust groups were marching. We tested two different types of food distribution: uniform and clustered. The starved locust groups were used to simulate how encountering vegetation affected locusts after crossing a large bare area. We analyzed the directed motion and mean speed of the locust groups. On the small scale of the arena, the results did not show any effects of vegetation distribution on the oriented motion and mean speed of the groups (fed group). However, encountering vegetation greatly affected the oriented movement and walking speed in the starved group, mimicking the crossing of a large bare area (group starved for 24 h). After feeding, the individuals entered a post-prandial period. That period was significantly longer for the starved hoppers than for the fed hoppers. After the post-prandial period, the hoppers started marching and did not return to feed on the food. It is therefore suggested that the marching activity of hoppers is not directly related to their hunger level. The effect of the spatial distribution of vegetation on the hunger status of hoppers and the implication for barrier treatments used in locust control are further discussed