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For decades, humans have been confronted with numerous pest species, with the desert locust being one of the most damaging and having the greatest socio-economic impact. Trying to predict the occurrence of such pests is often complicated by the small number of records and observations in databases. This paper proposes a methodology based on a combination of classification and regression techniques to address not only the problem of locust sightings prediction, but also the number of locust individuals that may be expected. For this purpose, we apply different machine learning (ML) and related techniques, such as linear regression, Support Vector Machines, decision trees, random forests and neural networks. The considered ML algorithms are evaluated in three different scenarios in Western Africa, mainly Mauritania, and for the elaboration of the forecasting process, a number of meteorological variables obtained from the ERA5 reanalysis data are used as input variables for the classification–regression machines. The results obtained show good performance in terms of classification (appearance or not of desert locust), and acceptable regression results in terms of predicting the number of locusts, a harder problem due to the small number of samples available. We observed that the RF algorithm exhibited exceptional performance in the classification task (presence/absence) and achieved noteworthy results in regression (number of sightings), being the most effective machine learning algorithm among those used. It achieved classification results, in terms of F-score, around the value of 0.9 for the proposed Scenario 1. [ABSTRACT FROM AUTHOR]

Group living has various benefits, but it also carries costs, such as risk of cannibalism. Molting is a vulnerable period of being cannibalized in juvenile arthropods, but how gregarious arthropods avoid this threat is poorly understood. Here, we examined how actively migrating gregarious nymphs of desert locust, Schistocerca gregaria , avoid cannibalism during molting, in the Sahara Desert of Mauritania. In the field, gregarious nymphs cyclically march and feed on grass during the day. Our field observations found that marching behavior helped separating pre-molting and cannibalistic non-molting nymphs. Cannibalistic non-molting nymphs marched away from roost plants, leaving sedentary pre-molting nymphs behind, creating cannibal-free spaces. Some non-molting nymphs reached a pre-molting state after daytime marching, thus both pre- and non-molting nymphs roosted on same plants at night. However, pre-molting nymphs moved away from conspecifics prior to molting. Starvation experiments confirmed that food-satiation decreased cannibalistic necrophagy. Physiological surveys of diel feeding and molting patterns revealed that nymphs molted at times when conspecifics were food-satiated rather than hungry. Hence, our results indicate that behavioral and physiological traits of gregarious locusts could function to spatiotemporally separate molting locusts from cannibalistic conspecifics, thus reducing molting-associated cannibalism. This is the first report of migration-dependent molting synchrony as a mechanism reducing costs of aggregation in gregarious arthropods. [ABSTRACT FROM AUTHOR]

Despite substantial efforts to control locusts they remain periodically a major burden in Africa, causing severe yield loss and hence loss of food and income. Distribution maps indicating the value of the basic reproduction number R0 was used to identify areas where an insect pest can be controlled by a natural enemy. A dynamic process-based mathematical model integrating essential features of a natural enemy and its interaction with the pest is used to generate R0 risk maps for insect pest outbreaks, using desert locust and the entomopathogenic fungus Metarhizium acridum (Synn. Metarhizium anisoliae var. acridum) as a case study. This approach provides a tool for evaluating the impact of climatic variables such as temperature and relative humidity and mapping spatial variability on the efficacy of M. acridum as a biocontrol agent against desert locust invasion in Africa. Applications of M. acridum against desert locust in a few selected African countries including Morocco, Kenya, Mali, and Mauritania through monthly spatial projection of R0 maps for the prevailing climatic condition are illustrated. By combining mathematical modeling with a geographic information system in a spatiotemporal projection as we do in this study, the field implementation of microbial control against locust in an integrated pest management system may be improved. Finally, the practical utility of this model provides insights that may improve the timing of pesticide application in a selected area where efficacy is highly expected. [ABSTRACT FROM AUTHOR]

All terrestrial ectotherms are constrained to some degree by their thermal environment and the extent to which they can behaviorally buffer variable thermal conditions. New biophysical modeling methods (NicheMapR) allow the calculation of the body temperature of thermoregulating animals anywhere in the world from first principles, but require detailed observational data for parameterization and testing. Here we describe the thermoregulatory biology of marching bands of the desert locust, Schistocerca gregaria, in the Sahara Desert of Mauritania where extreme heat and strong diurnal fluctuations are a major constraint on activity and physiological processes. Using a thermal infrared camera in the field, we showed that gregarious nymphs altered the microhabitats they used, as well as postural thermoregulatory behaviors, to maintain relatively high body temperature (nearly 40°C). Field and laboratory experiments demonstrated that the preferred body temperature accelerated digestive rates. Migratory bands frequently left foraging sites with full guts before consuming all vegetation and moved to another habitat before emptying their foregut. Thus, the repertoire for behavioral thermoregulation in the desert locust strongly facilitates foraging and digestion rates, which may accelerate developmental rates and increase survival. We used our data to successfully parameterize a general biophysical model of thermoregulatory behavior that could capture hourly body temperature and activity at our remote site using globally available environmental forcing data. This modeling approach provides a stronger basis for forecasting thermal constraints on locust outbreaks under current and future climates. [ABSTRACT FROM AUTHOR]

Abstract Desert locust plagues have threatened food security in northern African countries for centuries. To prevent their effects, current early warning systems in arid environments need to be improved using the latest and most advanced modelling techniques and Earth observation datasets. Previous studies have analysed certain environmental predictors such as NDVI or soil moisture individually in an effort to detect suitable areas. However, we introduce new variables (Surface Temperature, LAI and Soil Moisture Root Zone) from the SMAP satellite and apply different machine learning methods in our species distribution model in order to identify desert locust presence. We obtain highly satisfactory model results (KAPPA & TSS = 0.901 and ROC = 0.986) to detect the probability of presence and, hence, likely breeding areas based on environmental factors. The most relevant variables were surface temperature, NDVI and soil moisture at root zone under different time scenarios. This study also confirms the potential of the SMAP satellite to retrieve critical temperatures due to its time pass, in addition to reinforcing the NDVI product from MODIS as a reliable environmental predictor. These results demonstrate the validity of this new approach based on machine learning methods to identify favourable breeding areas in Mauritania. Graphical abstract Image 1 Highlights • Machine learning algorithms improve accuracy in locust breeding areas detection. • The temporal evolution of the environmental predictors has a great influence in model performance. • High suitability of SMAP products in locust monitoring. • Egg stage is sensitive to surface temperature, especially over 25 °C in average. • Hopper stage is likely to be found under 35 °C of mean ST/SMAP and over 0.12 NDVI/MODIS values. [ABSTRACT FROM AUTHOR]

For desert locusts, Schistocerca gregaria ( Forskål) ( Orthoptera: Acrididae), the hopper density threshold of gregarization remains poorly documented. Field sampling was carried out in traditional seasonal breeding areas of Mauritania during two successive years without invasion to approximate the gregarization threshold. Hopper densities were assessed at numerous sampling sites. Vegetation was also sampled to characterize the habitats. Hopper behavior was analyzed in situ with the help of a behavioral circular arena to test our assumptions on empirical locust phases determination based on physical appearance (coloration and behavior) following FAO guidelines. The results provided a critical density value around 2.45 hoppers m−2, above which gregarious hoppers were expected to be seen more frequently in nature. Hopper density was confirmed as the main factor explaining the presence of gregarious individuals. The level of involvement of vegetation parameters such as plant density, basal area, volume, distance between plants, greenness, or combinations of these indicators was low in explaining the observation of gregarious hoppers compared with hopper density. Vegetation cover and height were the only vegetation characteristics that could enhance the prediction of phase status with hopper density. The hoppers' phase determined from their behavior observed in the arena was similar to that characterized through FAO guidelines phase assessment, making consistent the field sampling method. Additionnally, the use of this arena illustrated that the grouping behavior of hoppers is a gradual response to density. This study can be seen as a step forward in the estimation of hopper density thresholds of gregarization in the field. This should improve the decision making for intervention during preventive control operations. [ABSTRACT FROM AUTHOR]

In the desert locust, Schistocerca gregaria ( Forskål) ( Orthoptera: Acrididae), the threshold density inducing the gregarization phenomenon has never been determined under natural conditions. The influence of environmental factors on this phenomenon has been studied mostly in controlled environments. Based on data collected during several years by the survey teams of the National Center for Locust Control in Mauritania, we analyzed the influence of locust density, vegetation cover, and vegetation status on the probability of observing gregarious locusts. We assumed that a probability to observe gregarious locusts of 0.5 corresponded to the density threshold of gregarization. The results showed in detail the change in the threshold of gregarization according to the cover and status of the vegetation. Low cover and dry vegetation led to a low density threshold of gregarization probably due to high probability of individuals to touch each other. Dense and green vegetation favored a high threshold of gregarization probably due to a dispersion of the individuals and a low probability of individual encounters. These findings should help the management of locusts and decision making during control operations. [ABSTRACT FROM AUTHOR]

The present study involves the tracking of marching bands of more than 300,000 gregarious nymphs of the desert locust, Schistocerca gregaria, to examine shelter plant preference and how species and size of shelter plants and nymphal group sizes jointly influence the escaping behavior of 4th- and 5th-instar gregarious nymphs. Field observations are conducted during daytime and night-time in the Sahara Desert in Mauritania. Three dominant plant species have been identified at the survey site: Hyoscyamus muticus, Panicum turgidum, and Nucularia perrini. The smallest mean plant size among the three plant species is H. muticus. Gregarious nymphs perch on all the three plant species irrespective of time, and form various sizes of groups ranging from <10 to >10,000 nymphs. Groups of gregarious locusts perching on the plants show either escaping or sheltering behavior in response to an approaching observer. Percentages of nymphal groups showing escaping behavior for H. muticus, P. turgidum and N. perrini are 96.4, 47.6 and 19.5 %, respectively. Defensive behavior is not affected by nymphal group size but by species and size of shelter plants. Nymphal groups tend to show escaping behavior when their perching plants are relatively small. No groups escape from their perching plants during night. These results might indicate that gregarious nymphs do not have a strong shelter plant preference and change their defensive behavior depending on species and size of sheltering plants and light conditions. [ABSTRACT FROM AUTHOR]

Spatial resource distribution patterns play an important role in mediating density-dependent phase change (gregarization) in locusts. The degree of contagion or aggregation of resources in a habitat can increase the probability of locust gregarization by increasing the frequency of contact among individual locusts. The spatial distribution patterns of two resources upon which gregarization can occur, the tussock grasses Aristida pungens and Panicum turgidum (Poaceae), were examined in two adjacent regions of the desert locust (Schistocerca gregaria Forskål) plague recession area in Mauritania that differ in their frequencies of locust gregarization. The hypothesis that the distribution of grass tufts should be more aggregated and thus more likely to promote locust phase change in the high frequency gregarization area was tested. Tufts were more abundant, and both species were larger in the high frequency gregarization area. The spatial distribution patterns of tufts in both areas were largely aggregated at the 200- to 2000-m² scale corresponding to the population-level scale of locust resources. As predicted, the degree of aggregation was more extreme across the high frequency gregarization area. This study provides support across a large area for the predicted association between local resource distribution and locust gregarization. The observed differences in grass abundance and size between the high and low frequency gregarization areas suggest that factors such as topography or hydrology may underlie differences in plant distribution and contribute to locust gregarization in the high frequency area. [ABSTRACT FROM AUTHOR]

Fipronil, a compound belonging to a new chemical family, the phenylpyrazols, was tested as a barrier treatment in Mauritania against bands of hoppers of the desert locust (Schistocerca gregaria, Forskal1775). An ultra-low volume formulation (ADONIS 12.5UL) was applied at 15.7 and 16.6/km. The doses were 1.96 and 1.04 g ai/ protected ha. Two sites of approximately 2800 and 7200 ha were sprayed from a helicopter flying at 20m. There were 12 track spacings, ranging from 330m to 2600m. The effects of fipronil on hopper bands were determined by comparison with the initial locust populations at the two sites. Several hopper bands were monitored in two untreated areas. The hopper bands were controlled within two days in the area up to 500m from the flight path, within 7 days in the area between 1000 and 2000m, and within 12 days in the area between 2000 and 2600m. The speed of mortality was related to the upwind distance from the flight path. When ADONIS 12.5UL (12.5g ai/l of fipronil) is applied at 16 l/km, at 20m height, with track spacings up to 1000m, the efficacy was similar to that obtained with a blanket treatment (11 g ai/ha) performed the previous year in Mauritania. [ABSTRACT FROM AUTHOR]

In 1994 and 1995 the insect growth regulator Triflumuron (`Alsystin') was tested on Schistocerca gregaria in Mauritania. In these trials two different methods ofapplication were used: barrier applications and roosting place treatments. Based on measurements of population densities, it was shown that barrier treatments caused mortality rates of up to 80% after 5 to 15 days. Even 25 days after barrier applications a mortality rate of 70% was achieved. Hence, these treatments are well suited for preventive control measures in recession areas and for the protection of smaller cultivated areas in large vegetation areas which cannot be totally blanket-treated. With topical application, especially using motorized blowsprayers on roosting areas, a mortality rate of over 90% was achieved in 3 to 7 days. Therefore, Triflumuron acts as a feeding poison and as a contact poison as well. This method is also suitable for acute invasions. Moreover, since the products are only applied at specific points, one advantage is that significant amounts of pesticide (up to 80%) are saved when compared with blanket treatment. Even higher doses applied in the roosting areas maybe tolerable, due to the relatively low environmental impact of Triflumuron. [ABSTRACT FROM AUTHOR]

The desert locust, Schistocerca gregaria, is a major migratory pest that causes substantial agricultural damage. Flying adult swarms disperse widely during the daytime, but they densely roost on plants at night. Swarm control operations are generally conducted during the daytime, but night-time control is a significant potential alternative. However, the night-roosting behavior of swarms is poorly understood. We determined night-roosting plant preferences of migrating sexually immature swarms of S. gregaria at four different sites in the Sahara Desert in Mauritania during winter. The night-roosting sites were divided into two types based on presence or absence of large trees. Swarms tended to roost on the largest trees and bushes at a given site. Swarms used medium-sized plants when large trees were not locally available, but the same medium-sized plant species were hardly used when large trees were available. Plant choice influenced roosting group size—large locust groups roosted on larger plants. Night-roosting locusts rarely fled from approaching observers. These results suggest that swarms of S. gregaria exhibit plasticity in their utilization patterns of night-roosting plants depending on the plant community encountered and they selectively use larger plants. We propose that this predictable plant-size dependent night-roosting can be used to particularly ease locust swarm control and to generally adopt anti-locust night control strategy. [ABSTRACT FROM AUTHOR]

Animals often aggregate at certain sites during vulnerable periods such as night-roosting as an anti-predatory strategy. Some migratory gregarious animals must regularly find new night-roosting sites, but how they synchronously choose such sites is poorly understood. We examined how gregarious nymphs of the desert locust, Schistocerca gregaria Forskål (Orthoptera: Acrididae), aggregate at certain plants for night-roosting in the Sahara Desert. Migratory bands of last instar nymphs climbed trees around dusk and roosted there overnight. A spatial autocorrelation analysis of plants indicated that the larger locust groups formed at the larger plants within the local plant community. Other large groups were not formed near the large tree, but smaller groups were patchily distributed. Plant height was the primary cue used by migratory bands to choose night-roosting plants. A nearest-neighbor distance analysis showed that single conspicuous large trees with scattered smaller plants were distributed locally. This plant community structure and negative geotactic ascending behavior of gregarious nymphs may force them to concentrate at the landmark plant from all directions and afar. This plant-size-dependent roosting site choice may contribute for developing artificial trapping systems for locusts and inciting to a new environment-friendly night control approach. [ABSTRACT FROM AUTHOR]