Daily microhabitat shifting of solitarious-phase Desert locust adults: implications for meaningful population monitoring

Abstract

The Desert locust Schistocerca gregaria is a major world pest that causes substantial agricultural and economic damage. Effective pest control relies on effective monitoring, which requires knowledge of locust microhabitat selection. Yet little is known about microhabitat selection of solitarious adult locusts in the field. We conducted field surveys to investigate fine-scale diel temporal and spatial distributions of solitarious adults in the Sahara Desert in Mauritania, a major breeding and recession area. We found that solitarious adults moved among different, specific microhabitats throughout the 24-h period in a cyclical manner. At night, they roosted in trees, moved to the ground to feed shortly after dawn, sheltered in low vegetation during the hot midday, and returned to the ground in the late afternoon. Hence, they switched microhabitats and plant species throughout each day. These cyclical daily movements among diverse microhabitats and specific plant species were correlated with time of day, light intensity, temperature, humidity, and specific plant species, and may relate to anti-predator defence, thermoregulation, and feeding. The present study suggests that locust monitoring should be adjusted, based on time of day, locust age, phase state and relative abundance of specific plant species. For example, we recommend surveying ground after morning and trees at night, for solitarious adults, when at low density.

Aggregation Site Choice by Gregarious Nymphs of the Desert Locust, Schistocerca gregaria, in the Sahara Desert of Mauritania

“…However, we frequently observed that dense aggregations occurred at certain night-roosting plants even within a uniform plant distribution in the field, so plant distribution alone cannot explain the aggregation formation. In S. gregaria , night-roosting plant preference influence on their distribution: solitarious nymphs and adults and gregarious adults selectively roost on relatively large plants during a night [ 18 , 19 , 20 ]. It is reasonable to assume that night-roosting plant preference of gregarious nymphs may lead aggregation.…”

Defence tactics cycle with diel microhabitat choice and body temperature in the desert locust,Schistocerca gregaria

“…For example, many warm‐blooded mammal insectivores such as jerboas ( Jaculus jaculus ) and hedgehogs avoid high daytime temperatures by hunting at night, when its cooler, but also when their high body temperatures allow them to easily overcome cold‐chilled invertebrates. Locusts avoid such nocturnal ground predators by roosting in large bushes and trees (Maeno & Ould Babah Ebbe, ; Maeno et al, , ). Although a few nocturnal mammals do hunt in trees, the size, complex branching and three‐dimensional architecture of trees, as well as the roosting height, make it difficult for such predators to find roosting locusts when the locusts are at low density (Maeno et al, ).…”

“…Locusts avoid such nocturnal ground predators by roosting in large bushes and trees (Maeno & Ould Babah Ebbe, ; Maeno et al, , ). Although a few nocturnal mammals do hunt in trees, the size, complex branching and three‐dimensional architecture of trees, as well as the roosting height, make it difficult for such predators to find roosting locusts when the locusts are at low density (Maeno et al, ). When locusts are at medium or high densities, aggregating together in tall trees at night produces another effective defence: predator‐swamping (= dilution effect).…”

“…Desert Locusts are distributed across North Africa, where desert air temperatures cycle on a 24‐hr period and can vary from below freezing to over 40°C in a single day (Ward, ). Locusts match this strong daily rhythm in photoperiod and temperature with their own daily rhythm, by switching microhabitats throughout the day (see Material and Methods) (Maeno et al, ; Symmons & Cressman, ).…”

Sexual behavior of the desert locust during intra-and inter-phase interactions

“…In marked contrast, the solitarious locusts' life history involves very different and major 254 challenges in the path to successful mating and reproduction. These include: (1) locating 255 a mate: while both male and female solitarious locusts may participate in mate location, 256 it is accepted that it is mainly the males that are faced with the challenge of searching for 257 and locating the females in a scarce population (Ely et al, 2006;Maeno et al, 2016); 258…”