Desert Locust Invasion in Eastern Africa

08 Apr, 2020 Article 21

Lead Authors: Jasper Batureine Mwesigwa and Kenneth Kemucie Mwangi. Contributions by ICPAC Climate Change Technical Working Group

ICPAC Desert Locust Prediction April 1-15 2020 GIF.gif

The 2019–2020 Desert Locust Invasion

Approximately 70% of the rural populations in Sub Saharan Africa rely mainly on agriculture. The presence of agricultural pests and disease-causing pathogens in cropping and grazing areas are major limiting factors to food and fodder production. Agricultural pest and disease outbreaks have been linked to climate change (Ahanger et al. 2013). In the past 30 years, there have been at least 6 major outbreaks and/or re-emergence of pests and diseases in the Eastern Africa region. These include: Coffee Wilt Disease that killed nearly 50% of all Robusta coffee plants in the region (early 1990s); Banana Bacterial Wilt that wiped out nearly 60% of bananas (early 2000s); Cassava Brown Streak that caused significant cassava losses (since mid-2000s); Maize Lethal Necrotic Virus Disease that almost caused maize shortages in Kenya (early 2010s); and Fall Army Worm that has destroyed millions of hectares of maize (from 2016 to present). Currently, the Desert Locust (Schistocerca gregaria) is threatening food production in Ethiopia, Kenya, Somalia, Sudan, Eritrea, Djibouti, Uganda, and South Sudan. The presence of the desert locust swarms in these countries poses a great concern for food and economic security for the IGAD region as a whole.

Unlike most pests and diseases which are host-specific (feed/ invade/ damage specific hosts/ crops), the desert locust is non-selective; it feeds on almost all kinds of green vegetation including crops, pastures and forests. Climatic conditions play a big role in locust reproduction, spread and survival. According to a publication by WMO and FAO, all the different phases in the life cycle of a locust (including laying of eggs, egg development, hopper development, moulting, hardening of hopper wings, maturing of locusts, speed of movement of hopper bands and adult swarms, and transition from the solitarius phase to the gregarious phase) require ideal meteorological conditions (such as rainfall, soil moisture, soil and air temperatures, surface and boundary winds, synoptic-scale patterns and the convective state of the atmosphere). This means, changes in climate could potentially limit or favour locust spread, reproduction and survival. None of the most recent upsurges (which happened in 1985, 1992–1994, 1996–1998 and 2003) reached the current scale, probably due to unconducive climatic and ecological conditions.

In August 2019, the regional crop monitoring network in Eastern Africa first highlighted concerns of a developing desert locust invasion in parts of northern Ethiopia and coastal Sudan. This was published in the Eastern Africa Crop Monitor December 2019 edition and in several monthly Food Security and Nutrition Working Group (FSNWG) statements. The FSNWG in December 2019 issued an Alert on the Severe Desert Locust Outbreak that was threatening rural food security and livelihoods across the Eastern Africa. The two networks made of agriculture monitoring national institutions and food security analysts continued to raise early concerns that the desert locust, which is not new to parts of the region, was invading the Eastern Africa region in exceptionally large swarms like never seen before.

For the first time in over 25 years, swarms of mature locust grew en masse in the Middle East, and due to their gregarious nature, they crossed to eastern and north-eastern regions of Ethiopia through Djibouti and northern Somalia from Yemen between June and September 2019. The swarms then spread to inland Ethiopia, Eritrea, and Sudan; those in Ethiopia spread further south to western and southern Somalia and later to northern Kenya following seasonal winds. From Kenya, locust swarms spread to northern Uganda, southern South Sudan and one swarm reached northern Tanzania. The desert locusts have since spread to all countries in Eastern Africa, mainly invading the pastoral and agro-pastoral communities[1]. While they moved, they settled and laid eggs along their path. These eggs are now hatching and forming a new generation of locust breeds which continue to spread upon maturity. But, why has the ongoing desert locust upsurge reached unprecedented levels in the Eastern African region? Scientists have linked the current outbreak to unusually favourable climate and resultant ecological conditions, both in Arabia and Eastern Africa regions, primarily driven by climate change.

Figure 2: October-December 2019 rainfall as percentage of long-term rainfall

Extreme Weather, Desert Locust Development and Spread

Between June and December 2019, there was significant warming of the Indian Ocean waters adjacent to the Eastern Africa coast, leading to a significantly positive Indian Ocean Dipole (IOD). During the October- December 2019 short rains season, the north western Indian Ocean experienced the highest number of tropical cyclones. A combination of positive IOD and tropical cyclones (Kyarr in Nov and Pawan in Dec) brought about unprecedented wetter-than-normal conditions throughout Eastern Africa (Figure 2), middle-east and other neighbouring areas. Consequently, the sustained wet conditions from June through December 2019 and January 2020, facilitated above-average vegetation growth, moisture retention in the soil, and high relative humidity within the hotter Arid and Semi-Arid Lands (ASALs) areas.

The resultant prolonged wet conditions across the would-be dry areas provided unusually favourable ecological and climatic conditions for desert locust reproduction, development and survival, and spread across the entire Eastern Africa. Continued reproduction was sustained by availability of moist sandy soils across most ASALs of IGAD and the middle-east, and conducive surface temperatures.

Desert locust lay their eggs in moist sandy soils. It should be noted that locust egg development rate increases with temperature. Similarly, locust survival was sustained by an abundance of lush vegetation cover (in cropped areas, rangelands and forests) that dominated the region’s drylands; considering that adult locusts mature more rapidly in areas that recently received significant rains. The vast spread was facilitated by south-ward monsoonal winds.

Forecasted Desert Locust Spread and Impact

Despite recent intensification of control operations in most of the affected countries, breeding has continued with 1st to 2nd generation hoppers expected to keep developing through May 2020. In some cropping and pastrol areas of Ethiopia, Kenya and Somalia there is continued presence, breeding, re-infestation and emergence of mature and immature locust swarms including new generations of hopper bands and groups. This raises further concern over food security in the coming months.

In the worst case scenario, widespread destruction of crops and pasture by locusts will lead to a deterioration of food security outcomes, given the already high levels of acute food insecurity in the Eastern Africa region.

Continued surveillance, monitoring and control are highly recommended in order to avert the likely negative impacts of this upsurge.

Ahanger R.A., Bhat H.A., Bhat T.A. et al.: Impact of climate change on plant diseases. Int. J. Mod. Plant Animal Sci. 1: 105–115, 2013.

[1] FSNWG Desert Locust Alert, Dec 2019

Tags: Agriculture