Fall Armyworm, Spodoptera frugiperda Infestations in East Africa: Assessment of Damage and Parasitism.

Josephine Simiyu,Esayas Mendesil,Gashawbeza Ayalew,Paddy Likhayo,Sevgan Subramanian,Tadele Tefera,Samira Mohamed,Birhanu Sisay

doi:10.3390/insects10070195

Abstract

The fall armyworm (FAW), Spodoptera frugiperda, threatens maize production in Africa. A survey was conducted to determine the distribution of FAW and its natural enemies and damage severity in Ethiopia, Kenya and Tanzania in 2017 and 2018. A total of 287 smallholder maize farms (holding smaller than 2 hectares of land) were randomly selected and surveyed. FAW is widely distributed in the three countries and the percent of infested maize fields ranged from 33% to 100% in Ethiopia, 93% to 100% in Tanzania and 100% in Kenya in 2017, whereas they ranged from 80% to 100% and 82.2% to 100% in Ethiopia and Kenya, respectively, in 2018. The percent of FAW infestation of plants in the surveyed fields ranged from 5% to 100%. In 2017, the leaf damage score of the average of the fields ranged from 1.8 to 7 (9 = highest level of damage), while 2018, it ranged from 1.9 to 6.8. In 2017, five different species of parasitoids were recovered from FAW eggs and larvae. Cotesia icipe (Hymenoptera: Braconidae) was the main parasitoid recorded in Ethiopia, with a percent parasitism rate of 37.6%. Chelonus curvimaculatus Cameron (Hymenoptera: Braconidae) was the only egg-larval parasitoid recorded in Kenya and had a 4.8% parasitism rate. In 2018, six species of egg and larval parasitoids were recovered with C. icipe being the dominant larval parasitoid, with percentage parasitism ranging from 16% to 42% in the three surveyed countries. In Kenya, Telenomus remus (Hymenoptera: Scelionidae) was the dominant egg parasitoid, causing up to 69.3% egg parasitism as compared to only 4% by C. curvimaculatus. Although FAW has rapidly spread throughout these three countries, we were encouraged to see a reasonable level of biological control in place. Augmentative biological control can be implemented to suppress FAW in East Africa.

Highlights

Maize (Zea mays L.) is the most important staple food crop in Africa [1] and is predominantly grown by smallholder farmers
fall army worm (FAW) is widely distributed across maize-growing districts of Ethiopia, Kenya and Tanzania (Tables 3 and 4) and was present in most fields surveyed
In 2017, the percentage of infested fields ranged from 33% to 100% in Ethiopia, 93% to 100% in Tanzania and was 100% for the farms observed in Kenya (Table 3)

Summary

Introduction

Maize (Zea mays L.) is the most important staple food crop in Africa [1] and is predominantly grown by smallholder farmers. FAW was first reported in late 2016 in West Africa and it rapidly spread to different parts of Insects 2019, 10, 195; doi:10.3390/insects10070195 www.mdpi.com/journal/insects. In the Americas, there are two races of FAW, namely the rice strain (R-strain), which is most consistently found in millet and grass species associated with pasture habitats, whereas the corn strain (C-strain) prefers maize and sorghum. The two strains of FAW have been reported in Africa [2,6,7,8]. FAW causes devastating damage to almost 100 plant species, including maize, sorghum, rice, soybean, cotton, wheat and sugarcane. The recent review by Montezano et al [9] documented a total of 353 FAW larval host plant species belonging to 76 plant families, with the greatest number of host taxa in the family Poaceae (106 taxa), followed by Asteraceae and Fabaceae (31 taxa each)

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