Parasitoid Distribution and Parasitism of the Fall Armyworm Spodoptera frugiperda (Lepidoptera: Noctuidae) in Different Maize Producing Regions of Uganda.

Michael Hilary Otim,Stella Adumo Aropet,Wee Tek Tay,Henry Nakelet Opolot,Moses Opio,Dalton Kanyesigye

doi:10.3390/insects12020121

Abstract

Simple SummaryThe fall armyworm (FAW), a native of the Americas that was confirmed in Africa in 2016, has been reported to cause substantial damage to maize and sorghum in all sub-Saharan African countries. In Uganda, farmers rely mainly on synthetic insecticides, which can be harmful to humans, the environment, and significantly increase the cost of production. To lessen the disadvantages associated with synthetic insecticides, the use of parasitoids could be exploited. Fall armyworm parasitoids have been reported from the Americas, Asia, and some African countries, but not from Uganda. In this study, we aimed to determine the identity and distribution of FAW parasitoids in Uganda. We found 13 species of parasitoids attacking FAW in the surveyed locations. These included 11 species of insects in the wasp order and two in the fly order. Four of these are wasps that attack the eggs of FAW, while the remaining seven wasps and two fly species attack the larvae of FAW. Two wasp genera (Chelonus and Coccygidium spp.) were more abundant and widely distributed when compared with the other parasitoid species. All parasitoids contributed to an average of 9.2% FAW larval mortality rate across the study locations.The fall armyworm (FAW) Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) has successfully invaded Africa, where it has significantly impacted maize and sorghum production. Management of FAW in Africa predominantly relies on synthetic insecticides, which are expensive, and negatively impact the environment and beneficial insects. We, therefore, conducted field surveys in Uganda in 2017 and 2019 to identify egg and larval parasitoids of FAW for possible use in integrated pest management (IPM) programs. Parasitoids were identified by their mitochondrial DNA cytochrome c oxidase subunit 1 (mtCOI) gene sequences. We identified 13 parasitoid species belonging to three families of Hymenoptera: Platygastridae, Braconidae and Ichneumonidae, as well as one Dipteran family (Tachinidae). Coccygidium spp. and Chelonus bifoveolatus were the most abundant and widely distributed parasitoids. Overall, parasitism averaged 9.2% and ranged from 3.1% to 50% in 2017, and 0.8% to 33% in 2019. Parasitism by Sturmiopsis parasitica, Diolcogaster sp., and Cotesia flavipes on FAW in maize crops are reported for the first time. Our results suggest high biological diversity of FAW parasitoids, which should be exploited in the IPM of the FAW in Uganda.

Highlights

IntroductionThe fall armyworm (FAW) Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), a native to the tropical and sub-tropical regions of the Americas, was first reported in WestAfrica from Nigeria, and the island of São Tomé and Principe in 2016 [1], and subsequently in almost all sub-Saharan African countries [2,3,4,5,6,7]
In Africa, smallholder farmers manage fall armyworm (FAW) using synthetic insecticides [9,10,11], and several other practices including early planting, handpicking of FAW eggs and larvae, frequent weeding, manure and fertilizer applications, destruction of infested plants, application of sand and ash, crop rotation, habitat management (e.g., maize intercropped with Greenleaf desmodium (Desmodium intortum)), with Bracharia planted around the intercrop [12], and intercropping
The egg parasitoids included two species of Telenomus: T. remus Nixon and Telenomus sp., and an unidentified Platygastrid that matched to Telenomus sp. at 87.44% nucleotide identity

Summary

Introduction

The fall armyworm (FAW) Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), a native to the tropical and sub-tropical regions of the Americas, was first reported in WestAfrica from Nigeria, and the island of São Tomé and Principe in 2016 [1], and subsequently in almost all sub-Saharan African countries [2,3,4,5,6,7]. In Uganda, FAW was estimated as capable of causing maize losses of 558.9 to 1391 tons annually under no control, translating to USD 163.7 to 407.5 million annually [8]. In the Americas, chemical insecticides, genetically modified maize/cotton/soy, resistant varieties, and augmentative control methods are used to manage FAW [8]. In Africa, smallholder farmers manage FAW using synthetic insecticides [9,10,11], and several other practices including early planting, handpicking of FAW eggs and larvae, frequent weeding, manure and fertilizer applications, destruction of infested plants, application of sand and ash, crop rotation, habitat management (e.g., maize intercropped with Greenleaf desmodium (Desmodium intortum)), with Bracharia planted around the intercrop [12], and intercropping. The management of FAW should, explore alternative options including the use of beneficial insects where possible

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