Factors influencing the occurrence of fall armyworm parasitoids in Zambia

Abstract

Invasive alien species have environmental, economic and social impacts, disproportionally threatening livelihood and food security of smallholder farmers in low- and medium-income countries. Fall armyworm (FAW) (Spodoptera frugiperda), an invasive insect pest from the Americas, causes considerable losses on maize to smallholder farmers in Africa since 2016. The increased use of pesticides to control FAW in Africa raises concerns for health and environmental risks resulting in a growing interest in research on biological control options for smallholder farmers. In order to evaluate the occurrence of local natural enemies attacking FAW, we collected on a weekly basis FAW eggs and larvae during a maize crop cycle in the rainy season of 2018–2019 at four locations in the Lusaka and Central provinces in Zambia. A total of 4373 larvae and 162 egg masses were collected. For each location and date of collection, crop stage, the number of plants checked and amount of damage were recorded to analyse which factors best explain the occurrence of the natural enemy species on maize. Overall parasitism rates from local natural enemies at each location varied between 8.45% and 33.11%. We identified 12 different egg-larval, larval and larval-pupal parasitoid species. Location, maize growth stage, pest density and larval stage significantly affected parasitoid species occurrence. Our findings indicate that there is potential for increasing local populations of natural enemies of FAW through conservation biological control programmes and develop safe and practical control methods for smallholder farmers.

A deadly encounter: Alien invasive Spodoptera frugiperda in Africa and indigenous natural enemy, Cotesia icipe (Hymenoptera, Braconidae)

“…Hence, the need to identify more suitable parasitoids in West and North Africa exists. Overall, the Maxent model (AUC = 0.997 ± 0.001) predicted broader potential area for the parasitoid establishment compared to the GARP model and was consistent with the recent surveys conducted in Ghana, Benin and Zambia [83,84].…”

“…Additionally, countries such as South Africa, Madagascar, Namibia, Mozambique, Zambia, and Zimbabwe provide a suitable niche for the parasitoid establishment under current climatic conditions. Similar surveys confirmed the presence of C. icipe in Ghana, Benin, Senegal and Zambia, thereby validating the accuracy of our model [83,84]. At the same time, there is a moderate likelihood of establishment and colonisation in North Africa, due to abiotic factors, such as physical barriers (Sahara Desert) that might impede dispersal of the parasitoid.…”

Assessing the Potential of Inoculative Field Releases of Telenomus remus to Control Spodoptera frugiperda in Ghana

“…Noctuids in general, including FAW, have high fecundity but at the same time are relatively easy prey for a large number of natural enemies, as shown in studies conducted in the Americas [8][9][10]. Interestingly, several natural enemies of FAW have been identified in Africa as early as 2017, including egg and larval parasitoids, and some of them already play a significant role in the control of the pest [11][12][13][14]. A third biological control approach is augmentative releases of natural enemies.…”

Eiphosoma laphygmae, a classical solution for the biocontrol of the fall armyworm, Spodoptera frugiperda?

“…However, it is considered less specific than E. laphygmae, being recorded from several other Lepidoptera (Yu et al 2005), and several other Chelonus spp. are among the main parasitoids of FAW in Africa and Asia (Agboyi et al 2020;Gupta et al 2020;Durocher-Granger et al 2021). Thus, compared to E. laphygmae, the introduction of Ch.…”

“…In the Americas, most maize fields are either sprayed with chemical insecticides or planted with GM maize. The latter also affects parasitoid populations because FAW parasitoids are strongly host-density-dependent (Durocher-Granger et al 2021). Area-wide control of FAW and other crop pests has a strong negative long term effect on parasitoids and, therefore, in such environments it is not surprising that field parasitism assessments, even when conducted on unsprayed, non-GM maize varieties, will provide low parasitism rates.…”