A survey of cultivated and wild host plants for the invasive fall army worm (Spodoptera frugiperda) in Kenya

Abstract

The fall army worm (FAW), Spodoptera frugiperda (J.E.Smith) invaded Kenya in 2017 and is known globally as polyphagous pest. This pest invaded and immediately spread in many regions including Western, Rift valley, Central and Eastern Kenya and has become an important economic pest, posing serious food security threat across the country. This study was carried out to determine the range of host plants (both cultivated crops and wild plants) of FAW and to confirm its occurrence in various regions of the country. The survey was conducted in 13 counties, located between 34^o and 37^o east longitude and latitude 0^o42’N and 03^o24’S and altitude range of 905-2500m a.s.l in February and March 2018. The fall army worm was observed on 18 plant species representing Poaceae and Cyperacea plant families. The frequency of occurrence of fall army worms was 45.8% for maize (Zea mays L.) followed by napier grass (Pennisteum purpurea) (9.7%) and crabgrass (Digitaria spp) (8.0%), sorghum (Sorghum bicolor) (7.8%), Masai love grass (Seteria verticillate) (4.8%) and sudan grass (Sorghum halapense) (3.2%). Barn yard grass (Echinocloa colona), Bermuda grass (Cynodon dactylon) and sedge grass (Cyperus rotunda) each had 2.4% of FAW leaf damage symptoms. The frequency of occurrence of fall army worm on wild finger millet (Eleusine indica) and cultivated millet (Eleusine coracana) was (2.3%). Fall army worm infestation was high for maize (1.9) followed by crabgrass (1.3) and masai love grass (0.1) compared with the other host plants. The proportion of egg masses (0.2) and number of caterpillars on plants (1 .6) was higher in Maize. More caterpillars were recorded on napier grass (0.4) and crab grass (0.3). The egg masses (0.3 and 0.3) and the numbers of caterpillars (2.2 and 1.6) on maize crop was more in the vegetative V7 and V9 growth stages respectively. Fall army worm infestation was highest in Meru (2.2), Machakos, (1.9), Makueni, Taita and Tharaka Nithi (1.8) and lowest in Narok (1.2), Trans-Nzoia (1.0) and Baringo counties. Mean egg masses was highest in Makueni (0.8), followed by Machakos, Nakuru and Taita ( 0.4) and was lowest in Tharaka-Nithi, Kakamega and Trans-Nzoia counties. The number of caterpillars in the host plants was highest in Kirinyaga (3.1) followed by Meru (2.3) and Machakos (2.1) counties and lowest in Nakuru (0.0) County. 76% of the farms surveyed used insecticide to control fall army worm, except in one farm in Nakuru where pheromone traps were used to manage the pest. Mean fall army worm infestation score (1.5), number of egg masses (0.1) and number of caterpillars (1.4) was higher on cultivated crops and grass weeds growing under irrigated farms compared to those under rain-fed farming systems in the surveyed areas. Different types of insecticides were used across the counties that included; escort, cyclone duduthrin, profen, pentagon, coragen, actra, ranger and bestox. The study provides important understanding of pest distribution and potential host plants that should be taken into consideration when developing integrated pest management strategies.

Keywords: Fall army worm, Spodoptera frugiperda, host plants, farming systems, infestation, IPM, Kenya