Effects of Entomopathogenic fungi and Bacillus thuringiensis‐based biopesticides on Spoladea recurvalis (Lepidoptera: Crambidae)

Abstract

Spoladea recurvalis (Fabricius) is one of the most devastating pests of amaranths causing severe yield losses of 60%–100% to the crop. Unfortunately use of chemical pesticides is the most common control strategy that vegetable farmers rely on to control the pest. However, it is not effective and harmful to environmental and human health. Aiming to provide more environmentally friendly alternatives, this study evaluated the effects of various entomopathogenic fungal isolates and commercial based Bacillus thuringiensis Subsp. kurstaki product Halt®, on the pest. Twenty‐four entomopathogenic fungal (EPF) isolates from three genera (14 Metarhizium anisopliae, 9 Beauveria bassiana and 1 lsaria fumosorosea) were screened in the laboratory to assess their pathogenicity against second instar larvae of S. recurvalis. Only M. anisopliae ICIPE 30 reached a moderate threshold, causing 58.3% larval mortality. All the 11 isolates (8 M. anisopliae, 2 B. bassiana and 1 l. fumosorosea) tested against adult S. recurvalis were pathogenic, with M. anisopliae ICIPE 30 and B. bassiana ICIPE 725 causing the highest mortality of 92% and 83%, respectively. Metarhizium anisopliae ICIPE 30 had the shortest LT50 value of 4.8 days. Bacillus thuringiensis Subsp. kurstaki product Halt® caused <50% mortality on S. recurvalis larvae. A consecutive application of M. anisopliae ICIPE 30 and Bt did not cause a significant increase in larval mortality compared to separate applications of both products. Results of this study suggest that M. anisopliae ICIPE 30 was the most potent candidate and could be used in an autodissemination approach for management of adult S. recurvalis.

Entomopathogenic fungus isolates for adult Tuta absoluta (Lepidoptera: Gelechiidae) management and their compatibility with Tuta pheromone

“…Contrary to the efficacy of M. anisopliae isolates to late instars of T. absoluta reported in this study, Opisa et al (2018) observed that most of the 24 fungal isolates screened against 2nd instar larvae of S. recurvalis caused only mortalities below 30%, except for M. anisopliae ICIPE 30 which caused 58.3% mortality. In the present study, though M. anisopliae ICIPE 30 was not very virulent against adults of T. absoluta (30%), it caused about 90% mortality to fourth instar larvae through soil inoculation.…”

“…For the controls, 2 g of dry conidia was also applied on the velvet cloth but not exposed to the T. absoluta pheromone in a Delta trap. Conidia germination was assessed after 18 hr using standard procedures as described above (Goettel & Inglis, 1997 To determine the effects of the exposed conidia to Tuta pheromone under semi field conditions on T. absoluta adults, newly emerged adult moths were exposed to 1 g of dry conidia from contaminated velvet surfaces that had been exposed to T. absoluta pheromone in field cages for 3 min after every week following the methodology described above (Migiro et al, 2010;Opisa et al, 2018). Twenty (20) newly emerged adult moths (at the ratio of 1:1 (male: female)) were used per replicate and repeated four times.…”

“…A = group where males were used as donors and females were receivers; B = group where females were used as donors and males were receivers. Bars denote means mortalityOpisa et al, 2018). The high mortality rates obtained on T. absoluta adults in our current study by the most potent M. anisopliae isolates ICIPE 18, ICIPE 20 and ICIPE 665 ranged between 86.3% and 95%, in addition to their short LT 50 .…”

Biopesticide Research and Product Development in Africa for Sustainable Agriculture and Food Security – Experiences From the International Centre of Insect Physiology and Ecology (icipe)

“…Several arthropod pathogens are being developed into biopesticides against plant and animal pests, and disease vectors ( Table 3). The majority of arthropod pathogenic strains belong to M. anisopliae, and include M. anisopliae strain ICIPE 18 (against T. absoluta, Maruca vitrata, C. partellus and B. fusca) (Maniania, 1993), M. anisopliae strain ICIPE 20 (against T. absoluta and S. frugiperda and the pea leafminer Liriomyza huidobrensis) (Migiro et al, 2010;Mohamed et al, 2017;Akutse et al, 2019a), M. anisopliae strains ICIPE 40, ICIPE 41, ICIPE 315 and ICIPE 655 (against S. frugiperda) (Akutse et al, 2019a), M. anisopliae strain ICIPE 30 (against the amaranth leaf webber Spoladea recurvalis (Opisa et al, 2018(Opisa et al, , 2019; the stemborers C. partellus and B. fusca (Maniania, 1993); the mosquitoes A. gambiae and A. aegypti; the tsetse flies G. morsitans morsitans, G. fuscipes fuscipes and G. pallidipes; and the sand flies Phlebotomus martini and P. duboscqi) (Ngumbi et al, 2011;Ngure et al, 2015); and M. anisopliae strain ICIPE 51 (against the termite Macrotermes michaelseni) (Mburu et al, 2009(Mburu et al, , 2013. In addition, strains that already have been commercialized are being tested against others pests: M. anisopliae strains ICIPE 7 and ICIPE 78 against S. frugiperda (Akutse et al, 2019a); and M. anisopliae strain ICIPE 69 against T. leucotreta (Mkiga et al, 2020) and M. vitrata (Tumuhaise et al, 2015(Tumuhaise et al, , 2018.…”

Chemical additives enhance the activity of a Bt‐based biopesticide targeting the beet webworm larvae

“…In a recent study conducted by Opisa, Plessis, Akutse, Fiaboe, and Ekesi () on the efficacy of entomopathogenic fungi and Bt‐ based biopesticides for the control of S. recurvalis , low efficacy of the commercial Bt Subsp. kurstaki ‐based product, Halt®, was reported.…”