Selection of fungal isolates for virulence against three aphid pest species of crucifers and okra

Abstract

Aphids are regarded as important pest problems of vegetable crops worldwide. Most vegetable growers in sub-Saharan Africa heavily rely on synthetic chemical insecticides for aphids' control. Fungus-based biopesticides are being considered as alternatives to chemical insecticides. This study evaluates virulence of five isolates of Metarhizium anisopliae and three of Beauveria bassiana against Brevicoryne brassicae, Lipaphis pseudobrassicae, and Aphis gossypii, and their thermotolerance and conidial yield as a prerequisite for strain selection. The study also evaluates performance of the best isolate in screenhouse experiment against target aphid species. Three isolates of M. anisopliae ICIPE30, ICIPE62, and ICIPE69 outperformed the others, causing mortality of 85-98 %, 83-97 %, and 73-77 %, in B. brassicae, L. pseudobrassicae, and A. gossypii, respectively, 7 days post-inoculation. Isolate ICIPE62 had the shortest LT 50 values of 3.4, 2.5, and 2.6 days at 1 9 10 8 conidia ml -1 , and the lowest LC 50 values of 7.3 9 10 5 , 9.3 9 10 4 , and 3.0 9 10 4 conidia ml -1 on day 7 against A. gossypii, B. brassicae, and L. pseudobrassicae, respectively. Furthermore, ICIPE62 produced more conidia on the surface of aphid cadavers than ICIPE30 and ICIPE69 and showed wider thermotolerance with optimum ranges between 25 and 30°C. Application of conidia of ICIPE62 formulated in aqueous and emulsifiable formulations negatively affected aphid population growth rate on kale and okra plants compared to controls in screenhouse experiments. These results have demonstrated the potential of M. anisopliae isolate ICIPE62 in suppression of A. gossypii, B. brassicae, and L. pseudobrassicae populations and could therefore be considered as biopesticide candidate for the control of these target aphids. Key messages• Several isolates of B. bassiana and M. anisopliae were screened for selection of isolate(s) that are virulent against three aphid pests infesting vegetables in subSaharan Africa. • M. anisopliae isolate ICIPE62 outperformed the other isolates in terms of virulence against the three aphid pests conidial production and thermotolerance. • Aqueous and emulsifiable formulations of M. anisopliae ICIPE62 provided acceptable control of the three aphid species in the screenhouse.

Efficacy of aqueous and oil formulations of a specific Metarhizium anisopliae isolate against Aphis craccivora Koch, 1854 (Hemiptera: Aphididae) under field conditions

“…isolate ICIPE 62 in the management of A. craccivora under field conditions. The efficacy of this isolate in inducing high mortality on A. craccivora and other aphid species has been also demonstrated under laboratory conditions and screenhouse in previous studies (Bayissa et al, ; Mweke et al, ). Application of both M. anisopliae ICIPE 62 formulations did not result in significant decline in aphid densities in wet season compared to untreated control.…”

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

“…Apart from T. absoluta adults, previous studies have shown the efficacy of these isolates to other insect pests and their life stages. For instance, M. anisopliae isolate ICIPE 18 has been reported to be infective to pests such as African Tephritid fruitflies (Dimbi, Maniania, Lux, Ekesi, & Mueke, 2003; Ekesi, Maniania, & Lux, 2002), the cabbage aphid, Brevicoryne brassicae (Linnaeus) (Hemiptera: Aphididae), turnip aphid Lipaphis pseudobrassicae (Davis) (Hemiptera: Aphididae), the melon/cotton aphid, Aphis gossypii (Glover) (Hemiptera: Aphididae) (Bayissa et al., 2017), the cowpea aphid, Aphis craccivora Koch (Hemiptera: Aphididae) (Mweke et al., 2018), legume flower thrips, Megalurothrips sjostedti (Trybom) (Thysanoptera: Thripidae) (Ekesi, Maniania, Onu, & Löhr, 1998), western flower thrips, Frankliniella occidentalis Pergande (Thysanoptera: Thripidae) (Niassy, Maniania, Subramanian, Gitonga, & Ekesi, 2012), termite Macrotermes michaelseni (Sjostedt) (Isoptera: Termitidae) (Mburu et al., 2009), the spider mite Tetranychus evansi Baker and Pritchard (Acari: Tetranychidae) (Wekesa, Maniania, Knapp, & Boga, 2005) and the maize stemborers, Chilo partellus (Swinhoe) (Lepidoptera: Pyralidae) and Busseola fusca (Fuller) (Lepidoptera: Noctuidae) (Maniania, 1992). Similarly, M. anisopliae isolate ICIPE 20 has been reported to be effective against Tephritid fruitflies (Dimbi et al., 2003; Ekesi et al., 2002), western flower thrips (Niassy et al., 2012), pea leafminer, Liriomyza huidobrensis (Blanchard) (Diptera: Agromyzidae) (Migiro et al., 2010) and sweet potato weevil, Cylas puncticollis (Coleoptera: Apionidae) (Ondiaka, Maniania, Nyamasyo, and Nderitu (2008).…”

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

“…Spoladea recurvalis pest is reported for the first to be susceptible to B . bassiana ICIPE 725 although a wide range of insects have already been reported to be susceptible to M. anisopliae ICIPE 30, namely the cabbage aphid, Brevicoryne brassicae (Linnaeus) (Hemiptera: Aphididae), turnip aphid Lipaphis pseudobrassicae (Davis) (Hemiptera: Aphididae) and the melon/cotton aphid, Aphis gossypii (Glover) (Hemiptera: Aphididae) ( Bayissa et al., ) , legume flower thrips, Megalurothrips sjostedti (Trybom) (Thysanoptera: Thripidae) (Ekesi, Maniania, Onu, & Löhr, ) and termite Macrotermes michaelseni (Sjostedt) (Isoptera: Termitidae) (Gitonga, ). Therefore, the diverse host range of M. anisopliae ICIPE 30 makes it a suitable candidate to be developed as a fungal biopesticide against a broad range of insect pests, and especially against S. recurvalis adults where the extension of labels upon registration and commercialization could benefit many users especially small scale farmers.…”