Metarhizium anisopliae and Beauveria bassiana: Pathogenicity, Horizontal Transmission, and Their Effects on Reproductive Potential of Thaumatotibia leucotreta (Lepidoptera: Tortricidae)

Abstract

The polyphagous moth, Thaumatotibia leucotreta (Meyrick) is among the major constraints to the horticultural industry in East Africa. In a search of sustainable control methods, the pathogenicity of the dry conidia of 17 Metarhizium anisopliae (Metschn.) and five Beauveria bassiana (Bals.) (Vuill.) isolates were tested against T. leucotreta moths. The conidial uptake by a single moth, horizontal transmission, and effect of fungal inoculant on egg-laying and hatchability for the pest were also assessed. The findings from this study showed that tested fungi were virulent to the moths, with 12 isolates causing mortality that ranged between 58.8 and 94.2% for M. anisopliae and three isolates between 57.6 and 84.6% for B. bassiana. The entomopathogenic fungi isolates, M. anisopliae ICIPE 69 and B. bassiana ICIPE 279 were highly virulent with low lethal times to 50% mortality (LT50) of 3.81 and 5.13 d, respectively. The isolate, ICIPE 69 conidia acquisition by a single moth were approximately 4.58 × 106 and 3.51 × 106 for males and females, respectively. The lowest survival rate (3.33 %) caused by inoculum transmission was recorded in donor males compared to 16.67% in recipient males. Fecundity was reduced by 33.6 and 25.9% for donor and recipient females, respectively. The pest can acquire conidia from the treated substrate and transmission is then possible between adults. ICIPE 69 is virulent and reduces the reproduction potential of the pest after transmission. The findings are discussed in the prospects of microbial control of this pest using an autodissemination technique.

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

“…When considering the general trend for all the three potent isolates, a significantly high mortality rates were also observed in both the "donor" and "recipient" groups when females were used as donors. Similar results were obtained by Mkiga et al (2020), where the survival rate of 3. in both "donor" and "recipient" moth groups were significantly different when referring to the sex of the infected moths, where fungal inoculum transfer caused high mortalities in the donors than the recipients' group. Furthermore, the mortalities recorded in the recipients' group when T. absoluta males were used as donors were higher than those obtained in recipients' group when females were used as donors.…”

“…This finding highlights the potential for the use of entomopathogens in an autodissemination approach for management of T. absoluta . Horizontal transmission of fungal conidia from treated to healthy individuals has also been demonstrated in other lepidopterans, such as the beet webworm, Spoladea recurvalis (Lepidoptera: Crambidae) (Opisa et al., 2019), the stem borer, Busseola fusca (Fuller) (Lepidoptera: Noctuidae) (Maniania et al., 2011), the false codling moth, T. leucotreta (Mkiga et al., 2020) and the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae) (Furlong & Pell, 2001). This horizontal transmission can occur through direct contamination by passive transfer from inoculated adults, indirect contamination by conidia deposited on the host crop by inoculated/infected adults and secondary transmission of conidia from the sporulating mycosed cadavers of diseased individuals (Dimbi, Maniania, & Ekesi, 2013; Furlong & Pell, 2001).…”

“…This differential effect of sex of T. absoluta adults infected and serving as vector in fungal inoculum transmission might therefore be due to reduced mating frequencies by females that could be attributed to their weakness after acquisition of the conidia; or due to release of certain chemical cues that could be deterring the males from mating. However, these hypotheses need to be further ex- Noctuidae) (Maniania et al, 2011), the false codling moth, T. leucotreta (Mkiga et al, 2020) and the diamondback moth, Plutella…”

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

“…Five B. bassiana strains (ICIPE 284, ICIPE 279, ICIPE 281, G1LU3 and S4SU1) are being tested against S. frugiperda, T. leucotreta and Liriomyza sp. (Migiro et al, 2010;Akutse et al, 2019b;Mkiga et al, 2020). Beauveria bassiana strain ICIPE 279, especially, is highly pathogenic to T. leucotreta (Mkiga et al, 2020), and we are confident that, in combination with M. anisopliae strain ICIPE 69, a biopesticide will soon be available against this devastating pest.…”

“…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.…”