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.
Interactions among vegetable infesting aphids, the fungal pathogen Metarhizium anisopliae (Ascomycota: Hypocreales) and the predatory coccinellid Cheilomenes lunata (Coleoptera: Coccinellidae)
AbstractEntomopathogenic fungi are among biocontrol agents being considered for the control of aphids on a variety of crops. Predatory coccinellids, although generalist, are also among important natural enemies that must be conserved for aphid management.Laboratory studies were carried out to investigate interaction between three vegetable infesting aphids, Metarhizium anisopliae isolate ICIPE 62 and the coccinellid predator Cheilomenes lunata. At concentration of 1 10 8 conidial ml -1 , the fungus was found to cause mortality of 7.5% to C. lunata, compared to 2.5% mortality in the control at 10 days post-treatment. Female adult C. lunata to which fungus-infected aphids were offered as prey never accepted them as food source in non-choice bioassays. However, live and dead non-infected aphids were fed upon. In choice bioassay, a total of 1-3 out of 24 infected non-sporulating aphids per species (average of 0.1-0.4 aphids per arena) were consumed by 48 h starved C. lunata within a period of 60 min, but avoided sporulating cadavers. Foraging adult C. lunata enhanced the spread of conidia of M.anisopliae from infected cadavers to fourth instars A. gossypii feeding on okra (0.8-15.0% mortality), B. brassicae (3.3-15.0% mortality) and L. pseudobrassicae (0.8-14.2% mortality) on kale plants. Results of this study demonstrate compatibility between M. anisopliae and C. lunata, and could provide a sustainable strategy for effective management of aphids on crucifers and okra cropping systems.
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