The effect of host larvae on three Psyttalia species (Hymenoptera: Braconidae), parasitoids of fruit-infesting flies (Diptera: Tephritidae)

Publication Type

Journal Article

Journal Name

Journal of Economic Entomology

Publication Date

8-3-2018

Abstract

Cowpea, Vigna unguiculata ((L.) Walp; Fabales: Fabaceae), is an important indigenous vegetable and grain legume in the tropics where it represents a major diet component. Cowpea aphid, Aphis craccivora (Koch; Hemiptera: Aphididdae) is a major pest causing up to 100% yield losses. Aiming at establishing alternative approach to synthetic insecticides, we evaluated the pathogenicity of 23 fungal isolates including Metarhizium anisopliae ((Metschn.) Sorokin; Hypocreales: Clavicipitaceae), Beauveria bassiana ((Bals.) Vuill.; Hypocreales: Cordycipitaceae), and Isaria sp. (Hypocreales: Cordycipitaceae) against adult A. craccivora in the laboratory. Adult apterous aphids were sprayed with conidial suspensions titred at 1 × 10 8 conidia ml -1 for pathogenicity tests while 1 × 10 4, 1 × 10 5, 1 × 10 6, 1 × 10 7 and 1 × 10 8 conidia ml -1 were used in dose response bioassays. All the fungal isolates were found pathogenic to A. craccivora, causing mortality of between 34.5 and 90%. The lethal 50% mortality time (LT 50) values varied between 3.3 and 6.3 d, with the best isolates being ICIPE 62, ICIPE 41 and ICIPE 644. The lethal concentration mortality (LC 50) values were 2.3 × 10 6, 1.3 × 10 8 and 1.3 × 10 9 for ICIPE 62, ICIPE 41, and ICIPE 644, respectively. M. anisopliae isolate ICIPE 62 produced more conidia on aphid cadavers (4.5 × 10 7) than ICIPE 41 (2.7 × 10 7) and ICIPE 644 (2.1 × 10 7) 6 d post-treatment. Relative potency comparison showed that ICIPE 62 was more potent than the other two isolates. In the screenhouse, conidia of ICIPE 62 significantly reduced A. craccivora population compared to control but there was no significant difference between emulsifiable and aqueous formulations. Small-holder leafy vegetable producers could gain more profits using fungal-based biopesticides in Aphid-IPM strategies, leading to reduction of pre-harvest intervals after their application compared to synthetic insecticides.

Keywords

biological control, cowpea aphid, entomopathogenic fungi, mortality, pathogenicity

PubMed ID

29788178

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