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Yeo, Helen (2000) Mycoinsecticides for aphid management: a biorational approach. PhD thesis, University of Nottingham.

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Abstract

This study considered a novel approach to selecting isolates of Hyphomycete fungi as mycoinsecticides for biological control of aphids in arable crops in the UK. The approach was designed to select isolates which were compatible with both the biotic and abiotic environment.

Aphis fabae was chosen as a representative target aphid for bioassays, based on results of preliminary experiments. Eighteen isolates of fungi were screened at a single concentration of 1x 10⁸ conidia ml⁻¹ against apterous adult A. fabae, which were incubated at 23°C. Spray applications were made using an electrostatic rotary atomiser in both laboratory and field experiments. Isolates that originated from aphid hosts were most pathogenic to A. fabae. Four isolates were selected for further studies; ARSEF 2879 (Beauveria bassiana), HRI 1.72 (Verticillium lecanii), Mycotrol strain GHA (B. bassiana) and Z11 (Paecilomyces fumosoroseus).

Isolate HRI 1.72 was most virulent to A. fabae in dose-response assays compared to other isolates; at concentrations of 1x 105 conidia ml⁻¹ and above, mortality of aphids due to infection by HRI 1.72 was 100%. Isolates of P. fumosoroseus and V. lecanii were able to grow and germinate better in vitro at low temperatures (10 & 15°C), than isolates of B. bassiana and Metarhizium anisopliae. Aphis fabae and Myzus persicae, inoculated with isolate HRI 1.72 and incubated at 10°C, succumbed to infection after a significantly shorter period of time compared to other isolates.

Rhopalosiphum padi was most resistant to infection by the four isolates compared to five other species of aphid. Aphis fabae, Acyrthosiphon pisum, Sitobion avenae, Metopolophium dirhodum, R. padi and M. persicae were most susceptible to infection by isolate HRI 1.72. Aphids infected with isolates of V. lecanii often had fungal sporulation on their legs and died attached to leaves on which they were feeding.

The isolates Mycotrol strain GHA and ARSEF 2879 were pathogenic to the 7-spot ladybird Coccinella septempunctata and the generalist parasitoid Praon volucre. The isolates HRI 1.72 and Z11 had very little impact on these natural enemies tested.

When aphids of A. fabae were co-inoculated with isolates of Hyphomycete fungi and Erynia neoaphidis, most individuals succumbed to infection with E. neoaphidis. A significant number of aphids died within 24 hours of inoculation and showed no signs of external sporulation. The potential interactions between these natural enemies in the biocontrol of aphids are discussed.

The spatial and temporal distribution of aphids and their natural enemies, in field bean and wheat crops, was determined in two field seasons (1997 & 1998). Aphids sampled from the field, after application of Hyphomycete fungi in 1998, mostly succumbed to infection with E. neoaphidis. Epizootics of E. neoaphidis were recorded in both years. Greater numbers of healthy laboratory aphids succumbed to infection with Hyphomycete fungi when they were bioassayed on leaves sampled immediately following spraying (51 - 100%) compared to 24 hours later (8 - 65%). Microclimate recordings showed humidity in both crops was generally >90% overnight and differences were as great as 15% between the top and bottom of crop canopies. Temperature differences were as great as 5-7°C between individual sensors.

The implications of using a biorational approach as part of the development of Hyphomycete fungi as mycoinsecticides for the control of aphids is discussed.

Item Type:	Thesis (University of Nottingham only) (PhD)
Supervisors:	Alderson, P.G. Pell, J.
Keywords:	aphids, mycoinsecticides, Hyphomycetes
Subjects:	S Agriculture > SB Plant culture
Faculties/Schools:	UK Campuses > Faculty of Science > School of Biosciences
Item ID:	11603
Depositing User:	EP, Services
Date Deposited:	26 Oct 2010 12:36
Last Modified:	16 Dec 2017 11:45
URI:	https://eprints.nottingham.ac.uk/id/eprint/11603

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