Developing an IPM strategy for managing aphids on brassica crops

The Food and Agriculture Organisation (FAO) of the United Nations have declared 2020 as the International Year of Plant Health (IYPH) and have called for organisations to raise global awareness on how protecting plant health can help end hunger, reduce poverty, protect the environment, and boost economic development.

Much of the research in the School of Life Sciences is aimed at improving crop productivity and combating pests and diseases while conserving the environment in order to feed an increasing population. In this series of articles we highlight just some of the work related to IYPH2020.

Aphids are economically important pests of a wide range of crops and control relies mainly on applications of synthetic chemical pesticides. However, pressures on growers to reduce the use of pesticides, together with increasing failures of aphid control due to the evolution of pesticide resistance, have raised serious questions about the long-term viability of this approach. Alternative methods of managing aphids are needed urgently.

raising different brassica accessions in controlled environment prior to screening

The focus of Andrew Gladman’s PhD project at the Crop Centre is the development of a novel management strategy for pest aphids of Brassica crops which aims to combine partial host plant resistance with biological control (left picture: raising different brassica accessions in controlled environment prior to screening).

The project focuses on the cabbage aphid, Brevicoryne brassicae (right picture), which is a major pest of vegetable and oilseed brassicas in the UK and more widely.

Partial host plant resistance

Partial host plant resistance does not completely prevent aphid infestation, instead reducing the rate of aphid population development by either slowing aphid growth or reducing the rate of reproduction. It is also multigenic, meaning that it is likely to be more durable than complete, single gene resistance. To identify partial-resistance, a range of Brassica accessions from the germplasm collection at Warwick were evaluated in laboratory bioassays for their effects on the development of cabbage aphid populations (left picture). Using this system, several partially-resistant accessions have been identified, reducing aphid infestations by two-thirds compared to susceptible plants.

aphid population development experiment assessing different Brassica accessions for partial resistance to cabbage aphid

Insect pathogenic fungi

Partial-resistance alone is unlikely to reduce aphid-associated damage to acceptable levels. However, its deployment alongside complementary crop protection tools such as insect pathogenic fungi could offer a viable aphid management strategy. While successful at controlling many pest species, the use of insect pathogenic fungi against aphids has proven problematic because developing aphids (nymphs) can rid themselves of fungal spores when they moult as they grow. However, comparison of the susceptibility of cabbage aphid to a range of insect pathogenic fungi (right picture) has identified a strain able to successfully infect and kill cabbage aphid nymphs. Work is now underway to investigate the effects of combining this strain with partial-resistance, with the hypothesis being that aphids feeding on partially-resistant plants should be less fit and develop more slowly, extending the window for successful infection. Any reductions in aphid populations caused by fungal infection should complement reductions caused by plant-resistance, meaning this integrated approach maximises the effect of both approaches.

The future

Bioassay procedure evaluating different entomopathogenic fungi against different aphid life stages

For future deployment of this strategy, partially-resistant varieties, and fungal products based on the effective fungus, would need to be developed and growers could be given advice on when to spray the fungal products, dictated by weather and aphid population density.

This project is part of a larger Sustainable Agriculture Research and Innovation Club (SARIC) project led by Dr Dave Chandler entitled ‘Biological crop protection: a new 'slow down/speed up' strategy for aphid management’. It is in collaboration with Durham, Harper Adams and Keele Universities and ADAS.

To more articles as part of International Year of Plant Health 2020