SA Grain May 2017

May 2017

Graph 2: Area planted per production area over seasons (South African wheat crop quality report 2015/2016 season).

decrease in the 2013 season, onwards (

Graph 2

). This coincided with

a drastic increase in the percentage of fields not infested by Russian

wheat aphid in these areas during the next season in 2014 (Graph 1).

There was a slight increase in the area planted with wheat in the

winter rainfall region during the 2014 season (Graph 2). This co-

incided with a gradual decrease in fields not infested by Russian

wheat aphid from 2014 to 2016, indicating an increase in Russian

wheat aphid populations in the Western Cape (Graph 1).

The arrangement of habitat patches in landscapes plays an impor-

tant role in determining the abundance and diversity of insects.

Insects will increase within an area that contain the most suitable

host plant and decrease with isolation of the patch. Wheat and

barley are the main host plants for Russian wheat aphid in South

Africa, but can survive on a few alternative host plants, including

oats, wild oats, false barley and rescue grass.

This aphid cannot survive on any of the other crop plants commonly

cultivated in South Africa. With a decrease in wheat cultivation in

the summer rainfall areas of South Africa, the habitat for Russian

wheat aphid became fragmented. Not only is there a spatial frag-

mentation, but also a temporal fragmentation when other crops are

planted in different seasons.

This resulted in Russian wheat aphid populations being limited to

certain habitat patches. At the same time, the beneficial insect/

pathogen complex associated with a wider crop spectrum in-

creases, thereby exerting additional pressure on the survival of the

pest species.

These observations emphasise the value of intercropping and

crop rotation in managing insect pests and can serve

as model for Russian wheat aphid management in

areas where wheat and barley are still the predomi-

nant crops.

1: Russian wheat aphid damage on wheat.

2: Russian wheat aphid population on wheat.