South Africa is the most important wheat producer in Sub-Saharan Africa after Ethiopia. As a result of a rise in wheat demand to feed the rising populace, manufacturing wants to accentuate.

Nevertheless, intensified agriculture by means of monoculture farming is the primary menace to various ecosystems, creating excellent habitats for economically necessary pests to ascertain, reproduce and trigger harm.

READ Administration of necessary grain illnesses

Roughly 75% of South Africa’s wheat is produced beneath dryland situations and the remaining 25% beneath irrigation. Winter wheat produced on dryland within the Western Cape accounts for about 50% of the nation’s whole manufacturing.

Within the winter rainfall space, wheat is planted between mid-April and mid-June and in the summertime rainfall space (japanese Free State) between mid-Might and the tip of July.

Russian wheat aphid (Diuraphis noxia) is probably the most severe wheat pest in South Africa and most problematic in drier, low yield-potential situations.

Russian wheat aphid is indigenous to central Asia, southern Russia and nations bordering the Mediterranean Sea, Iran and Afghanistan. Nevertheless, this pest is now present in all wheat manufacturing areas of the world, except Australia.

In South Africa, it was first recorded within the Free State in 1978, however now happens all through the area. It solely reaches pest standing often within the central dryland areas of South Africa.

The Russian wheat aphid nymph resembles the wingless grownup feminine, however has a smaller physique.

The nymph develops quickly and moults 4 instances inside a time-frame of seven to twenty days earlier than reaching the grownup stage. The grownup is small, about 2mm in measurement, and has a yellow-green to grey-green and waxy look.

The grownup has a particularly brief antennae, a couple of quarter of its physique size. Females can have wings or not. Each of those are comparable to one another, besides that the thorax and head of the winged type is darker.

Females produce as much as 4 reside younger a day, totalling roughly 70 over their lifespan. There are quite a few generations yearly, with a build-up of huge numbers, particularly in cool to heat, dry situations.

Initially, all of the aphids within the colony are normally wingless. Nevertheless, because the numbers enhance, overcrowding outcomes and winged people are produced in order that the Russian wheat aphid could disperse to different beneficial habitats to start out new colonies.

The mixture of their excessive dispersal charge and excessive reproductive charge implies that the pest can quickly attain damaging ranges over broad areas if not correctly managed.

Russian wheat aphid females are parthenogenetic, which means they don’t have to mate to supply younger, and males are absent in Southern African populations. Males are solely identified to happen in chilly climates at excessive altitudes.

Host vary

This aphid feeds totally on the small-grain cereals, i.e. wheat (Triticum aestivum), barley (Hordeum vulgare), and, to a lesser extent, on rye (Secale cereale), oats (Avena sativa) and triticale (a man-made species developed by crossing wheat and rye).

A wide range of wild grasses can function host vegetation for the Russian wheat aphid and could also be necessary for aphid survival when cereal crops usually are not out there.

Cool-season grasses that host this insect embrace bromegrass (Bromus diandrus), wild ryes (Elymus sp.) and jointed goatgrass (Aegilops cylindrica).

Jointed goatgrass is exceptionally appropriate due to its shut relationship with wheat. Extra hosts recorded in South Africa embrace rescue grass (Bromus catharticus), different Bromus spp. in addition to wild barleys (Hordeum murinam and Hordeum sp.).

Russian wheat aphid feeds on the upper-leaf floor of latest development, in axils of leaves, or inside rolled leaves utilizing their piercing-sucking mouthparts to suck sap from the vascular tissue.

Throughout this course of, saliva is secreted into the plant, inflicting harm to plant cells. Yield losses of 35% to 90% have been recorded on inclined wheat vegetation, with the share infestation, development stage of the plant and the period of the infestation figuring out the severity of the harm.

Heavy infestations in younger vegetation trigger tillers to develop into prostate and leaves to roll closed tightly.

In older vegetation, typical signs embrace white or pale-yellow stripes which might flip purple when chilly situations prevail, tightly rolled leaves and heads trapped within the rolled flag leaf.

Different management measures

Addressing the problem of Russian wheat aphid in South Africa requires a multifaceted strategy that mixes host plant resistance, and organic, cultural and chemical management methods.

Built-in pest administration practices can assist cut back the reliance on chemical pesticides and mitigate the affect of this pest.

The combination of a number of management measures is simplest when making an attempt to fight this pest.

A variety of pure enemies have been related to Russian wheat aphid. Parasitic wasps embrace indigenous species of the households Braconidae and Aphelinidae with two unique species, Aphidius matricariae and by chewing a gap by means of the host’s exoskeleton.

Parasitoid females feed on plant nectar and honeydew, a sugary liquid secreted by aphids and different sap-feeding bugs.

Additionally they feed on aphids to acquire vitamins for egg manufacturing by piercing or “stinging” the aphids with their ovipositor and consuming the insect’s blood from the wound, killing about two aphids per day by such feeding. Predators could embrace many species of ladybird beetles.

This contains the variegated ladybug, Hippodamia variegata, which was by accident launched into South Africa from the UK.

Different species embrace the alien invasive harlequin beetle, Harmonia axyridis, and different predaceous beetles. Floor beetle predators prey on aphids which have dropped from vegetation as a consequence of disturbance.

Girl beetle predators could trigger aphids on the vegetation to fall from the plant onto the bottom, the place they’re consumed by carabid predators. Each grownup and larvae of ladybirds are voracious predators of aphids.

This predation helps to scale back the variety of Russian wheat aphids in infested fields.
Hymenopterous parasitoids are extra generally discovered when aphid inhabitants densities are low, whereas beetles happen when increased inhabitants densities are current.

Conservation organic management is turning into more and more necessary for pest management to keep away from adversarial results related to using on-farm inputs. Farmers ought to goal to implement practices to minimise the “inexperienced bridge” of volunteer and alternate grass-host species, on which aphids survive from one season to the following.

The destruction or elimination volunteer host vegetation can assist cut back or delay the build-up of Russian wheat aphid populations. Standard methods which might be surrounded by, or in shut proximity to uncultivated land, which has completely different grass species, could enhance aphid densities in these methods.

Decrease abundances of aphids have been discovered to seem in natural and diversified methods as a consequence of increased predator abundances in these methods.

Natural Programs

Natural and diversified cropping methods resemble pure ecosystems in that there are not any chemical practices, whereas there’s a range of various vegetation.

Growing agricultural habitats with excessive crop rotation, polyculture and canopy crops are advantageous to pure enemies and their efficacy of organic pest management of miscellaneous pests similar to Russian wheat aphid.

Abiotic elements similar to temperature, relative humidity and rainfall influences the density of pests and their pure enemies’ abundance, in addition to plant well being.

Due to this fact, the upkeep of sufficient soil moisture and fertilisation can cut back harm as a result of vegetation pressured for water or vitamins are extra inclined to wreck from pests.

Obtainable resistant cultivars ought to be planted and fields inspected often as it might be obligatory to make use of chemical management in opposition to the aphids ought to the populations enhance.

When making use of chemical management, it should be achieved mindfully, as a result of spraying unnecessarily will intrude with the pure enemies of the aphid.

Conclusion

Wheat pests jeopardise each the amount and high quality of this crop. The implications prolong past monetary losses for farmers, impacting meals safety and the nation’s means to satisfy its wheat wants independently.

A complete and sustainable strategy to pest administration is crucial.

E-mail Zunel van Heerden at [email protected].