**7. Host plant resistance**

measures. Control of cereal aphids can be achieved with systemic insecticides applied as seed dressings or foliar spray and contact insecticides applied with aerial or ground equipment. The seed dressing insecticides controls the colonizing migrant aphids and prevents primary

Control recommendations in Kenya include the use of systemic insecticides as shown in **Table 5** [33]. The rolling of leaves as a result of the feeding habit of RWA causes the leaves to roll around *D. noxia* aphid colonies thus protecting the aphids from being reached by the contact insecticides. A characteristic behavior of RWA is to feed and develop inside the rolled leaf whorl confining insecticide options to active ingredients with systemic action able to penetrate the rolled leaf [23]. Systemic insecticides presented in **Table 5** have proven to be effective against Russian wheat aphid and other cereal aphid species in rainfed wheat crops with resultant high grain yields [33].

**Trade name of chemical Active ingredient (a.i.) Application rate**

1. Gaucho 350FS Imidacloprid 350 g/L 200 mL/100 kg seed 2. Cruiser 350FS Thiamethoxam 350 g/L 150 mL/100 kg seed 3. Redigo Deter 300FS Clothianidin 250g/L + prothioconazole 50g/L 200 mL/100 kg seed 4. Celest Top 312FS Thiamethoxam 262.5 g/L + fludioxonil 25 g/L + difenoconozole 25 g/L 150 mL/90 kg seed

1. Pirimor 50WG Pirimicarb 500 g/kg 0.75 kg/ha 2. Bulldock star 262.5EC Betacyfluthrin 12.5 g/L + chlorpyrifos 250 g/L 0.5 L/ha 3. Thunder OD 145 Imidacloprid 100 g/L + betacyfluthrin 45 g/L 0. 3 L/ha 4. Nurelle\* D 50/500 EC Cypermethrin 50 g/L + chlorpyrifos 500 g/L 0.5 L/ha 5. Engeo 247SC Thiamethoxam 141 g/L + lambda‐cyhalothrin 106 g/L 150 mL/ha

**Table 5.** Recommended insecticides for control of cereal aphids in rainfed wheat in Kenya.

Seed dressing is an insurance against infestation by early seedling pests such as the Russian wheat aphid. The use of seed dressers ensures a better crop establishment, more uniform and healthier crops with increased yields and quality. Cereal aphids occurring during other growth stages of wheat are controlled using foliar applied insecticides (**Table 5**). Applications of Gaucho 350FS followed by applications of systemic foliar insecticides achieved very good control of the Russian wheat aphid [26, 29, 33]. Contact insecticides are not effective against Russian wheat aphid but they are effective against *R. maidis*, *S. graminum*, *Sitobion* spp., *M. dirhodum* and *R. padi*. Satisfactory control of RWA using foliar applied aphicides depends on early detection of infestation through periodic scouting. This approach will therefore offer a cheaper strategy for cereal aphid and BYD control. Farmers are advised to scout their fields weekly in order to make an accurate decision on whether or not treatment is required. It is important for wheat growers to know that not all insects are pests. One should know the insects, which are beneficial to mankind. Ladybird beetles, hoverflies, lacewings, spiders, dragonflies and praying mantis feed on other insects. Using insecticides indiscriminately

infestation. The foliar applied insecticides controls primary spread.

*Seed dressing insecticides*

218 Wheat Improvement, Management and Utilization

*Foliar applied insecticides*

Host plant resistance is an integral part of IPM of cereal aphids and is one of the most impor‐ tant alternative methods of management of cereal aphids. BYD resistance in wheat has been more difficult to assess and screening programs have yielded only a few possible sources of resistance, many of which showed susceptibility upon repeated testing due to the wide variation of BYDV strains. In addition, severe epidemics may render genotypes with useful resistance as being apparently highly susceptible [50]. All commercially available wheat vari‐ eties are susceptible to Russian wheat aphid and other cereal aphids and have to be chemi‐ cally protected [20, 26, 35]. In Kenya, the development of RWA‐resistant varieties has been constrained by variation in resident RWA populations and by concerns of possible existence of virulent biotypes [21, 36, 46, 45]. Collapse of resistant crop varieties due to biotype devel‐ opment is a major threat to food security and even a greater catastrophy would be caused by the unavailability of advanced breeding lines containing genetic variability potentially resistant to future biotypes [23]. Investigations to evaluate seven commercial bread wheat cultivars (Pasa, Mbuni, Kenya Heroe, Kenya Fahari, Chozi, Duma and Kwale) in five different environments in Kenya revealed that varieties K. Fahari and Duma suffered the lowest RWA damage [35]. K. Fahari which had been previously reported to be resistant to green bug *Schizaphis graminum* was observed to have some resistance to RWA.

While some protection against Russian wheat aphid can be realized by crop management practices, resistant varieties offer the greatest opportunity for reduction of crop losses. The sudden appearance of Russian wheat aphid has made resistance breeding program of high priority now as farmers are currently relying on pesticides to control the aphids. The high cost of chemical control and concern for extensive and frequent use of insecticides has led to search for Russian wheat aphid resistance. Using host plant resistance instead could be economical, effective throughout the growing season, environmentally safe and it will require no elabo‐ rate technology transfer to farmers. Natural enemies and host plant resistance are considered as more desirable alternatives to insecticides because of their low cost and environmentally friendly mitigation strategy [12, 51] for effective management of cereal aphids in wheat.

Research has focused on screening wheat genotypes for possible source or sources of resistance against Russian wheat aphid for use in our national wheat breeding program as an alternative to chemical control. A search for sources of resistance from among introductions collected from other countries (CIMMYT, Mexico, South Africa and Turkey) identified four sources of resis‐ tance, viz., RWA 9, RWA 8, RWA 16 and RWA 230 [34]. These sources have been incorporated into the breeding program using back‐crossing technique. In addition, doubled haploid tech‐ nique is being used to shorten the breeding cycle by about 5 years. Host plant resistance should be used as on more control strategy with IPM, as the strategy is nonpollutant to the environ‐ ment and does not demand specific knowledge by the wheat farmers. The use of host plant resistance that rarely requires treatment by application of aphicides has also been reported elsewhere as one of the most important methods for control of cereal aphids [10, 11, 19, 38, 61].
