**3. Distribution of cereal aphids in Kenya**

is still a gap between production and consumption of wheat in Kenya [44]. Increased popula‐ tion growth, urbanization and change in eating habits have led to increased wheat demand. The national demand is estimated at more than 990,000 tons per year while production is as low as 360,000 leading to importation to meet the difference [52]. It is mainly grown in Nakuru, Trans Mara, Uasin Gishu, Nyandarua, Narok, Meru Central, Trans Nzoia, Keiyo and Laikipia counties. The crop is grown in diverse agro‐ecological zones at altitudes ranging

The country in its strategic plan is struggling to become self‐sufficient in wheat produc‐ tion either by increasing yields per unit area or by expanding the area under production in the marginal areas. This is possible when the gap between potential yield of wheat varieties (6–7 t/ha) and the actual yields (2.3 t/ha) realized by wheat growers in Kenya is filled. This gap is attributed to the lack of good quality seed, lack of appropriate technology and attack by diseases and pests, which have presented a continuous challenge to wheat productivity in Kenya. Cereal aphids are considered as one of most serious insect pests attacking rainfed wheat [8, 60]. Cereal aphid outbreaks are frequent in Kenya and are responsible for most of the control interventions on wheat. They are capable of completely devastating the crop by mak‐ ing it a total failure during years of severe infestation [59]. Aphids damage the cereals by direct feeding and transmitting barley yellow dwarf virus (BYDV) diseases, both causing losses in yield [22, 57]. Outbreaks of cereal aphids that are vectors of barley yellow dwarf are frequent in Kenya and often result in extensive use of insecticides [39, 58]. Their relative importance as pests/vectors varies considerably from one area with losses in the range of 1–100% [28]. Yield losses of 47% due to BYDV have been reported in wheat [57]. It is transmitted by cereal aphids in a persistent, circulative but nonpropagative manner. Five strains occur in Kenya and their principal vectors are RPV (*Rhopalosiphum padi*), RMV (*R. maidis*), MAV (*Sitobion avenae*), SGV (*Schizaphis graminum*) and PAV (*R. padi*, *S. avenae* and others) [25]. In the field, symptoms appear as yellow or red patches of stunted plants. In general, PAV causes severe symptoms, MAV moderately severe and RPV, RMV and SGV produce mild symptoms [16]. This chapter reports on cereal aphids affecting wheat in Kenya with emphasis on Russian wheat aphid

*Diuraphis noxia*, their problem and possible integrated pest management strategies.

The six most important cereal aphid species reported as pests that attack wheat and bar‐ ley include: Greenbug *Schizaphis graminum* R*.*, English grain aphid *Sitobion avenae* F*.*, Oat bird cherry aphid *Rhopalosiphum padi* L, Cereal leaf aphid *R. maidis* F*.*, Rose grain aphid *Metopolophium dirhodum* W*.* and Russian wheat aphid *D. noxia* M*.* [31, 32, 42]. Of these species, the Russian wheat aphid which is a recent introduction in Kenya in 1995 is the most destruc‐ tive followed by Greenbug *S. graminum* [25]. The other species are less serious and usually cause no significant yield reduction. In reality, there are usually two or more aphid species

The Russian wheat aphid was first officially detected in June 1995 [25] and affected areas experienced damaging infestations resulting in 90–100% crop loss. Since then most reports

**2. Cereal aphids occurring on rainfed wheat in Kenya**

present at one time.

from 1500 to 2900 m.a.s.l. in areas with 700–1000 mm rain per year.

212 Wheat Improvement, Management and Utilization

National aphid surveys were conducted in farmers' fields [32, 42] during wheat cropping seasons in Mt Kenya area, Mau Narok, Nakuru, Narok, Trans Nzoia and Uasin Gishu in order to determine the abundance and distribution of cereal aphids. In each area, 10 random assessments were taken. On every plant, the sampled aphid species were identified using taxonomic keys [37] and recorded. The different species of aphids found in the wheat fields were Russian wheat *aphid D. noxia*, which was the most predominant species with the highest overall density of 80.0%, followed by *M. dirhodum* (10.0%). The least species appeared were *R. padi* (5.3 %) and *R. maidis* (3.7%), while infestations of *S. graminum* was relatively low (1.0%) in all the areas (**Table 1**). It has also been reported elsewhere that wheat cultivars are usually attacked by a complex of cereal aphids' species [14]. The high incidence of Russian wheat aphids on the crops made the leaves to remain furled for a long time, thus creating condu‐ cive environment for other species such as *R. padi*, *R. maidis* and *S. graminum* to stay longer in the wheat crops after crop heading. The surveys complemented the Cereal aphid Forecast Bulletins in advising growers on control decisions [27].

Alternate host plants of RWA and other cereal aphids found in Kenya during the surveys included wild oats *Avena fatua*, brome grass *Bromu*s spp., wild rye grass *Elymus* spp and foxtail grass *Setaria* spp. These grass weed are common in high altitude wheat growing areas in Mt Kenya and west Mau regions of Kenya and serve as reservoirs of cereal aphids during dry weather. Neglected volunteer wheat, barley and oats plants were also impor‐ tant for the survival of Russian wheat aphids and other cereal aphids. These host plants have also been reported [2, 6, 33] supporting RWA and thus provide a bridge for infesta‐ tion of the next season wheat crop. These alternate host plants play an important role in supporting cereal aphids between crop harvest and emergence of the new crop in the next planting season.


**Table 1.** Incidence of Russian wheat aphid and other cereal aphids in wheat growing regions of Kenya.

Continuous cropping of wheat was practiced by wheat growers in Mt Kenya region, eastern Aberdares ranges and West Mau areas of Kenya [31, 33]. This enabled cereal aphids to migrate from one field to another and survive from one season to the next. Similar observations have been reported in wheat growing areas in the highlands of Ethiopia [40]. It was also observed that the different crop planting dates and eco‐zones across the country as well as the presence of volunteer cereals and alternate host grasses provide a continuous source of alternative host plants and consequent spread source of cereal aphids to wheat crops planted the following season. The information being generated from field surveys has been used to advice farmers when to plant and which control options to adopt in order to escape the damaging species of cereal aphids.

Cereal aphids also have preferential performance on different hosts. Results observed in Kenya [49] revealed that aphid species differed in their time of colonization on wheat varieties. Aphid abundance differed among the species, wheat varieties and crop growth stages*. R. padi* appeared at two leaf stage, followed by *S. graminum* at the two tiller stage and *M. dirhodum* appeared at stem elongation stage. The aphids also differed in their points of colonization, thus the studies confirmed crop growth stage and feeding preferences among cereal aphids in wheat.
