**5. Survey of natural enemies of cereal aphids**

All commercial wheat varieties are susceptible to cereal aphid's damage and control is achieved by extensive use of insecticides. Chemicals improve yields in the short term, but adversely affect ecological and human health. There is a lot of concern about the expense and possible environmental pollution from insecticidal applications and farmers would prefer to minimize losses through the use of resistant cultivars and effective natural enemies (predators and para‐ sites) because of sustainability and environmentally friendly action. Most farmers in Kenya are not aware of biological control and therefore do not perceive it to be effective. However, major‐ ity of farmers will be willing to stop spraying should the biological control strategy be effective.

In view of the large wide range of aphid species that attack wheat in Kenya, causing substan‐ tial yield losses, biological control strategies must be developed that will enhance the integra‐ tion of these control agents in an IPM control strategy. Therefore, surveys were initiated to document the natural enemies that attack the Russian wheat aphid and other cereal aphids on infested wheat crops in farmers' fields.

A number of predators and parasitoids were observed to attack cereal aphids (**Tables 3** and **4**) but none of these biocontrol agents exerted adequate controls. The absence of successful aphid predators and parasitoids may be a prime reason for the rapid spread of Russian wheat aphid. Field observations also revealed that the natural enemies of Russian wheat aphid were only present late in the crop season when damage to wheat had already taken place. Ladybird bee‐ tles *Adonia variegata* and parasitic wasp *Aphidius* sp. were the most important natural enemies.


*Key*: a, Russian wheat aphid *D. noxia*; b, *R. maidis*; c**,** *S. graminum*; d, *Sitobion* spp.; e, *M. dirhodum*; f, *R. padi*.

**Table 3.** Predators and parasitoids recorded attacking cereal aphids in wheat in Kenya in 2004 cropping season.

The Russian wheat aphid was the most prevalent insect pest of rainfed wheat [31, 32]. The maximum number of RWA per tiller was 58.0 while rose grain (*M. dirhodum*), oat‐bird‐cherry aphid (*R. padi*) and corn leaf aphid (*R. maidis*) were prevalent at low density ranging from 0.1 to 9.0 per tiller. The general aphid predators *Cheilomenes* spp., spiders, lacewings and the parasitoid *Aphidius* spp. were the natural enemies of cereal aphids found in Kenyan wheat.

**5. Survey of natural enemies of cereal aphids**

216 Wheat Improvement, Management and Utilization

infested wheat crops in farmers' fields.

**Scientific name Cereal aphid species\***

**Predators**

• Diptera

• Coleoptera (beetles)

**Parasitoids** *(*Hymenoptera)

All commercial wheat varieties are susceptible to cereal aphid's damage and control is achieved by extensive use of insecticides. Chemicals improve yields in the short term, but adversely affect ecological and human health. There is a lot of concern about the expense and possible environmental pollution from insecticidal applications and farmers would prefer to minimize losses through the use of resistant cultivars and effective natural enemies (predators and para‐ sites) because of sustainability and environmentally friendly action. Most farmers in Kenya are not aware of biological control and therefore do not perceive it to be effective. However, major‐ ity of farmers will be willing to stop spraying should the biological control strategy be effective. In view of the large wide range of aphid species that attack wheat in Kenya, causing substan‐ tial yield losses, biological control strategies must be developed that will enhance the integra‐ tion of these control agents in an IPM control strategy. Therefore, surveys were initiated to document the natural enemies that attack the Russian wheat aphid and other cereal aphids on

A number of predators and parasitoids were observed to attack cereal aphids (**Tables 3** and **4**) but none of these biocontrol agents exerted adequate controls. The absence of successful aphid predators and parasitoids may be a prime reason for the rapid spread of Russian wheat aphid. Field observations also revealed that the natural enemies of Russian wheat aphid were only present late in the crop season when damage to wheat had already taken place. Ladybird bee‐ tles *Adonia variegata* and parasitic wasp *Aphidius* sp. were the most important natural enemies.

1. *Adonia variegata* a b c d e – 2. *Cheilomenes* spp. a b c d e –

1. Syrphidae (hover flies) a – c d e f • Arachnoidea (spiders) a b c d e f • Neuroptera (lacewings) a b c d e f

1. *Aphidius* spp. a – c d e f 2. *Aphelinus* spp. a – c d e f *Key*: a, Russian wheat aphid *D. noxia*; b, *R. maidis*; c**,** *S. graminum*; d, *Sitobion* spp.; e, *M. dirhodum*; f, *R. padi*. **Table 3.** Predators and parasitoids recorded attacking cereal aphids in wheat in Kenya in 2004 cropping season.

The Russian wheat aphid was the most prevalent insect pest of rainfed wheat [31, 32]. The maximum number of RWA per tiller was 58.0 while rose grain (*M. dirhodum*), oat‐bird‐cherry


**Table 4.** Predators and parasitoids attacking cereal aphid species in Kenya 2015 cropping season.

Generalist predators, namely, Coccinellid beetle (*Cheilomenes* spp.), spiders (Arachnidea) and lacewings (*Chrysoppa* spp.), were observed to occur at very low population densities from tillering stage to heading growth stages (**Table 4**). Similar observations have been reported in Ethiopia [2].

The natural enemies such as *Aphidius* spp., appeared late in the crop season when the cereal aphids population levels had passed damaging levels. Therefore, they may not contribute to season long control of RWA and other cereal aphids in the wheat crop.

The survey data revealed that the Russian wheat aphid is the most important and predomi‐ nant cereal aphid. Its feeding habit led to leaf rolling, which enabled the other cereal aphids to stay longer on the crop thereby increasing their inoculation period of viral diseases such as barley yellow dwarf virus. Leaf rolling particularly the rolling of flag leaf interferes with the pollination of wheat flowers. The survey also revealed that grass weeds support cereal aphids; hence, good control of grass weeds is essential. Moreover, though the number of predator and parasitoid species recorded were sufficient, because of their low density, they are unable to keep cereal aphid populations below damaging levels. However, efforts should therefore be made to conserve these natural enemies as they are of great importance in con‐ trolling the cereal aphids. For development of an effective cereal aphids IPM package, there is need for comprehensive studies on population dynamics of cereal aphids' species and their natural enemies in wheat crops.
