Aphids are soft bodied and small plant sucking insects with almost all generations comprising parthenogenetic females. They are commonly known as plant lice or green flies belong to the super family Aphidoidea. Theysuck sap from stem and foliage which gets stunted with yellow, reddish or purple spots on it. Some species can cause chlorosis and tissue death [1]. Infestation normally started at beginning of the ear-formation and reached its peak at milky stage.Aphids are serious pests worldwide, able to cause severe damage in cereal crops, particularly wheat, by direct feeding and by transmitting plant pathogenic viruses such as barley yellow dwarf virus [2,3].

In India wheat is a premier winter cereal crop. Although, wheat is grown primarily as a food crop, itis also used as inputs for many industrial products as well as feedstock. However, productivity of the crop is heavily affected by several insect pests. Wheat crop is attacked by more than a dozen of insect pests from sowing till harvesting [4]. Among the major insect pests of wheat in India, aphids have gained status of regular pests and reported from all major wheat growing regions [5]. Wheat isattacked by more than eleven aphid species, out of them four species namely Sitobion avenae (Fabricius), S. miscanthi and Rhopaosiphum padi and R maidis are reported to be most predominant [6] and their composite population is designated as wheat aphid complex [7]. Wheat crop is infested by aphid from seedling stage onwards, but they are not easily detected due to their small size and green color [8]. Long lasting infestation can reduce tillering, number of spikelets and seed [9]. Its damage in the boot stage can result in 19-31% yield loss; later infestation can cause the yield loss up to 20% [10]. During the grain fill period infestation may result in low grain protein content. Aphid’s number 5, 15, 30 and 50 per ear head can cause 13.3, 27.8, 38.1 and 47.7% reduction in grain weight, respectively [11]. With climate change, aphid pests are gaining importance because many aphids are able to feed through the winter on cereal crops without recourse to sexual reproduction.

Pest status, species composition and seasonal dynamics of cereal aphid species are influenced by a complex of factors (region, climate, biotype status, seasons, life cycles, agro technical practices, natural enemies) [12,13,14,15]. Although, there are many publications on the diversity of aphid species infesting wheat there are no systematic studies for the State of Bihar. In this paper we record the diversity of cereal aphids attacking wheat genotypes and their natural enemies.

The present investigation was conducted at the Experimental area of the PUSA farm having a history of more than 100 years of organised farming. The farm is located in the Indo-Gangetic plains of North Bihar representing subtropical zone with hot, humid summer(27±1°C) and cool, dry winter. The weather conditions almost remain same during both the years of experiment. The experimental site is geographically situated at a North latitude of 25.984⁰, East longitude of 85.674⁰ and altitude of 52.20 m above mean sea level. The farm is surrounded from its three sides by the river Buddhi-Gandak with good vegetation around. Rice-wheat cropping system is predominantly followed at the farm. This specific area was chosen after sampling in previous years which had indicated that it was usually heavily infested with cereal aphids. The experiments were conducted in the field where no insecticide had been applied in the preceding crop to control the aphid pest and no insecticide was applied for the control of any pest during the experiment. For the study eleven genotypes of wheat were planted under Randomized Complete Block Design (RCBD) with three replications. Each genotype was grown in a 5rows of 3 m length. The rows were planted with a spacing of 23 cm. For maintaining around 10 cm distance between plants to plants, the seeds were sown at the rate of 100 seeds per meter. The plot-to-plot spacing was kept at 0.75 m to reduce insect movement between the plots. The crop was sown during last week of November in 2012-13 and 2013-14. All the recommended cultural and agronomical practices were followed uniformly to raise a good crop. Each plot was assessed for natural infestation by the aphid pest and its natural enemies. The observations carried out when crops were mostly between 58 to 69 Zadok’s growth stages during the peak period of the insect’s activity. To determine the abundance, density for aphids was recorded from five randomly selected tillers per plot using fuzzy recognition technique by 6 regular investigators divided into 3 groups. Different types/species were recognised through unaided eye or handheld simple microscope. The mean number of aphids per stem and the percentage of each type (of the total number of respective insect) were calculated. Analysis of variance (ANOVA) was used to analyze the data of aphid’s population after square root transformation.

During the year 2013 and 2014 a total of 3128 aphids were counted on diverse genotypes of wheat, of which 46.96% were S. avenae, 45.84% S. miscanthi,5.05% Rhopalosiphum padi and 2.14% R. maidis. Figiure 1. In this study, the dominance of S. avenae innatural aphid populations is in agreement with previous reports [16,17,18,19,20,21]. Similarly, Thies et al. [22] and Schmidt et al., [23] also reported high S. avenae and low R. padi abundance on wheat crop, and Khan and Maqbool [24] mentioned S. miscanthias major aphid pest of wheat. The composition of the species, however, differed between years, with S. miscanthi being the most common aphid in 2013 (48.84%) and declining in 2014 (43.82%), while S. avenae was most common species in 2014 (49.49%) (Fig.1). Tomanovic et al., 2008 also reported that species composition of aphids differed between years under investigation. The relative abundance of the cereal aphids on eleven diverse genotypes of wheat was also investigated. The overall aphid density was higher during 2014, with 14.16±15.34 aphids per tiller, while in 2013 the density was found lower, with 9.54±11.75 aphids per tiller. Aphid infestations were well above the threshold level of economic damage (five per shoot; Giller et al. 1995; 3–5 per shoot; Pflanzenschut-zamt Hannover 2002). S. miscanthi peaked in abundance during 2013, with 18.64 ± 11.66 aphids per tiller followed by S. avenae, with 16.48 ±11.40 aphids per tiller, while during 2014 S. avenae had the highest density (28.03±12.07 aphids per tiller) followed by S. miscanthi (24.82±11.70 aphids per tiller). There was less abundance of R. padi and R. maidis during both cropping seasons Figure 2. Previous workers reported different level of aphid infestation, Schmidt et al., [23] and Iqbal et al, found infestation well below the threshold level of economic damage, whereas, Thies et al., [22] and Riazuddin et al., [25] recorded aphid density exceeding the threshold level of economic damage. Similar to present work Khan et al., [26] also observed very high aphid density per tiller.Presence of relatively high aphid density in present investigation may be due to existence of structurally complex landscapes and cropping system at the experimental site as high availability of perennial habitats provides shelterfrom disturbances by agricultural practices, overwinteringsites, and alternative host throughout the year.

In 2013 the maximum aphid density was observed on genotype VL914, with 15.33±15.20 aphids per tiller. All the four species of aphids were present on the genotype of which S. avenae was the most predominant followed by S. miscanthi. The other two species were less abundant. The minimum aphid density was recorded on genotype DBW16, with 3.08±   aphids per tiller. Only two out of four species were present on the genotype of which S. miscanthi was most common followed by S. avenae Figure 3. During 2014 the maximum number of aphids was found on genotype Kauz/AA/Kauz, with 21.75± aphids per tiller. Only S. avenae and S. miscanthi were recorded on the genotype of which former was most predominant. The minimum number of aphids was present on genotype Cu/79/Purulla (8.67±aphids per tiller).  Only S. avenae and S. miscanthi were observed on the genotype of which former peaked in abundance Figiure 4. The results regarding population of aphidsper tiller on various genotypes of wheat reveal highly significant difference among genotypes. Similar findings were also observed by Aheer et al., [27], Havlickova, [28], Zia et al., [29], Singh et al., [30], Iqbal et al., [31]. The aphid density also differs between both the years of investigation. Thies et al., [22] also found significant difference for aphid density between years. 

Figure 1: Abundance of aphid species during the years of study

Figure 2: Fluctuation of aphid species density during years of study

Figure 3: Differences in mean abundance of aphid species on the genotypes during 2013

Figure 4: Differences in mean abundance of aphid species on genotypes during 2014

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