Research on the Control Effects of Several Insecticides on Wheat Aphids

[Objective] The aim was to determine control effects of the 6 insecticides and recommended the optimal doses. [Method] In 2014, the control effects of sophocarpidine, pymetrozine, beta-cypermethrin, acetamiprid, imidacloprid, and chlor- pyrifos on wheat aphids were tested, and every pesticide was designed with three doses in Shou County, Anhui Province, to explore the significance of differences on control effects. [Result] The results showed that the control effects of the 6 insecti- cides were satisfied, and the insecticides were safe on wheat. [Conclusion] During initial diseasing stage of aphid, it is recommended to use sophocarpidine soluble concentrate （1.5%）, pymetrozine water dispersible granule （50%）, imidacloprid wet- table powder （25%）, and acetamiprid wettable powder （5%）, and chlorpyrifos missi- ble oil （40%）, cypermethrin missible oil （4.5%） and imidacloprid wettable powder （25%） can be applied in peak-diseasing stage.

Effect of aerial spray adjuvant applying on the efficiency of small unmanned aerial vehicle for wheat aphids control

Small unmanned aerial vehicles(UAVs)have been widely used in different aspects of modern farming management,including pest and disease control in China in recent years.In this study,the spray performance of a small plant protection UAV at low volume spray was evaluated by adjusting the pesticide dosage and adding aerial spraying adjuvants.Droplet deposition,droplet density,coverage,control effect and pesticide residue from field trials were assessed.In addition,the residue and control effect of UAV spray were compared to manual knapsack at high volume spray.The results showed that,the adjuvant applying improved the efficiency of UAV spray.Also,the adjuvant applying reduced the dosage of imidacloprid by 20%.However,there was no significant difference on initial residue between UAV spray and knapsack spray.Thus,plant protection UAV spraying pesticide by adding appropriate adjuvant showed the ability of improving the pesticide effectiveness by improving the control efficiency,reducing the pesticide dosage and residue.

Spatial Distribution Pattern and Sampling Technique of Spring Wheat Aphid

[ Objective] The aim was to study the spatial distribution pattern and field sampling method of aphid population in spring wheat. [ Method] The aphid quantity in tested wheat field was calculated, the field distribution pattern of wheat aphid was calculated by using aggregated index method, the aggregated reason was analyzed and the field theoretical sampling number was ascertained. [ Result] The wheat aphid population showed aggregation distribution and negative binomial distribution, and such aggregation distribution was induced by interaction of its behavior and environmental factors. The field theoretical sampling number of wheat aphid was related to sample variance and permissible error; the less the sam- ple variance [ S^2 ） was, the less the permissible error [ d＇） was, the bigger the theoretical sampling number without replacement was; when the initial population numbers were different, the theoretical sampling numbers were also different; after the permissible error being set, the bigger the sample variance （ S^2 ） was, the bigger the theoretical sampling number was. [ Conclusion] This study supplied scientific basis for prediction and field control of wheat aphid.

Toxicity and Antifeedant Activity of Extracts from Walnut Green Husk against Wheat Aphid

[Objective] The research aimed to study the toxicity and antifeedant activity of walnut green husk extract on wheat aphid. [Method] Using ultrasonic extraction, 5 kinds of different polarity solvents were used to prepare the extracts from walnut green husk. The toxicity and antifeedant activity on wheat aphid were determined, [ Result ] Walnut green husk extracts in the solvent of ethanol, acetone, ethyl acetate had higher toxicity and antifeedant activity on wheat aphid. When the concentration was 100 mg/ml, after 24 h, the toxicity and antifeedant activity of three kinds extracts on wheat aphid were greater than 84.35% and 66.98%, respectively. After 48 h, the toxicity and antifeedant activity were greater than 85.91% and 79.34%, respectively. Among 5 kinds extracts,ethanol extracts had the highest toxicity and antifeedant activity on wheat aphid. After 24 h, the corrected mortality rate was 93.64% and the antifeedant rate was 83.61%. After 48 h,the corrected mortality rate was 94.95% and antifeedant rate was 92.21%. Petroleum ether extract had the smallest toxicity and antifeedant activity on wheat aphid. After 24 h,the corrected mortality rate and antifeedant rate were 19.54% and 34.65%, respectively. After 48 h,the corrected mortality rate and antifeedant rate were 20.13% and 39. 03%, respectively. [ Conclsion] The extracts from walnut green husk with larger polarity solvent had better toxicity and higher antifeedant activity on wheat aphid.

Field Screening of Lesotho and South African Wheat Cultivars for Russian Wheat Aphid Resistance

Russian wheat aphid (Diuraphis noxia) is an international wheat pest and was first recorded in South Africa in 1978 in the Bethlehem area in the Eastern Free State. Le-sotho lies adjacent to one of the largest wheat producing areas in South Africa, the Eastern Free State, where winter wheat and facultative types are cultivated under dry land conditions. Wheat (Triticum aestivum L.) is an important crop adapted to all agro-ecological zones of Lesotho. Russian wheat aphid may have a significant impact on wheat yield. No monitoring or pest control is being done in Lesotho and at this stage there is very little information on the Russian wheat aphid resistance of wheat culti-vars cultivated in Lesotho. In view of this it is important to monitor the distribution of Russian wheat aphid biotypes in Lesotho and determine the level of Russian wheat aphid resistance in local Lesotho wheat cultivars. Two local Lesotho wheat cultivars, Bolane and Makalaote were screened together with South African cultivars Elands, Matlabas, Senqu, PAN3379, PAN3118 and SST387, in the glasshouse against all four known biotypes that occur in South Africa. All these cultivars were also planted in 5 m plots in the field at two localities Leribe and Roma in the lowlands of Lesotho. These cultivars were screened in the field for Russian wheat aphid resistance. The predomi-nant Russian wheat aphid biotypes in these areas were also determined. The Lesotho cultivar, Bolane had resistance against RWASA2 in the glasshouse, while Makalaote did not have any Russian wheat aphid resistance in either the glasshouse or field screenings. To contribute to food security an increasing wheat yield potential is a high priority. Russian wheat aphid has been included in the list of important international cereal pests. Russian wheat aphid adapts to changing environments and taking their ecology, distribution, virulence patterns, and variability into account is important in minimizing the gap between actual and attainable yields. Current management prac-tices for winter wheat in South Africa include the use of resistant cultivars, which is the most economical management strategy for Russian wheat aphid. Introducing Russian wheat aphid resistant cultivars in Lesotho will improve overall yield and as a result food security. This will also result in lower Russian wheat aphid pest pressure in the adjacent wheat production areas in the Eastern Free State, South Africa.

Resistance in Barley (<i>Hordeum vulgare</i>L.) to New Invasive Aphid, Hedgehog Grain Aphid (<i>Sipha maydis</i>, Passerini) (Hemiptera: Aphididae)

Sipha maydis Passerini (Hemiptera: Aphididae) is a pest of cereals in many regions of the world and was identified as an invasive pest of the US in 2007. Regional surveys from 2015-2017 revealed this pest was broadly distributed throughout many of the western Great Plains states where it is a potential threat to cereal production. The common name hedgehog grain aphid, HGA, has been associated with Sipha maydis in the US. Cross-resistance where a plant is resistant to one aphid species and is also resistant to another species that is known to occur. Six barleys were evaluated for cross-resistance to HGA: Russian wheat aphid, RWA, resistant germplasms STARS 9301B and STARS 9577B and cultivar “Mesa”;greenbug, GB, resistant germplasm STARS 1501B and cultivar “Post 90”;and RWA and GB resistant experimental line 00BX 11-115. Cultivars “Morex” and “Schuyler” were susceptible controls. Antixenosis was measured 5 days after infestation by HGA. Seedling damage ratings and reductions in seedling growth were recorded after 17 days of infestation. Intrinsic rate of increase, rm, of HGA was determined by following the development of newborn aphids to adulthood and reproduction. 00BX 11-115 and Post 90 had significantly greater antixenosis (fewer aphids/seedling), significantly lower plant damage ratings, and significantly lower intrinsic rates of increase than other entries. Differences in seedling growth were not significant. 00BX 11-115 and Post 90 were the only entries with the Rsg1 greenbug resistance gene. Rsg1 greenbug resistance confers cross-resistance to HGA in the seedling stage.

Polymorphisms in salivary-gland transcripts of Russian wheat aphid biotypes 1 and 2

The Russian wheat aphid （RWA）, Diuraphis noxia （Mordvilko） （Homoptera： Aphididae）, is a major pest of small grains. As with plant-feeding aphids in general, the interaction between RWA and host plants is governed, on the insect side, by proteins and enzymes in saliva. In this work, we examined sequence variations in transcripts encoding proteins and enzymes of RWA salivary glands. We conducted reverse transcription - polymerase chain reaction in RWA biotypes 1 and 2 using primers derived from pea aphid orthologs, and cloned regions of 17 putative salivary gland transcripts. For four of the transcripts, we observed no difference in sequences between the two biotypes. For the other 13 transcripts, for example, the transcripts encoding sucrase, trehalase and protein C002, large amount of variations, both within each biotype and between the two biotypes, were observed. Usually the two biotypes shared only one variant, which was typically the most common variant in both biotypes. Most of the transcripts had more non-synonymous than synonymous codon changes among their variants. Our results offer possible molecular markers for distinguishing the two biotypes and insights into their evolution.

Differential colonization of wheat cultivars by two biotypes of Russian wheat aphid （Homoptera： Aphididae）

Susceptible and resistance wheat cultivars, Triticum aestivum L, were presented to two biotypes of Russian wheat aphid, Diuraphis noxia （Mordvilko）, in multiple choice tests to assay their relative acceptability as host plants. Both apterae （third and fourth instars） and alate adults were offered plants at the two-leaf stage in different cultivar combinations at 22±1℃ and 16：8 （L： D） hour photoperiod. Apterae were released from Petri dishes in the center of a circle of test plants, whereas alatae dispersed from a mature aphid colony to settle on plants arranged in rows. Both alatae and apterous nymphs of both biotypes readily colonized all cultivars tested：‘2137＇, ‘Akron＇,‘Ankor’,‘ Halt’ ,‘ Jagger’ ,‘ Prairie Red’ , ‘Stanton＇,‘TAM 107＇,‘TAM 110＇,‘Trego＇, ‘ Yuma＇, and ‘Yumar＇. Fewer biotype I apterae responded （settled and fed） in the combination containing more resistant （Dn4- and Dny-expressing） cultivars, compared to the combinations that had fewer. The reverse was true for biotype 2 apterae; more aphids responded in the combination containing the largest number of Dn4 expressing cultivars. Differential colonization of cultivars was observed in only one combination, in which biotype 2 apterae colonized Akron and Yumar in larger numbers than they did Stanton and Yuma. A separate experiment confirmed that, 48 hours after infestation, more biotype 2 apterae abandoned plants of Yuma than plants of Yumar. This differential response was likely due to genetic differences between the two ＇ near isogenic＇ lines that include the lack of Dn4 expression in Yuma. Choice tests with alatae did not result in differential rates of cultivar colonization by either biotype in any combination tested. These results suggest that young wheat plants appear to lack any meaningful antixenosis toward D. noxia, even though the aphids appear to perceive, and sometimes respond to, certain differences in cultivar suitability.

Induced life cycle transition from holocycly to anholocycly of the Russian wheat aphid (Homoptera: Aphididae)

The Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko),exists with holocyclic life cycle in Tacheng, Xinjiang in Northwest China. It produces males and oviparae to mate and oviposit for overwintering by eggs. Under laboratory conditions with 14 h/d photophase and temperature not lower than 15℃, RWA occurred in parthenogenesis and produced no males. The laboratory popu-lations of Russian wheat aphid, which were kept under natural conditions in fall by 15th, 49th and 81st generation while wild populations produced males and oviparae for mating, produced males and oviparae with their number decreased gradually, but viviparae and nymphs increased sequen-tially. As a result, it produced a small amount of oviparae and no males emerged in fields by 49 generations' reproduction in laboratory. After development of 81 generations, oviparae happened occasionally and no eggs occurred for overwintering instead of viviparae and nymphs. A hypothesis of RWA disastrous process was proposed. The life cycle of RWA can be changed from holocycly to anholocycly in its long-term spread and evolution. Anholocycly is more dangerous than holocycly to small grains for its strong adaptability and dispersal ability.

Fitness traits and underlying genetic variation related to host plant specialization in the aphid Sitobion avenae

Sitobion avenae （E） is an important cereal pest worldwide that can survive on various plants in the Poaceae, but divergent selection on different host plants shouldpromote the evolution of specialized genotypes or host races. In order to evaluate their resource use strategies, clones of S. avenae were collected from oat and barley. Host-transfer experiments for these clones were conducted in the laboratory to compare their fitness traits. Our results demonstrated that barley clones had significantly lower fecundityand tended to have longer developmental times when transferred from barley to oat. However, oat clones developed faster after they were transferred to barley. Clones fromoat and barley had diverged to a certain extent in terms of fecundity and developmental time of the nymphs. The separation of barley clones and oat clones of S. avenae was alsoevident in a principal component analysis. Barley clones tended to have higher broad-sense heritabilities for fitness traits than oat clones, indicating the genetic basis of differentiationbetween them. Barley clones showed significantly higher extent of specialization compared to oat clones from two measures of specialization （i.e., Xsp and Ysp）. Therefore, barleyclones were specialized to a certain extent, but oat clones appeared to be generalized. The fitness of S. avenae clones tended to increase with higher extent of specialization. Theevolution toward ecological specialization in S. avenae clones, as well as the underlying genetic basis, was discussed.