Aphid Abundance Research Articles

Evaluation of Bean Common Mosaic Disease and Associated Aphid Vector, Aphis fabae L., on Common Bean (Phaseolus vulgaris L.) Production in Lower Eastern Kenya

Production of common bean in Kenya is constrained by pests and diseases and to improve bean yields amongst majority small-scale farmers, appropriate management strategies should be adopted. Bean common mosaic disease (BCMD) caused by bean common mosaic virus and vectored by bean aphids and infected seeds, substantially inhibit common bean production in Kenya. An extensive and diagnostic field survey was conducted in six agro ecological zones (AEZs) of lower eastern Kenya during the long and short rains of 2018 to determine BCMD incidence (BCMD-I), severity (BCMD-S), bean aphid abundance (BAA), bean aphid incidence (BAI) and the management strategies applied by farmers. Significant (P≤0.001) variations observed for these traits between bean varieties, rainy seasons and AEZs implied that farmers could select and grow a tolerant bean variety or grow a variety either in a season or an AEZ with low BCMD and bean aphid pressure. Such included AEZ-UMSA with least mean BCMD-I (42%), BCMD-S (1.9) and BAI (11%) compared to two AEZs (LHSH & LM4) that showed BCMD-I of >70%, BCMD-S >3.0 and BAI >50%. The AEZs differences could be attributed to variations in altitudes, temperature and humidity that influences vector (aphid) movement. Of the nine bean varieties identified during the survey, Selian 14 was the most preferred by farmers (at ~35%) with relatively lower BCMD-I (~49%) and BAI (~35%) compared to the least (<5%) farmer-preferred variety Wairimu that showed higher BCMD-I (56%) and BAI (~68%). Therefore variety Selian 14 was considered tolerant to BCMD and bean aphid. Significant (P≤0.001) and positive correlations (r = 0.67) between BAI and BCMD-I implied an effective control of bean aphids could reduce the impact of BCMD on bean production. On visual diagnostics, >75% of farmers could generally identify diseased or pest-infested bean crops and stage of growth of the crop most affected. None (0%) could however identify BCMD symptoms although ~40% identified the vector bean aphids with ~26% implementing some form of aphid or pest management strategy. On management, season-driven early planting and bean intercropping were the most applied strategies (>80%), crop rotation and weed control accounted for ~71%, certified seeds at 1% and non-chemical or pesticide applications (0%). Both low adoption of certified seeds and no chemical aphid control were attributed to high costs, despite the possibility the two factors could have contributed to higher incidences and severity of BCMD in the study area as the disease is both seed and vector-borne. In summary, lack of knowledge and training among farmers on diagnosis and management of aphid-pests and BCMD, were cited as the main constraints for low bean cultivation. This study therefore recommends provision of adequate extension services and farmer training in lower eastern Kenya for improved bean yield and subsequent better family livelihoods and income.

Ecological requirements drive the variable responses of wheat pests and natural enemies to the landscape context

Abstract Semi‐natural habitats (SNH) are considered essential for pest‐suppressive landscapes, but their influence on crop pests and natural enemies can be highly variable. Instead of SNH per se, the availability of resources, such as pollen and nectar, may be more relevant for supporting pest control. Here, we assessed the spatiotemporal variation of multiple insect pests (cereal leaf beetles and aphids) and natural enemies (predators and aphid parasitoids) in wheat fields and their responses to landscape context and flower availability. We combined detailed information on pollen use by natural enemies with the specific distribution of pollen‐providing plants across a gradient of landscape composition and configuration. The abundance of wheat pests was tightly linked to wheat development stage. Syrphids colonised the fields early in the season, while the abundance of other enemies increased later in the season. The responses of pests to landscape structure were variable and, while some pests had low abundances in landscapes with high edge density and SNH cover, Sitobion avenae abundance was positively associated with SNH cover. Lacewings, syrphids and cereal leaf beetles were abundant in landscapes with diverse and abundant flower resources, whereas the abundance of parasitoids and Nabis sp. was driven by aphid abundance. We detected no significant indirect effects of landscape on pests via natural enemies. Synthesis and applications. Our findings highlight the need for conservation biological control to go beyond ‘one size fits all’ and consider the specific ecology of the involved organisms, even for a single crop type. Landscapes with high edge density and flowering woody plants may support natural enemies, in particular syrphids, which colonised the fields early in the season. Incentives for pest‐suppressive landscapes should focus on tailored strategies that disfavour dominant cereal pests and simultaneously enhance natural enemies according to their ecological requirements.

Intraguild interference of spiders and ladybirds in a cotton field: Evidence from their active time and aphid control efficiency

AbstractIn field crop systems, biocontrol efficiency supported by various predators is not always enhanced with occurring simultaneously but can be reduced by predator interference, i.e., competition between predator individuals over access to their prey. Such interference may be related to the active time of each predator. In this study, predator exclusion experiments were used to selectively exclude either one or both predators and to examine the impact of the two predator groups on the suppression of cotton aphid (Aphis gossypii Glover) populations in a cotton field. Main predator species included Propylaea japonica (Thunberg) and Harmonia axyridis Pallas in the ladybird group, and Lycosa spp. and Erigone spp in the spider group. A greater number of spiders was observed in the morning and evening, while ladybird densities did not vary during the day. Removing all predators led to an increase in aphid numbers compared to the other treatments where predators were present. Removing either spiders or ladybirds had similar impacts on aphid control. It is likely that spiders provide an equal level of aphid mortality as ladybirds. When both spiders and ladybirds were present, aphid abundance did not differ from those treatments where only one predator group was present. The presence of both predators did not lead to more aphid suppression, indicating that interference between these predators may have occurred in the cotton field. Although these two predators partly diverged in their activity rhythms, interference may still have occurred and could be common in cotton fields.

The effects of mycorrhizal colonization on phytophagous insects and their natural enemies in soybean fields.

The use of belowground microorganisms in agriculture, with the aim to stimulate plant growth and improve crop yields, has recently gained interest. However, few studies have examined the effects of microorganism inoculation on higher trophic levels in natural conditions. We examined how the diversity of phytophagous insects and their natural enemies responded to the field-inoculation of soybean with a model arbuscular mycorrhizal fungus (AMF), Rhizophagus irregularis, combined with a nitrogen-fixing bacterium, Bradyrhizobium japonicum, and a plant growth-promoting bacterium, Bacillus pumilus. We also investigate if the absence or presence of potassium fertilizer can affect this interaction. We found an increase in the abundance of piercing-sucking insects with the triple inoculant irrespective of potassium treatment, whereas there were no differences among treatments for other insect groups. A decrease in the abundance of the soybean aphid, Aphis glycines, with the double inoculant Rhizophagus + Bradyrhizobium was observed in potassium enriched plots and in the abundance of Empoasca spp. with potassium treatment independent of inoculation type. Although it was not possible to discriminate the mycorrhization realized by inoculum from that of the indigenous AMF in the field, we confirmed global negative effects of overall mycorrhizal colonization on the abundance of phytophagous piercing-sucking insects, phytophagous chewing insects, and the alpha diversity of phytophagous insects. In perspective, the use of AMF/Rhizobacteria inoculants in the field should focus on the identity and performance of strains to better understand their impact on insects.

Transgenic Cry1Ac + CpTI cotton does not compromise parasitoid-mediated biological control: An eight-year case study.

The on-farm deployment of genetically modified crops may negatively affect nontarget arthropods, potentially disrupting food web structure and ecosystem functions. Aphid-parasitoid interactions are well-suited to study these potential impacts in agro-ecosystems. Over the span of 8 years, we systematically compared infestation levels of the aphid Aphis gossypii, its associated parasitoid community and overall parasitism rate between transgenic Cry1Ac + CpTI cotton and nontransgenic cotton. Furthermore, we measured the impact of transgenic Cry1Ac + CpTI cotton on structural traits and interspecies interactions within quantitative aphid-parasitoid food webs. Transgenic Cry1Ac + CpTI cotton did not affect the abundance of aphids and parasitoids, or in-field parasitism rates. Despite weak interannual variability, transgenic Cry1Ac + CpTI cotton also did not alter food web architecture or biological control services. Our work not only elucidates the impact of transgenic Cry1Ac + CpTI cotton on different nontarget arthropods (i.e. aphids, parasitoids, hyperparasitoids) and their associated ecosystem services or disservices, but also diversifies the ecological risk assessment toolbox for transgenic insecticidal crops. © 2021 Society of Chemical Industry.

Reuse of wastewaters in irrigation of broad bean and their effect on plant-aphid interaction

Response of faba bean to irrigation with wastewater obtained from different wastewater treatment plants along with the combined effect of wastewater and aphids on plant growth and aphid fitness were evaluated under greenhouse conditions. Results indicated that the pH, electrical conductivity, total dissolved solids, and macro-elements were varied widely among wastewater resources and were higher than that of tap water. Seed germination percent did not significantly affect by wastewater, but germination index was considerably influenced by some types of wastewaters. Plant growth was reduced by irrigation with Wadi Hassan wastewater and Zarqa river. Leaf macro-elements greatly varied between treatments. Aphid infestation reduced plant growth compared to the control. Plants treated with wastewater enhanced the abundance of aphids at different magnitudes, while plant growth was equal and/or better than that of infested control plants. We conclude that the properly treated wastewater was not only as effective as fresh water in enhancing the plant growth, but also mitigated the adverse consequence of high infestation level of aphids on the plant.

Aphidophagous ladybirds (Coleoptera: Coccinellidae) and climate change: a review

Abstract I here review the potential effects of climate change on aphidophagous ladybirds and their future diversity. Aphidophagous ladybirds face challenges arising directly from climatic change and indirect challenges due to the effect of climate on their aphid prey and other organisms with which they interact. Ladybirds show at least some potential to respond to changes of climate through genetic change or phenotypic plasticity, notably through changes in colour pattern, dormancy and voltinism but also through thermal physiology and microhabitat or habitat plasticity. Phenological changes will likely occur in many aphidophagous species arising from relations with their prey. Changes in aphid abundance may lead to changes in ladybird prey associations over the season. The tendency to prey on multiple aphid species will insulate many ladybird predators from decline resulting from changes in the abundance of particular aphids. Like other insects, the geographic ranges of aphidophagous ladybird species will change as they track the climate. This is evidenced by the fossil record of ladybirds and by recent changes in ladybird biogeography. Such changes may be accompanied by a degree of thermal or phenological adaptation. It is likely that cold‐adapted ladybirds and some island species will go extinct. Specialised species may also be threatened. A problem in assessing the threat to the latter is the minimal amount of research carried out on specialised species. In summary, aphidophagous ladybirds exhibit some potential resilience against climate change, but future climatic effects on their overall biodiversity are not fully clear.

Organic farming supports lower pest infestation, but fewer natural enemies than flower strips

Abstract Agricultural intensification has led to dramatic losses of species and associated ecosystem services. In the European Union, agri‐environment schemes (AESs) have been developed to mitigate these challenges. There are two opposing AES strategies, targeting either production or non‐production areas. Organic farming focuses on production and conservation on the same land‐use area, whereas flower strips adjacent to crop fields are in favour of intensified conventional production combined with conservation strips outside the cultivated area. We investigated pest and natural enemy abundances of organic farming versus establishing flower strip in 10 agricultural landscapes in Central Germany along a gradient of mean field size (1.24–6.78 ha). We focused on three winter wheat fields per landscape: conventional field (control), conventional field with adjacent flower strip and organic field. We sampled crop pests such as cereal leaf beetles (CLBs) and cereal aphids as well as their natural enemies. Our results indicated that the abundance of CLB larvae was more than two times higher in conventional farming with and without flower strip than that in the organic farming. The abundance of natural enemies was supported by landscapes with small mean field size, that is their numbers increased c. threefold when field size decreased from 7 to 2 ha. Aphid abundance was lower in organic fields and conventional control fields than in conventional fields with flower strips suggesting a potential disservice of flower strips. Parasitoids and natural enemies benefited from flower strips, but they were obviously not able to control the aphids. Synthesis and applications. The major pests in cereals, aphids and CLBs infested organic farming less than flower strips along conventional fields. However, the abundance of natural enemies of pests benefited from flower strips and, in addition, from decreasing field size in agricultural landscapes. Hence, enhancing predator populations for more effective biological pest control may be best with decreasing field sizes combined with organic farming and flower strips. Altogether, organic farming might contribute much more to low pest damage than a conventional farming strategy with flower strips.

Impact of foliar insecticide sprays on Melanaphis sacchari (Hemiptera: Aphididae) and natural enemy populations in grain sorghum

The sugarcane aphid, Melanaphis sacchari is an important pest of grain sorghum (Sorghum bicolor) in the United States. Current M. sacchari management programs aim to control M. sacchari with insecticides while minimizing impacts on natural enemies that contribute to biological control of aphid populations. As a result, balancing both insecticide efficacy on the target pest and preservation of biological control agents remains an important step toward sustainable management of M. sacchari in grain sorghum. To document tradeoffs between M. sacchari control and non-target impacts, we evaluated three common aphicides (afidopyropen, flupyradifurone, and sulfoxaflor) for M. sacchari control and natural enemy safety. Treatments were paired with surfactants when recommended. Insect abundance was measured before and after foliar insecticide application using randomized complete clock design small plot studies during the 2019 and 2020 field seasons. All plots were harvested at maturity to document the relationship between in-season aphid abundance and grain yield. In this two year study, the average aphid abundance three days after insecticide application was lower in some but not all insecticidal treatments when compared to the untreated control, suggesting some insecticides had limited aphid suppression capabilities. Mean cumulative aphid days were lower in all treated plots compared to the untreated control with the exception of Sefina (afidopyropen). Twenty-eight days after foliar insecticide application, there were no differences in total natural enemy abundance in any of the treatments including the untreated control, suggesting that while M. sacchari populations were reduced by foliar insecticide treatments, the insecticides did not have clear adverse effects to natural enemy populations.

Reciprocal plant‐mediated antagonism between a legume plant virus and soil rhizobia

Abstract Beneficial plant‐associated soil microbes can promote plant tolerance to stress and promote nutrient uptake. Yet, the benefits of microbes for plant health can be altered by above‐ground stressors like herbivores and pathogens. However, few studies have assessed reciprocal plant‐mediated interactions between beneficial soil microbes and multiple above‐ground stressors. We assessed if soil rhizobia influenced complex interactions among pea host plants, a vector herbivore (aphids) and a plant virus (Pea enation mosaic virus, PEMV). We also examined how aphids and PEMV affected the function of soil rhizobia. We show that plants attacked by PEMV produced fewer root nodules and had lower fresh root nodule biomass per g of fresh plant root biomass, and decreased expression of genes associated with nodulation, suggesting PEMV inhibited nitrogen fixation by rhizobia. However, soil rhizobia decreased aphid abundance and PEMV titre on host plants, such that rhizobia decreased the susceptibility of plants to herbivores and pathogens. Assays of amino acids, and gene expression related to hormone signalling, show interactions among rhizobia, plants, aphids and PEMV were mediated by plant defence and nutrients. Viruliferous aphids induced salicylic acid in plants, and salicylic acid suppressed the function of rhizobia. Aphids feeding on plants grown in rhizobia‐inoculated soil also obtained fewer essential amino acids than those feeding on plants grown in un‐inoculated sterilized soil. Mutually antagonistic plant‐mediated interactions between soil microbes and above‐ground stressors affected plant susceptibility and herbivore nutrient uptake. This suggests ecological effects of soil microbes and above‐ground stressors for plant health will likely vary based on multi‐trophic plant‐mediated interactions among herbivores, pathogens and soil microbes. A free Plain Language Summary can be found within the Supporting Information of this article.

A Comparison of Flower and Grass Strips for Augmentation of Beneficial Arthropods in Apple Orchards

Sowing plants that provide food resources in orchards is a potential habitat management practice for enhancing biological control. Flowering plants (providing pollen and nectar) and grasses (providing alternative prey) can benefit natural enemies in orchards; however, little is known about their relative importance. We studied the effect of management practices (flower strips, grass strips, and spontaneous grass) on arthropod predators under organic apple management regimes in apple orchards in Beijing, China. Orchards located at two different sites were assessed for 3 years (2017–2019). The cover crops had a significant impact on the abundance and diversity of arthropod predators. The grass treatment consistently supported significantly greater densities of alternative prey resources for predators, and predators were more abundant in the grass than in the other treatments. The Shannon–Wiener diversity was significantly higher for the cover crop treatment than for the control. Community structure was somewhat similar between the grass and control, but it differed between the flower treatment and grass/control. Weak evidence for an increase in mobile predators (ladybirds and lacewings) in the orchard canopy was found. Ladybirds and lacewings were more abundant in the grass treatment than in the other treatments in 2019 only, while the aphid abundance in the grass treatment was lowest. The fact that grass strips promoted higher predator abundance and stronger aphid suppression in comparison to the flower strips suggests that providing alternative prey for predators has great biocontrol service potential. The selection of cover crops and necessary management for conserving natural enemies in orchards are discussed in this paper.

Influence of drought on interactions between Rhopalosiphum padi and ground dwelling predators – A mesocosm study

AbstractClimate change will lead to extreme droughts, but it is difficult to predict how this will affect crop pests. In particular, it is unclear how interactions between natural enemies and pests will be influenced. In the field, bird cherry‐oat aphids (Rhopalosiphum padi (L.)) have been observed to reside close to, or below the ground surface during dry conditions. We hypothesized that this will increase the niche overlap between R. padi and ground‐dwelling predators such as carabid beetles and wolf spiders and that aphid numbers will therefore decline during dry conditions. A fully factorial mesocosm experiment was conducted testing the combined effects of drought and predator presence on aphid position and abundance on barley (Hordeum vulgare) plants. In support of our hypothesis, we found that (a) aphids moved below ground during dry conditions, (b) predators reduced aphid numbers, but only during dry conditions, and (c) predators reduced the proportion of aphids below ground in dry conditions. This increased predation effect during dry conditions was, however, compensated for by a corresponding increase in aphid performance on the plants and so the net effect of drought on aphid numbers ended up being neutral. Thus, pests can be affected by drought in complex ways via a combination top‐down and bottom‐up mechanisms. Predicting how pest populations will be affected by droughts in the future is thus a formidable research challenge.

Prevalence and Impact of Sucking Insect Pests on Cotton Crop

Background: Cultivation of cotton, the staple fiber crop, is expanding in Bangladesh. The crop suffers from the infestation of the sucking insect pests i.e., aphid and jassid. This study investigated the physiomorphic traits, yield and quality of cotton plants regarding the abundance of aphid and jassid.Methods: The study was conducted in Gazipur, Bangladesh with the cotton varieties namely CB12, CB13, CB14, CB15 and HC1. Abundance of the insect pests was recorded through weekly inspection of the field.Result: The tested cotton varieties showed differences in physiomorphic traits, yield and quality attributes. Statistically, aphid and jassid showed the lowest abundance on CB14 and HC1 varieties, respectively and the variety CB14 revealed the lowest plant deformities and resulted the highest yield and quality attributes. Aphid and jassid populations revealed a negative correlation with leaf trichomes and phytochemical contents but showed a positive correlation with the number of leaves plant-1.

Plant silicon application alters leaf alkaloid concentrations and impacts parasitoids more adversely than their aphid hosts.

Grasses accumulate large amounts of silicon (Si) which acts as a highly effective physical defence against insect herbivory, however recent evidence shows that Si supplementation also modifies plant secondary metabolite concetrations. Changes in plant secondary metabolites concentrations can have cascading effects on higher trophic levels, such as parasitoids, as they are dependent on the host herbivore for growth and development. However, relatively little is known about how Si application affects higher trophic levels. We examined the effects of Si addition on alkaloid content in leaves of Phalaris aquatica (Poaceae) and the effect on interactions between an aphid (Rhopalosiphum padi) and its parasitoid (Aphidius colemani). Si supplementation had no effect on aphid abundance or parasitism rate. Adult aphids, aphid mummies (parasitised aphids) and the emergent parasitoids were, however, significantly smaller on Si+ plants. Parasitoid traits (size and emergence) were correlated with aphid mummy size. Si addition reduced parasitoid emergence rate and size due to reduced host mummy size, in addition, significantly fewer females emerged from mummies on Si+ plants. Aphid infestation significantly altered alkaloids concentrations, reducing gramine by 80% while increasing tryptamine by 91% in Si- plants. Si addition reduced aphid-induced tryptamine concentrations by 64% and increased 5-MeO-tryptamine by over 800% in control and 142% in aphid infested plants. Our results show that while Si addition has modest impacts on the herbivore, it significantly alters secondary metabolites and has stronger effects on the higher trophic level through changes in the quality of the parasitised host.

New slow release mixture of (E)-β-farnesene with methyl salicylate to enhance aphid biocontrol efficacy in wheat ecosystem.

Semiochemical use is a promising way to reduce damage from pests by improving natural control in agro-ecosystems. The aphid alarm pheromone (E)-β-farnesene (EβF) and herbivore-induced methyl salicylate (MeSA) are two volatile cues to induce changes in aphid behavior with functional significance. Because of limitations related to the volatility and oxidization of EβF and MeSA under natural conditions, slow-release and antioxidant techniques should be developed and optimized before application. Here, a slow-release alginate bead of EβF mixed with MeSA was first designed and manufactured. We hypothesized that a mixture of these two semiochemicals could be effective in controlling Sitobion miscanthi in wheat crops. Both MeSA and EβF in alginate beads were released stably and continuously for at least 15 days in the laboratory, whereas EβF in paraffin oil and pure MeSA were released for only 2 and 7 days, respectively. In 2018 field experiments, EβF and MeSA alone or in association significantly decreased the abundance of alate and apterous aphids. An increased abundance of mummified aphids enhanced by higher parasitism rates was observed when using EβF and MeSA in association, with a significant reduction of apterous abundance, more so than EβF or MeSA alone. In 2019, plots treated with a mixture of EβF and MeSA showed significantly decreased abundance of alate and apterous aphids with higher parasitism rates compared with the control. The new slow-release alginate bead containing a mixture of EβF with MeSA could be the most efficient formulation to control S. miscanthi population by attracting parasitoids in the wheat agro-ecosystem. © 2021 Society of Chemical Industry. © 2021 Society of Chemical Industry.

Use of plants by Myzus persicae in agroecosystems: Potential applications in conservation biological control

AbstractMyzus persicae (Sulzer) is a highly polyphagous aphid species that attacks several economically important crop plants. Here, trophic webs involving M. persicae, its host plants and its parasitoids were described and quantified in wheat, oat and alfalfa agroecosystems from central Argentina, with special emphasis on the sub‐habitats where interactions occur: crops and adjacent field margins. Three fields cultivated with each crop species and their margins were sampled during three years; aphid abundance and mummification percentage were compared among crop plants and the diverse natural vegetation in the borders. Interactions were described using a quantitative food web approach, and abundance and mummification percentage e data were analysed using a generalized linear model. Four plant species present in the borders (Capsella bursa‐pastori, Rapistrum sp., Melilotus sp. and Trifolium repens) hosted M. persicae and its parasitoids. The alfalfa agroecosystem produced a significantly higher number of aphids than oat and wheat; however, in all cases, crops and borders sustained similar aphid abundance. A total of six Aphidiinae species attacked M. persicae, with no significant differences in the richness of parasitoid species between the borders and the crops, but with significant differences in parasitoid abundance, being higher in the crops. Mummification percentage were higher in crops than in the borders, with Lysiphlebus testaceipes, Aphidius colemani and A. ervi being the most abundant species. Almost 70% of M. persicae individuals were collected from fields borders, which highlights the importance of including these sites in studies of trophic interactions in crop fields.

Organic fertilizer amendment promotes wheat resistance to herbivory and biocontrol services via bottom-up effects in agroecosystems

Excessive mineral fertilizer input results in little extra yield but exacerbates insect herbivory and affects environmental health and ecosystem services. The use of organic fertilizer is considered to have promise for mitigating those impacts. How organic fertilizer amendment modifies crop resistance to insect herbivory and modulates biocontrol services on a landscape scale has not been well studied. We conducted a series of field experiments on a large spatial scale with three fertilization regimes (mineral fertilizer, mineral fertilizer amended with organic matter, and no fertilizer control) in Shandong Province, northern China. Soil nutrient content, wheat plant metabolism, cereal aphid abundance, parasitism rate, and wheat yield were quantified. Maize straw amendment combined with mineral fertilization significantly reduced cereal aphid abundance and promoted parasitism during the peak aphid period, compared with mineral fertilizer alone and the no fertilizer control. Modeling simulations showed increased biological pest control when a larger proportion of fields were additionally treated with maize straw amendment. Foliar chemical analyses revealed that the types and content of plant free amino acids, rather than plant defensive compounds, most likely accounted for the variation in aphid abundance and biological control efficiency. A mineral fertilization regime plus plant straw amendment may promote wheat resistance to herbivory and benefit biocontrol via bottom-up effects. Heterogeneity in fertilizer regimes between fields may be the key ecological force shaping pest control at a landscape scale.

Seasonal dynamics of bean aphids and its relationship with the abundance of Lady Bird Beetles

The seasonal dynamics of aphid Aphis craccivora Koch (Hemiptera: Aphididae) on four bean species namely country bean Lablab purpureus, yard long bean Vigna sesquipedalis, hyacinth bean Dolichos lablab and bush bean Phaseolus vulgaris were studied from September to December 2017 in the experimental field of the Department of Entomology, Bangabandhu Sheikh Mujibur Rahman Agricultural University, Gazipur, Bangladesh. The study also investigated the relationship between the abundance of aphid and its predatory insect lady bird beetle. Aphid abundance on the bean species showed increasing trend from the 4th week of September and reached to the peak during the 2nd week of November and then declined. Bush bean and yard long bean, respectively depicted the higher and lower abundances of aphid throughout the study. Relationship between the abundance of aphid and lady bird beetle on the bean species were positively correlated. Aphid showed negatively correlation with temperature and rainfall, and positive correlation with relative humidity, and the correlations were not significant. Multiple regression equation showed that temperature had the highest effect which contributed 16.1 - 19.2% role on the population of aphid.
 Bangladesh J. Zool. 48(2): 357-363, 2020

Pollination, Crop Productivity, and Arthropod and Bird Communities Are Marginally Impacted by Border Vegetation in Highbush Blueberry Production

Herbaceous flowering or woody plant borders adjacent to highbush blueberry (Vaccinium corymbosum) fields have the potential to benefit both native pollinators and species of predatory and parasitic arthropods and birds that feed on key highbush blueberry pests, such as spotted wing drosophila [SWD (Drosophila suzukii)]. However, they may also draw pollinators away from the crop, serve as overwintering and/or refugia sites for SWD, and increase the abundance of wild birds that feed on fruit and harbor foodborne pathogens. The objective of this 1-year, observational study was to explore the potential impacts of border vegetation adjacent to commercial highbush blueberry fields on pollination, crop productivity, and arthropod and bird communities within the Pacific Northwest region in the United States. The study included three highbush blueberry cultivars (Duke, Draper, and Liberty), and three field border vegetation treatments: 1) woody perennial vegetation; 2) herbaceous vegetation; and 3) medium-height grasses (control). There was one border treatment per cultivar for a total of nine sites. No cultivar effects nor interactions for any of the variables were detected, so results were combined across cultivars. No differences in pollinator abundance, pollinator visitation rates, estimated yield, berry weight, and seed number were observed across the treatments. Herbaceous borders had more natural enemies than the woody perennial borders, but both were similar to the control. This trend is attributed to higher abundances of parasitic wasps (suborder Apocrita) in the herbaceous and control borders compared with the woody perennial borders. Increased abundances of aphids (family Aphididae), a host for parasitic wasps, likely influenced these results. Differences in predatory arthropods were not observed. Insect abundances were overall low in all field sites measured in this study, likely influenced by SWD insecticide applications. There were no differences in total wild bird density by treatment except for barn swallows (Hirundo rustica), which were greatest in the control treatment. Overall, the border treatments evaluated in this study had small-to-negligible impacts on the measured variables, and there was no clear crop production benefit. Additionally, none of the investigated border treatments negatively impacted highbush blueberry production. Taken together, border vegetation treatments can provide benefits such as reducing pesticide drift, deterring trespassers, and serving as a windbreak; but any potential benefits from a pollination or biocontrol aspect are likely diminished due to current SWD management practices.

Primacy of plants in driving the response of arthropod communities to drought

Drought threatens arthropod communities worldwide. Water limitation affects the quantity and quality of plants available to herbivores as food, and can also affect higher trophic-level consumers through variability in prey quality and reduced availability of suitable habitats. Our study assessed the response of an arthropod community to water limited wheat (Triticum aestivum L.) in a field setting. We used rainout shelters to exclude precipitation, irrigated raised bed plots to create three levels of water availability, and monitored arthropod community development over 8weeks. First, we compared arthropod communities in habitats with different levels of water limitation and found that community composition was reliant on the magnitude of the water stress. This difference was largely due to the loss of piercing-sucking herbivores and predators in high-stress environments. Next, we focused on aphids and their natural enemies to investigate the underlying mechanisms driving community responses using structural equation modeling (SEM). Aphid abundance was negatively affected by water limitation, and this response was primarily associated with stress-induced plant physiological changes and not plant biomass or natural enemy abundance. Natural enemy abundance was also reduced in water-limited habitats, but natural enemies responded to plant biomass and not prey availability. These effects were exacerbated as water stress increased. The absence of natural enemy effects on aphids indicates that top-down predation effects were dampened by strong bottom-up effects of plant water limitation. This study revealed the importance of considering water stress intensity when predicting outcomes of droughts for arthropod communities.