Efficacy of Plant Materials in Controlling Aphids on Okra (Abelmoschus esculentus L. Moench) in Limpopo Province of South Africa

Smallholder farmers in Limpopo Province generate income through growing vegetable crops such as cabbage, tomato, and okra. These crops are produced for local and national markets. Okra crops are highly constrained by aphids. Smallholder farmers rely only on synthetic insecticides to manage aphids. This paper evaluated the efficacy of five plant materials (bio pesticides): pawpaw (Carica papaya L.), Mexican marigold (Tagetes minuta L.), serrano pepper (Capsicum annuum L.), common lantana (Lantana camara L.) and tobacco (Nicotiana tabacum L.) on Aphis gossypii population in okra production. The field experiment was laid in a randomized complete block design, with seven treatments (five plant materials, mercaptothion insecticide as a control and the absolute control) replicated three times. Aphid abundance, leaf damage and the correlation between leaf damage and aphid abundance were analyzed using analysis of variance. Carica papaya L. (0.87) and Tagetes minuta L. (0.87) were more effective in reducing aphid abundance. Leaf damage caused by aphids was lowest in the Carica papaya L. treatment (1.11) and the Tagetes minuta L. treatment (1.12). There was a strong positive correlation between aphid abundance and leaf damage (r = 0.86). Plant materials: Carica papaya L. and Tagetesminuta L. could be incorporated into an overall integrated pest management system to reduce aphid abundance and leaf damage.

Early snowmelt reduces aphid abundance (Aphis asclepiadis) by creating water-stressed host plants (Ligusticum porteri) and altering interactions with ants

Declining snow cover is reshaping ecological communities. Early loss of snow cover initiates changes in key interactions that mediate herbivore abundance, i.e., top-down and bottom-up effects. In this study, we used a field experiment to test the effects of host plant water stress and phenology on the multitrophic interactions that determine aphid abundance. The aphid, Aphis asclepiadis, in our study system colonizes the flowering stalks of the host plant Ligusticum porteri and relies on a protection mutualism with ants. We added snow and water to replicate host plants and tested for a variety of phenological and physiological responses to these treatments. Relative to host plants in ambient conditions, both water and snow addition reduced key signals of water stress (senescence and abscisic acid levels) and increased seed set. While aphid colonies were generally larger with reduced host plant water stress, the ant–aphid mutualism interacted with plant quality in complex ways. Without ant tending, we did not detect differences in aphid colony growth with host plant treatment. When tended by ants, aphid colony growth was greatest on host plants with snow addition. Host plant quality also altered the benefits exchanged in this mutualism. Ant-tended colonies hosted by plants with snow addition produced honeydew enriched in trehalose, which may have decreased both ant and natural enemy abundance. Our results suggest that early loss of snow reduces aphid abundance by creating low-quality, water-stressed host plants, and this effect may be exacerbated by natural enemies and the costs of ant attendance.

Non-consumptive effects stabilize herbivore control over multiple generations

Understanding the factors that influence predator-prey dynamics requires an investigation of oscillations in predator and prey population sizes over time. However, empirical studies are often performed over one or fewer predator generations. This is particularly true for studies addressing the non-consumptive effects of predators on prey. In a previous study that lasted less than one predator generation, we demonstrated that two species of parasitoid wasps additively suppressed aphid populations through a combination of consumptive and non-consumptive effects. However, the non-consumptive effects of one wasp reduced the reproductive success of the other, suggesting that a longer-term experiment may have revealed antagonism between the wasps. The goal of our current study is to evaluate multi-generation consumptive and non-consumptive interactions between pea aphids (Acyrthosiphon pisum) and the wasps Aphidius ervi and Aphidius colemani. Aphidius ervi is a common natural enemy of pea aphids. Aphidius colemani is a non-consumptive enemy that does not consume pea aphids, but negatively affects pea aphid performance through behavioral disturbance. Large field cages were installed to monitor aphid abundance in response to the presence and absence of both species of wasp over four weeks (two parasitoid generations). We found that the non-consumptive enemy A. colemani initially controlled the pea aphid population, but control in the absence of parasitism was not sustainable over the long term. Aphidius ervi suppressed pea aphids through a combination of consumptive and non-consumptive effects. This suppression was more effective than that of A. colemani, but aphid abundance fluctuated over time. Suppression by A. ervi and A. colemani together was complementary, leading to the most effective and stable control of pea aphids. Therefore, promoting a diverse natural enemy community that contributes to pest control through consumptive and non-consumptive interactions may enhance the stability of herbivore population suppression over time.

Annual Wildflower Strips as a Tool for Enhancing Functional Biodiversity in Rye Fields in an Organic Cultivation System

Ecological intensification of agriculture (e.g., with the use of wildflower strips) is being currently discussed as a mean for gaining high yields, preserving high biodiversity of farmland. The aim of this study was to assess the efficiency of annual wildflower strips (WFSs) established in rye field (RF) in (1) increasing species richness and abundance in terms of beneficial arthropod groups (carabids, ground spiders, plant spiders, butterflies, insect pollinators and plant-dwelling insect predators), (2) decreasing the abundance of insect pests, (3) decreasing damages of the crop, and (4) increasing the yield. The field survey was carried out in 2019, in two WFSs and in the adjacent crop field at the distances of 3, 9, 21 and 45 m. The study was not skewed by pesticide use as it was carried out on an organic farm. Mean “site” species numbers (α-diversity) and the abundance of most groups were found to be significantly higher in WFSs than in RF. A negative relationship was found in most groups between distance from WFSs and species numbers and abundance. The mean total abundance of all observed pest insects was positively related to distance from WFSs and increased by 83% at distances between 3 and 45 m from WFSs. There was a negative exponential relationship between aphid abundance and total predator abundance, which suggests a mechanism reducing aphid abundance resulting from high levels of predator abundance in the nearby WFSs. The study shows that annual WFSs can be an efficient measure for enhancing cropland biodiversity and should be taken into account in agri-environmental schemes in the Common Agricultural Policy after 2020.

Mild Drought Facilitates the Increase in Wheat Aphid Abundance by Changing Host Metabolism

Water shortages and water pollution are current issues in ecosystems around the world, and the stress induced by drought can further increase negative impacts on agriculture in these areas. In the present experiment, we examined the effect of mild drought on wheat plants grown in association with the wheat aphid Sitobion avenae Fabricius (Hemiptera: Aphididae) in 2019 and 2020. Using plot experiments, we tested the hypothesis that mild drought tends to enhance the performance of this wheat aphid by changing the nutritional quality of the wheat plants. We found that mild drought treatment significantly increased aphid abundance and population growth rates. Also, mild drought significantly increased total amino acid concentration of the wheat ear as well as concentrations of key amino acids, including Arg, Ile, Leu, Lys, Phe, Try, Gly, Ala, Tyr, and Cys in 2019, and Arg, Ile, Leu, Lys, Gly, and Cys in 2020. Mild drought led to a shift in the composition of amino acids in the plants, causing cascading effects at higher trophic levels. Such changes suggest that the carrying capacity of the environment with respect to aphids will increase if mild drought events continues to increase in frequency with climate change.

Pruning from spheroidal to cubic canopy induced aphid outbreak by altering the plant performance in Box tree

Backgrounds: Plant-animal interactions comprise the fundamental relationships of ecological research, and are sensitive to environmental change. However, The effects of pruning on animal-plant interactions have rarely been studied. Methods: We conducted field experiments to examine the impact of artificially-pruned shapes (e.g. cubic and spheroidal canopy) on the performance of the Box tree and the resulting aphid abundance at three sites; on a university campus, at a road green belt, and in a residential area. The differences of aphid abundance and plant morphology were determined with ANOVAs and paired-sample tests. Relationships between the investigated parameters were detected with simple regression and structural equation modelResult: Abundance was higher in plants with a cubic canopy than with a spheroidal canopy. Plants with a cubic canopy had lower leaf dry mass content and inflorescence numbers, but greater fresh twig length than the plants with a spheroidal canopy. The aphid abundance was negatively correlated with the leaf dry mass content and inflorescence numbers, and positively correlated with the fresh twig length. Conclusion: Our findings have proven that pruning shape can significantly affect the abundance of herbivores on the pruned plants. The results can provide data support for human actives can alter plant performance, and thereby to change insect preference.

The combined impacts of wheat spatial position and phenology on cereal aphid abundance

Background Wheat is a staple crop that suffers from massive yield losses caused by cereal aphids. Many factors can determine the abundance of cereal aphids and the damage they cause to plants; among them are the plant’s genetic background, as well as environmental conditions such as spatial position within the plot, the composition and the distance from neighboring vegetation. Although the effects of these factors have been under scrutiny for many years, the combined effect of both factors on aphid populations is not fully understood. The goal of this study was to examine the collective impact of genotype and environment on wheat phenology (developmental stages), chemical diversity (metabolites), and insect susceptibility, as manifested by cereal aphid abundance. Methods To determine the influence of plant genotype on the metrics mentioned above, we measured the phenology, chemical profile, and aphid abundance of four wheat genotypes, including the tetraploid wild emmer (Triticum turgidum ssp. dicoccoides cv. Zavitan), tetraploid durum (Triticum turgidum ssp. durum cv. Svevo), and two hexaploid spring bread (Triticum aestivum), ‘Rotem’ and ‘Chinese Spring’. These genotypes are referred to as “focal” plants. To evaluate the impact of the environment, we scored the distance of each focal plant (spatial position) from two neighboring vegetation types: (i) natural resource and (ii) monoculture wheat resource. Results The results demonstrated that the wild emmer wheat was the most aphid-resistant, while the bread wheat Rotem was most aphid-susceptible. Aphids were more abundant in plants that matured early. The spatial position analysis demonstrated that aphids were more abundant in focal plants located closer to the margin monoculture wheat resource rather than to the natural resource, suggesting a resource concentration effect. The analysis of metabolic diversity showed that the levels of three specialized metabolites from the flavonoid class, differed between the wheat genotypes and some minor changes in central metabolites were shown as well. Altogether, these results demonstrate a combined effect of genetic background and spatial position on wheat phenology and aphid abundance on plants. This exposes the potential role of the marginal vegetation environment in shaping the insect population of desirable crops. These findings highlight the importance of maintaining plant intra-specific variation in the agriculture system because of its potential applications in reducing pest density.

Mixed effects of ecological intensification on natural pest control providers: a short-term study for biotic homogenization in winter wheat fields

Agricultural intensification is one of the major drivers of biotic homogenization and has multiple levels ranging from within-field management intensity to landscape-scale simplification. The enhancement of invertebrate assemblages by establishing new, semi-natural habitats, such as set-aside fields can improve biological pest control in adjacent crops, and mitigate the adverse effect of biotic homogenization. In this study we aimed to examine the effects of ecological intensification in winter wheat fields in Hungary. We tested how pests and their natural enemies were affected at different spatial scales by landscape composition (proportion of semi-natural habitats in the surrounding matrix), configuration (presence of adjacent set-aside fields), and local field management practices, such as fertilizer (NPK) applications without applying insecticides. We demonstrated that at the local scale, decreased fertilizer usage had no direct effect either on pests or their natural enemies. Higher landscape complexity and adjacent semi-natural habitats seem to be the major drivers of decreasing aphid abundance, suggesting that these enhanced the predatory insect assemblages. Additionally, the high yield in plots with no adjacent set-aside fields suggests that intensive management can compensate for the lower yields on the extensive plots. Our results demonstrated that although complexity at the landscape scale was crucial for maintaining invertebrate assemblages, divergence in their response to pests and pathogens could also be explained by different dispersal abilities. Although the landscape attributes acted as dispersal filters in the organization of pest and pathogen assemblages in croplands, the presence of set-aside fields negatively influenced aphid abundance due to their between-field isolation effect.