Long-term animal impact modifies potential production of N<Subscript>2</Subscript>O from pasture soil

At cattle overwintering areas, inputs of nutrients in animal excrements create conditions favourable for intensive microbial activity in soil. During nitrogen transformations, significant amounts of N₂O are released, which makes overwintering areas important sources of N₂O emission. In previous studies, however, increasing intensity of long-term cattle impact did not always increase emissions of N₂O from the soil: in some cases, N₂O emissions from the soil were lower at the most impacted area than at the moderately impacted one. Thus, the relationships between the level of long-term animal impact and potential production of N₂O from soil by denitrification were investigated in field and laboratory experiments. Field measurements indicated that the production of N₂O after glucose and nitrate amendments was greater in severely and moderately impacted locations than in an unimpacted location, while differences between the severely and moderately impacted locations were not significant. In laboratory experiments, the potential production of N₂O (measured as anaerobic production of N₂O after addition of glucose and nitrate) was highest in the moderately impacted soil. Surprisingly, potential N₂O production was lower in the most impacted than in the moderately impacted soil, and the net N₂O production in the highly impacted soil was further decreased by a significant reduction of N₂O to N₂. The expected stimulating effect of an increasing ratio of glucose C to nitrate N on the reduction of N₂O to N₂ during denitrification was not confirmed. The results show that cattle increase the denitrification potential of the soil but suggest that the denitrification potential does not increase indefinitely with increasing cattle impact.     

First report of a 16SrIII-B subgroup phytoplasma associated with leaf reddening, virescence and phyllody of purple coneflower

Purple coneflower plants showing leaf reddening and flower abnormalities were observed in South Bohemia (Czech Republic). Transmission electron microscopy observations showed phytoplasmas in sieve cells of symptomatic plants but not in healthy ones. Polymerase chain reactions with universal and group specific phytoplasma primers followed by restriction fragment length polymorphism analyses of 16S rDNA allowed us to classify the detected phytoplasmas into the X-disease group, ribosomal subgroup 16SrIII-B. Sequence analyses of the 16S-23S ribosomal operon (1684 bp), ribosomal protein L15, and protein translocase genes (1566 bp) confirmed the closest relationship with phytoplasmas belonging to the 16SrIII ribosomal group, specifically the 16SrIII-B subgroup. The current study reports purple coneflower as a new host for the X-disease phytoplasma group in the Czech Republic and worldwide.     

Insecticide resistance compromises the control of Aedes aegypti in Bangladesh

BACKGROUND

With no effective drugs or widely available vaccines, dengue control in Bangladesh is dependent on targeting the primary vector Aedes aegypti with insecticides and larval source management. Despite these interventions, the dengue burden is increasing in Bangladesh, and the country experienced its worst outbreak in 2019 with 101 354 hospitalized cases. This may be partially facilitated by the presence of intense insecticide resistance in vector populations. Here, we describe the intensity and mechanisms of resistance to insecticides commonly deployed against Ae. aegypti in Dhaka, Bangladesh.

RESULTS

Dhaka Ae. aegypti colonies exhibited high-intensity resistance to pyrethroids. Using CDC bottle assays, we recorded 2–24% mortality (recorded at 24 h) to permethrin and 48–94% mortality to deltamethrin, at 10× the diagnostic dose. Bioassays conducted using insecticide–synergist combinations suggested that metabolic mechanisms were contributing to pyrethroid resistance, specifically multi-function oxidases, esterases, and glutathione S-transferases. In addition, kdr alleles were detected, with a high frequency (78–98%) of homozygotes for the V1016G mutation. A large proportion (≤ 74%) of free-flying and resting mosquitoes from Dhaka colonies survived exposure to standard applications of pyrethroid aerosols in an experimental free-flight room. Although that exposure affected the immediate host-seeking behavior of Ae. aegypti, the effect was transient in surviving mosquitoes.

CONCLUSION

The intense resistance characterized in this study is likely compromising the operational effectiveness of pyrethroids against Ae. aegypti in Dhaka. Switching to alternative chemical classes may offer a medium-term solution, but ultimately a more sustainable and effective approach to controlling dengue vectors is required. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

Leaching of mineral nitrogen in the soil influenced by addition of compost and N-mineral fertilizer

This paper deals with the problem of mineral N leaching from arable lands due to the fertilization method. The influence of different doses of compost (50 and 100?Mg ha^?1) and N-mineral fertilizer (35-70-140 kg N ha^?1) on leaching of N_min in a lysimetric experiment with winter wheat. The area of our interest represents the main source of drinking water for the city of Brno and its neighborhoods. To demonstrate the effect of compost and mineral nitrogen addition, the lysimetric experiment was established there. Seven variants of the experiment with different fertilization schemes were studied during two vegetation seasons (2013 and 2014), each with three repetitions. The experiment was carried out in plastic experimental containers of 0.3 m diameter and 0.5 m height. Therefore, each lysimeter was the same size and was filled with 25 kg of subsoil and 25 kg of topsoil. The highest leaching of N_min was detected in the variant C2 where 140 kg N ha^?1 was applied, in both vegetation periods (5.97 kg N_min ha^?1 after the first vegetation period and 17.02 kg N_min ha^?1 after the second vegetation period). The positive effect of compost application (individually or in combination with the mineral N) on decrease in mineral N leaching was found during both vegetation period in comparison with variant C2. The highest doses of compost (100?Mg per ha) significantly decreased the concentration of mineral nitrogen in the soil eluate in both periods (3.03 kg N_min ha^?1 and 5.79 kg N_min ha^?1, respectively), by 197% and 293% in comparison with variant C2. There is evidence that the application of compost has a positive effect on the reduction of N_min leaching.