Beyond selectivity: Are behavioral avoidance and hormesis likely causes of pyrethroid-induced outbreaks of the southern red mite Oligonychus ilicis?

Secondary pest outbreak is a counterintuitive ecological backlash of pesticide use in agriculture that takes place with the increase in abundance of a non-targeted pest species after pesticide application against a targeted pest species. Although the phenomenon was well recognized, its alternative causes are seldom considered. Outbreaks of the southern red mite Oligonychus ilicis are frequently reported in Brazilian coffee farms after the application of pyrethroid insecticides against the coffee leaf miner Leucoptera coffeella. Selectivity favoring the red mite against its main predatory mites is generally assumed as the outbreak cause, but this theory has never been tested. Here, we assessed the toxicity (and thus the selectivity) of deltamethrin against both mite species: the southern red mite and its phytoseid predator Amblyseius herbicolus. Additionally, behavioral avoidance and deltamethrin-induced hormesis were also tested as potential causes of red mite outbreak using free-choice behavioral walking bioassays with the predatory mite and life-table experiments with both mite species, respectively. Lethal toxicity bioassays indicated that the predatory mite was slightly more susceptible than its prey (1.5×), but in more robust demographic bioassays, the predator was three times more tolerant to deltamethrin than its prey, indicating that predator susceptibility to deltamethrin is not a cause of the reported outbreaks. The predator did not exhibit behavioral avoidance to deltamethrin; however insecticide-induced hormesis in the red mite led to its high population increase under low doses, which was not observed for the predatory mite. Therefore, deltamethrin-induced hormesis is a likely cause of the reported red mite outbreaks

Protein oligomers studied by solid-state NMR – the case of the full-length nucleoid-associated protein histone-like nucleoid structuring protein

Members of the histone-like nucleoid structuring protein (H-NS) family play roles both as architectural proteins and as modulators of gene expression in Gram-negative bacteria. The H-NS protein participates in modulatory processes that respond to environmental changes in osmolarity, pH, or temperature. H-NS oligomerization is essential for its activity. Structural models of different truncated forms are available. However, high-resolution structural details of full-length H-NS and its DNA-bound state have largely remained elusive. We report on progress in characterizing the biologically active H-NS oligomers with solid-state NMR. We compared uniformly (13C,15N)-labeled ssNMR preparations of the isolated N-terminal region (H-NS 1–47) and full-length H-NS (H-NS 1–137). In both cases, we obtained ssNMR spectra of good quality and characteristic of well-folded proteins. Analysis of the results of 2D and 3D 13C–13C and 15N–13C correlation experiments conducted at high magnetic field led to assignments of residues located in different topological regions of the free full-length H-NS. These findings confirm that the structure of the N-terminal dimerization domain is conserved in the oligomeric full-length protein. Small changes in the dimerization interface suggested by localized chemical shift variations between solution and solid-state spectra may be relevant for DNA recoginition

Evaluation of the nutritive value of muiumba (Baikiaea plurijuga) seeds: chemical composition, in vitro organic matter digestibility and in vitro gas production

One of the main constraints hindering the increase of animal production in semi-arid regions of Africa is the inadequate supply of nutrients during the dry season. Incorporation of alternative feed resources in ruminant diets during this period could be a viable approach to overcome these limitations. The objective of this study was to evaluate the nutritive value of muiumba (Baikiaea plurijuga) tree seeds as an alternative nutrient source for ruminants. Muiumba seeds were compared to other eight feedstuffs including two cereal grains (corn and oat), two wheat by-products (wheat bran and distilled wheat) and four protein meals (coconut meal, sunflower meal, soybean meal and rapeseed meal) as to its chemical composition, in vitro organic matter digestibility (IVOMD) and in vitro gas production. The moderate crude protein concentrations (145 g/kg DM) of muiumba seeds indicate that this feedstuff could not be used as a protein supplement, contrarily to the majority of multipurpose tree seeds. Although the starch content was scarce (15 g/kg DM), the low neutral detergent fibre (235 g/kg DM), low molecular weight sugar (76.1 g/kg DM) and non-starch polysaccharide (510.5 g/kg DM) contents indicate that this feedstuff has potential feeding value. This was confirmed by the IVOMD (0.770) and by the data provided by the in vitro gas production showing that muiumba seeds had high (P <0.05) maximum gas production and fractional fermentation rates, suggesting that these seeds are characterized by a highly fermentable fraction