The agricultural intensification and the subsequent habitat changes in agroecosystem can strongly affect biological control services. We here examine the influence of inter-annual landscape change in wheat field area on interactions of cereal aphids and their natural enemies, as well as the efficacy of biological control using data collected from a 4-year experiment in Northwest China. Two hypotheses were tested. (i) Population densities decline following an inter-annual expansion of wheat crop proportion cover due to dilution and crowding effects. (ii) Species that are specialists or at higher trophic levels are more sensitive to bottomup disturbance by inter-annual change in percent cover of wheat crop. Results showed the population densities of one cereal aphid (Macrosiphum avenae), one parasitic wasp (Aphidius avenae), two specialist predators (ladybirds: Hippodamia variegata and H. tredecimpunctata) and one hyperparasitic wasp (Pachyneuron aphidis) declined following the expansion of wheat crop areas, supporting the predictions of inter-annual dilution and crowding effects. In contrast, the populations of one cereal aphid (Schizaphis graminum), one parasitic wasp (A. gifuensis), two generalist predators (spiders: Pardosa astrigera; carabid beetles: Chlaenius pallipes), and two hyperparasitic wasps (Asaphes suspensus, and Alloxysta sp.) did not respond to inter-annual landscape change. The two hypotheses were partially supported but with noticeable exceptions, and the bio-control efficiency declined with the increase of the proportion cover of wheat field in agricultural landscape. Overall, different responses of cereal aphids and their natural enemies make it difficult but still possible to optimize inter-annual landscape change for enhancing the parasitism rate and predator-prey ratio. ZusammenfassungDie Intensivierung der Landwirtschaft und die daraus folgenden Änderungen der Habitate in Agrarökosystemen können die biologische Schädlingsbekämpfung stark beeinflussen. Wir untersuchen hier den Einfluss der jährlichen Änderungen des Flächenanteils von Weizenfeldern in der Landschaft auf die Interaktionen zwischen Getreideblattläusen und ihren natürlichen Feinden sowie auf die Effektivität der biologischen Schädlingsbekämpfung. Wir nutzten Daten aus einem vierjährigen Experiment im Nordwesten Chinas. Zwei Hypothesen wurden getestet: (1) Nach einer Ausweitung des Flächenanteils der Weizenfelder gehen die Populationsdichten zurück als Folge von Verdünnungs-und Konzentrationseffekten. (2) Spezialisten und

Food-producing animals carrying extended-spectrum β-lactamase-producing Escherichia coli (ESBL-EC) have posed a potential threat to human and animal health. However, information regarding ESBL-EC in the intensive broiler breeding areas of Shandong Province, People's Republic of China, is very limited. The goal of our study was to investigate the prevalence and drug resistance characteristics of ESBL-EC in healthy broilers from Shandong Province. A total of 142 ESBL-EC isolates were collected from four prefectures in Shandong Province from October 2014 to February 2015. ESBL-EC isolates were frequently detected (142 of 160 samples, 88.8%) in healthy broilers. Antibiotic susceptibility testing showed that all 142 ESBL-EC isolates were resistant to ampicillin, piperacillin, and cefazolin but were sensitive to imipenem and meropenem. All ESBL-EC isolates carried one or more of the bla genes, in which blaCTX-M, blaTEM-1, and blaSHV-5 genes were identified in 142, 106, and 5 isolates, respectively. The blaCTX-M gene includes blaCTX-M-15 (56), blaCTX-M-65 (42), blaCTX-M-55 (36), blaCTX-M-14 (21), blaCTX-M-79 (1), blaCTX-M-3 (1), blaCTX-M-123 (1), and blaCTX-M-132 (1). In addition, 17 ESBL-EC isolates cocarried the genes of the CTX-M-1 and CTX-M-9 groups. Our findings indicate that healthy broiler flocks in Shandong Province in China are an important reservoir for ESBL-EC, with blaCTX-M and blaTEM-1 being the prevalent resistance genes identified.

No abstract

Models that accurately estimate maximum crop biomass to obtain a reliable forecast of yield are useful in crop improvement programs and aiding establishment of government policies, including those addressing issues of food security. Here, we present a new sigmoidal growth model (NSG) and compare its performance with the beta sigmoidal growth model (BSG) for capturing the growth trajectories of eight crop species. Results indicated that both the NSG and the BSG fitted all the growth datasets well (R2 > 0.98). However, the NSG performed better than the BSG based on the calculated value of Akaike’s information criterion (AIC). The NSG provided a consistent estimate for when maximum biomass occurred; this suggests that the parameters of the BSG may have less biological importance as compared to those in the NSG. In summary, the new sigmoidal growth model is superior to the beta sigmoidal growth model, which can be applied to capture the growth trajectory of various plant species regardless of the initial biomass values at the beginning of a growth period. Findings of this study will be helpful to understand the growth trajectory of different plant species regardless of their initial biomass values at the beginning of a growth period.

Abstract:To study the effects of wheat-maize intercropping on the population dynamics of wheat aphids and their natural enemies, wheat-maize intercropping patterns were divided into four levels: 8:2, 6:2, and 4:2 intercropping, and monoculture wheat. The results showed that as the wheat coverage rate decreased, the quantities of immigrating winged aphids and their natural enemies significantly differed; the population densities of the natural enemies of wheat aphids continuously rose and reached the highest levels in the 4:2 intercropping. During the stable periods, the maximum population density of wheat aphids was the highest in monoculture wheat. With a reduction in the wheat coverage ratio, the maximum population density of wheat aphids showed a decreasing trend. The control imposed by predatory natural enemies in intercropped wheat was higher than that in monoculture wheat; it was strongest in the 8:2 intercropping and the lowest in wheat monoculture. With an increase in the proportion of wheat, the parasitism rate of parasitic wasps increased gradually and reached the highest level in 4:2 intercropping. The effect of host density on hyperparasitism was significant in the intercropped wheat. The intercropping pattern had a great effect on the wheat aphids' natural enemies. In different agricultural landscapes, the diversity of wheat aphids' natural enemies differed significantly between intercropped wheat and monoculture wheat; in the heterogeneous landscape, the natural enemy diversity was highest in intercropped wheat, and it was far higher than that in the other wheat cultivation patterns. The natural enemy diversity was also slightly different between monoculture wheat in the heterogeneous landscape and intercropped wheat in the homogeneous agricultural landscape.