Opposite effects of different mineral oil treatments on <Emphasis Type="Italic">Macrosiphum euphorbiae</Emphasis> survival and fecundity

Mineral oil has been considered for several decades as an effective mean to control aphids and reduce the spread of non-persistent viruses. Mineral oil seems to reduce virus transmission efficiency interfering with the binding of the virions in the aphid stylets. However, several studies have shown the possible disruption of host selection process by mineral oil and some works have demonstrated a direct effect on the aphid vector. In this study the insecticidal properties of mineral oil (Finavestan EMA) alone against Macrosiphum euphorbiae (Thomas) (Homoptera: Aphididae) were evaluated through the three main routes of exposure (topical contact, inhalation and ingestion). Results showed that no aphid survived after topical contact at oil concentrations ranging from 3 to 100% v/v. However, surprisingly, at a lower concentration (0.3%), survival was not affected but fecundity was enhanced. Moreover, exposure to oil volatiles enhanced aphid survival at the highest concentrations (30 and 100%) and daily fecundity at the lowest ones (0.3 and 3%). Delivered via artificial diet, mineral oil only affected aphid survival at the 0.3% concentration. This study demonstrates that mineral oil alone, regardless of a potential plant effect can induce either probiotic effects or toxic effects, depending on the mode of application and the concentration tested. These results can be of significance for the understanding of mineral oil properties in the fields.     

Assessment of nematode biodiversity using DGGE of 18S rDNA following extraction of nematodes from soil

Soil nematodes are both taxonomically and functionally diverse, respond quickly to soil perturbation and have much potential as indicators of soil health. However, because of the perceived difficulty of identifying nematodes to species level morphologically, they are frequently neglected in soil ecological studies. Recently, extraction of soil DNA, amplification of 18S rDNA genes using nematode consensus primers and subsequent separation by denaturing gradient gel electrophoresis (DGGE) has been used to estimate nematode diversity in soil. Here, we investigate an alternative approach whereby nematodes are first extracted from the soil prior the 18S rDNA gene amplification using universal primers. We used this system to estimate nematode species richness in 10 soil samples—five from Scotland and five from the Netherlands. There was no direct correlation between species richness as estimated morphologically and by the PCR-DGGE method. However, inspection of the data suggested that the samples fell into two discrete groups, which was confirmed by canonical and stepwise discriminant function analysis; the values for the Shannon and equitability indices being important discriminators. Further analysis revealed a significant relationship between morphological species richness and DGGE estimates for species that represented greater than 1% of the sample biomass.     

Contacts between domestic livestock and wildlife at the Kruger National Park Interface of the Republic of South Africa

One of the most important transboundary animal diseases (TADs) in the southern African region is foot-and-mouth disease (FMD). In this region, a pathway for spread of FMD virus is contacts between cattle and certain species of wildlife. The objective of this study was to evaluate contacts between cattle and wildlife in the Kruger National Park (KNP) and the adjacent Limpopo province for the time periods October 2006 to March 2007 and April to September 2007. In this study, 87 livestock owners and 57 KNP field rangers were interviewed. Fifteen (17%) livestock owners reported contacts between wildlife and cattle. More livestock owners reported observing contacts between cattle and all wildlife species during October-March than April-September (p = 0.012). However, no difference was found between these periods for contacts between cattle and individual wildlife species. A total of 18 (32%) field rangers reported contacts between cattle and wildlife. The most common species-specific contacts were between cattle and buffalo (63/year), cattle and impala (17/year) and cattle and lion (10/year). There were no significant differences in rangers reporting observed contacts between cattle and wildlife during October-March versus April-September or between rangers reporting observed contacts outside versus within the KNP. Overall, there was no evidence of higher contact rates between cattle and wildlife in the study area during October-March compared to April-September. Contact data collected in this study can be used to better understand the transmission of FMD virus in this region.     

Harvest management effects on alfalfa (Medicago sativaL.) production and quality in Mediterranean areas

The effects of plant harvest stage, autumn harvest dateand cultivars on alfalfa production and quality weredetermined in a 3-year field experiment established in1992. Harvesting stage influenced annual yield andquality. Late bud-first flower harvests increased harvestfrequency and forage quality in comparison with har-vestingat the full bloom stage while decreasing dry-matteryield by 18% (25·5 vs. 21·6 t ha 21 ). Harvestingstage significantly affected autumn forage productionand quality and yield at the first spring cut. Harvests atfull bloom allowed greater autumn and spring regrowththan cutting at the late bud stage, possibly because ofthe accumulation of higher root reserves. Autumn har-vestsand cultivar significantly influenced the yields atthe first spring cut in any growing season. Cuttingbefore the first frost in autumn reduced the vigour ofboth cultivars, and the subsequent yield at the first cutin any year, in comparison with harvests taken after ornear the first autumn frost. It is concluded that theeffects of the stage of harvesting alfalfa on dry-matterproduction and quality are important in theMediterranean environment of the Ebro Valley; theeffects of autumn management were observed mainlyon the yields of the subsequent first cut in spring but noton the total annual production.     

Pesticide Use and Mycotoxin Production in Fusarium and Aspergillus Phytopathogens

The major mycotoxigenic species of Fusarium and Aspergillus phytopathogens have been identified in this review. Since fungicides are widely used to control crop diseases caused by these fungi, it is pertinent to assess efficacy with respect to mycotoxin production. In both laboratory studies with pure cultures of phytopathogens and field trials with crop plants, the overall evidence concerning the effectiveness of fungicides is contradictory and in certain cases somewhat unexpected. In particular, at sub-lethal doses of a number of fungicides including carbendazim, tridemorph, difenoconazole and tebuconazole with triadimenol, mycotoxin production from Fusarium phytopathogens may increase. Furthermore, the efficacy of propiconazole and thiabendazole in the control of deoxynivalenol production from F. graminearum is not consistent. Evidence has been presented to suggest, for the first time, that fungicide-resistance in F. culmorum may be accompanied by a more persistent pattern of mycotoxin production. The limited evidence on the effects of fungicides on mycotoxin production in Aspergillus species is also conflicting. Under laboratory conditions, miconazole and fenpropimorph have been shown to increase aflatoxin production from A. parasiticus. Moreover, fenpropimorph increased production of the more toxic aflatoxin B1. Since fungal infection of plant products is often preceded by insect damage, there is interest in the effectiveness of insecticides to reduce infestation, infection and mycotoxin contamination. Additionally, insecticides may be effective in their own right, causing a direct effect on mycotoxin synthesis. The bulk of the evidence relates to effects on aflatoxin (AF) components B1, B2, G1 and G2. Under laboratory conditions, AFB1 production was most resistant to inhibition by insecticides, followed by AFG1, AFG2 and AFB2. This pattern of inhibition was particularly consistent for the organophosphorus insecticides. In one field study, Bux and carbaryl were considerably more effective than naled in reducing AFB1 contamination of maize kernels. It is concluded that if pesticide control is to be more effective in the future, additional criteria may be required in developing evaluation protocols for candidate compounds. In particular, the issue of fungicide-resistance in relation to mycotoxin production needs to be addressed in a concerted programme of research. Additionally, the potential of breeding and selecting cultivars resistant to disease caused by toxigenic fungi needs to be exploited in a parallel search for an environmentally acceptable solution to the question of mycotoxin contamination of plant products.     

Effects on the aphid parasitoid <Emphasis Type="BoldItalic">Aphidius ervi</Emphasis> of an insecticide (Plenum<Superscript>®</Superscript>, pymetrozine) specific to plant-sucking insects

The use of a selective insecticide is highly recommended for Integrated Pest Management programs. Plenum (a.i.: pymetrozine; Syngenta Agro), a systemic insecticide, is regarded as a good candidate for use in situations where plant-sucking insects have to be controlled and where natural enemies can play a substantial role as biological control agents. In this context, the effects of Plenum on a host–endoparasitoid relationship were investigated. Potato aphids Macrosiphum euphorbiae were reared for 4 days on an artificial diet supplemented with a low concentration of Plenum (sublethal concentration inducing 15% aphid mortality) before parasitization by the endoparasitoid Aphidius ervi. The development of A. ervi larvae was negatively affected, especially during the early stages of development, and the sex ratio of the progeny was strongly male-biased. Moreover, the host-choice experiment showed that A. ervi was not able to discriminate between control and Plenum-contaminated aphids. These results show that Plenum may not be as selective as it was previously thought to be, and the observed effects need to be considered when developing IPM systems.     

Effect of susceptibility to enterotoxigenic Escherichia coli F4 and of dietary tryptophan on gut microbiota diversity observed in healthy young pigs

Healthy weaned pigs susceptible to enterotoxigenic Escherichia coli F4 (ETEC) require more tryptophan (Trp) to maximize their performance. This may be related to an effect on intestinal microbiota. We studied the intestinal bacterial diversity of healthy pigs with different susceptibility to ETEC and fed different Trp levels. Thirty-six littermate weaned pigs were selected to obtain a set potentially formed of 50% ETEC-susceptible and 50% non-susceptible pigs, based on a Mucin 4 gene polymorphism. Pigs were fed a diet with 0.17 (TrpL) or 0.22 (TrpH) standardized ileal digestible Trp:Lys ratio for 21 days. Slaughtered pigs were classified into non-susceptible, mildly susceptible, and susceptible, by testing ETEC adhesion to intestinal villi. Bacterial diversity in jejunum content was assessed by the 16S rRNA gene-targeted denaturing gradient gel electrophoresis (DGGE) fingerprinting analysis and expressed by the Shannon index. Susceptible pigs had a reduced bacterial diversity, particularly with TrpL diet (p = 0.003). The ETEC adhesion class affected the quantification of enterobacteria DNA (p = 0.027). One DGGE band, which referred to Clostridium bartlettii, was not evidenced in all the susceptible pigs; less DNA from this microbe was quantified by RT-PCR in the jejunum from TrpH susceptible pigs (p = 0.025) compared to TrpL. The gene expression for β-galactoside α-2,3-sialyltransferase 1 was higher in jejunal tissue of ETEC-susceptible pigs (p = 0.019). In studies on pig gut microbiota, the presence of intestinal receptors for ETEC should be considered because of their contribution to a reduced bacterial diversity. This effect could be partially reversed by dietary Trp addition.