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PubMed1985

Estimated risks and benefits from introducing Marisa cornuarietis into the Sudan.

As it has been proposed that Marisa cornuarietis, the ampullarid snail from the tropical Americas be used in the Sudan as a biological control agent against schistosomiasis, an estimate was made of the potential ecological hazards which might result from its widespread distribution in the Nile River Valley, and also of the potential benefits. The only foreseeable hazard would result from colonization of rice fields by the ampullarid snail and subsequent crop damage. However calculations on population dynamics indicated that Marisa cornuarietis would not be able to establish significant populations in rice fields in the Nile Valley as the flooded periods are too short. Thus the expected benefits of schistosomiasis control far outweigh any expected risks, and the ampullarid should be used in expanded field trials in the Gezira Irrigated Area as a control method for schistosomiasis.

Agriculture↗
PubMedDate not supplied

Electrophysiological responses of Atta sexdens rubropilosa workers to essential oils of eucalyptus and its chemical composition.

The leaf-cutting ant Atta sexdens rubropilosa Forel, 1908 is the most harmful of the Eucalyptus pests, causing severe losses in wood production through defoliation. Various strategies have been tried and effort spent on the development of methods to control this pest, however no practical and environmentally acceptable one currently exists. In this work the chemical composition of the essential oil of seven Eucalyptus species was identified and the selectivity and sensitivity of antennal receptors of A. sexdens rubropilosa workers to the volatile compounds were determined using the electroantennographic technique (EAG and GC-EAD). Analysis by GC-EAD showed in E. cloesiana and E. maculata, respectively, seventeen and sixteen terpenes that elicited responses in ant workers' antennae, indicating the potential role of the essential oils as allelochemicals that determine the choice of the foraging material.

Animals↗
PubMed2005

Season-long variation in expression of Cry1Ac gene and efficacy of Bacillus thuringiensis toxin in transgenic cotton against Helicoverpa armigera (Lepidoptera: Noctuidae).

The insertion of genes encoding insecticidal Cry1A delta-endotoxins from the bacterium Bacillus thuringiensis Berliner variety kurstaki (Bt) into varieties of cotton (Gossypium spp.) was undertaken to assist in the control of a range of lepidopteran pests. In Australia, where Helicoverpa armigera (Hübner) and Helicoverpa punctigera (Wallengren) are major pests, the level of control is useful, but not complete, because efficacy declines as the crop matures. Fluctuations in the efficacy of Bt cotton, to the extent that some insects survive, provide opportunities for H. armigera to develop resistance to the Bt toxin. Therefore, variations in the efficacy of Bt cotton need to be understood if we are to plan rational resistance management strategies to retard the rate of the development of resistance. We measured the changes in efficacy associated with plant development over the growing season, in the field and glasshouse. In addition, the levels of Cry1Ac protein toxin and cry1Ac RNA were determined. In this first demonstration of the relationship between these three factors, we found that the developmental decline in bioefficacy in field-grown plants was associated with reduced cry1Ac transcript levels and Bt toxin levels in postsquaring cotton. In addition, changes in plant chemistry associated with the maturation of the cotton plant were observed to contribute to changes in the efficacy of Bt toxin. Results from the field and glasshouse suggested that variations in efficacy within the growing season and between seasons also may be influenced by environmental factors.

Animals↗
PubMed2006

Evaluation of the time-concentration-mortality responses of Plutella xylostella larvae to the interaction of Beauveria bassiana with a nereistoxin analogue insecticide.

Six bioassays were conducted to evaluate the interaction between Beauveria bassiana SG8702 and a nereistoxin analogue insecticide, diammonium S,S'-(2-dimethylaminotrimethylene)di(thiosulfate), which is highly compatible with the fungal biocontrol agent against diamondback moth Plutella xylostella (L.). Second-instar larvae were exposed to sprays of B. bassiana alone (assay 1) at concentrations of 21-38, 157-232 and 822-1133 conidia mm(-2) or together with the insecticide at the low application rates of 5, 10, 25, 50 and 100 microg AI ml(-1) (assays 2-6), and then maintained at 25 degrees C and 12:12 h light:dark photoperiod for daily monitoring of mortality for 8 days. Based on the modelling of the resultant time-concentration-mortality data sets, the fungal agent was highly virulent to P. xylostella with an LC50 decreasing from 269 conidia mm(-2) on day 4 to 107 on day 8. Lower lethal concentrations or shorter median lethal times resulted from fungal sprays including the tested chemical rates; the latter never caused higher mortalities than the fungal treatments alone. The fungal action over 3-7 days after spray was significantly enhanced by including in the fungal sprays the chemical at rates of > or =25 microg ml(-1) for 2.6- to 1756-fold reduction of LC50 values, > or =50 microg ml(-1) for 4- to 274-fold reduction of LC70 values and 100 microg ml(-1) for 9- to 33-fold reduction of LC90 values respectively. These rates were equivalent to 5-20% of the chemical rate labelled for field application. The fungal and chemical interaction outlined above highlights the feasibility of combined formulation or application of B. bassiana and the chemical insecticide for P. xylostella control.

Animals↗
PubMed2003

Investigation of alternatives to methyl bromide for management of Meloidogyne javanica on greenhouse grown tomato.

The root galling index and the densities of eggs in roots and juveniles in soil of the root-knot nematode Meloidogyne javanica (Treub) Chitwood on tomato, and the effect of these on crop yield were assessed in greenhouse experiments applying various treatments at two different sites in Crete, Greece. Tomato crops were grown for four cycles by rotating nematode-resistant (first and third spring crops) with susceptible (second and fourth autumn crops) cultivars and receiving the following treatments: (a) untreated control; (b) methyl bromide application before the first and third crops; (c) application of the fungus Pochonia chlamydosporia (Goddard) Zare, Gams & Evans before planting the first, third and fourth crops with a supplementary application three weeks after the beginning of the fourth crop; (d) application of oxamyl in both sites and fenamiphos in site 1 only at the second and fourth crops; (e) combination of treatments (c) and (d). The fungus density in soil was monitored three weeks after application and at the end of each crop, when roots were lifted. Pochonia chlamydosporia had a variable establishment and did not control the nematode. Its pathogenicity on eggs was not demonstrated, as in all cases galls were big, with all egg masses inside and protected from infection. The methyl bromide treatment significantly reduced root galling and egg production compared to other treatments in all crop cycles and the yield of the fourth crop was significantly greater. Nematicides reduced nematode densities compared with untreated controls and the fungus treatment, but they were less effective than methyl bromide and resulted in increased yield in one site only.

Animals↗