Eco-physiological response of two marine bivalves to acute exposition to commercial Bt-based pesticide.

Microbial products based on the entomopathogenic bacterium Bacillus thuringiensis (Bt) are among the most common biopesticides used worldwide to suppress insect pests in forests, horticulture and agricultural crops. Some of the effects of commercial Bt have been recorded for terrestrial and freshwater non-target organisms but little research is available on marine fauna. Nevertheless, due to the contiguity of agro-ecosystems and coastal habitats, marine fauna may be highly influenced by this control method. We studied the effect of a commercial Bt product on the physiological and ecological responses and the energy budget of two of the most frequent marine intertidal bivalves in the Mediterranean, the native Mytilaster minimus and the invasive Brachidontes pharaonis. To test the effects experimentally, we simulated the worst scenarios possible using the average dose applied to fields and a hypothetical accumulation dose. The results showed the feeding rates of both species were affected detrimentally by the different experimental conditions; higher concentrations led to higher respiration rates, however neither species showed any significant difference in excretion rates. The biopesticide had a significant effect on the energy budget, the values decreasing with doses. In addition, it led to high mortality for the worst treatments and, in both species, induced significantly higher cardiac activity than in the controls. These results indicate a measurable effect of Bt commercial products on marine organisms, and great attention should be paid to biopesticides composed by entomopathogenic bacteria and addictive compounds. In addition, the results highlight the urgent need to study not only the effects of anthropogenic pressures on target organisms but also to extend our view to other ecosystems not expected to be influenced. Gaining data at the organismal level should help increase the sustainability of pest control and reduce the consequences of side-effects.

Evaluating resistance to Bt toxin Cry1Ab by F2 screen in European populations of Ostrinia nubilalis (Lepidoptera: Crambidae).

The large-scale cultivation of transgenic crops producing Bacillus thuringiensis (Bt) toxins have already lead to the evolution of Bt resistance in some pest populations targeted by these crops. We used the F2 screening method for further estimating the frequency of resistance alleles of the European corn borer, Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae), to Bt maize, Zea mays L., producing the Cry1Ab toxin. In France, Germany, and Italy, 784, 455, and 80 lines of European corn borer were screened for resistance to Mon810 maize, respectively. In Slovakia, 26 lines were screened for resistance to the Cry1Ab toxin. The cost of F2 screen performed in the four countries varied from U.S. dollars 300 to dollars 1300 per line screened. The major difference in cost was mostly due to a severe loss of univoltine lines during the screen in Germany and Slovakia. In none of the screened lines did we detect alleles conferring resistance to Mon810 maize or to the Cry1Ab toxin. The frequency of resistance alleles were < 1.0 x 10(-3), < 1.6 x 10(-3), < 9.2 x 10(-3), and < 2.6 x 10(-2) in France, Germany, Italy, and Slovakia, with 95% probability, respectively. The average detection probability over all lines was approximately 90%. Making the assumption that European corn borer populations in these countries belong to the same genetic entity, the frequency of alleles conferring resistance to the Cry1Ab produced by the Mon810 maize in western and central Europe was 1.0 x 10(-4), with a 95% confidence interval of 0-3.0 x 10(-4).

A mathematical model of exposure of non-target Lepidoptera to Bt-maize pollen expressing Cry1Ab within Europe.

Genetically modified (GM) maize MON810 expresses a Cry1Ab insecticidal protein, derived from Bacillus thuringiensis (Bt), toxic to lepidopteran target pests such as Ostrinia nubilalis. An environmental risk to non-target Lepidoptera from this GM crop is exposure to harmful amounts of Bt-containing pollen deposited on host plants in or near MON810 fields. An 11-parameter mathematical model analysed exposure of larvae of three non-target species: the butterflies Inachis io (L.), Vanessa atalanta (L.) and moth Plutella xylostella (L.), in 11 representative maize cultivation regions in four European countries. A mortality-dose relationship was integrated with a dose-distance relationship to estimate mortality both within the maize MON810 crop and within the field margin at varying distances from the crop edge. Mortality estimates were adjusted to allow for physical effects; the lack of temporal coincidence between the susceptible larval stage concerned and the period over which maize MON810 pollen is shed; and seven further parameters concerned with maize agronomy and host-plant ecology. Sublethal effects were estimated and allowance made for aggregated pollen deposition. Estimated environmental impact was low: in all regions, the calculated mortality rate for worst-case scenarios was less than one individual in every 1572 for the butterflies and one in 392 for the moth.

Role of Myzus persicae (Hemiptera: Aphididae) and its secondary hosts in plum pox virus propagation.

Plum pox virus (family Potyviridae, genus Potyvirus, PPV) is one of the most important viral pathogens of plants in the genus Prunus, particularly Prunus persica L. The role of the Myzus persicae (Sulzer) (Hemiptera: Aphididae) as a vector of PPV-M, and its role in spreading PPV-M, was investigated. PPV-M-infected peach trees were used as inoculum sources, and transmission to 15 herbaceous species commonly present in and around peach orchards was evaluated. The presence of PPV-M in secondary hosts after aphid transmission was verified by reverse transcription-polymerase chain reaction tests. The results indicate that Saponaria ocymoides L., Pisum sativum L., Trifolium repens L., Trifolium pratense L., Lepidium sativum L., Matricaria chamomilla L., Centaurea cyanus L., Bellis perennis L., Papaver rhoeas L., and Zinnia elegans L. became infected. Although Lupinus polyphyllus Lindley, Taraxacum officinale L., Achillea millefolium L., Amaranthus retroflexus L., and Linum rubrum L. did not become infected, they are hosts of M. persicae. Among the 10 positive species that were infected, the species most common in peach orchards, T. pratense, T. repens, B. perennis, and M. chamomilla, were used as source plants for the transmission studies to the peach tree. Our study reveals the ability of M. persicae to transmit PPV-M from herbaceous hosts to peach trees, describes PPV-M symptoms in herbaceous species, and discusses the role of M. persicae and its hosts as a source of PPV-M in peach orchards.

Biodiversity of nematofauna of oilseed rape (Brassica napus L.).

Few data is available on the nematodes found in Brassicaceae, except for the most important plant parasite. However, studying the structure of nematofauna could be an important database for the soil quality and in order to assess the effects of future disturbance. This is particularly important considering that the diffusion of the canola crop in the world is increasing because of its use as a bio-diesel. Very diffused is also the Bt variety of oil seed rape, and, in this case, the study of the impact on the soil health and on bio-diversity is essential. In this research we have analyzed the nematode community, used as a bio-indicator of the soil condition. The nematofauna found in canola (Brassica napus var. oleifera) fields located in Southern Italy (Metaponto - MT) was investigated. The nematode community was studied considering its abundance, genus composition and trophic structure. Maturity and biodiversity indices were also calculated. A total of 5286 nematodes were extracted. They belong to 14 families and 24 genera. Bacterial and fungal feeders, 50.18% and 42.90% of the total respectively, dominated the trophic structure. Aphelencus is the most abundant genus (23.71%) followed by Acrobeloides (20.49%) and Aphelencoides (19.18%). Among plant feeders (6.59%), Pratylenchus is the dominant genus (2.20%) and Tylenchidae the main family (3.54%). No infestation of Meloidogyne, Heterodera or Naboccus, important plant-parasitic nematodes of canola crops, was recorded. Other important phytophagous were Helycotylenchus (0.5%), Trichotylenchus (0.5%) and Filenchus (0.9%). All of them had an abundance level below injury level. The indices of biodiversity are rather low (H'=0.93, J'=0.67), as is typical for agro ecosystems. However, the nematofauna community is quite well structured (N2=6.31, D=0.16) and the maturity index rather high (EMI=1.94). These values demonstrate that oilseed rape has a lower impact on the soil compared to other crop systems and that it could be taken into consideration for crop rotation programs. Canola could follow other more stressful crops, trying to maintain soil equilibrium.

Nematodes associated with the rhizosphere of corn (Zea mays L.).

The research was carried out during 1999 in 8 different localities in Northern Italy. The nematodes were extracted from soil samples of rhizosphere of corn plants (Zea mays L.). The objective of the study was to investigate plant-parasite nematodes associated with maize. Some phytophagous genera are common pests of this crop and its yield-loss are often due to their high densities. In addition the nematode community was investigated for the genus composition, the trophic structure and its biodiversity. After the extraction from soil with a Bearmann funnel and Ludox centrifugation, nematodes were identified at genus level. They belonged to 22 families and 45 different genera. The genus Rhabditis, Pratylenchus, Helicotylenchus and Acrobeloides made up more than 70% of the total nematodes collected. The dominant trophic group was the bacterial feeders (61%) in particular Rhabditis, that was the most abundant and often the dominant one. Phytophagous represented in almost all fields more than 30% of the total nematodes. In all the examined sites biodiversity was quite low, being the H' values no more than 1.08. The data indicates a high level of disturbance. In some localities high densities of Helicotylenchus and Pratylenchus were found. While these nematodes have been identified as being potentially harmful for corn plants in our latitudes, especially in light soils, this research could give an indication for further monitoring studies regarding plant parasitic nematodes of corn crops. This data is particularly important considering that methyl bromide, often used in Italian agriculture against soil pathogens, has been banned since the beginning of 2005.