R. Campos-Herrera

Effect of mine tailing on the spatial variability of soil nematodes from lead pollution in La Union (Spain)

The Cartagena-La Union mining district, exploited since the end of the 3rd century BC, was one of the worlds largest lead producers in the 19th century. Although activity ceased in 1991, today mining residues pose a huge pollution problem. This study characterises lead contents (total and DPTA) and other soil parameters (N, P, K, pH, SOM, CaCO3, granulometric fraction, etc.) using multivariate geostatistical methods in relation to nematode diversity. In this work, trophic groups and metabolic footprints of soil nematodes were measured using 193 samples from the mining, natural and agricultural areas in this district. We explored the relationship between soil health and nematode communities. High lead concentrations were quantified: mean 8,500 mg kg(-1) for total and 340 mg kg(-1) for DPTA in this mining area. Although nematode diversity was broad (81 taxa), their diversity, abundance and metabolic footprints significantly reduced in the mining area. Significant differences in the nematode community structure were observed, and the relative abundance of predators was sensitive to mine and agricultural activities, whilst omnivores reduced only in the agricultural area, and bacterial feeders exhibited a differential response to both anthropogenic disturbances. The total abundance of nematodes, trophic groups and c-p groups correlated negatively with soil Pb contents, and a positive relationship was found with SOM and N, P and K contents.

Effect of soil properties, heavy metals and emerging contaminants in the soil nematodes diversity.

Among soil organisms, nematodes are seen as the most promising candidates for bioindications of soil health. We hypothesized that the soil nematode community structure would differ in three land use areas (agricultural, forest and industrial soils), be modulated by soil parameters (N, P, K, pH, SOM, CaCO3, granulometric fraction, etc.), and strongly affected by high levels of heavy metals (Cd, Pb, Zn, Cr, Ni, Cu, and Hg) and emerging contaminants (pharmaceuticals and personal care products, PPCPs). Although these pollutants did not significantly affect the total number of free-living nematodes, diversity and structure community indices vastly altered. Our data showed that whereas nematodes with r-strategy were tolerant, genera with k-strategy were negatively affected by the selected pollutants. These effects diminished in soils with high levels of heavy metals given their adaptation to the historical pollution in this area, but not to emerging pollutants like PPCPs.

Comparative study of the effect of selected agrochemical products on Steinernema feltiae (Rhabditida: Steinernematidae)

Abstract The effect of three neurotoxic insecticides, three photosynthetic inhibitor herbicides and three enzymatic inhibitor herbicides on infective juveniles (IJs) of Steinernema feltiae Rioja (native) and ENTONEM® (commercial) strains were evaluated after a 48-h exposure at field tank concentrations and overnight treatment in mQ-water, using Spodoptera littoralis as target. Nematode survival was not affected by acetyl-cholinesterase inhibitors chlorpyrifos and pirimicarb, although chlorpyrifos seriously reduced their virulence. Both nematode strains showed differential sensitivity to cypermethrin, which affects the sodium channels of the nerve membrane, with the ENTONEM® strain being more tolerant than Rioja strain. However, these chemicals showed a strong sublethal effect on the nematode reproductive potential, limiting seriously their possible recycling in the field. Herbicides showed differential toxic effects on nematode survival. The commercial strain was tolerant to enzymatic inhibitor herbicides, whereas tribenuron and chlorsulfuron reduced Rioja strain survival. However, photosynthetic inhibitor herbicides severely affected survival of both nematode strains, with the Rioja strain being more sensitive. Sublethal effects on both nematode strains were observed only after exposition to terbutryn+chlortoluron+triasulfuron, increasing the time to kill insect larvae. These results are useful to optimize EPN dosages and to estimate their field recycling.

Screening Spanish isolates of steinernematid nematodes for use as biological control agents through laboratory and greenhouse microcosm studies.

Entomopathogenic nematodes (EPNs) are one of the best non-chemical alternatives for insect pest control, with native EPN strains that are adapted to local conditions considered to be ideal candidates for regional biological control programs. Virulence screening of 17 native Mediterranean EPN strains was performed to select the most promising strain for regional insect pest control. Steinernema feltiae (Filipjev) (Rhabditida: Steinernematidae) Rioja strain produced 7%, 91% and 33% larval mortality for the insects Agriotes sordidus (Illiger) (Coleoptera: Elateridae), Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae) and Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), respectively, and was selected as the most promising strain. The S. feltiae Rioja strain-S. littoralis combination was considered the most suitable to develop the Rioja strain as a biocontrol agent for soil applications. The effect of soil texture on the virulence of the Rioja strain against S. littoralis was determined through dose-response experiments. The estimated LC(90) to kill larvae in two days was 220, 753 and 4178 IJs/cm(2) for soils with a clay content of 5%, 14% and 24%, respectively, which indicates that heavy soils produced negative effects on the virulence of the Rioja strain. The nematode dose corresponding to the LC(90) for soils with a 5% and 14% clay content reduced insect damage to Capsicum annuum Linnaeus (Solanales: Solanaceae) plants under greenhouse microcosm conditions. The results of this research suggest that an accurate characterization of new EPN strains to select the most suitable combination of insect, nematode and soil texture might provide valuable data to obtain successful biological control under different ecological scenarios in future field applications.

Biocontrol potential of the entomopathogenic nematodes Heterorhabditis bacteriophora and Steinernema carpocapsae on cucurbit fly, Dacus ciliatus (Diptera: Tephritidae)

Entomopathogenic nematodes (EPNs) from the families Steinernematidae and Hererorhabditidae are considered excellent biological control agents against many insects that damage the roots of crops. In a regional survey, native EPNs were isolated, and laboratory and greenhouse experiments were conducted to determine the infectivity of EPNs against the cucurbit fly, Dacus ciliatus Loew (Diptera: Tephritidae). Preliminary experiments showed high virulence by a native strain of Heterorhabditis bacteriophora Poinar (Rhabditida: Heterorhabditidae) and a commercial strain of Steinernema carpocapsae Weiser (Rhabditida: Steinernematidae). These two strains were employed for further analysis while another native species, Steinernema feltiae, was excluded due to low virulence. In laboratory experiments, larvae and adult flies were susceptible to nematode infection, but both nematode species induced low mortality on pupae. S. carpocapsae had a significantly lower LC50 value against larvae than H. bacteriophora in filter paper assays. Both species of EPNs were effective against adult flies but S. carpocapsae caused higher adult mortality. When EPN species were applied to naturally infested fruit (150 and 300 IJs/cm2), the mortality rates of D. ciliatus larvae were 28% for S. carpocapsae and 12% for H. bacteriophora. Both EPN strains successfully reproduced and emerged from larvae of D. ciliates. In a greenhouse experiment, H. bacteriophora and S. carpocapsae had similar effects on fly larvae. Higher rates of larval mortality were observed in sandy loam and sand soils than in clay loam. The efficacy of S. carpocapsae and H. bacteriophora was higher at 25 and 30°C than at 19°C. The results indicated that S. carpocapsae had the best potential as a biocontrol agent of D. ciliatus, based on its higher virulence and better ability to locate the fly larvae within infected fruits.

Characterization of Xenorhabdus isolates from La Rioja (Northern Spain) and virulence with and without their symbiotic entomopathogenic nematodes (Nematoda: Steinernematidae)

Eighteen Xenorhabdus isolates associated with Spanish entomopathogenic nematodes of the genus Steinernema were characterized using a polyphasic approach including phenotypic and molecular methods. Two isolates were classified as Xenorhabdus nematophila and were associated with Steinernema carpocapsae. Sixteen isolates were classified as Xenorhabdus bovienii, of which fifteen were associated with Steinernema feltiae and one with Steinernema kraussei. Two X. bovienii Phase II were also isolated, one instable phase isolated from S. feltiae strain Rioja and one stable phase from S. feltiae strain BZ. Four representative bacterial isolates were chosen to study their pathogenicity against Spodoptera littoralis with and without the presence of their nematode host. The four bacterial isolates were pathogenic for S. littoralis leading to septicemia 24h post-injection and killing around 90% of the insect larvae 36 h post-injection, except for that isolated from S. kraussei. After 48 h of injection, this latter isolate showed a lower final population in the larval hemolymph (10(7) instead of 10(8)CFU per larvae) and a lower larval mortality (70% instead of 95-100%). The virulence of the nematode-bacteria complexes against S. littoralis showed similar traits with a significant insect larvae mortality (80-90%) 5 days post-infection except for S. kraussei, although this strain reached similar of larval mortality at 7 days after infection.

Comparative study of entomopathogenic nematode isolation using Galleria mellonella (Pyralidae) and Spodoptera littoralis (Noctuidae) as baits

Abstract Entomopathogenic nematode (EPN) occurrence in soil from natural areas and crop field edges from La Rioja (northern Spain) was compared using two insects as baits: Galleria mellonella (Lepidoptera: Pyralidae) and Spodoptera littoralis (Lepidoptera: Noctuidae). Both insects trapped Steinernema feltiae, S. kraussei and S. carpocapsae, with G. mellonella being more efficient than S. littoralis recording 5.4 and 2.6% of positive soil samples, respectively. EPN recovery frequency and abundance obtained with G. mellonella were not statistically different between natural and crop field edges values; however, S. littoralis was more successful trapping EPNs from crop field edges. Statistical differences were observed for recovery frequency recorded by both hosts in natural areas. Significant differences in larval mortality between both insects were not observed. The use of S. littoralis in entomopathogenic nematode surveys is discussed.

Entomopathogenic Nematode Production and Application: Regulation, Ecological Impact and Non–target Effects

Production and commercialization of biocontrol agents is a growing market with over 225 microbial biopesticides manufactured in 30 countries (Kabaluk & Gazdik, 2007). Although the use of Bacillus thuringiensis Berliner (Bacillales: Bacillaceae) (BT) was the dominant product in US, Mexico and Canada, being the selected product for 75 % of the crop and forest management, in the European market decreased to 25 % in 2004, with the expansion and use of other bioagents such as entomopathogenic nematodes (EPNs) (Cuddeford, 2008). Despite the drop in sales of the conventional products during early years in 2000s, detecting a decline of 1.5 % per year for pesticides and even a 2.5 % for herbicides and fungicides (CropLife International, 2007; Research, 2006; Thakore, 2006), still, the overall market of conventional pesticides is above 90 % compared with biopesticides (Bailey, Boyetchko, & Langle, 2010). One of the critical point in the development of biopesticides, including EPN, is the connection between the research and commercialization. Firstly, the new bioproducts should overpass the characteristics of conventional pesticides products, or at least, provide successful benefits under particular scenarios. Second, the development implies producing the documents required for the permits, following the regulations that are still unclear. At this moment, where IPM is the most recommended practice, and by law should be implemented in some countries, such as those belonging to EU, advancing on the clarification of those regulations and the new legal framework is urgent. Significant advances have been accomplished during the past years in the regulation and implementation of the biopesticides, which regulations and law directly affecting the EPN development for enterprises and other agents. In this chapter, issues related with the development and release of new bioproducts, such as those containing EPN, are illustrated. In particular, we cover the evolution related to the pesticides in EU, the environmental impact of their production with the example of the carbon footprint assessment and the potential non–target effects of the EPN release.

It Takes a Village: Entomopathogenic Nematode Community Structure and Conservation Biological Control in Florida (U.S.) Orchards

Root weevils in Florida comprise several species, Diaprepes abbreviatus L. (Coleoptera: Curculionidae), Pachnaeus litus Schoenherr (Coleoptera: Curculionidae), Pachnaeus opalus Schoenherr (Coleoptera: Curculionidae), Artipus floridanus Horn (Coleoptera: Curculionidae), Myllocerus undecimpustulatus Faust (Coleoptera: Curculionidae) and Naupactus godmani (Crotch) (Coleoptera: Curculionidae) being those which are commonly encountered in citrus orchards. The first two of these species are the most economically important arthropod pests of citrus other than Diaphorina citri Kuwayama (Hemiptera: Psyllidae), which vectors the devastating disease huanglongbing, Candidus liberobacter asiaticus Jagoueix (Rhizobiales: Rhizobiaceae) (Duncan, McCoy, Stansly, Graham, & Mizell, 2001; McCoy, 1999). We focus here on the most widely studied of these weevils, D. abbreviatus (commonly called Diaprepes root weevil); however, all of the species have similar life cycles, host plant interactions, and susceptibility to entomopathogenic nematodes (EPNs).