Jaime Ruiz-Vega

Mechanical production of pellets for the application of entomopathogenic nematodes: factors that determine survival time of Steinernema glaseri

Applications of infective juveniles (IJ) of entomopathogenic nematodes (EPN) formulated in pellets are still limited. This is principally due to limited advances in the technology of formulation. We aimed to develop a new method of mechanical formulation through material flow and to analyse its effect on the survival time of encapsulated EPN by varying the granular materials, the components of the aqueous suspension, the age of the nematodes and by applying a surface coating (C) to the pellet. Three-day-old and two-month-old Steinernema glaseri IJ were encapsulated with different proportions of diatomaceous earth (DE) and attapulgite clay (AC). The aqueous suspension containing the nematodes was prepared with double distilled water (DDW), varying proportions of Opuntia ficus-indica mucilage (OM) or gelatin (GL), and a sunflower oil surface treatment. The pellets were stored at an average room temperature of 23 ± 6°C. The best results were obtained with the following proportions: 100DE:0AC and 50DE:50AC, using the OM suspension, three-day-old nematodes and a surface C, which resulted in an average of 14 days survival time. These results confirmed that the nematodes do not die during mechanical encapsulation and that the age of the IJ as well as the loss of moisture during storage at room temperature were the factors that decreased the survival of encapsulated EPN. It was concluded that it is necessary to use neonate IJ and to reduce the moisture transfer rate in the granular structure in order to delay the desiccation of the encapsulated nematodes.

Inhibition of the growth and development of mosquito larvae of Culex quinquefasciatus (Diptera: Culicidae) treated with extract from leaves of Pseudocalymma alliaceum (Bignonaceae).

OBJECTIVE To determine larvicidal activity of the essential oil, hydrolat and botanical extracts derived from leaves of Pseudocalymma alliaceum on mosquito larvae of Culex quinquefasciatus. METHODS Groups of twenty larvae were used in the larvicidal assays. The mortality, relative growth rate, the larval and pupal duration and viability was estimated. The essential oil was analyzed by solid phase microextraction using gas chromatography coupled to mass spectrometry. RESULTS Essential oil at 800 ppm showed larvicidal activity at 24 h with lethal values of LC50 and LC90 of 267.33 and 493.63 ppm. The hydrolat at 20% and 10% on 2nd stage larvae showed 100% effectiveness after 24 h. The aqueous extract at 10% had a relative growth index of 0.58, while the ethanolic and methanolic extract obtained values of 0.76 and 0.70 and control reached 0.99. Larvae treated with 10% of methanol, ethanol and aqueous extract showed a reduction in larval duration of 5.00, 2.20 and 4.35 days; ethanol extract at 1% provoke decrease of 2.40 days in the development and exhibited an increment of 3.30 days when treated with 0.01%. Aqueous, ethanol and methanol extracts at 10% reduced in 6.15, 3.42 and 5.57 days pupal development. The main compounds were diallyl disulfide (50.05%), diallyl sulfide (11.77%) and trisulfide di-2-propenyl (10.37%). CONCLUSIONS The study demonstrated for the first time, the larvicidal activity of the essential oil and hydrolat of Pseudocalymma alliaceum; aqueous, ethanol and methanol extracts inhibited the normal growth and development of mosquito larvae, prolonging and delaying larval and pupal duration.

Effect of moisture evaporation from diatomaceous earth pellets on storage stability of Steinernema glaseri

ABSTRACT Induction of anhydrobiosis and storage stability of entomopathogenic nematodes are influenced by moisture availability. Decreasing moisture content in diatomaceous earth (DE) pellets containing the Steinernema glaseri NJ-43 strain and its effect on survival time and infectivity of the nematode were determined. Pelletisation was performed in a vortex mixer, using DE Celite® 209 as the desiccant material. Pellets were stored at room temperature (23 ± 2°C) and high relative humidity (96–100%). Nematode survival and infectivity against last instar greater wax moth, Galleria mellonella, were tested daily. Initial average and average equilibrium moisture content in pellets were 66.7% and 13.6%, respectively, and the infective juveniles mean survival time was 8.8 days. A moisture transfer model based on diffusion and evaporation was evaluated to predict moisture fluctuations within the pellets. We concluded that 84% of variation in S. glaseri infectivity on G. mellonella larvae was explained by the survival of the nematode, whereas 52% of variation in S. glaseri survival was explained by the loss of moisture from the pellets. The moisture transfer model achieved 78% reliability in predicting moisture content and fluctuations. Therefore, the mechanisms of moisture diffusion and evaporation from the surface to the surrounding atmosphere contribute significantly to moisture loss from the pellets.

Mechanical production of pellets for the application of entomopathogenic nematodes: effect of pre-acclimation of Steinernema glaseri on its survival time and infectivity against Phyllophaga vetula

ABSTRACT The low survival time and diminished infectivity by entomopathogenic nematodes (EPNs) from granular formulations limit their efficiency against agricultural insect pests. This study determined the benefit of pre-acclimating infective juveniles (IJs) of Steinernema glaseri (NJ-43 strain) on extending their mean survival time (STm) in diatomaceous earth (DE) pellets and increasing their infectivity against Phyllophaga vetula. The IJs were reared in Galleria mellonella larvae placed in Petri dishes containing plaster of Paris (PP) or modified White traps (WTs). Pelletisation was performed in a machine operating on the principle of laminar flow using DE Celite® 209. Pellets were stored at room temperature (23 ± 3°C) and high relative humidity (96–100%). IJs harvested from WTs between the 3rd and the 5th days after the onset of emergence were more infective on P. vetula and pre-acclimation of S. glaseri in PP increased significantly its STm in the pellets; from 23.1 to 34.5 days, compared with non-pre-acclimatised IJs from WTs. However, juveniles with or without pre-acclimation formulated in DE pellets failed to achieve significant control of P. vetula. These results are discussed in light of the relationship between EPN survival and host infection by EPNs with possible effects of the formulation in DE pellets.

Biological Control of Phyllophaga vetula (Horn)1 with Entomopathogenic Nematodes in Various Formulations and Moisture Conditions

Abstract. The aim of this study was to determine the possibility of using formulations of entomopathogenic nematodes in two soil moisture conditions for effective control of larvae of white grub, Phyllophaga vetula (Horn) (Coleoptera: Melolonthidae). Mortality of P. vetula larvae was compared using Steinernema glaseri Steiner, Heterorhabditis bacteriophora Poinar, and Steinernema feltiae Filipjev in three forms of application (formulated in cadavers of Galleria mellonella L. larvae, bentonite pellet, and aqueous suspension) and two soil moisture conditions (moderate,11.8%, and high, 20.5%). The difference among treatments was very significant: S. glaseri was the most effective nematode, killing 75% of larvae when applied in aqueous suspension with moderate moisture. Next most effective was S. glaseri in cadavers with the same moisture conditions that killed 55%. The nematodes H. bacteriophora and S. feltiae applied in all three forms (aqueous medium, infected cadaver, and bentonite pellet) and with the two moisture conditions (11.8 and 20.5%) were statistically similar to the check and did not control Ph. vetula.

Biological Control of Phyllophaga vetula (Horn)1, and Lethal Concentrations and Times of Entomopathogenic Nematodes

Abstract. Numbers of Phyllophaga vetula (Horn) (Coleoptera: Melolonthidae) larvae killed after application of nematodes Steinernema glaseri Steiner, Heterorhabditis bacteriophora Poinar, and Steinernema feltiae Filipjev at five concentrations (50, 100, 200, 500, and 1,000 nematodes per larva) in aqueous suspension were compared. Lethal concentrations and times for each species were determined. The difference between the treatments was very significant. The nematode most effective for pest control was S. glaseri at a dose of 1,000 per larva that killed 97.5%. H. bacteriophora at the same dose killed 87.5%, and S. feltiae killed 60.0%. With 500 per larva, all three nematodes were statistically the same. S. glaseri at any concentration had the lowest lethal concentration (LC50 and LC95) and lethal time (LT50 and LT95), followed by H. bacteriophora and S. feltiae. The three species of nematodes showed a positive dose-response relationship.

Evaluación de la Virulencia de Steinernema riobrave y Rhabditis blumi contra Larvas del Tercer Instar de Spodoptera frugiperda1

Resumen. Se evaluó la virulencia de los nematodos Steinernema riobrave (Poinar y Raulston, 1994) y la de un aislamiento nativo de Rhabditis blumi (Sudhaus, 1974) contra gusano cogollero del maíz Spodoptera frugiperda (J.E. Smith). Ambos nematodos fueron usados para inocular larvas del tercer instar de desarrollo concentraciones de 100, 250, y 500 juveniles infectivos (JI) por larva y determinar la mortalidad de las larvas cada 24 h durante 7 días. El nematodo S. riobrave causó 90% de mortalidad a 500 JI, 96 h después de la inoculación, mientras que con la especie R. blumi no hubo mortalidad de larvas a las concentraciones y tiempo de evaluación. El nematodo S. riobrave tuvo alta virulencia, por lo que esta especie se consideran viable para usarse en una prueba de efectividad para el control de S. frugiperda en campo.

Isolation and Identification of Native Entomopathogenic Nematodes (Nematoda: Rhabditidae) and Potential for Controlling Scyphophorus acupunctatus in a Laboratory

Abstract. Entomopathogenic nematodes are potential control agents for insect pests in cryptic habitats and are found in many environments worldwide. Native entomopathogenic nematodes were collected from March to June 2012 in soil from agave (Agave angustifolia Haw) fields in the Central Valleys of Oaxaca to evaluate potential for control of agave weevil, Scyphophorus acupunctatus Gyllenhal (Coleoptera: Curculionidae). The technique of insect-baiting with larvae of Galleria mellonella (L.) was used. Using sequencing internal transcribed spacer regions of ribosomal DNA and the 28s or subunit, Steinernema websteri Cutler & Stock and Steinernema carpocapsae (Weiser) Wouts, Mracek, Gerdin & Bedding nematodes were identified. The entomopathogenicity of the nematodes was verified by Kochs postulates. The efficacy of the strains at concentrations of 100, 500, and 1,000 infective juveniles per milliliter was tested on S. acupunctatus larvae in Petri dishes. Both nematode species at concentrations of 500 and 1,000 infective juveniles per larva killed 85–100% of agave weevils. The lethal mean concentrations (LC50) were 168 infective juveniles of S. websteri and 147 of S. carpocapsae, while the LC90 values were 890 and 3,739 infective juveniles per larva, respectively. This study is the first report of a native S. websteri strain in Mexico, which is proposed as a potential biological control agent against S. acupunctatus.

Indicators of Agroecological Sustainability of Three Tillage Systems for Maize (Zea mayz L.) Production

Of the three tillage systems studied, the plots under the full animal traction system showed the largest values for total dry matter production as well as for the indicators of soil quality, crop health, and socioeconomic sustainability. Overall, the indicators that contributed the most to a higher soil quality ranking were: biological activity, soil structure, and soil cover. In the mixed traction and fully mechanized systems, the indicators that decreased plant health most were the use of mono-cropping and a low surrounding biodiversity. The sites with higher total value for socioeconomic indicators had smaller indebtedness and subsidy dependence, as well as a higher control of local resources.