Efficacy of entomopathogenic nematodes against soil-dwelling life stages of western flower thrips, Frankliniella occidentalis (Thysanoptera: Thripidae).

The efficacy of six entomopathogenic nematode (EPN) strains was tested in a laboratory study against soil-dwelling life stages of western flower thrips (WFT), Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae). The EPN strain collections screened included two Heterorhabditis bacteriophora species, i.e., H. bacteriophora HK3 (H.b H) and H. bacteriophora HB Brecan (H.b B), three Steinernema feltiae species, i.e., S. feltiae Sylt (S.f S), S. feltiae OBSIII (S.f O), and S. feltiae strain CR (S.f C), and the S. carpocapsae strain DD136 (S.c D). All soil-dwelling life stages of WFT were susceptible to the tested EPN strains. The most virulent strains were S.f S, S.c D, and H.b H. The S.f O strain was highly virulent against late second instar larvae and prepupae of WFT under high soil moisture conditions, but less effective against pupae under comparatively drier soil conditions. Results from dose rate experiments indicate that a comparatively high concentration of 400 infective juveniles (IJs) per cm(2) was needed to obtain high mortality in all soil-dwelling life stages of WFT. However, dose rates of 100-200 IJs/cm(2) already caused 30-50% mortality in WFT. The chances for combining EPNs with other biological control agents of WFT are discussed.     

Rapid age-related changes in infection behavior of entomopathogenic nematodes

Nonfeeding infective juvenile (IJ) entomopathogenic nematodes (EPNs) are used as biological agents to control soil-dwelling insects, but poor storage stability remains an obstacle to their widespread acceptance by distributors and growers as well as a frustration to researchers. Age is one factor contributing to variability in EPN efficacy. We hypothesized that age effects on the infectiousness of IJs would be evident within the length of time necessary for IJs to infect a host. The penetration behavior of "young" (<1-wk-old) and "old" (2- to 4-wk-old) Heterorhabditis bacteriophora (GPS 11 strain), Steinernema carpocapsae (All strain), and Steinernema feltiae (UK strain) IJs was evaluated during 5 "exposure periods" to the larvae of the wax moth, Galleria mellonella. Individual larvae were exposed to nematode-infested soil for exposure periods of 4, 8, 16, 32, and 64 hr. Cadavers were dissected after 72 hr, and the IJs that penetrated the larvae were counted. Larval mortality did not differ significantly between 72- and 144-hr "observation periods," or points at which larval mortality was noted, for any age class or species. However, age and species effects were noted in G. mellonella mortality and nematode penetration during shorter time periods. Initial mortality caused by S. carpocapsae and H. bacteriophora IJs declined with nematode age but increased with S. feltiae IJ age. Young S. carpocapsae IJs penetrated G. mellonella larvae at higher rates than old members of the species (27-45% vs. 1-4%). Conversely, old S. feltiae IJs had higher penetration rates than young IJs (approximately 8 to 57% vs. 4 to approximately 31%), whereas H. bacteriophora IJs had very low penetration rates regardless of age (3-5.6%). Our results show that the effect of age on IJ infectiousness can be detected in IJs aged only 2 wk by a 4-hr exposure period to G. mellonella. These results have important implications for storage and application of EPNs and suggest the possibility of shortening the time required to detect nematodes in the soil.     

Controlling the sugar beet fly Pegomyia mixta Vill. with entomopathogenic nematodes

Sugar beet, Beta vulgaris L. is a strategic crop of sugar industry in Egypt. It is threatened by several insect pests among most important of them is the beet fly Pegomyia mixta. This work deals with the biological control of this insect using four entomopathogenic nematodes (EPNs). The nematodes included Steinernema carpocapsae S2, Steinernema feltiae, Heterorhabditis bacteriophora (HB1-3) and Heterorhabditis bacteriophora S1. Daily mortality of larvae and pupae of P. mixta were recorded after treatment with serial concentrations (500, 1000, 2000 and 4000 infective juveniles (IJs)/ml) of each of four studied EPNs. In the laboratory all tested nematodes killed the larvae inside their mines in the sugar beet leaves and developed in their bodies in different extends. They also killed the insect pupae in the soil and developed in their bodies. Young larvae were more susceptible than old ones. New pupae were more susceptible than old ones. In the field a single spray of S. feltiae or H. bacteriophora caused 81.3 or 75.9% reduction in the larval population of the in sugar beet leaves.     

Comparison of Bioassays to Measure Virulence of Different Entomopathogenic Nematodes

Five bioassays were compared for their usefulness to determine the virulence of four nematode strains. The objective of this study was to develop standard assays for particular nematode species. In all assays, the nematodes Steinernema feltiae (strain UK), S. riobravis, S. scapterisci Argentina and Heterorhabditis bacteriophora HP88 were exposed to Galleria mellonella larvae. All bioassays except the sand column assay were conducted in multi-well plastic dishes. In the penetration rate assay, the number of individual nematodes invading the insect was determined after a 48-h exposure to 200 infective juveniles (IJs). In the one-on-one assay, each larva was exposed to an individual nematode for 72 h before insect mortality was recorded. In the exposure time assay, insect mortality was recorded after exposure to 200 IJs for variable time periods. The dose-response assay involved exposing larvae to different nematode concentrations over the range 1-200 IJs/insect and recording mortality every 24 h for a 96-h period. In the sand columns assay, insects were placed in the bottom of a plastic cylinder filled with sand. Nematodes were applied on top of the sand and insect mortality was determined after IJs had migrated through the cylinder. The highest mortality level in the sand column assay was obtained with IJs of S. feltiae followed by H. bacteriophora; treatments with S. riobravis and S. scapterisci produced low levels of insect mortality. In the other four assays, S riobravis was the most virulent, followed by S. feltiae, H. bacteriophora and S. scapterisci. In the exposure time assay, rapid mortality was achieved when the insects were exposed to S. feltiae and S. riobravis. For these nematode species, a gradual increase in the number of individuals which penetrated into cadavers was recorded. Conversely, the number of nematodes in the cadavers of insects infected by H. bacteriophora and S. scapterisci remained low during the entire exposure period. In this assay, exposing the insects to these nematodes resulted in a gradual increase in mortality. In the dose-response assay, complete separation among nematode species was obtained only after 48 h of incubation at a concentration of 15 IJs/insect. LD and LD values were calculated from 50 90 dose-response assay data. However, these values did not indicate differences among the different nematode species. The present study demonstrated the variation in entomopathogenic nematode performance in different bioassays and supports the notion that one common bioassay cannot be used as a universal measure of virulence for all species and strains because nematodes differ in their behavior. Furthermore, particular assays should be used for different purposes. To select a specific population for use against a particular insect, assays that are more laborious but which simulate natural environmental conditions (e.g. the sand column assay) or invasion by the nematode (e.g. the penetration rate assay) should be considered. In cases where commercial production batches of the same nematode strains are compared, simple and fast assays are needed (e.g. the one-on-one and exposure time assays). Further studies are needed to determine the relationships between data obtained in each assay and nematode efficacy in the field.     

Evaluation of entomopathogenic nematodes for control of the beetle, Luperomorpha suturalis Chen (Col., Chrysomelidae)

Abstract: The strains Steinernema feltiae Otio and A54, Steinernema ceratophorum D43 and Steinernema carpocapsae BJ were tested for their infectivity to the larvae and pupae of beetle ( Luperomorpha suturalis Chen) at 25 ± 0.5°C and 15 ± 0.5°C in laboratory conditions. The results, based on comparison of the insect mortalities and nematode penetration rates among four nematode strains, showed that S. feltiae Otio was a potential biocontrol agent of the larvae and pupae of L. suturalis . The mortalities of the larvae and pupae exposed to S. feltiae Otio strain were 95.8 and 97.1% at 25 ± 0.5°C and 78.0 and 83.0% at 15 ± 0.5°C, respectively. The nematode penetration rates of S. feltiae Otio of the larvae and pupae were 15.6 and 19.0% at 25 ± 0.5°C, 2.6 and 6.3% at 15 ± 0.5°C, respectively. Field efficacy of S. feltiae Otio strain was examined against beetle larvae in Hebei province, northern China. The population reduction of insect larvae was 77.8 and 13.9% at doses of 30 and 15 infective juveniles (IJs)/cm² of S. feltiae Otio after 38 days of treatment and 90.2 and 92.4% after 100 days of treatment. However, the population of the insect larvae was reduced only to 15.5 and 15.7% when treated with pesticide after 38 and 100 days, respectively. The efficiency between the two nematode doses was not significantly different but it was remarkably higher than that of the pesticide after 100 days of application. The results suggest that S. feltiae Otio strain could be an alternative to pesticide for beetle control.     

Biocontrol Potential of Entomopathogenic Nematodes Against Winter Moths (Operophtera brumata and O. fagata) (Lepidoptera: Geometridae) Infesting Urban Trees

Infectivity and biocontrol potential of entomopathogenic nematodes against winter moths (Operophtera brumata and O. fagata)pupating in the soil were examined in laboratory, semi-field and field conditions. A pilot experiment conducted in the field showed that Steinernema feltiae was completely ineffective against pupae of these moths in the soil. Subsequent laboratory tests revealed that none of the tested species (i.e. S. feltiae, S. affinae, S. carpocapsae, Heterorhabditis megidis and H. bacteriophora) could colonise the pupae, while mature larvae descending to the soil for pupation and prepupae were highly susceptible to nematode infection. No differences were observed between O. brumata and O. fagata in susceptibility to nematodes. In laboratory experiments H. megidis applied at 1.5×10⁵infective juveniles (IJ) m^-2infected almost 100% of insects exposed for 6 days in the soil. It was significantly more infective than H. bacteriophora (73-77%) and Steinernema species (29-50%). H. megidis was also highly effective in semi-field conditions when applied at an even lower dose, i.e. 10⁵IJ m^-2. After a 45-day experiment, only 3% of insects descending for pupation survived in the soil pre-treated with this species. This was significantly less than in soil with S. feltiae (43%) and control treated with water only (59%). Very high efficacy of H. megidis and a relatively easy method for its field application through ground spraying gives some promise for environmentally safe and successful biological control of winter moths during their pupation in the soil. The low application rate required and recycling in the host could be additional advantages for economic and long lasting protection of high value trees, particularly those in urban parks and forests.     

Assessing the Potential of Entomopathogenic Nematodes to Control the Grape Root Borer Vitacea polistiformis (Lepidoptera: Sesiidae) Through Laboratory and Greenhouse Bioassays

Seventeen entomopathogenic nematode species and strains were evaluated for virulence to the grape root borer, Vitacea polistiformis (Harris) in laboratory and greenhouse bioassays. Heterohabditis bacteriophora strain GPS11 and H. zealandica strain X1 produced a larval mortality rate of over 85% of larvae embedded in the root cambium in laboratory bioassays. The nematode species H. marelata and H. bacteriophora strain Oswego produced mortality rates of over 75%. Of the Steinernema species tested, S. carpocapsae strain 'All' performed the best with a mortality rate of 69%. All other nematode species and strains tested, with the exception of S. bicornutum , produced some degree of larval mortality. In the greenhouse bioassays, 93% control was achieved with H. zealandica strain X1 applied at 4 ×109 infective juveniles (IJs) acre1 -1 (9.88 ×10 9 IJs ha -1 ). H. bacteriophora strain GPS11 successfully reproduced in grape root borer larvae. The numbers of IJs produced within infected larvae were related to larval size. The survival rate of neonate larvae on grape root sections was 61%, which thus provides a means to rear the neonate larvae for bioassays.     

Laboratory Evaluation of Seven Pakistani Strains of Entomopathogenic Nematodes Against a Stored Grain Insect Pest, Pulse beetle Callosobruchus chinensis (L.)

Seven Pakistani strains of entomopathogenic nematodes belonging to the genera Steinernema and Heterorhabditis were tested against last instar and adult stages of the pulse beetle, Callosobruchus chinensis (L.). These nematodes included Steinernema pakistanense Shahina, Anis, Reid and Maqbool (Ham 10 strain); S. asiaticum Anis, Shahina, Reid and Rowe (211 strain); S. abbasi Elawad, Ahmad and Reid (507 strain); S. siamkayai Stock, Somsook and Reid (157 strain); S. feltiae Filipjev (A05 strains); Heterorhabditis bacteriophora Poinar (1743 strain); and H. indica Poinar, Karunakar and David (HAM-64 strain). Activity of all strains was determined at four different nematode densities in Petri dishes and in concrete containers. A significant nematode density effect was detected for all nematode species tested. Overall, Heterorhabditis bacteriophora, S. siamkayai, and S. pakistanense were among those that showed the highest virulence to pulse beetle larvae and adults. For all nematode species, the last larval stage of the pulse beetle seems to be more susceptible than the adult. LC(50) values in Petri dish and concrete containers were 14-340 IJs/larvae and 41-441 IJs/larvae, respectively, and 59-1376 IJs/adult and 170-684/adult, respectively.     

Efficacy of entomopathogenic nematode Steinernema feltiae (Rhabditida: Steinernematidae) as influenced by Frankliniella occidentalis (Thysanoptera: Thripidae) developmental stage and host plant stage

Entomopathogenic nematodes were investigated as an alternative biological control strategy for western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), in ornamental greenhouse crops, by using potted chrysanthemum as a model crop. The susceptibility of various life stages of F. occidentalis to different concentrations of the nematode Steinernema feltiae (Filipjev) (Rhabditida: Steinernematidae) was investigated in petri dish bioassays. This was followed with trials using potted chrysanthemums comparing the efficacy of nematode application to plants in vegetative (exposed habitat) versus flowering (cryptic habitat) stages. In both trials, the effect of the wetting agent Agral 90 (nonylphenoxy polyethoxyethanol), which is used in combination with the nematode spray, on F. occidentalis mortality was assessed. In petri dish trials, the prepupae and pupae were the most susceptible developmental stages of F. occidentalis to infection by S. feltiae. First and second instars were killed by very high rates of nematodes (> or =20,000 infective juveniles per milliliter), but corrected mortality was only approximately 28-37%. No significant mortality was observed for adult thrips. Results from the petri dish trials were confirmed on chrysanthemum plants. Foliar application of S. feltiae did not result in significant mortality in larvae or adults. No significant differences in efficacy were detected by application of nematodes on vegetative versus flowering chrysanthemum. Agral 90 had a significant impact on mortality on the first stage larvae and prepupae in the petri dish trials but not in the plant trials. Thrips control by S. feltiae in greenhouses may be partly or completely due to prepupal and pupal mortality.     

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.     

Assessment of establishment and persistence of entomopathogenic nematodes for biological control of western corn rootworm

Abstract:  The use of entomopathogenic nematodes (EPN) is potentially one ecological approach to control the invasive alien western corn rootworm ( Diabrotica virgifera virgifera LeConte, Col., Chrysomelidae) in Europe. This study investigated the establishment and the short- and long-term persistence of Heterorhabditis bacteriophora Poinar (Rhabditida: Heterorhabditidae), Heterorhabditis megidis Poinar, Jackson and Klein (Rh., Heterorhabditidae) and Steinernema feltiae Filipjev (Rh., Steinernematidae) in three maize fields in southern Hungary, using the insect-baiting technique. All three EPN species equally established and persisted in maize fields. The timing of application (April or June) did not influence the establishment of EPN species. EPNs persisted for 2–5 months, i.e. they survived up to and throughout D. v. virgifera larval occurrence in the soil. Results demonstrate that D. v. virgifera larvae can potentially be controlled by EPNs during the same year of EPN application but no long-term control effect is expected under intensive maize cultivation practices.     

Factors affecting entomopathogenic nematodes (Steinernematidae) for control of overwintering codling moth (Lepidoptera: Tortricidae) in fruit bins

Fruit bins infested with diapausing codling moth larvae, Cydia pomonella (L.), are a potential source of reinfestation of orchards and may jeopardize the success of mating disruption programs and other control strategies. Entomopathogenic nematodes (EPNs) were tested as a potential means of control that could be applied at the time bins are submerged in dump tanks. Diapausing cocooned codling moth larvae in miniature fruit bins were highly susceptible to infective juveniles (IJs) of Steinernema carpocapsae (Weiser) and Steinernema feltiae (Filipjev) in a series of experiments. Cocooned larvae are significantly more susceptible to infection than are pupae. Experimental treatment of bins in suspensions of laboratory produced S. feltiae ranging from 10 to 100 IJs/ml of water with wetting agent (Silwet L77) resulted in 51-92% mortality. The use of adjuvants to increase penetration of hibernacula and retard desiccation of S. feltiae in fruit bins resulted in improved efficacy. The combination of a wetting agent (Silwet L77) and humectant (Stockosorb) with 10 S. feltiae IJs/ml in low and high humidity resulted in 92-95% mortality of cocooned codling moth larvae versus 46-57% mortality at the same IJ concentration without adjuvants. Immersion of infested bins in suspensions of commercially produced nematodes ranging from 10 to 50 IJs/ml water with wetting agent in an experimental packing line resulted in mortality in cocooned codling moth larvae of 45-87 and 56 - 85% for S. feltiae and S. carpocapsae, respectively. Our results indicate that EPNs provide an alternative nonchemical means of control that could be applied at the time bins are submerged in dump tanks at the packing house for flotation of fruit.     

Combined releases of entomopathogenic nematodes and the predatory mite Hypoaspis aculeifer to control soil-dwelling stages of western flower thrips Frankliniella occidentalis

The effect of the predatory miteHypoaspis aculeifer Canestrini (Acarina:Laelapidae) on soil-dwelling stages of thewestern flower thrips (WFT) Frankliniellaoccidentalis Pergande (Thysanoptera: Thripidae)and the influence of combined releases of H.aculeifer and two entomopathogenic nematodes(EPNs) Heterorhabditis bacteriophora Poinar(Rhabditida: Heterorhabditidae) (strain HK3,HK3) and Steinernema feltiae Filipjev(Rhabditida: Steinernematidae) (Nemaplus®,SFN) were investigated in pot trials usingseedlings of green beans (Phaseolus vulgarisL.). Ten H. aculeifer adults per pot and 400infective juveniles (IJs) cm^–2 soil, of the twoEPN strains were used. In comparison withuntreated control, H. aculeifer reduced theproportion of adult F. occidentalis emergenceby 46%, while SFN and HK3 led to a reductionin adult thrips emergence by 46% and 61%,respectively. Significant differences in adultWFT emergence were found between combinedtreatments of EPNs and H. aculeifer, andindividual applications of EPNs and/or H.aculeifer, with significantly lower adultthrips emergence in the combined treatments.These findings highlight the potential for acombined use of EPNs with H. aculeifer for thecontrol of soil-dwelling stages of thrips.     

Efficacy of entomopathogenic nematodes against potato tuber moth,Phthorimaea operculella (Lepidoptera: Gelechiidae) under laboratory conditions

The susceptibility of potato tuber moth, Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae) to native and commercial strains of entomopathogenic nematodes (EPNs) was studied under laboratory conditions. Native strains of EPNs were collected from northeastern Iran and characterised as Steinernema feltiae and Heterorhabditis bacteriophora (FUM 7) using classic methods as well as analysis of internal transcribed spacer (ITS) and D2/D3 sequences of 28S genes. Plate assays were performed to evaluate the efficiency of five EPN strains belonging to four species including Steinernema carpocapsae (commercial strain), S. feltiae, Steinernem glaseri and H. bacteriophora (FUM 7 and commercial strains). This initial assessment with 0, 75, 150, 250, 375 and 500 IJs/ml concentrations showed that S. carpocapsae and H. bacteriophora caused the highest mortality in both larval and prepupal stages of P. operculella, PTM. Thereafter, these three strains (i.e. S. carpocapsae, H. bacteriophora FUM 7 and the commercial strains) were selected for complementary assays to determine the effects of soil type (loamy, loamy–sandy and sandy) on the virulence of EPNs against the second (L2) and fourth instar (L4) larvae as well as prepupa. A soil column assay was conducted using 500 and 2000 IJs in 2-ml distilled water. Mortality in the L2 larvae was not affected by the EPN strain or soil type, while there was a significant interactive effect of nematode strains and soil type on larval mortality. The results also showed that EPN strains have higher efficiency in lighter soils and caused higher mortality on early larvae than that in loamy soil. In L4 larvae, mortality of PTM was significantly influenced by nematode strain and applied concentrations of infective juveniles. The larval mortality induced by S. carpocapsae was higher than those caused either by a commercial or the FUM 7 strain of H. bacteriophora. Prepupa were the most susceptible stage.     

Infectivity of entomopathogenic nematode Steinernema carpocapsae Pocheon strain (Nematoda: Steinernematidae) on the green peach aphid Myzus persicae (Hemiptera: Aphididae) and its parasitoids

Infectivity of entomopathogenic nematode (EPN) Steinernema carpocapsae Pocheon strain on the green peach aphid Myzus persicae and its parasitic wasps (e.g., Aphidius colemani, Aphidius gifuensis and Diaeretiella rapae) was evaluated under laboratory conditions. Infective juveniles (IJs) of S. carpocapsae Pocheon strain had low infectivity against nymph and adult stages of M. persicae, showing 2% and 6.7% of mortality, respectively. Application of the EPNs had little effect on mummies caused by the three parasitoid species, allowing them to remain intact. No IJ invaded the host, regardless of EPN application rate. The parasitoid emergence from mummies ranged from 80% to 85% in the presence of EPN while 79–86% was recorded in the absence of EPN. However, the presence of the IJs reduced oviposition by the three parasitoid species, decreasing the rate up to 59% when the nematodes were applied before parasitoid release, while little difference in oviposition was observed when nematodes were applied after parasitoid release.     

病原线虫对桔小实蝇种群的控制作用

通过室内和田间实验研究了昆虫病原线虫对桔小实蝇Bactrocera (Bactrocera) dorsalis (Hendel)的控制作用。室内实验结果表明,供试的3种线虫的4个品系（小卷蛾斯氏线虫Steinernema carpocapsae All品系与A24品系,夜蛾斯氏线虫Steinernema feltiae SN品系和嗜菌异小杆线虫Heterorhabditis bacteriophora H06品系）,以小卷蛾斯氏线虫All品系对桔小实蝇的侵染力最强,其3天的LD₅₀和LD₉₅分别为35.0和257.1条/cm²土壤。按300条/cm²土壤的量施用,小卷蛾斯氏线虫All品系对当代桔小实蝇的控制效果为86.3%。用以虫期作用因子组建的生命表方法评价了小卷蛾斯氏线虫All品系对田间桔小实蝇下代种群的控制作用,结果表明,按300条/cm²土壤的量施用线虫,对照杨桃园的桔小实蝇种群趋势指数为105.9,而处理杨桃园的桔小实蝇种群趋势指数下降为15.5;小卷蛾斯氏线虫All品系对桔小实蝇的干扰控制指数为0.146,即线虫处理果园的下代种群密度仅为对照果园的14.6%。     

Compatibility of entomopathogenic nematodes with fipronil

The survival and infectivity of infective juveniles (IJs) of three species of entomopathogenic nematodes, Steinernema carpocapsae Weiser, S. arenarium (Artyukhovsky) (Rhabditida: Steinernematidae) and Heterorhabditis bacteriophora Poinar (Rhabditida: Heterorhabditidae), were determined after exposure to different concentrations (250, 500, 1000 and 2000 ppm) of fipronil, an insecticide acting on the GABA receptors to block the chloride channel. Heterorhabditis bacteriophora was very tolerant to all concentrations of fipronil, with the highest mortality of 17% being observed at 2000 ppm of fipronil after 72 h exposure. Steinernema carpocapsae showed a similar response, with the highest mortality of 11.25% of IJs being observed after 72 h exposure to 2000 ppm of fipronil. Steinernema arenarium was, however, more sensitive to fipronil, and at 2000 ppm mortality rates of 94.6% and 100% were observed after 24 and 72 h, respectively. Fipronil had negligible effects on the infectivity of the three nematode species tested. The IJs which survive exposure to all concentrations of fipronil tested can infect and reproduce in Galleria larvae. The moderate effects on entomopathogenic nematodes of a lower fipronil concentration (250 ppm) and the field rates (12-60 ppm) of fipronil used as insecticide, suggest that direct mixing of entomopathogenic nematodes and fipronil at field rates is a viable integrated pest management option.     

Efficacy and Persistence of Entomopathogenic Nematodes in Controlling Larval Populations of Thaumetopoea pityocampa (Lepidoptera: Thaumetopoeidae)

A 3-year study was conducted in a Pinus halepensis reforestation of Apulia Region (Southern Italy) injecting IJs (infective juveniles) of Steinernema feltiae , S. carpocapsae and Heterorhabditis bacteriophora in aqueous and gel suspensions (Idrosorb SR 2002 [Nigem ® ], and Compex) into the nests of Thaumetopoea pityocampa caterpillar. This study showed that the gel suspensions do not percolate and that slow release of water from the gels allowed nematodes to survive and complete their life cycle in the host. Results demonstrate the feasibility of reducing overwintering larval populations by injecting gel suspension of S. feltiae . We found no negative effects on the endoparasite Phryxe caudata .     

Field Efficacy of Entomopathogenic Nematodes against the Sugar-beet Weevil Temnorhinus ( = Conorrhynchus ) mendicus Gyll. (Coleoptera: Curculionidae)

In 1992 and 1993, the field effectiveness of Heterorhabditis sp. (NL-HL81 strain), H. bacteriophora (HP 88 strain) and Steinernema carpocapsae ('All' strain) against the larvae of Temnorhinus mendicus Gyll. was assessed. The biological tests were compared with two chemical treatments (cypermethrin or deltamethrin) and one untreated control. In 1992, S. carpocapsae gave better results than Heterorhabditis sp. in reducing the percentage of infested roots, as compared with the untreated sample and the chemical one; similarly, the irrigated control gave the best results. In 1993, three concentrations of entomopathogenic nematodes (EPNs) were tested: 0.250 106 infective juveniles (IJs) m - 2, 0.125 106 IJs m - 2 and 0.075 106 IJs m - 2. The different numbers of EPNs did not give very different results from each other; however, H. bacteriophora at 0.075 106 IJs m - 2 was the least effective. In general, cypermethrin was more effective than deltamethrin, but one treatment with EPNs followed by irrigation was always more effective than two chemical applications.     

Susceptibility of the boll weevil to Steinernema riobrave and other entomopathogenic nematodes

The susceptibility of the boll weevil (BW), Anthonomus grandis Boheman, to Steinernema riobrave and other nematode species in petri dishes, soil (Hidalgo sandy clay loam), and cotton bolls and squares was investigated. Third instar weevils were susceptible to entomopathogenic nematode (EN) species and strains in petri dish bioassays at 30 degrees C. Lower LC(50)'s occurred with S. riobrave TX- 355 (2 nematodes per weevil), S. glaseri NC (3), Heterorhabditis indicus HOM-1 (5), and H. bacteriophora HbL (7) than H. bacteriophora IN (13), S. riobrave TX (14), and H. bacteriophora HP88 (21). When infective juveniles (IJs) of S. riobrave were applied to weevils on filter paper at 25 degrees C, the LC(50) of S. riobrave TX for first, second, and third instars, pupae, and 1-day-old and 10-days-old adult weevils were 4, 5, 4, 12, 13, and 11IJs per weevil, respectively. The mean time to death, from lowest to highest concentration, for the first instar (2.07 and 1.27days) and second instar (2.55 and 1.39days) weevils were faster than older weevil stages. But, at concentrations of 50 and 100IJs/weevil, the mean time to death for the third instar, pupa and adult weevils were similar (1.84 and 2.67days). One hundred percent weevil mortality (all weevil stages) occurred 3days after exposure to 100IJs per weevil. Invasion efficiency rankings for nematode concentration were inconsistent and changed with weevil stage from 15 to 100% when weevils were exposed to 100 and 1IJs/weevil, respectively. However, there was a consistent relationship between male:female nematode sex ratio (1:1.6) and nematode concentration in all infected weevil stages. Nematode production per weevil cadaver increased with increased nematode concentrations. The overall mean yield of nematodes per weevil was 7680IJs. In potted soil experiments (30 degrees C), nematode concentration and soil moisture greatly influenced the nematode efficacy. At the most effective concentrations of 200,000 and 400,000IJs/m(2) in buried bolls or squares, higher insect mortalities resulted in pots with 20% soil moisture either in bolls (94 and 97% parasitism) or squares (92 and 100% parasitism) than those of 10% soil moisture in bolls (44 and 58% parasitism) or squares (0 and 13% parasitism). Similar results were obtained when nematodes were sprayed on the bolls and squares on the soil surface. This paper presents the first data on the efficacy of S. riobrave against the boll weevil, establishes the potential of EN to control the BW inside abscised squares and bolls that lay on the ground or buried in the soil.