Efficacy of entomopathogenic nematodes against neonate larvae of <Emphasis Type="Italic">Capnodis tenebrionis</Emphasis> (L.) (Coleoptera: Buprestidae) in laboratory trials

The efficacy of five entomopathogenic nematode strains of the families Steinernematidae and Heterorhabditidae was tested against the neonate larvae of Capnodis tenebrionis. The nematode strains screened included two of Steinernema carpocapsae (Exhibit and M137), and one each of S. feltiae (S6), S. arenarium (S2), and Heterorhanditis bacteriophora (P4). Exposure of neonate larvae of Capnodis to 10 and 150 infective juveniles (IJs) per larva (equivalent to 3 and 48 IJs/cm² respectively) in test tubes with sterile sand, resulted in mortality between 60–91% and 96–100%, respectively. At a concentration of 150 IJs/larva, all of the nematode strains were highly virulent. Both S. carpocapsae strains (Exhibit and M137) caused infection and mortality to larvae more quickly than the other strains. However, at a lower concentration assay (10 IJs/larva), S. arenarium was the most virulent strain. The penetration rate as an indicator of entomopathogenic nematode infection was also evaluated. The highest value was recorded for S. arenarium (36%), followed by H. bacteriophora (30.6%), S. feltiae (23.1%), and S. carpocapsae (20.7%).     

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.     

Selection responses and quantitative-genetic analysis of preadult performance on two host plants in the bean weevil, Acanthoscelides obtectus

The infectivity and biocontrol potential of entomopathogenic nematodes against two common urban tree leaf beetles (Altica quercetorum and Agelastica alni) pupating in the soil were examined under laboratory and semi‐field conditions. In the laboratory experiments, pre‐pupae and pupae of both insect species were shown to be highly susceptible to nematode infection when challenged in soil pre‐treated with the parasites’ infective juveniles. In general, Heterorhabditis megidis was more effective than Steinernema feltiae. However, significant differences were observed between individual isolates within the latter species. Nematodes developed and reproduced in cadavers of both insect species. A semi‐field experiment studying the biocontrol potential of selected nematode strains, conducted under the canopy of urban trees, confirmed the preliminary laboratory findings and revealed that H. megidis could eliminate most of the insects pupating in the soil, when applied at a relatively low dose of 10⁵ IJs m^?2. The potential of entomopathogenic nematodes as environmentally safe, effective, and economically viable agents for the biological control of tree leaf beetles in urban green areas is discussed.     

Differences in penetration routes and establishment rates of four entomopathogenic nematode species into four white grub species

We compared the penetration of the entomopathogenic nematodes Steinernema scarabaei (AMK001 strain), S. glaseri (NC1 strain), Heterorhabditis zealandica (X1 strain), and H. bacteriophora (GPS11 strain) into third-instars of the scarabs Popillia japonica, Anomala orientalis, Cyclocephala borealis, and Rhizotrogus majalis. When larvae were exposed to nematodes for 6-72 h larval mortality and nematode establishment rate and occasionally speed of kill often showed the same pattern within nematode-white grub combinations. But no two nematodes or white grub species had the same pattern for these observations for all white grub or nematode species, respectively. Mortality, establishment, and speed of kill followed a similar pattern for H. zealandica, S. glaseri, and S. scarabaei, but there was no clear relationship for H. bacteriophora. Significant nematode establishment was only observed after at least 48 h exposure in most nematode-white grub combinations. Faster establishment was observed only for H. zealandica in A. orientalis and R. majalis (after 24 h) and for S. scarabaei in P. japonica and R. majalis (after 12 h). Nematode establishment after 72 h in the different scarab species was generally low for S. glaseri (<1.5%) and H. bacteriophora (<3%), higher for H. zealandica (2-5%), and the highest for S. scarabaei (1-14%). However, in another experiment establishment was generally higher after 96h exposure. Nematode penetration sites were determined by comparing nematode establishment in larvae with mouth, anus, mouth+anus, or none sealed with glue. The trends for each nematode species were very similar in the different white grub species. H. zealandica and H. bacteriophora showed excellent cuticular penetration ability but may also penetrate through mouth and/or anus. S. glaseri also penetrated through the cuticle but lower establishment in larvae with mouth or mouth+anus sealed suggested that the mouth is an important penetration site. S. scarabaei showed a preference for the mouth as a penetration site, but it showed some cuticular penetration ability and may also use the anus as a penetration site. The methodology used cannot exclude that cuticular penetration also included penetration through the spiracles. To fully understand the effect of nematode and white grub species on nematode virulence, future studies will have to compare host immune response to the penetrating IJs and the role of the symbiotic bacteria in these interactions.     

Efficacy of entomopathogenic nematode,Steinernema carpocapsae against the diamondback moth,Plutella xylostella (L.) in laboratory condition

In vitro studies were carried out on the diamondback moth, Plutella xylostella larvae using an insect entomopathogenic nematode isolate, Steinernema carpocapsae obtained from the Koppert company, the Netherlands. Larvae of P. xylostella were collected from cabbage farms around Mashhad city of Iran. During the study, the responses of larvae at 25?°C for three periods of 24, 48 and 72?h with different concentrations of 0, 5, 10, 20, 40, 80, 160 and 320 third instar larvae of nematode (infective stage?=?IJs) per insect into 10?cm Petri dishes containing filter paper soaked with 1?ml of nematodes suspension were compared. Maximum mortality caused by S. carpocapsae nematode was 88% at 24?h, and it was 100% at 48 and 72 h. With increasing nematode population level and exposure time (ET in hour), mortality of P. xylostella larvae was increased. Based on probit analysis, LC₅₀ values of S. carpocapsae nematode in three test periods were 45.61, 12.02 and 40.80 IJs per insect, respectively. Initial ANOVA was performed for S. carpocapsae nematode. The effect of both nematode population levels (IJ) and ET on third instar larvae of the diamondback moth, P. xylostella and interaction between IJ and ET were significant. In general, it is recommended to apply this nematode in suitable condition for controlling diamondback moth.     

Evaluation of the efficacy of the entomopathogenic nematodes Heterorhabditis sp. against sap beetles (Coleoptera: Nitidulidae)

Absract Nitidulid beetles (Coleoptera) are considered serious pests of date palms throughout the world. They attack the ripe fruit, causing it to rot, and damage is reflected in both reduced yield and lower fruit quality. Previous studies demonstrated the susceptibility of larvae of this pest to entomopathogenic nematodes from the genus Heterorhabditidis. In the present study nematode efficacy was evaluated in greenhouse and field. In containers filled with soil, moderate reduction in insect emergence was achieved when the nematodes were applied at concentrations of 25 and 50 IJs/cm². However, the highest concentration (100 IJs/cm²) treatment resulted in a drastic reduction (by 70–90%) in emergence of the beetles. The lowest emergence was achieved by the IS-19 and IS-21 strains (>10%). Efficacy of the IS-19 strain was retained up to 7 days after application at a rate of 100 IJs/cm². When the insect larvae were introduced to the soil 2 weeks after nematode application, the percentage emergence of insects increased by 2–2.5 fold as compared to previous introductions but was still lower than in the control. Insect density per container did not have an effect on efficacy of the nematodes when the strains IS-19 and IS-12 were used. Two field trials were conducted in different sites in Israel. In the first trail, conducted in date palm orchard, four strains of Heterorhabditis sp. were tested. No significant difference in insect emergence was recorded among the various treatments or the control. Whereas in the second trial conducted in a fig orchard, substantial reduction (by 50–70%) in insect emergence was recorded following nematode treatment. Further studies, under natural conditions, are needed to optimize application efficiency and evaluate the commercial utilization of these biological control agents.     

Evaluation of chemical controls and entomopathogenic nematodes for control of Phyllophaga white grubs in a Fraser fir production field

The results of 2 yr of field trials evaluating various chemical and biological controls of Phyllophaga anxia (LeConte) white grubs in a Fraser fir [Abies fraseri (Pursh) Poir] Christmas tree production field are reported here. Chemical insecticides evaluated included bifenthrin, chlorantraniliprole, thiamethoxam, and time-released imidacloprid tablets (Coretect, Bayer CropScience, Research Triangle Park, NC). Entomopathogenic nematodes evaluated included Heterorhabditis bacteriophora (Poinar) and Steinernema carpocapsae (Weiser). Overall, the chemical controls provided the best root protection and grub control. Targeted treatments of an insecticide in the root zone may provide adequate tree protection and can be a way to reduce overall insecticide input compared with banded sprays. The nematode H. bacteriophora provided limited root protection and grub control, whereas S. carpocapsae did not provide effective control. Differences in efficacy and persistence of the two entomopathogenic nematode species can be attributed to the biology and environmental preferences of these organisms.     

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.     

Synergism of imidacloprid and entomopathogenic nematodes against white grubs: the mechanism

Entomopathogenic nematodes and the chloronicotinyl insecticide, imidacloprid, interact synergistically on the mortality of third-instar white grubs (Coleoptera: Scarabaeidae). The degree of interaction, however, varies with nematode species, being synergistic for Steinernema glaseri (Steiner) and Heterorhabditis bacteriophora Poinar, but only additive for Steinernema kushidai Mamiya. The mechanism of the interaction between imidacloprid and these three entomopathogenic nematodes was studied in the laboratory. In vials with soil and grass, mortality, speed of kill, and nematode establishment were negatively affected by imidacloprid with S. kushidai but positively affected with S. glaseri and H. bacteriophora. In all other experiments, imidacloprid had a similar effect for all three nematode species on various factors important for the successful nematode infection in white grubs. Nematode attraction to grubs was not affected by imidacloprid treatment of the grubs. Establishment of intra-hemocoelically injected nematodes was always higher in imidacloprid-treated grubs but the differences were small and in most cases not significant. The major factor responsible for synergistic interactions between imidacloprid and entomopathogenic nematodes appears to be the general disruption of normal nerve function due to imidacloprid resulting in drastically reduced activity of the grubs. This sluggishness facilitates host attachment of infective juvenile nematodes. Grooming and evasive behavior in response to nematode attack was also reduced in imidacloprid-treated grubs. The degree to which different white grub species responded to entomopathogenic nematode attack varied considerably. Untreated Popillia japonica Newman (Coleoptera: Scarabaeidae) grubs were the most responsive to nematode attack among the species tested. Untreated Cyclocephala borealis Arrow (Coleoptera: Scarabaeidae) grubs showed a weaker grooming and no evasion response, and untreated C. hirta LeConte (Coleoptera: Scarabaeidae) grubs showed no significant response. Chewing/biting behavior was significantly increased in the presence of nematodes in untreated P. japonica and C. borealis but not in C. hirta and imidacloprid-treated P. japonica and C. borealis. Our observations, however, did not provide an explanation for the lack of synergism between imidacloprid and S. kushidai.     

Storage of osmotically treated entomopathogenic nematode Steinernema carpocapsae

The infective juveniles (IJs) of Steinernema carpocapsae‘All’ were osmotically stressed by a mixture of ionic (fortified artificial seawater) and non‐ionic (3.2 mol/L glycerol) solutions to establish a method for osmotic storage of entomopathogenic nematodes. Seven combinations (termed solution A to G) with different proportions of these two solutions were tested, with sterile extra pure water (sepH₂O, termed solution H) as a control. The mortality of the IJs at a concentration of 5 × 10⁵ IJ/mL in the solutions A to G, and H were 13.2%, 16.2%, 16.7%, 13.5%, 25.2%, 31.6%, 44.6%, and 1.0%, respectively, after 21 days storage at 25°C. Most of the IJs shrunk and stopped motility after 6–9 hours incubation at 25°C in solutions A to D. Based on the results, solutions A to D and H were chosen to further test the osmotic survival of the IJs at different IJ concentrations (5 × 10⁵, 2.5 × 10⁵, 2 000 IJ/mL) and incubation temperature (30°C, 25°C, 10°C). The resulting IJs were exposed to a high temperature assay (45°C for 4 h, HTA). Osmotically stressed IJs showed improved heat tolerance. The mortality of the IJs increased with the increasing concentrations of the test IJs and the storage temperatures after exposing to the HTA. More than 88.4%, 62.3% or 2.4% of the treated IJs died at the above three IJ concentrations, respectively. At the three IJ concentrations (2 000 IJs/mL, 2.5 × 10⁵ IJs/mL or 5 × 10⁵ IJs/mL), the highest mortality was recorded in solution D (11.6%, 85.9% or 98.0%, respectively), and the lowest mortality in solution B (2. 4%, 62.3% or 86.6%, respectively). No untreated IJs survived after the heat treatment. During 42 days storage at 10°C, the IJs mortality in the solutions A to D and H were 7.19%, 5.97%, 4.41%, 4.34%, and 4.34% respectively, and showed no significant differences. In conclusion, osmotic treatment of the IJs of S. carpocapsae‘All’ in a mixture of ionic and non‐ionic solutions enhances the heat tolerance. The mortality of the IJs after HTA increased with the increasing concentrations of the test IJs and the storage temperatures after exposure to the HTA. The result is promising for the osmotic storage of the entomopathogenic nematodes.     

Infectivity of Steinernema mushtaqi (Rhabditida: Steinernematidae) against insect pests and their mass production

The infectivity of entomopathogenic nematode (EPN), Steinernema mushtaqi was tested against legume pod borer, Maruca vitrata, tobacco caterpillar, Spodoptera litura, blue butterfly, Lampides boeticus, red hairy caterpillar, Amsacta moorei, brown bug, Clavigralla gibbosa, mealy bug, Centrococcus somatics, fruit borer, Earias vittella and green bug, Nezara viridula larvae and in vivo mass production of the above-tested species of EPN have been carried out during 2008. S. mushtaqi was found to be more pathogenic to A. moorei, as it brought about 100% mortality within 48 h, than to S. litura, L. boeticus, N. viriduala and E. vittella, as mortality occurred within 72 h; whereas this level of mortality was recorded in C. somatis, C. gibbosa and M. vitrata within 144 h. No mortality was observed in the control treatment. Multiplication of S. mushtaqi and the yield of infective juveniles (IJs) on these insects was the highest (0.94 × 10⁵ IJs/cadaver) from N. viriduala, followed by S. litura (0.76 × 10⁵ IJs/cadaver), L. boeticus as also C. gibbosa (0.31 × 10⁵ IJs/cadaver) and M. vitrata (0.20 × 10⁵ IJs/cadaver). Very poor populations of IJs were found from A. moorei (0.15 × 10⁵ IJs/cadaver) and C. somatics (0.01 × 10⁵ IJs/cadaver). No multiplication of IJs was found from the cadaver of E. vittella. This opens a new hope of utilising S. mushtaqi in the insect pests management programme.     

Field evaluation of entomopathogenic nematodes for the biological control of the annual bluegrass weevil,Listronotus maculicollis (Coleoptera: Curculionidae), in golf course turfgrass

The ability of entomopathogenic nematodes to suppress larval populations of the annual bluegrass weevil, Listronotus maculicollis, was investigated under field conditions over a 3-year period (2006–2008). Combination of nematode species, application rate and timing produced strong numerical yet few statistically significant reductions. Steinernema carpocapsae Weiser, S. feltiae Filipjev, and Heterorhabditis bacteriophora Poinar applied at 2.5×10⁹ IJs/ha reduced first generation late instars between 69 and 94% in at least one field trial. Steinernema feltiae provided a high level of control (94%) to low densities (~20 larvae per 0.09 m²), but gave inadequate control for higher densities (24 and 50% suppression). No significant differences were found among treatment timings. However, applications timed to coincide with the peak of larvae entering the soil (fourth instars) generally performed better than applications made prior to (preemptive) or after the majority of the population advanced from the fourth instar. Nematode populations declined sharply between 0 and 14 days after treatment (DAT). Although nematode populations later increased (at 28 DAT), indicating an ability to recycle within hosts in the environment, they were nearly undetectable 56 DAT when the second generation host larvae were present in the soil. Applying commercially available nematode species at standard field rates cannot reliably reduce L. maculicollis immature densities on golf courses, nor will single applications suppress multiple generations. Future research will need to identify application strategies to improve biocontrol consistency.     

Steinernema scarabaei, an entomopathogenic nematode for control of the European chafer

A new entomopathogenic nematode species, Steinernema scarabaei, was evaluated for efficacy against two white grub species, the European chafer, Rhizotrogus majalis, and the Japanese beetle, Popillia japonica, in laboratory, greenhouse, and field trials. In laboratory assays, S. scarabaei caused greater mortality than Heterorhabditis bacteriophora. S. scarabaei was highly virulent with an LC₅₀ of 5.5–6.0 and 5.7 infective juveniles (IJs) per third-instar larva in R. majalis and P. japonica, respectively. In a greenhouse trial, S. scarabaei provided greater mortality of R. majalis at all application rates (0.156–1.25 × 10⁹ IJs/ha) than Steinernema glaseri and H. bacteriophora (both at 1.25 × 10⁹ IJs/ha). Combination of imidacloprid and S. scarabaei resulted in an antagonistic interaction. In a fall field trial, S. scarabaei provided 88 and 75% control of R. majalis at 2.5 × 10⁹ and 10⁹ IJs/ha, respectively, and 54% control of P. japonica at 10⁹ IJs/ha; H. bacteriophora had no effect on mortality of either white grub species. In a spring field trial, unusually cool temperatures impeded nematode activity. Against R. majalis, S. scarabaei provided moderate control (56–59%), whereas Heterorhabditis marelatus provided no control. Mortality of P. japonica was moderate (49–66%) in both S. scarabaei and H. marelatus treatments. Overwinter persistence of S. scarabaei activity was demonstrated in a spring assay of soil from fall treated plots in which nematode infection was absent from control plots and present in treated plots.     

Behavioural response of the entomopathogenic nematodes Steinernema carpocapsae and Heterorhabditis bacteriophora to oxamyl

Infective juveniles of the entomopathogenic nematode Steinernema carpocapsae show a low level of locomotory activity that is presumed to limit their usefulness as biological insecticides. A 30 μg ml^-1 solution of the carbamate pesticide oxamyl reduced the proportion of nonmobile nematodes by nearly two thirds to 35%, while stimulating a 7.5-fold increase in sinusoidal movement. This increase in activity did not result in a corresponding increase in host-finding. Oxamyl treatment did not enhance infective juvenile pathogenicity to Galleria mellonella larvae. At higher concentrations, oxamyl caused aberrant nematode movement and partial paralysis. Heterorhabditis bacteriophora infective juveniles maintain a high level of locomotory activity. Treatment with 30 μg ml^-1 oxamyl increased the proportion of sinusoidal over nonsinusoidal movements, but infective juvenile host-finding and pathogenicity were significantly reduced. Higher rates impaired movement and induced complete paralysis. We conclude that oxamyl is incompatible with S. carpocapsae and H. bacteriophora. The concept of chemically activating infective juveniles to increased locomotory activity and thereby achieving enhanced efficacy is inconsistent with our results.     

Impact of Entomopathogenic Nematodes on Different Soil-dwelling Stages of Western Flower Thrips, Frankliniella occidentalis (Thysanoptera: Thripidae), in the Laboratory and Under Semi-field Conditions

The impact of entomopathogenic nematodes (EPN) on mortality of soil-dwelling stages of western flower thrips (WFT), Frankliniella occidentalis (Thysanoptera: Thripidae) with different insect stage combinations was studied in the laboratory and under semi-field conditions. In laboratory experiments, the efficacy of Steinernema feltiae strain Sylt (Rhabditida: Steinernematidae) at a concentration of 400 infective juveniles (IJs) cm -2 was tested against different proportions of soil-dwelling stages of WFT, i.e. late second instar larvae (L2), prepupae and pupae. Soil was used as the testing medium. S. feltiae significantly affected the mortality of all soil-dwelling life stages of WFT at all tested insect stage combinations. The proportion of late L2 in the population negatively correlated to EPN-induced mortality. WFT prepupa and pupa were similarly susceptible to S. feltiae and their proportion in the population did not affect the EPN-induced mortality under laboratory conditions. The highest mortality (80%) was recorded when the population consisted only of prepupae and/or pupae. In the semi-field study, the impact of S. feltiae , S. carpocapsae strain DD136 and Heterorhabditis bacteriophora strain HK3 (Rhabditida: Heterorhabditidae) ( H. bacteriophora ) at concentrations of 400 and 1000 IJs cm -2 was evaluated against WFT reared on green beans, Phaseolus vulgaris L., as host plant in pot experiments in a controlled climate chamber. All tested EPN strains at both dose rates significantly reduced the WFT populations. Up to 70% reduction of the WFT population was obtained at the higher EPN concentration.     

Laboratory and field evaluation of entomopathogenic nematodes for control of Agriotes obscurus (L.) (Coleoptera: Elateridae)

The susceptibility of the dusky wireworm, Agriotes obscurus (L.) (Coleoptera: Elateridae), to different species and strains of entomopathogenic nematodes was tested in a virulence assay in the laboratory. Larvae were exposed to different nematode doses of 50 and 100 IJs/cm². At a dose of 50 IJs/cm², only a commercial strain Heterorhabditis bacteriophora Poinar and the native strain Steinernema carpocapsae (Weiser) B14 caused increased mortality compared with the control (11.1% and 13.3% mortality, respectively). At the higher dose tested, all strains (except Steinernema sp. D122) were virulent to A. obscurus larvae. Steinernema carpocapsae B14 caused higher mortality of wireworm (75.6%) and was used for the assay conducted in cages, with a dose of 100 IJs/cm², in field conditions. The results showed that S. carpocapsae B14 controlled 48.3% of A. obscurus larvae, demonstrating that some entomopathogenic nematodes have the potential to control larvae of A. obscurus. However, further work is needed to improve their efficacy.     

Entomopathogenic nematodes,a potential microbial biopesticide: mass production and commercialisation status – a mini review

Parasitic nematodes have several important attributes that make them excellent candidates for biological control of soil insects. These nematodes can be produced by in vivo by baiting technique on insects and commercially by in vitro solid/liquid culturing. Numerous insect pests on many different crops are being controlled by these insect parasitic nematodes, including root weevils, flea beetles, mint root borer, colorado potato beetle, white grubs, caterpillars and plant parasitic root nematode, e.g. root-knot nematodes. Utilisation of entomopathogenic nematodes (EPN) has raised intense interest and has been a growing concern globally mainly because of its potential efficiency, exemption from registration and other impressive attributes for utilising against the control of soil dwelling pests. This review highlights the mass production, commercialisation and utilisation of EPN as microbial biopesticide in bio-intensive pest management programmes.     

Selection of insect parasitic nematodes for biological control of the garden chafer,Phyllopertha horticola

Larvae ofPhyllopertha horticola L. (Coleoptera: Scarabaeidae) cause increasing problems on sports fields and lawns in NW-Europe. A biological control programme using insect parasitic nematodes is being developed. This paper contains the results of bioassays with various species and isolates of the nematode generaHeterorhabditis andSteinernema. In bioassays in small pots with moist sand, most of the nematode isolates gave 30–60% mortality against each of the three larval stages. The susceptibility of the grubs for nematode infection generally increased with larval development.H. bacteriophora, H. heliothidis, H. megidis, a DutchHeterorhabditis isolate NLH-E87.3 andS. glaseri 326 showed the highest mortality rates, with nearly 100% mortality of third instar grubs. The DutchHeterorhabditis isolate NLH-E87.3 andS. glaseri 326 were selected as candidates for further studies on their potential as biological control agents forP. horticola grubs in the field.     

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.     

A survival-reproduction trade-off in entomopathogenic nematodes mediated by their bacterial symbionts

In this work, we investigate the investment of entomopathogenic Steinernema nematodes (Rhabditidae) in their symbiotic association with Xenorhabdus bacteria (Enterobacteriaceae). Their life cycle comprises two phases: (1) a free stage in the soil, where infective juveniles (IJs) of the nematode carry bacteria in a digestive vesicle and search for insect hosts, and (2) a parasitic stage into the insect where bacterial multiplication, nematode reproduction, and production of new IJs occur. Previous studies clearly showed benefits to the association for the nematode during the parasitic stage, but preliminary data suggest the existence of costs to the association for the nematode in free stage. IJs deprived from their bacteria indeed survive longer than symbiotic ones. Here we show that those bacteria-linked costs and benefits lead to a trade-off between fitness traits of the symbiotic nematodes. Indeed IJs mortality positively correlates with their parasitic success in the insect host for symbiotic IJs and not for aposymbiotic ones. Moreover mortality and parasitic success both positively correlate with the number of bacteria carried per IJ, indicating that the trade-off is induced by symbiosis. Finally, the trade-off intensity depends on parental effects and, more generally, is greater under restrictive environmental conditions.