Effects of storage temperature on survival and infectivity of three indigenous entomopathogenic nematodes strains (Steinernematidae and Heterorhabditidae) from Meghalaya, India

Three locally isolated strains of entomopathogenic nematodes (EPNs), viz. Heterorhabditis indica, Steinernema thermophilum and Steinernema glaseri, from Meghalaya, India were characterized in terms of storage temperature and survival and infectivity of their infective juveniles (IJs). The survival and infectivity of nematode IJs was studied at, 5 ± 2 and 25 ± 2 °C, for a period of 120 days, using deionized water as storage medium. The viability of nematode IJs was checked by mobility criterion at different storage periods, while the infectivity of nematode IJs was ascertained on the basis of establishment of IJs, using Galleria mellonella larva mortality tests in petridishes. The results of this study revealed that storage temperature markedly affects the survival as well as the establishment of nematode IJs of the three EPN species. At 5 °C, comparatively higher rate of IJ's survival (i.e. 74-86 %) was observed for 15 days of storage, but the same reduced drastically to 28-32 % after 30 days of storage for H. indica and S. thermophilum. On the other hand, at 25 °C, the survival of nematode IJs was observed till 120 days for all the three studied EPNs. In case of S. thermophilum and S. glaseri, higher rate of IJs survival (>75 %) was observed respectively at 15 and 30 days of observation. The study also showed that the establishment of IJs of the three EPN species declines with increase in storage periods, at both the test temperatures. In general, the nematodes stored at 25 °C showed comparatively better establishment than those stored at 5 °C. Among the three EPN studied, the establishment of S. glaseri was comparatively better than the rest of the species at both the temperatures and for different storage durations. In conclusion, our study adds further valuable information about the effect of storage temperature on survival and infectivity of three indigenous EPN species of Meghalaya, India which appears to be promising biocontrol agents of local insect pests.

Efficacy of indigenous entomopathogenic nematodes from Meghalaya, India against the larvae of taro leaf beetle, Aplosonyx chalybaeus (Hope)

The efficacy of three entomopathogenic nematode (EPN) species, Heterorhabditis indica, Steinernema thermophilum, and S. glaseri, from Meghalaya, India was studied against the larvae of taro leaf beetle, Aplosonyx chalybaeus (Hope) (Coleoptera: Chrysomelidae), under the laboratory conditions. The beetle larvae (grubs) were exposed to 25, 50, 75, 100 and 200 infective juveniles (IJs) of each nematode species for different time periods and they were found to be susceptible to all the EPNs tested. However, the susceptibility of grubs to nematode infection varied according to the dosages of IJs and their exposure periods. Appreciably good performance was achieved by S. glaseri, which showed 100 % mortality of insect larvae in 48 h exposure time. At 48 h of incubation, its LC50 value was 90.3 IJs/larva, which was lower than that of S. thermophilum (115.0 IJs/larva) and H. indica (186.0 IJs/larva), at the same exposure time. All the tested nematode species were also found to reproduce within the host and produced infective juveniles. H. indica, however, showed comparatively more production of IJs per cadaver of infected host (168.9 × 10(3) IJs/larva), as compared to the other two tested nematode species. The production of IJs per cadaver of infected host by S. thermophilum was recorded to be 82.0 × 10(3) IJs/larva. In case of S. glaseri, while production of IJs increased initially to 18.9 × 10(3) IJs/larva at concentration of 100 IJs/larva, it declined thereafter to 14.7 × 10(3) IJs/larva at the dose of 200 IJs/larva. In conclusion, the evidence obtained in this study suggests that all the three indigenous EPN species are virulent enough to produce 100 % mortality in the last instar larvae of A. chalybaeus. These EPN species thus have potential scope for the management of A. chalybaeus in taro crops.

Evaluation of the efficacy of three indigenous strains of entomopathogenic nematodes from Meghalaya, India against mustard sawfly, Athalia lugens proxima Klug (Hymenoptera: Tenthredinidae)

The objective of this study was to evaluate the efficacy of three indigenous strains of entomopathogenic nematodes (EPN) from Meghalaya, India, namely Heterorhabditis indica Poinar, Karunakar and David, Steinernema thermophilum Ganguly and Singh, and Steinernema glaseri (Steiner) against the last instar larva of mustard sawfly, Athalia lugens proxima Klug, a serious pest of mustard and radish in India. The larvae of A. lugens proxima were exposed to 10, 25, 50, 75 and 100 infective juveniles (IJs) concentration of each nematode species in Petri dishes. Percentage larval mortality and nematode reproduction in insect larvae was studied. The sawfly larvae were found to be susceptible to all the three EPNs tested, but the degree of susceptibility to infection varied from among nematode species. Based on LC50 value, H. indica was the most pathogenic species. Nevertheless, S. thermophilum and S. glaseri also showed a high insect mortality. This study also revealed that all the three test nematodes are also able to propagate in the host cadaver and produce first generation infective juveniles. However, H. indica produced significantly more number of IJs per insect larva than the other two nematode species. The progeny production was recorded to be the least in case of S. glaseri. In conclusion, our findings suggest that of the three indigenous EPNs studied, H. indica and S. thermophilum have good potential as biological control agents against mustard sawfly, A. lugens proxima.

Entomopathogenic nematodes for control of insect pests above and below ground with comments on commercial production

Entomopathogenic nematodes (EPNs) have been utilized in classical, conservation, and augmentative biological control programs. The vast majority of applied research has focused on their potential as inundatively applied augmentative biological control agents. Extensive research over the past three decades has demonstrated both their successes and failures for control of insect pests of crops, ornamental plants, trees and lawn and turf. In this paper we present highlights of their development for control of insect pests above and below ground. The target insects include those from foliar, soil surface, cryptic and subterranean habitats. Advances in mass-production and formulation technology of EPNs, the discovery of numerous efficacious isolates/strains, and the desirability of reducing pesticide usage have resulted in a surge of commercial use and development of EPNs. Commercially produced EPNs are currently in use for control of scarab larvae in lawns and turf, fungus gnats in mushroom production, invasive mole crickets in lawn and turf, black vine weevil in nursery plants, and Diaprepes root weevil in citrus in addition to other pest insects. However, demonstrated successful control of several other insects, often has not lead to capture of a significant share of the pesticide market for these pests.

Soil moisture effects on the activity of three entomopathogenic nematodes (Steinernematidae and Heterorhabditidae) isolated from Meghalaya, India

Entomopathogenic nematodes (EPNs) are obligate parasites of insects that are widely distributed in soils throughout the world. They have great potential for use as biological control agents for insect pests. It is known that strains of Steinernema and Heterorhabditis isolated from different geographical regions exhibit differences in their ecological traits, such as infectivity, establishment, survival, reproduction, etc. A precise knowledge of these factors is therefore an essential pre-requisite for devising successful strategies to use these nematodes in biological control programmes. The present study investigated the effect of soil moisture on the activity (as measured by number of nematodes established in hosts) of three entomopathogenic nematode species (Heterorhabditis indica Poinar, Karunakar & David; Steinernema thermophilum Ganguly & Singh; Steinernema glaseri Steiner), isolated from forest soils in Meghalaya, India, under laboratory conditions. The experiments for EPNs were conducted at 25 ± 2°C (30 ± 2°C for S. thermophilum) in a sandy loam soil (85% sand, 12% silt and 3% clay, pH 6.54). Last instar larvae of wax moth, Galleria mellonella served as the experimental insect host. The soil moistures tested were 3, 4, 5, 6, 8, 10, 12, 14, 16, 18, 20, 22 and 25% (w/w). The study revealed that soil moisture has marked influences on establishment of infective juveniles of different nematode species in insect host. While, S. thermophilum showed establishment at 4% and above soil moistures, H. indica and S. glaseri showed establishment at 5% and above soil moistures. The optimum soil moisture for different nematode species were noted as: H. indica 8-18%, S. thermophilum 6-20%, and S. glaseri 8-25%. Further, a minimum of 6% soil moisture was noted to be essential for achieving 100% host mortality for all the three nematode species.

Do Organic Amendments Enhance the Nematode-Trapping Fungi Dactylellina haptotyla and Arthrobotrys oligospora?

Soil cages (polyvinyl chloride pipe with mesh-covered ends) were used to determine how the quantity of two organic amendments affected the nematode-trapping fungi Dactylellina haptotyla and Arthrobotrys oligospora, which were studied independently in two different vineyards. Each cage contained 80 cm(3) of field soil (120 g dry weight equivalent), fungal inoculum (two alginate pellets, each weighing 1.9 mg and containing assimilative hyphae of one fungus), and dried grape or alfalfa leaves (0, 360, or 720 mg equivalent to 0, 4,500, or 9,000 kg/ha) with a C:N of 28:1 and 8:1, respectively. Cages were buried in the vineyards, recovered after 25 to 39 days, and returned to the laboratory where fungus population density and trapping were quantified. Dactylellina haptotyla population density and trapping were most enhanced by the smaller quantity of alfalfa amendment and were not enhanced by the larger quantity of alfalfa amendment. Arthrobotrys oligospora population density was most enhanced by the larger quantity of alfalfa amendment, but A. oligospora trapped few or no nematodes, regardless of amendment. Trapping and population density were correlated for D. haptotyla but not for A. oligospora.

Infection of the Entomopathogenic Nematode, Steinernema carpocapsae, as Affected by the Presence of Steinernema glaseri

The infection behavior of Steinernema carpocapsae infective juveniles (IJ) was investigated in the presence and absence of S. glaseri. Mixed inoculation of S. carpocapsae with S. glaseri IJ significantly raised the nictation rates of S. carpocapsae IJ. Significantly more S. carpocapsae IJ migrated to the host insect in the mixed inoculation with S. glaseri IJ on agar plates. More S. carpocapsae IJ penetrated into the host insect placed 2 cm below the surface in the mixed inoculation with S. glaseri IJ. More S. glaseri than S. carpocapsae IJ penetrated into hosts placed 7 cm deep. Irrespective of host location, the male ratio of S. carpocapsae IJ established in the host body was always higher in the mixed inoculation with S. glaseri IJ.

Repulsion of Meloidogyne incognita by Alginate Pellets Containing Hyphae of Monacrosporium cionopagum, M. ellipsosporum, or Hirsutella rhossiliensis

The responses of second-stage juveniles (J2) of Meloidogyne incognita race 3 to calcium alginate pellets containing hyphae of the nematophagous fungi Monacrosporiura cionopagum, M. ellipsosporum, and Hirsutella rhossiliensis were examined using cylinders (38-mm-diam., 40 or 72 mm long) of sand (94% <250-mum particle size). Sand was wetted with a synthetic soil solution (10% moisture, 0.06 bar water potential). A layer of 10 or 20 pellets was placed 4 or 20 mm from one end of the cylinder. After 3, 5, or 13 days, J2 were put on both ends, on one end, or in the center; J2 were extracted from 8-ram-thick sections 1 or 2 days later. All three fungal pellets were repellent; pellets without fungi were not. Aqueous extracts of all pellets and of sand in which fungal pellets had been incubated were repellent, but acetone extracts redissolved in water were not. Injection of CO (20 mul/minute) into the pellet layer attracted J2 and increased fungal-induced mortality. In vials containing four randomly positioned pellets and 17 cm(3) of sand or loamy sand, the three fungi suppressed the invasion of cabbage roots by M. javanica J2. Counts of healthy and parasitized nematodes observed in roots or extracted from soil indicated that, in the vial assay, the failure of J2 to penetrate roots resulted primarily from parasitism rather than repulsion. Data were similar whether fungal inoculum consisted of pelletized hyphae or fungal-colonized Steinernema glaseri. Thus, the results indicate that nematode attractants and repellents can have major or negligible effects on the biological control efficacy of pelletized nematophagous fungi. Factors that might influence the importance of substances released by the pellets include the strength, geometry, and duration of gradients; pellet degradation by soil microflora; the nematode species involved; and attractants released by roots.

Gold-conjugated Reagents for the Labeling of Carbohydrate-Recognition Domains and Glycoconjugates on Nematode Surfaces

Various fluorescent conjugated lectins have been used for the detection of glycoconjugates on nematode surfaces under light microscopy. Several problems have been experienced with these reagents including penetration of the cuticle by fluorescent lectins, non-glycoconjugate specificity, strong nematode autofluorescence at the emission wavelength of the fluorescent dye, and prevention of persistent visualization due to rapid quenching of the fluorescent components. Gold-conjugated reagents combined with silver enhancement alleviated these difficulties when working with three phytonematode species (Heterodera avenae, H. latipons, and Meloidogyne javanica) and two entomopathogenic species (Steinernema carpocapsae and S. glaseri) under light-microscopy visualization of binding by fluorescent lectins and neoglycoproteins. Moreover, gold-conjugated reagents resulted in stable bindings that enabled long-term observations.

Optimal Release Rates for Attracting Meloidogyne incognita, Rotylenchulus reniformis, and Other Nematodes to Carbon Dioxide in Sand

Movement of vermiform stages of Meloidogyne incognita, Rotylenchulus reniformis, Ditylenchus phyllobius, Steinernema glaseri, and Caenorhabditis elegans in response to carbon dioxide was studied in 40- and 72-mm-long cylinders of moist sand inside 38-mm-d acrylic tubes. Meloidogyne incognita, R. reniformis, and S. glaseri were attracted to CO when placed on a linear gradient of 0.2%/cm at a mean CO concentration of 1.2%. When CO was delivered into the sand through a syringe needle at flow rates between 2 and 130 mul/minute, the optimal flow rate for attracting M. incognita and R. reniformis was 15 mul/minute, and maximal attraction of the two species from a distance of 52 mm was achieved after 29 and 40 hours, respectively. After 24 hours, a total CO volume of 20 cm(3) was sufficient to induce 96% of all M. incognita introduced to move into the half of the cylinder into which CO was delivered and more than 75 % to accumulate in the 9 cm(3) of sand volume nearest the source. Results indicate it may be possible to use a chemical or biological source of CO to attract nematodes to nematicide granules or biocontrol agents.

Influence of salinity on survival and infectivity of entomopathogenic: nematodes

Exposure to NaC1, KCI, and CaCl affected the entomopathogenic nematodes Heterorhabditis bacteriophora and Steinernema glaseri differently. Survival, virulence, and penetration efficiency of S. glaseri were not affected by these salts. At high concentrations, however, all three salts inhibited its ability to move through a soil column and locate and infect a susceptible host. Calcium chloride and KCl had no effect on H. bacteriophora survival, penetration efficiency, or movement through a soil column, but moderate concentrations of these salts enhanced H. bacteriophora virulence. NaCl, however, adversely affected each of these parameters at high salinities (>16 dS/m). Salt effects on S. glaseri are attributed solely to interference with nematode host-finding ability, whereas the NaCl effects on H. bacteriophora are attributed to its toxicity and possibly to interference with host-finding behavior.

Movement of Five Nematode Species through Sand Subjected to Natural Temperature Gradient Fluctuations

Temperature gradient fluctuations that occur naturally as a result of heating and cooling of the soil surface were reproduced within 15-cm-d, 15-cm-long acrylic tubes filled with moist sand. Sunny and rainy periods during the late summer in eastern Texas were simulated. Five ecologically different nematode species were adapted to fluctuating temperatures for 20-36 hours at a simulated depth of 12.5 cm before being injected simultaneously into the centers of tubes at that depth. When heat waves were propagated horizontally to eliminate gravitational effects, the movement of Ditylenchus phyllobius, Steinernema glaseri, and Heterorhabditis bacteriophora relative to the thermal surface was rapid and largely random. However, Rotylenchulus reniformis moved away from and Meloidogyne incognita moved toward the thermal surface. When heat waves were propagated upward or downward, responses to temperature were the same as when propagated horizontally, irrespective of gravity. The initial direction of movement 1.5 hours after introduction to 20-era-long tubes at five depths at five intervals within a 24-hour cycle indicated that M. incognita moved away from and R. reniformis moved toward the temperature to which last exposed. Differences in movement of the five species tested relative to gravity appeared related to body length, with the smallest nematodes moving downward and the largest moving upward.

Location of the Phasmids on Infective Juveniles of Steinernema glaseri

Scanning electron microscopy revealed the location of the phasmids on infective juveniles of Steinernema glaseri. The phasmids are located about 40% of the tail length posterior to the anus and are at or near the same level. Instead of being in the center of the lateral fields, they are located just ventral to the lateral fields, or interrupting the ventral-most lateral ridge. The phasmids were covered often by an exudate.

Influence of Soil pH and Oxygen on Persistence of Steinernema spp

Survival of infective juveniles of Steinernema carpocapsae and Steinernema glaseri gradually declined during 16 weeks of observation as the tested soil pH decreased from pH 8 to pH 4. Survival of both species of Steinernema dropped sharply after 1 week at pH 10. Survival or S. carpocapsae and S. glaseri was similar at pH 4, 6, and 8 during the first 4 weeks, but S. carpocapsae survival was significantly greater than S. glaseri at pH 10 through 16 weeks. Steinernema carpocapsae and S. glaseri that had been stored at pH 4, 6, and 8 for 16 weeks, and at pH 10 for 1 or more weeks were not infective to Galleria mellonella larvae. Steinernema carpocapsae survival was significantly greater than that of S. glaseri at oxygen:nitrogen ratios of 1:99, 5:95, and 10:90 during the first 2 weeks, and survival of both nematode species declined sharply to less than 20% after 4 weeks. Survival of both nematode species significantly decreased after 8 weeks as the tested oxygen concentrations decreased from 20 to 1%, and no nematode survival was recorded after 16 weeks. Steinernema carpocapsae pathogenicity was significantly greater than that of S. glaseri during the first 2 weeks. No nematode pathogenicity was recorded at oxygen concentrations of 1, 5, and 10% after 2 weeks and at 20% after 16 weeks.

Steinernema feltiae (DD-136) and S. glaseri: Persistence in Soil and Bark Compost and Their Influence on Native Nematodes

Infective juveniles (J3) of the entomogenous nematodes Steinernema feltiae DD-136 (ca. 10,000 J3/100 ml) and S. glaseri (ca. 2,500 J3/100 ml) were incubated in steam-sterilized and nonsterilized sandy soil and bark compost for 8 weeks at 25 C. The nematodes were recovered by a two-step extraction procedure at 1-week intervals, and their infectivity to lepidopterous larvae (Spodoptera litura and Galleria mellonella) and their effect on the population and community of native nematodes in soil were determined. Survival of inoculated nematodes and mortality of insects were enhanced in sterilized media. Nonsterilized bark compost proved to be equally as suitable a medium as sterilized compost. In nonsterilized soil, the survival curve of S.feltiae declined more rapidly than that or S. glaseri which was less infective to insects despite its greater persistence even in nonsterilized soil. Soon after the addition of steinernematids to soil, the population of native nematodes showed a fluctuation with an increase in rhabditids and a decrease in other kinds of nematodes.

Growth and Virulence of Steinernema glaseri Influenced by Different Subspecies of Xenorhabdus nematophilus

Three Xenorhabdus nematophilus subspecies influenced Steinernema glaseri growth profiles and growth rates, but this was not necessarily because of different bacterial growth rates. Virulence of dauer nematodes in larval Galleria mellonella varied with the number of dauers retaining bacteria and the bacterial subspecies. Virulence was least for dauers grown on X. nematophilus subsp. bovienii because of the lack of retained bacteria. Virulence was subsequently restored by culturing these nematodes on X. nematophilus subsp. poinari.