Two entomopathogenic nematodes, Steinernema colombiensesp. nov. (strain SNIO198) (Rhabditida: Steinernematidae) and Heterorhabditis bacteriophora Poinar (strain Fresno HNI0100) (Rhabditida: ...Heterorhabditidae), were isolated from the Colombian Andes and cultured in the laboratory. In semi-field tests against the ground pearl Eurhizococcus colombianus Jakubski (Hemiptera: Margarodidae) on blackberry, neither species was pathogenic to crawlers and only S. colombiense was moderately infective against adults at 105 IJ/ml. Higher activity for both nematodes was observed against immature spittlebugs Aeneolamia sp. (Hemiptera: Cercopidae) infesting kikuyu grass, with H. bacteriophora and S. colombiense killing 100% and 75% of insects, respectively, in our tests. Our results demonstrate the potential use of native strains of entomopathogenic nematodes as biological control agents in Colombia.
Metarhizium anisopliae (MET) and entomopathogenic nematodes (EPN) are microorganisms that attack the larvae of Oryctes rhinoceros. The effects of MET, EPN and the combination of both on the O. ...rhinoceros larvae were studied during the rainy season in Jepara Indonesia. This study aimed to determine the effectiveness of Metarhizium anisopliae and entomopathogenic nematodes to control Oryctes rhinoceros larvae in the rainy season.
There were four level doses of MET, four level doses of EPN and four mixture of MET and EPN. The experiment used 72 containers that were placed in the garden with coconut palm shade. Five kilograms of organic soil that was mixed with biological control agents (MET, EPN and MET+EPN) and ten O. rhinoceros larvae 3rd instar were put in each other container. The data were analyzed by descriptive analysis.
Every larvae mortality was observed once a week and observations are for 8 weeks. The result showed that the larval mortality due to MET treatment occurred on 2nd-7th week. Meanwhile, the larval mortality due to EPN treatment took place on 2nd-8th weeks and the larval mortality due to MET+EPN treatment occurred on 1st-5th weeks.
The combination of MET and EPN was simultaneously effective to control O. rhinoceros larvae than separate use of MET or EPN. Result of this study showed that using two agents of biocontrol was more effective, so that it can be beneficial for controlling O. rhinoceros larvae in the field.
Steinernematid nematodes form obligate symbioses with bacteria from the genus Xenorhabdus. Together Steinernema nematodes and their bacterial symbionts successfully infect, kill, utilize, and exit ...their insect hosts. During this process the nematodes and bacteria disassociate requiring them to re-associate before emerging from the host. This interaction can be complicated when two different nematodes co-infect an insect host.
Non-cognate nematode-bacteria pairings result in reductions for multiple measures of success, including total progeny production and virulence. Additionally, nematode infective juveniles carry fewer bacterial cells when colonized by a non-cognate symbiont. Finally, we show that Steinernema nematodes can distinguish heterospecific and some conspecific non-cognate symbionts in behavioral choice assays.
Steinernema-Xenorhabdus symbioses are tightly governed by partner recognition and fidelity. Association with non-cognates resulted in decreased fitness, virulence, and bacterial carriage of the nematode-bacterial pairings. Entomopathogenic nematodes and their bacterial symbionts are a useful, tractable, and reliable model for testing hypotheses regarding the evolution, maintenance, persistence, and fate of mutualisms.
Summary
Trade‐offs in an herbivore's ability to feed, avoid predation and succeed on alternative hosts are thought to be major driving factors in host specialization. In this study, we compared how ...two closely related milkweed beetles (Tetraopes spp.) that have specialized on separate Asclepias species respond to host switching to alternative milkweed plants. By additionally examining effects on the beetles’ entomopathogenic natural enemies, we test whether host plant specialization is driven by plant–herbivore interactions alone or whether there is a role for the tritrophic interactions.
Tetraopes beetles feed on milkweed roots as larvae and on milkweed shoots as adults, and they sequester toxic cardenolides from their host plants. We predicted that growth and sequestration would be compromised on alternative hosts as a consequence of specialization. Larvae of each Tetraopes species were reared on their native host plant, the host plant of the other species and two closely related Asclepias species that do not typically host Tetraopes.
Regardless of beetle specialization, survival of both beetles was highest on A. syriaca, which has the second‐to‐lowest levels of root cardenolides and is the native host for T. tetraophthalmus. Larval growth was not affected by host plant for T. texanus, but T. tetraophthalmus grew best on A. exaltata, a close relative of A. syriaca that does not typically experience beetle feeding.
We found that larval sequestration of cardenolides largely mirrored host plant values in the roots, with the exception of T. texanus on A. asperula, which sequestered a low proportion of the cardenolides from this host. Although all larvae were susceptible to entomopathogenic nematodes (EPNs), the number of EPNs emerging from cadavers depended on the beetle–plant combination, with more EPNs produced when beetles were feeding on native compared to non‐native hosts.
The observed consequences for tritrophic interactions did not fit expectations for specialized herbivores (i.e. EPN predation was highest when beetles were on their native hosts), suggesting that specialization may be driven primarily by a plant–herbivore interaction in this system, not by a tritrophic effect.
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Lay Summary
Entomopathogenic nematodes (EPNs) have been used against especially soil borne insect pests. EPNs are feasible and attractive for biological control, because of their virulence against various insect ...pests, host seeking ability, being usable with standard equipment, and long-term efficacy. In addition EPNs can be applied simultaneously with some pesticides. These properties make EPNs ideal biocontrol agent in integrated pest management. In the present study, effects of 4 widely used pesticides (Glyphosate, Chlorpyrifos-ethyl, Captan, Fosetyl-al) on virulence and mortality of three EPN strains (Heterorhabditis bacteriophora Alman, H. bacteriophora HbH and Steinernema carpocapsae DD-136) were examined at 24 and 48 h periods. All strains were able to infect Galleria mellonella larvae averagely above 90 % rate, after 24 and 48 h treatments with all pesticides. However, some of the pesticides showed negative impact on the viability of the strains. Especially, DD-136 and Fosetylal seemed like incompatible, as the mortality rates were significantly higher than control for both 24 and 48 h. The results of the present study showed that it may be possible to use some EPN strains with some pesticides. It is expected that the results of the study will provide useful information for future integrated pest management programs.
Entomopathogenic nematodes (EPNs) in the families Heterorhabditidae and Steinernematidae have a mutualistic-symbiotic association with enteric γ-Proteobacteria (Steinernema-Xenorhabdus and ...Heterorhabditis-Photorhabdus), which confer high virulence against insects. EPNs have been studied intensively because of their role as a natural mortality factor for soil-dwelling arthropods and their potential as biological control agents for belowground insect pests. For many decades, research on EPNs focused on the taxonomy, phylogeny, biogeography, genetics, physiology, biochemistry and ecology, as well as commercial production and application technologies. More recently, EPNs and their bacterial symbionts are being viewed as a model system for advancing research in other disciplines such as soil ecology, symbiosis and evolutionary biology. Integration of existing information, particularly the accumulating information on their biology, into increasingly detailed population models is critical to improving our ability to exploit and manage EPNs as a biological control agent and to understand ecological processes in a changing world. Here, we summarize some recent advances in phylogeny, systematics, biogeography, community ecology and population dynamics models of EPNs, and describe how this research is advancing frontiers in ecology.
The intensive use of chemical insecticides against mosquitoes has led to the development of widespread insecticide resistance. Control of Anopheles mosquitoes in malaria endemic areas of sub-Saharan ...Africa has become increasingly difficult. There is an urgent need for malaria control programmes to adopt more integrated mosquito management approaches that include sustainable, nonchemical solutions. The mermithid nematode Romanomermis iyengari is one of several natural control alternatives to synthetic pesticides for mosquito suppression. This study evaluated the effectiveness of the nematode R. iyengari for control of Anopheles gambiae.
The nematode R. iyengari was mass-produced, and pre-parasitic stage (J2) were used for laboratory and field experiments. In laboratory experiments, two concentrations of pre-parasitics (5 and 10 J2 per larva) were tested against first- (L1), second- (L2) and third-instar (L3) larvae of An. gambiae. Infected larvae were observed daily to determine their mortality rate and the number of post-parasitic nematodes emerging from dead larvae. In field experiments, 3500, 4000 and 5000 J2/m
were sprayed in separate natural Anopheles breeding sites. After treatment, the larval mosquito density in the breeding sites was assessed every 5-7 days.
Laboratory results showed that larval An. gambiae is susceptible to nematode infection: 100% L1 larvae died within 24 hours post-treatment, and 100% of both L2 and L3 larvae died within 7 days, regardless of nematode concentrations. The average number of post-parasitic nematodes emerging per larva increased with increasing nematode concentration. In field experiments, the monthly applications of 3500 to 5000 pre-parasitic nematodes per m
eliminated larval mosquito development in Anopheles- and mixed breeding sites. Larval mosquito density dramatically decreased five days after the first treatment in all treated sites and was maintained at a very low level during the whole experimental period. Basically, only early instar larva were detected in treated sites throughout the test period. The average number of post-parasitic nematodes emerging per larva collected in treated sites was 1.45, 2, and 5.7 respectively for sites treated with 3500, 4000, and 5000 J2/m
.
Malaria mosquito larvae is susceptible to R. iyengari infection in West Africa. Parasitism intensity depends on tested nematode concentrations. Monthly application of 3500 J2/ m
was enough to control effectively larval An. gambiae in wetlands and floodable locations in West Africa.
Encapsulation is an effective cellular immunity feature in insects, but the mechanism by which hemocytes recognize and encapsulate invading nematodes remains unclear. In addition, insect ...susceptibility to nematodes differs, indicating differences in immunity. We compared cellular encapsulation with non-parasitic and parasitic nematodes in two lepidopteran insects in vivo and ex vivo. The percentage of the free-living nematode
Caenorhabditis elegans
(Maupas) (Rhabditida: Rhabditidae) encapsulated following injection into
Galleria mellonella
Linnaeus (Lepidoptera: Pyralidae) larvae in vivo was low, whereas most larvae were encapsulated in
Mythimna separata
walker (Lepidoptera: Noctuidae). Similarly, the entomopathogenic nematode
Steinernema carpocapsae
(Rhabditida: Steinernematidae) was rarely encapsulated in
G. mellonella
, but > 50% were encapsulated in
M. separata
. Adhesion of
G. mellonella
hemocytes on the surface of live
C. elegans
was infrequently observed ex vivo, whereas dead nematodes were partially covered with hemocytes. A significantly higher percentage of live nematodes was covered with hemocytes in
M. separata
in the presence and absence of insect plasma compared with
G. mellonella
. These results indicate that there is a difference in immunity against nematodes between the two insects and that the difference largely depends on the capabilities of the hemocytes.
An overview is given on several aspects of evolutionary history, ecology, host plant use, and pharmacophagy of
spp. with a focus on the evolution of host plant breadth and effects of plant compounds ...on natural enemies used for biocontrol of pest species in the group. Recent studies on each aspect are discussed, latest publications on taxonomic grouping of
spp., and new findings on variations in the susceptibility of corn varieties to root feeding beetle larvae are presented. The further need for in-depth research on biology and ecology of the large number of non-pest species in the genus is pointed out.
The current approaches to sustainable agricultural development aspire to use safer means to control pests and pathogens. Photorhabdus bacteria that are insecticidal symbionts of entomopathogenic ...nematodes in the genus Heterorhabditis can provide such a service with a treasure trove of insecticidal compounds and an ability to cope with the insect immune system. This review highlights the need of Photorhabdus-derived insecticidal, fungicidal, pharmaceutical, parasiticidal, antimicrobial, and toxic materials to fit into current, or emerging, holistic strategies, mainly for managing plant pests and pathogens. The widespread use of these bacteria, however, has been slow, due to cost, natural presence within the uneven distribution of their nematode partners, and problems with trait stability during in vitro culture. Yet, progress has been made, showing an ability to overcome these obstacles via offering affordable mass production and mastered genome sequencing, while detecting more of their beneficial bacterial species/strains. Their high pathogenicity to a wide range of arthropods, efficiency against diseases, and versatility, suggest future promising industrial products. The many useful properties of these bacteria can facilitate their integration with other pest/disease management tactics for crop protection.
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