Potential of Steinernema carpocapsae(Weiser) as a biological control agent against potato tuber moth, Phthorimaea operculella(Zeller)(Lepidoptera: Gelechiidae)

The entomopathogenic nematode,Steinernema carpocapsae,was evaluated for control of the potato tuber moth,Phthorimaea operculella,under laboratory conditions.We evaluated different concentrations of S.carpocapsae for control of 2 nd,3 rd,and 4 th instar P.operculella.The median lethal concentration(LC50)of S.carpocapsae infective juveniles(IJs)to 2 nd,3 rd and 4 th instar larvae of P.operculella was 200,363,181 IJs mL–1,respectively.With the extension of treatment time,the cumulative mortality increased for 2 nd,3 rd,and 4 th instar larvae and pupae of P.operculella.Fourth instars were the most susceptible for all observation periods.Therefore,our results suggest that S.carpocapsae could be an effective biological control agent for P.operculella.

Microbial control of diamondback moth, Plutella xylostella L. （Lepidoptera： Yponomeutidae） using bacteria （Xenorhabdus nematophila） and its metabolites from the entomopathogenic nematode Steinernema carpocapsae

Cells and cell-free solutions of the culture filtrate of the bacterial symbiont, Xenorhabdus nematophila taken from the entomopathogenic nematode Steinernema carpocapsae in aqueous broth suspensions were lethal to larvae of the diamondback moth Plutella xylostella. Their application on leaves of Chinese cabbage indicated that the cells can penetrate into the insects in the absence of the nematode vector. Cell-free solutions containing metabolites were also proved as effective as bacterial cells suspension. The application of aqueous suspensions of cells of X.nematophila or solutions containing its toxic metabolites to the leaves represents a possible new strategy for controlling insect pests on foliage.

Storage of osmotically treated entomopathogenic nematode Steinernema carpocapsae

The infective juveniles （IJs） ofSteinernema 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 （sepH20, termed solution H） as a control. The mortality of the IJs at a concentration of 5×10^5 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℃. Most of the IJs shrunk and stopped motility after 6-9 hours incubation at 25℃ 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× 10^5, 2.5×10^5, 2 000 IJ/mL） and incubation temperature （30℃, 25℃, 10℃）. The resulting IJs were exposed to a high temperature assay （45℃ for 4 h, HTA）. Osmotically stressed IJs showed improved heat tolerance. The mortality of the Lls increased with the increasing concentrations of the test Lls 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, 2.5×10^5 IJs/mL or 5 ×10^5 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℃, the IJs mortality in the solutiors 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.

Modulation of immune responses of Rhynchophorus ferrugineus （Insecta： Coleoptera）induced by the entomopathogenic nematode Steinernema carpocapsae （Nematoda： Rhabditida）

Aim of this study was to investigate relationships between the red palm weevil （RPW） Rhynchophorusferrugineus （Olivier） and the entomopathogenic nematode Stein- ernema carpocapsae （EPN）; particularly, the work was focused on the immune response of the insect host in naive larvae and after infection with the EPN. Two main immunological processes have been addressed： the activity and modulation of host prophenoloxidase- phenoloxidase （proPO） system, involved in melanization of not-self and hemocytes recog- nition processes responsible for not-self encapsulation. Moreover, immune depressive and immune evasive strategies of the parasite have been investigated. Our results suggest that RPW possess an efficient immune system, however in the early phase of infection, S. carpocapsae induces a strong inhibition of the host proPO system. In addition, host cell- mediated mechanisms of encapsulation, are completely avoided by the parasite, the elusive strategies orS. carpocapsae seem to be related to the structure of its body-surface, since induced alterations of the parasite cuticle resulted in the loss of its mimetic properties. S. carpocapsae before the release of its symbiotic bacteria, depress and elude RPW immune defenses, with the aim to arrange a favorable environment for its bacteria responsible of the septicemic death of the insect target.

Management of cotton bollworms Helicoverpa armigera and Earias vittella by ento mopathogenic nematodes

Background: The bollworm complex consisting of Helicoverpa armigera and Earias vittella is a major threat in cotton production globally. The habit of developing resistance to many insecticides including Bt transgenic cotton necessitates the exploration of an alternate strategy to manage bollworms. The entomopathogenic nematodes(EPN) Steinernema carpocapsae strain APKS2 and Heterorhabditis bacteriophora strains KKMH1 and TRYH1 at different concentrations of 1 × 10^(9) infective juveniles(IJs)·hm^(-2), 2 × 10^(9)IJs.hm^(-2), and 3×10^(9)IJs·hm^(-2) in 500 L of water were evaluated as a foliar spray in fields naturally infested with H.armigera and F.vittella located at Eastern Block and and Cotton Research Farm of Tamil Nadu Agricultural University, Coimbaotre, India during October 2010–February 2011 and October 2011–February 2012, respectively.Results: In general, all three tested EPN strains reduced the larval population of H. armigera and E. vittella;reduced square and boll damage;and subsequently increased cotton yield compared with the untreated control. The S. carpocapsae APKS2 is most e ective against H. armigera whereas both S. carpocapsae APKS2 and H. bacteriophora KKMH1 were equally effective against E. vittella. The higher dose of 3×10^(9)IJs·hm^(-2) was highly significant in the reduction of H. armigera larvae. However, the doses 2×10^(9)IJs·hm^(-2)and 3×10^(9)IJs·hm^(-2) were equally effective for E. vittella control. The S. carpocapsae APKS2 at 3×10^(9)IJs·hm^(-2) caused a 62.2% reduction of H. armigera larvae, 34% reduction of square damage, 58.5% reduction of boll damage, and yielded 45.5% more seed cotton than the untreated control plots. In E. vittella infested field, S. carpocapsae strain APKS2 and H. bacteriophora strain KKMH1 at 2×10^(9)IJs·hm^(-2)resulted in 60.6%~62.4% larva reduction, 68.4%~70.7% square damage reduction, 66.6%~69.9% boll damage reduction and 45.9% yield increase over the untreated control. The effective EPN treatments were comparable to the chemical insecticide chlorpyriphos 20% emulsifiable concentrate spraying at 2 mL·L^(-1).Conclusions: This study has shown that EPN have great potential in the management of the bollworm complex in cotton. Foliar spraying EPN strain S. carpocapsae(APKS2) at 3×10^(9)IJs·hm^(-2) and S. carpocapsae(APKS2) or H. bacteriophora(KKMH1) at 2×10^(9)IJs·hm^(-2) five times at 10days intervals are the best for the management of H. armigera and E. vittella, respectively.

Assessing immunocompetence in red palm weevil adult and immature stages in response to bacterial challenge and entomopathogenic nematode infection

Parasites and pathogens can follow different patterns of infection depending on the host developmental stage or sex.In fact,immune function is energetically costly for hosts and trade-offs exist between immune defenses and life history traits as growth,de-velopment and reproduction and organisms should thus optimize immune defense through their life cycle according to their developmental stage.ldentifying the most susceptible target and the most virulent pathogen is particularly important in the case of insect pests,in order to develop effective control strategies targeting the most vulnerable individuals with the most effective control agent.Here,we carried out laboratory tests to identify the most susceptible target of infection by infecting different stages of the red palm weevil Rhynchophorus ferrugineus(larvae,pupae,male,and female adults)with both a generic pathogen,antibiotic-resistant Gram-negative bacteria Escherichia coli XL1-Blue,and two specific strains of entomopathogenic nematodes(EPNs),Steinernema carpocapsae ItS-CAO1 and Heterorhabditis bacteriophora ItH-LUI.By evaluating bacterial clearance,host mortality and parasite progeny release,we demonstrate that larvae are more resistant than adults to bacterial challenge and they release less EPNs progeny after infection despite a higher mortality compared to adults.Considering the two EPN strains,S.carpocapsae was more virulent than II.bacteriophora both in terms of host mortality and more abundant progeny released by hosts after death.The outcomes attained with unspecific and specific pathogens provide useful information for a more efficient and sustainable management of this invasive pest.