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Effect of entomopathogenic nematodes and some pharmaceutical inhibitors of eicosanoid biosynthesis on the desert locust Schistocerca gregaria (Forskal)
Abstract
The entomopathogenic nematodes, Heterorhabditis and Steinernema together with their associated bacteria Photorhabdus and Xenorhabdus, respectively have come about because of their biological control potentials. To address the immunocompetence of the host insect Schistocerca gregaria following nematode infection, we tested a hypothesis that the insect immune-mediating eicosanoid pathway may be affected by the virulent action of the Egyptian nematode isolate H. indica(RM 1). Haemocoelic injection of the nematode into the fifth instar nymphs of Sc. gregaria evoked the haemocyte microaggregation and nodulation reactions as well as increased the mortality percentages of these economically important pest. Separate treatments with specific inhibitors of the phospholipase A 2 ; the cyclooxygenase and the dual cyclooxygenase / lipoxygenase pathways, reduced both haemocyte microaggregation and nodulation reactions, supporting the point of view that nodule formation is a complex process involving both cyclooxygenase and lipoxygenase products. The inhibitory effects of the phospholipase A 2 inhibitor, dexamethasone, on microaggregation and nodulation were obviously apparent during the first hour of injection and these effects increased greatly over the following 24h . The dexamethasone effects were expressed in a dose-dependent manner and they were reversed by the co-injection of the nematode-injected insects with the exogenous eicosanoid-precursor polyunsaturated fatty acid, arachidonic acid (C20:4n-6). These findings strongly support the identification of microaggregation and nodulation as a specific insect cellular defense reactions that are mediated by eicosanoids. The Sc. gregaria nymphs contain trace levels of the
... Control nymphs were injected with 2 l of ethanol (95%). Three to ten min after injection of the inhibitor, the nymphs w ere injected with five individuals of infective juvenile nematodes (Shairra 2007). At 12 h post injection, the nymphs were anesthetized on ice and haemocyte microaggregations were assessed. ...
... The efficacy of the entomopathogenic nematode S. glaseri on S. gregaria 5 th instar nymphs is presented in From the present work, it was evident that S. gregaria nymphs were comparably susceptible to the tested nematode S. glaseri with significant different levels of potencies depending upon IJs dosage. Coincided results were also observed by Shairra (2007) she working on S. gregaria nymphs was comparably susceptible to the two tested nematodes Heterorhabditis bacteriophora (RM1) and S. glaseri with significant different levels of potencies depending upon IJs dosage. Generally, the host mortality percentage of was positively correlated with the nematode IJs dose. ...
... The dual cyclooxygenase/lipoxygenase inhibitor, phenidone reduced the formation of microaggregates in locust nymphs (Table 2). Similar results were obtained by Miller et al., 1996& 1999and Shairra, 2007. They observed that, the inhibitory effects of the phospholipase A2 inhibitor, dexamethasone, on nodulation were apparent 1 h after infection in larvae of the tenebrionid beetle, Zophobas atratus and in adults of the cricket, Gryllus assimilis; also, in locust, S. gregaria nymphs within 2h of injection, and nodulation was significantly reduced, relative to control tenebrionid beetle, over 24h. ...
The present work mainly focused on the susceptibility of Schistocerca gregaria (Forskal(5 th instar nymphs to the entomopathogenic nematodes, Steinernema glaseri (Rhabditida: Steinernematidae) as a natural exposure experiment. The entomopathogenic nematode, S. glaseri turned out to be successful parasitoid of the orthopteran insect S. gregaria. The death rate of locusts (sprayed with nematode on clover leafs) was remarkably high. Nematode killed approximately 65% of the locust with in 72 hours post infection at semi-field trial. The impact of parasitation on locusts' immune defense was closely investigated for S. gregaria parasitized by S. glaseri. Nymphs died within 48-72h after being fed clover leafs contaminated with 1500/ml S. glaseri juveniles or previously contaminated with the dual cyclooxygenase/lipoxygenase inhibitor, phenidone. The injection of S. gregaria nymphs with, phenidone exhibited significant reduction in microaggegation in response to the nematode injections. At 12h post-injection, insignificant differences were recorded of the individual inhibitor on microaggregation, compared to the ethanol-treated (control) nymphs. Cellular defense components were strongly influenced by parasitation within the first 12h after injection of the nematodes. Nymph's haemolymph was assayed.
... The tested fungal isolate was found pathogenic to all tested insect species. The results data showed that the mortality percentage increased by increasing the fungal spore concentrations Shairra (2007) and that the younger larval instar was more susceptible to the tested fungus than the older larval one Purwar and Sachan (2005). ...
... ELB. were with the highest activity, giving a 100% mortality to S. littoralis larvae in a Petri dish assay after 24 h post exposure, while S. monticolum caused the highest mortality rate for larvae (100%) at the concentration of 1600 IJs/dish for all larval instars. Despite the results obtained from Hassan et al. (2016) who reported that the effect of S. glaseri was greater than the nematode, H. bacteriophora, the obtained results agree with those of Shairra and Nouh (2014) who reported that higher concentrations of nematodes caused an acute effect, while the latent effect was observed in the case of lower ones and Shairra (2007) who found a positive relationship between concentration and larval mortality, mainly due to the concentration of IJs. However, the defense reactions against the nematodes and their associated bacteria may play an important role. ...
Abstract The study aimed to evaluate the efficacy of the EPNs against the larvae of Egyptian cotton leaf worm Spodoptera littoralis (Boisduval) and the black cutworm Agrotis ipsilon (Hufnagel) (Lepidoptera: Noctuidae) in vitro before in vivo study. The susceptibility of both larval species to the entomopathogenic nematode species, Steinernema monticolum and Heterorhabditis bacteriophora, was evaluated under laboratory conditions. The concentration of 400 IJs/dish for S. monticolum achieved up to 97.77 and 95.55% mortality rates of the 5 larval instars from 2nd to 6th instars of S. littoralis and A. ipsilon, respectively after 72 h. The concentration of 800 IJs/dish recorded larval mortality rates of 41.86 to 100% against 2nd to 6th instars of A. ipsilon larvae, after 72 h. At the lowest concentration (50 IJs/dish), the larvae of S. littoralis were more susceptible to H. bacteriophora than the larvae of A. ipsilon. The data indicated that 200 IJs/dish was the most effective concentration for all larval stages of both insect pests because the mortality percentage was 100%.
... Also, some pharmaceutical drugs had the same suppressive effect by inhibiting eicosanoids synthesis. One of these drugs is aspirin, the anti-inflammatory drug which acts by inhibiting of the enzyme cyclooxygenase (COX) and the core enzyme in eicosanoid biosynthesis (Shairra, 2007). The present data showed that treatments with aspirin separately or in combination with M. anisopliae had a lethal effect against locust nymphs where the combined treatments were the most effective. ...
Use of contact bioassays of certain bio-products, as aspirin (eicosanoid inhibitor), lactose (lectin inhibitor) and garlic oil, solely or in combination with the fungus, Metarhizium anisopliae showed efficacy against 5 th nymphal instar of Schistocerca gregaria (Forskal). Direct effects on some biological and physiological parameters of the pest were recorded. Moreover, combination treatments showed higher virulence assay than the single ones. Blood cells (plasmatocytes and granulocytes) were swallowed by rupture in plasma membrane. At the same time, granulocytes showed shrinkage with distortion in the cell membrane and undistinguished nucleus when compared with control cells. Pathological changes in the plasmatocytes and granulocytes indicated that the use o f fungus and bio-products might act as immune-suppressants. These findings might be taken into consideration in evaluating the success of microbial insecticides and certain bioproducts against S. gregaria as they open new possibilities to develop highly efficient combined bioproducts on the basis of the effects of the entomopathogenic fungi and the inhibitors.
... Also, some pharmaceutical drugs had the same suppressive effect by inhibiting eicosanoids synthesis. One of these drugs is aspirin, the anti-inflammatory drug which acts by inhibiting of the enzyme cyclooxygenase (COX) and the core enzyme in eicosanoid biosynthesis (Shairra, 2007). The present data showed that treatments with aspirin separately or in combination with M. anisopliae had a lethal effect against locust nymphs where the combined treatments were the most effective. ...
... From the present work, it is evident that S. gregaria nymphs and adults were comparably susceptible to the tested nematode S. carpocapsae with significant different levels of potencies depending upon IJS dosage. These results are in agreement with those of Shairra (2007) who reported that S. gregaria nymphs who reported comparable susceptibility to nematodes H. bacteriophora (RMI) and S. carpocapsae. Generally, the host mortality percentage was positively correlated with the nematode IJS dose. ...
The efficiency of entomopathogenic fungi, Beauveria bassiana and Entomophthora sp. as well as the nematode, Steinernema carpocapsae, against 3rd, 5th instar nymphs and adults of the desert locust, Schistocerca gregaria (Forskal) had been studied under laboratory conditions. Fungi at the concentrations 2.3 × 105, 7 × 107, 3.9 × 109 and 4 × 105, 6.7 × 107, 2.2 × 109 spores/ml and nematode at 5000, 2500, 1250 IJS/ml, respectively were applied on the desert locust by two different treatment methods; spray and soil application. The obtained results revealed that all the locust nymphs and adults were susceptible to fungi and nematode with high mortality rate records. The nematode killed approximately 100% of the tested locust individuals within 3–5 days postinfection and was found more effective than fungi in less time. On the other hand entomopathogenic fungi and nematode were found to be more effective when applied on the soil surface rather than spray treatment. This was common at any concentration used. Based on mortality percentages, all tested fungi and nematode had high potentials for biocontrol agents against S. gregaria.
... Desert locust, Schistocerca gregaria (Forsk.) is a major pest in northern Africa and Middle East. Entomopathagenic nematodes of the family Heterorhabditidae have been used commercially as biocontrol agents of insect pests (Georgis, 1992& Shairra, 2007. ...
The 5 th nymphal instar of Schistocerca gregaria (Forskal) was treated with different doses of the entomopathagenic nematodes Heterorhabditis bacteriophora Hp 88 or Allium sativum (garlic) extract, as well as a combination of both of them. Activity of Hp 88 and garlic extract showed a significant increase in the mortality by increasing the concentration and the post infection time. The study included also defense reaction of the treated nymphs' haemocytes. The role of garlic oil on treated nymphs was studied on the detoxification and the digestive enzymes. Activity of the lactatedehydrogenase (LDH) and the α-esterase increased significantly by increasing the post infection time. On the other hand, the activity of β-esterase increased significantly only after 3 hours post infection, but decreased significantly by increasing the post infection time, whereas the activity of the digestive enzymes and the amylase activity decreased significantly. Obtained results revealed that the studied biocontrol agents can be recommended for controlling S. gregaria.
Pathogenicity of two entomopathogenic nematodes, Heterorhabditis bacteriophora Poinar (HP88 strain) and Steinernema riobrave and two fungi isolates, Metarhizium anisopliae and Beauveria bassiana against 3rd larval instars of cotton leaf worm, Spodoptera litraltois (Boisd.) and the effect of the combination of these pathogen on 3rd instar larvae. The obtained data clearly revealed that, the tested nematodes differed in their efficacies against 3rd instar larvae of S. littoralis. There for the LT50 of nematode, H. bacteriophora (HP88) recorded 152.06; 277.111; 125.064; 83.027& 57.2 respectively at each concentration 16, 32, 64, 128 and 256 Ijs/ml/100g diet separately. Also, LT50 of other nematode, S. riborave recorded 645.362; 287.204; 128.955; 89.354 and 61.716 respectively. The LD50 values of S. riobrave was the most potent nematodes after 48 & 72 hours of treatment (LC50 reached 438.779 & 180.113/ IJs ml/100g diet, with toxicity index (Ti=100) respectively. On the contrary, H. bacteriophora Poinar (HP88 strain) was 584.4752 &199.182/ IJs ml/100 g diet with toxicity index (Ti) 75.07& 90.4, respectively. The fungus, B. bassiana revealed least mortality percentage against the targeted insect pest. M. anisopolie showed the highest mortality rate against S. littoralis larvae. M. anisopliae was the most potent fungi after 7 days of treatment (LC50 reached 2.897E+08 conidia ml-1 with toxicity index, Ti = 100). On the contrary, B. bassiana fungi (LC50= 7.839E+11 spores ml-1 with toxicity index, Ti = 36.96) were the least effective fungi. The median lethal time (LT50 & LT90) for 3rd instar larvae were (2.497&7.959 hours); (2.397 & 11.24 hours) and (2.397&18.032 hours) respectively. In contrast, our results also show the influence of (LT50& LT90) on the enhancement of combination virulence to for 3rd instar larvae were (1.094& 4.296 hours); (0.542& 3.436 hours ) and (1.447&7.214 hours ) at concentration of (108+16Ijs); (106+32Ijs) & (104+64Ijs/ ml/L/100g diet) with M. ansoplae + S. riobrave. Our data observed that, the highest larval mortality of S. littoralis increased with increase in fungi spores and nematodes infective juveniles concentrations and time elapsed after treatment.
Keywords: Spodoptera littoralis; Entomopathogenic; Nematodes; bacteriophora Poinar (HP88 strain) ; Steinernema riobrave; Fungi;Metarhizium anisopliae; Beauveria bassiana; Heterorhabditis.
Pathogenicity of the two entomopathogenic nematodes, Heterorhabditis bacteriophora Poinar (HP88 strain) and Steinernema riobrave and two fungi, Metarhizium anisopliae and Beauveria bassiana as well the combined effect of both against 3 rd instar larvae of the cotton leaf worm, Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae) was studied under laboratory conditions. Data revealed that the tested nematodes differed in their efficacy against 3 rd instar larvae of S. littoralis. The LD50 values for S. riobrave reached 438.8 and 180.1/ IJs ml/100g diet indicated the most potent nematodes at 48 and 72 h post treatment, respectively. On the contrary, LC50 reached 584.5 and199.2/ IJs ml/100 g diet, for H. bacteriophora, respectively. The LC50 values of fungus, B. bassiana revealed least mortality percentage (7.84 x 10 11 spores ml -1), while M. anisopolie was the most potent (2.89x 10 8 spores ml -1) after 7 days of treatment. Probit regression lines for the combination of the tested concentration of fungi and nematodes (B. bassiana+HP88) and (M. ansoplae + S. riobrave) against 3 rd instar of S. littoralis showed that highest larval mortality increased with increasing fungal spores and/ or nematodes juvenile's concentrations.
This chapter presents a historical and comprehensive review of the understanding of arachidonic acid and its oxygenated metabolites in insects and other arthropods. This chapter discusses prostaglandis and eicosanoids in insects. Eicosanoid is an umbrella term for all of the biologically active metabolites of arachidonic and two other C20 polyunsaturated fatty acids (PUFAs). Certain PUFAs are transformed into eicosanoids, which mediate a bewildering array of biological activities, many of which centre around signalling or regulating events within cells. The chapter discusses models of eicosanoid action. An appreciation of the roles of eicosanoids, such as prostaglandins (PGs) and related compounds, in various animal groups entails a broadly comparative physiology. Lying amid nutrition and physiology, arachidonic acid oxygenation involves three major biochemical pathways. The products of each major pathway are often themselves substrates of other pathways. The result is a plethora of oxygenated metabolites, each with a singular potential to exert a potent biological effect on cell function.
1) Nodulation is the first, and qualitatively predominant, cellular defense reaction to bacterial infections in insects and other invertebrates; 2) treating silkworms, Bombyx mori, with the eicosanoid biosynthesis inhibitor, dexamethasone, strongly reduced nodulation responses to bacterial infections; 3) the influence of dexamethasone was reversed by injecting the eicosanoid-precursor polyunsaturated fatty acid, arachidonic acid (20:4n-6), into dexamethasone-treated, infected larvae; 4) the presence of an eicosanoid biosynthesis system in silkworms was documented. Demonstrated elements include a digestive phospholipase A2, incorporation of exogenous 20:4n-6 into fat body phospholipids, the presence of 20:4n-6 in cellular phospholipids, a fat body intracellular phospholipase A2 that can hydrolyze 20:4n-6 from cellular phospolipids, and eicosanoid biosynthetic enzymes; and 5) these findings support the hypothesis that eicosanoids mediate cellular immune responses to bacterial infections in silkworms.
Experiments utilizing a range of bacteria of differing pathogenicities injected into larvae have shown that:1. At levels above 103 bacteria/μm hemolymph, phagocytosis is usually augmented by nodule formation.2. The cellular defenses elicited are dependent on the nature of the test bacteria.3. Non-pathogens are effectively contained and killed within nodules while pathogenic forms can escape from these structures and induce a fatal septicemia.4. Hemolymph from naive insects contains no antibacterial factors.5. Bacteriostatic and bactericidal factors can be induced in larvae by immunization with pathogens, non-pathogens or saline.These results are discussed in terms of the interaction of cellular and humoral defense reactions in the production of an integrated and complete immunoresponsiveness.
Suitability of different plants as food for the grasshopper H. littoralis was studied in the laboratory by breeding just hatched hoppers and newly fledged adults on a restricted diet. Hoppers and adults of this species possess almost the same food taste. Out of 11 plant species only 4 species (clover, cotton, flax, bean) proved favourable as pure diets for survival, development, and reproduction of this grasshopper, with little differences in the growth rates of the hoppers. Garden purslane and lupin were readily devoured, but the hoppers showed a high mortality rate (70–80%), and the adults were short-lived. Fecundity was much lowered on purslane, and no eggs were laid when fed on lupin. The remaining 5 gramineous plants (maize, wheat, barley, stargrass, alfa) proved strictly unfavourable. Hoppers could not moult, and adults could not survive or lay eggs. This may show that H. littoralis is a non-graminivorous species.
Entwicklung und Überleben von Heteracris littoralis Rambur an bestimmten Nabrungspflanzen (Orthoptera: Acrididae)
Es wurde die Eignung bestimmter Pflanzenarten als Nahrung für die Heuschrecke H. littoralis im Labor, am Objekt frisch geschlüpfter Larven sowie neu gebildeter Adulten untersucht. Von 11 Pflanzenarten gewährleisteten nur 4 (Klee, Baumwolle, Flachs und Bohne) Überleben, Entwicklung und Reproduktion der Heuschrecke bei geringen Unterschieden in der Wachstumsrate. Portulak und Lupine wurden zwar gefressen, doch zeigten die Larven hohe Mortalität (70–80%) und die Adulten lebten nur kurze Zeit. Portulak bewirkte eine starke Verminderung der Fekundität, Lupine ein Ausbleiben der Eiablage. Die übrigen grasartigen Pflanzen (Mais, Weizen, Gerste, Sterngras und Alfagras) waren als Nahrung absolut ungeeignet. Die Larven konnten sich nicht häuten und die Adulten keine Eier ablegen. Dies zeigt, daß H. littoralis nicht zu den Gramineen-Fressern gehört.
The time course of clearance of an injected dose of 106 CFU ml−1 hemolymph of Pseudomonas aeruginosa ATCC 9027 in larvae of the tobacco hornworm, Manduca sexta, has been examined in detail. The clearance process has been subdivided into three stages during which the rates of reduction in concentration of circulating viable bacteria were clearly different. Contributions of hemocyte reactions to bacterial clearance were examined during stages I and II. During stage I (0–2 hr postinoculation (PI), nodule formation produced a dramatic reduction in circulating bacteria by entrapping over 90% of the injected dose in the first 30 min. Phagocytosis of bacteria by circulating hemocytes and subsequent intracellular digestion contributed significantly to reductions in circulating bacteria during stage II (2–8 hr PI). Viable cells of the virulent P. aeruginosa P11-1 were trapped in nodules as efficiently as the less virulent 9027 during the first 30 min after injection into M. sexta. Bacteria of strain P11-1 were also phagocytosed by hemocytes during stage II, however, phagocytosed bacteria were observed less frequently in P11-1-treated insects and intracellular digestion of these bacteria was only rarely observed. The increased virulence of P11-1 in larvae of M. sexta may be due to less efficient phagocytosis by circulating hemocytes and to insensitivity of this strain to killing reactions in nodules and following phagocytosis.
The extent of hemocytic aggregation (“nodule formation”) induced in the locust, Schistocerca gregaria, and the cockroach, Periplaneta americana, by injecting suspensions of conidiospores from the entomopathogenic fungus, Metarhizium anisopliae, or solutions of molecules from microbial cell walls was quantified by flushing out and both counting and noting the size of the aggregates produced. In the locust, all the suspensions and solutions tested stimulated large numbers of nodules to form within 1 hr postinjection, compared with the saline-injected controls. The size of the nodules induced varied with the inducing agent. A fresh spore suspension stimulated the formation of large nodules, generally >100 μm in diameter. Nodules in the medium size range (40–100 μm) were induced by a solution of Laminarin, an algal β-1,3-glucan oligomer, whereas a solution of mixed β-1,3- and β-1,6-glucans from Zymosan (cell walls from the yeast, Saccharomyces cerevisiae) or solutions of bacterial lipopolysaccharides (LPS) induced nodules in the small size range (< 40 μm). A 24-hr-old spore suspension induced formation of both large and small nodules, and it was found that small nodules could be induced by injection of only the supernatant from this suspension. Since the locust is known to exhibit a poor cellular response, compared with the cockroach, to many types of injected biotic and abiotic particles, the effect of injecting LPS and Zymosan solutions into cockroaches was investigated and was found to induce the same order of response as in the locust. Nodule formation was not induced in insects injected with saline or a solution of dextran (α-1,6-linked glucans). The results are discussed in the context of recognition of non-self, and a hypothesis is proposed to account for the differences in size of the nodules stimulated by the different inducers.
A technique for the collection of stable hemolymph from larvae of Manduca sexta has been developed. The method avoids the cell clumping and melanization reactions commonly encountered with insect hemolymph by minimizing contact between hemocytes and surfaces which provoke defensive or repair responses. The circulating hemocyte population of second-day, fifth-instar larvae (2dL5) of M. sexta consisted of 4.5 ± 2.5 × 106 cells/ml (n = 15, range 2–7 × 106 cells/ml) and contained five cell types: prohemocytes, plasmatocytes, granulocytes, spherulocytes, and oenocytoids. Two strains of Pseudomonas aeruginosa which differ in pathogenicity (P11-1 and 9027) and Escherichia coli D31 grew well at 26°C in cell-free hemolymph prepared from naive (nonimmunized) 2dL5 M. sexta. When viable cells of any of the three bacteria were injected into M. sexta larvae, changes in both the total hemocyte count (THC) and differential hemocyte count were observed. Viable bacteria were not required to produce these changes since formalin-killed cells of P. aeruginosa 9027 produced a qualitatively and quantitatively similar response. Following injection of bacteria, the THC increased, reaching a maximal level at 1 hr postinjection, and remained elevated for at least 4 hr after injection. While prohemocytes, plasmatocytes, granulocytes, and spherulocytes all increased in number, 80% of the increased cell population at 1 hr postinjection of bacteria were the latter two cell types. Granulocytes and spherulocytes are cells with recognized defensive capabilities. The increased numbers of these cells in circulation soon after injection of bacteria may confer an advantage on M. sexta larvae in dealing with bacterial infections. This could explain in part the unusual resistance of M. sexta to certain bacterial pathogens.
Octopamine (1) injected into Galleria mellonella induced changes in the haemograms of the larvae identical to those in insects infected with Bacillus cereus, (2) was elevated during bacterial infection in vivo, and (3) accelerated the removal of microorganisms from the haemolymph. The modulation of these non-self responses by octopamine was independent of prophenoloxidase activation. Octopamine in vitro bound to the surface of the insect pathogens B. cereus and Xenorhabdus nematophilus. Injecting the octopamine-coated bacteria accelerated their removal from haemolymph over a 30 min post-injection period. It is proposed that octopamine is a bifunctional molecule acting as both a modulator of haemocyte activity and mediating bacterial attachment to haemocytes.
Nodulation, which begins with the formation of cellular microaggregates, is the predominant cellular defense reaction to bacterial infections in insects. We suggested that these reactions to bacterial infections are mediated by eicosanoids. The lipopolysaccharide (LPS) component of some bacterial cells stimulates defense reactions in mammals and insects. Here, we report on experiments designed to test the hypothesis that eicosanoids mediate microaggregation reactions to LPS. Injections of LPS (purified from the bacterium, Serratia marcescens) into larvae of the tenebrionid beetle, Zophobas atratus, stimulated microaggregation reactions in a dose-dependent manner. Treatments with eicosanoid-biosynthesis inhibitors immediately prior to LPS challenge sharply reduced the microaggregation responses. Separate treatments with specific inhibitors of phospholipase A2, cyclooxygenase and lipoxygenase reduced microaggregation, supporting our view that microaggregate formation involves lipoxygenase and cyclooxygenase products. The inhibitory influence of dexamethasone was apparent within 30 min after injection, and microaggregation was significantly reduced, relative to control insects, over the following 90 min. The dexamethasone effects were reversed by treating LPS-injected insects with the eicosanoid precursor, arachidonic acid. These findings indicate that cellular defense reactions to a specific component of bacterial cells are mediated by eicosanoids, and open up new possibilities for dissecting detailed hemocytic actions in insect immune reactions to bacterial infections.