Spodoptera Exigua Larvae Research Articles

Drought Stress in Tomatoes: Changes in Plant Chemistry and Potential Nonlinear Consequences for Insect Herbivores

Insect herbivores respond variably to drought-stressed plants; in some cases herbivore performance (e.g. fecundity, survival) is enhanced, in others it is negatively affected. We used tomato plants to examine the consequences of drought stress intensity on plant chemistry potentially important to insect herbivores in order to gain insights into resolving these conflicting results. In a series of experiments conducted out-of-doors, we measured the concentration of five chemicals previously shown to act as growth reducers against herbivores (2 oxidative enzymes, 2 phenolics, proteinase inhibitor) in control plants and drought-stressed plants over a period of about 14 d. Three of the five defenses increased in response to increasing drought (polyphenol oxidase, rutin, chlorogenic acid), one showed no response (peroxidase) and one was inconsistent in its response (proteinase inhibitor). Simultaneously, we measured three chemicals thought to be important nutrients for insect herbivores (water content, total nitrogen, and soluble carbohydrates). Water content declined with increasing drought stress intensity, total nitrogen increased at severe stress in one experiment and did not respond in a second, and soluble carbohydrates showed a convex response to drought stress. In one experiment we also fed leaf tissue, incorporated into non-nutritive agar, from control and drought-stressed plants to neonate Spodoptera exigua larvae. Growth of these larvae over a 7-d period was negatively affected by drought stress while survival was not significantly affected. This study represents one of the first to assess both chemical defenses and nutrients in plants subjected to drought as it develops from slight stress to a very severe condition. Depending on the direction and shape of response curves for nutrients and defenses, many possible effects on herbivores are predicted, some of them complex and nonlinear. By studying the particular kinetics of defenses and nutrients in plants we may be in a better position to understand why insect herbivores show such variable responses to drought-stressed plants.

Feeding Deterrence of Spodoptera exigua (Lepidoptera: Noctuidae) Larvae by Low Concentrations of Linear Furanocoumarins

We conducted choice tests and behavioral observations of Spodoptera exigua (Hubner) larvae to study the effect of linear furanocoumarins (bergapten, xanthotoxin, and psoralen) individually or in combination at concentrations commonly found in Apium graveolens L. and UV-A light on larval preference and feeding behavior. Linear furanocoumarins had a negative and concentration-dependent effect on diet preference by S. exigua larvae. Behavioral observations showed that preference of control diet is the result of feeding deterrence by these compounds. The larvae leave the furanocoumarin-containing diet more frequently by becoming more mobile after ingestion of the treated diet, as measured by time spent questing (in which larvae walk or lift their thoraxes, and move from side to side in a searching motion) and number of questing occurrences. The UV-A effect was not significant. We conclude that linear furanocoumarins (at the concentrations found in A. graveolens ) can play an important role as behavioral modifiers rather than as toxic defenses against larvae of the generalist herbivore S. exigua .

In vivo recombination between two strains of the genus Nucleopolyhedrovirus in its natural host, Spodoptera exigua.

The DNA restriction map for the enzymes BamHI, BglII, PstI, and XbaI of SeMNPV-US (Se-US), the best-studied Nucleopolyhedrovirus strain isolated from Spodoptera exigua in California, was used as a reference to construct that of SeMNPV-SP2 (Se-SP2), a closely related Spanish strain of the same virus. After coinfection of S. exigua with both the Se-US and Se-SP2 strains per os, a recombinant virus (SeMNPV-SUR1 [Se-SUR1]) was detected after one passage which quickly replaced the parental viruses. A physical map of Se-SUR1 DNA was constructed for BamHI, BglII, PstI, and XbaI and compared to that of the parental viruses, Se-US and Se-SP2. Se-SUR1 is the result of at least four crossover events between Se-US and Se-SP2 and not of selection of a minor variant in one of the parental viruses. Bioassays of the recombinant and parental strains against L2 beet armyworm larvae demonstrated that their 50% lethal dose values were not significantly different. The differences in median lethal time values are too small to explain the replacement of the parental viruses by the recombinant virus upon successive passage in vivo, although it cannot be ruled out as an explanation for the selective advantage of the recombinant strain, Se-SUR1. The consequences of the release of nonindigenous or recombinant baculovirus strains in agro-ecosystems are discussed.

Growth Inhibitory, Insecticidal, and Feeding Deterrent Effects of (12Z, 15Z)-1-Acetoxy-2-Hydroxy-4-Oxo-Heneicosa-12,15-Diene, a Compound from Avocado Fruit, to Spodoptera exigua

We isolated and identified (12Z,15Z)-1-acetoxy-2-hydroxy-4-oxoheneicosa-12,15-diene (persin) from avocado as a compound toxic to Spodoptera exigua larvae. Persin was obtained from oil extracted from the specialized idioblast cells of avocado fruit. When tested for activity using neonates in no-choice artificial diet bioassays, persin at concentrations of 200 μg/g inhibited growth; larvae gained only ∼50% of the weight attained by control insects after seven days. At concentrations of 400 μg/g or above, larval growth was reduced by >70% as measured by weight gain, and significant mortality occurred. In choice tests, persin at concentrations of 400 μg/g or higher deterred feeding, with significantly more larvae being found on control diet than on persin-treated diet. Possible applications of persin as a natural insecticide are discussed.

Attraction of Colorado Potato Beetle to Herbivore-Damaged Plants During Herbivory and After Its Termination

Large, undamaged potato plants (>60 cm, 5–6 weeks old) attract the Colorado potato beetle (Leptinotarsa decemlineata), but small potato plants (15–25 cm high, 2–3 weeks old) do not. However, small plants become attractive to CPB when they are damaged. Mechanical damage inflicted with scissors results in short-term (lasting less than 15 min) attraction, while more severe damage with carborundum powder results in a longer lasting attraction (at least 1 hr). CPB adults are also attracted to small plants infested with CPB and Spodoptera exigua larvae. After the larvae had been removed for 50 min following a short duration (30 min) of feeding, CPB adults were no longer attracted to the plants. However, when CPB larvae had been removed after they had fed for 60–90 min, the plants were somewhat attractive to the beetles, although significantly less than they had been when the larvae were feeding. Attraction increased with time after feeding ceased. Furthermore, beetles were strongly attracted to plants 50 min after larvae were removed when the plants had been fed upon by larvae for 18–24 hr. Thus it appears that there are two stages of attraction, first, to volatiles released directly from the wound site, and second, to volatiles that are induced in response to herbivory. Chemical analyses of the headspace of infested potato plants show that infestation results in the emission of a mixture of chemicals that is qualitatively quite similar to that emitted by undamaged plants. The major components of the mixture are that emitted by undamaged plants. The major components of the mixture are terpenoids and fatty acid derivatives such as aldehydes and alcohols. The emission rate of some of these chemicals declines after removal of the beetles, while the emission rate of other chemicals increases with the duration of beetle feeding and remains at a high level even after removal of the beetles. Thus, the composition of the mixture changes temporally during and after herbivore feeding, which may explain the recorded behavior of the beetles.

Cytolytic activity of Bacillus thuringiensis CryIC and CryIAc toxins to Spodoptera sp. midgut epithelial cells in vitro.

A sensitive lactate dehydrogenase (LDH) assay was modified to determine the cytolytic activity of Bacillus thuringiensis CryIC and CryIAc delta endotoxins to viable collagenase-dissociated midgut epithelial cells (MEC) from larvae of Spodoptera frugiperda and Spodoptera exigua. The MEC preparations from these Spodoptera sp. consisted predominantly of columnar cells (65-75%) and goblet cells (25-35%). Time course microscopy experiments indicated that only the columnar cells became swollen during CryIC toxin incubation. Also, comparative cytotoxicity studies were run with cell lines of nonmidgut origin established from S. frugiperda (SF21AE) and S. exigua (SEUCR1A). Optimum conditions for the cytotoxicity assay were similar for MEC and cell lines of both species, and were met in an assay in which 0.1-ml cell concentrations (8.5 +/- 0.5 x 10(4) cells) were incubated with toxin dilutions (0.01-20 micrograms) for 1 h at 24 degrees C at a final pH of 7.8. The Spodoptera sp. MEC were twofold more sensitive to CryIC (68% lysis) than CryIAc (32% lysis) at optimum toxin levels (2.5-5 micrograms). Also, the SEUCR1A cells were more sensitive (2.3-fold) to CryIC (70% lysis) than CryIAc (30% lysis) at optimum toxin levels of 5-10 micrograms. The SF21AE cells, however, were twofold less sensitive to CryIC (30% lysis) than SEUCR1A cells and response to CryIAc and CryIC was similar. Immunoblot analysis of either Spodoptera sp. MEC or brush border membrane vesicles (BBMV) identified seven CryIC binding proteins with molecular mass of 137, 120, 115, 68, 65, 63, and 45 kDa. Occasionally, a 148-kDa protein band was observed. The CryIAc toxin bound to two proteins on MEC and BBMV with molecular mass of 137 and 120 kDa.

Progeny Allocation by the Parasitoid Lespesia archippivora (Diptera: Tachinidae) in Larvae of Spodoptera exigua (Lepidoptera: Noctuidae)

Field-collected Spodoptera exigua (Hubner) larvae always produce small brood sizes of the gregarious parasitoid Lespesia archippivora (Riley) (1–2 progeny). To further investigate this finding we characterized life history attributes of the parasitoid's offspring in different host instars in the laboratory. Changes in offspring fitness and mortality and rate of successful parasitization can indicate opportunities for tachinids to influence fitness of their progeny. Effects of host instar and parasitoid brood size on parasitoid survival, development, size, and fecundity were investigated. Fecundity was indirectly assessed by measuring parasitoid puparial weight; female puparial weight and egg load are positively correlated. L. archippivora is able to successfully parasitize all investigated instars of S. exigua . The percentage of hosts yielding puparia was highest (95.1%) in 4th instars; it was only 65.5% in prepupal stages of the host. Lower parasitoid emergence rates in younger host instars were caused by higher host survival or premature host mortality. Parasitoid puparial weight decreased with increasing brood size but was not affected by host instar when equal brood sizes were compared. Parasitoid puparial weight from broods of 2 offspring was significantly reduced in broods of 2 female progeny compared with that of females from mixed sex broods of 2 progeny. Progeny allocation of L. archippivora and fitness consequences associated with that allocation are independent of host size. We conclude that by consistently allotting small broods to hosts, L. archippivora adults may reduce strong competition between offspring and maximize successful parasitization, thereby resulting in highly fit females.

Control of Armyworm And Pepper Weevil on Bell Pepper, Fall 1995

Abstract Transplants were set 5 Sep, 12 inches apart on 8-inch-high and 32-inch-wide beds of EauGallie fine sand covered with white polyethylene mulch. Each plot consisted of a single row of 10 plants with rows on 5 ft centers. Treatments were replicated 4 times in a RCB design and were applied with a 2.5 gal, hand-held CO2-powered sprayer on 9 Sep, 6, 13, 20, 27 Oct, 10, 17, 25 Nov, 2, 8, 15, 22 and 29 Dec. The sprayer was outfitted with a single nozzle with a D-5 disk and #45 core and delivered 100 gpa at 60 psi. On 13 Nov, each plot was rated 1 to 12 for increasing defoliation due to armyworm feeding using the Horsfall-Barratt scale. Fruit were harvested on 13, 27 Nov, 18 Dec and 5 Jan. The number and weight of undamaged fruit and the number of fruit damaged by beet armyworm larvae were determined. Fruit also were examined for the presence of surface oviposition scars and larval feeding damage inside, caused by the pepper weevil.

Beet Armyworm (Lepidoptera: Noctuidae) Control on Cotton in Louisiana

Efficacy of selected labeled and experimental insecticides against beet armyworm, Spodoptera exigua (Hubner), populations from Louisiana were determined in both a laboratory diet bioassay and in replicated field plots. Significantly higher LC 50 's for chlorpyrifos and thiodicarb were observed for one of two field-collected strains relative to a laboratory-reference strain in the laboratory diet bioassays. No significant differences in susceptibility between the reference strain and field-collected strains were observed for chlorfenapyr (proposed common name), spinosad or tebufenozide. For the reference strain, LC 50 's (ppm) for tebufenozide, spinosad, chlorfenapyr, chlorpyrifos, and thiodicarb were 2.6, 2.8, 4.8, 4.9, and 319.8, respectively. In two field tests, all three experimental insecticides (chlorfenapyr, spinosad, and tebufenozide) as well as chlorpyrifos significantly reduced the numbers of beet armyworm larvae relative to the untreated control at all sampling periods (3, 5, 7, and 10 days after treatment), except for Test 2 at 3 days after treatment. Thiodicarb provided satisfactory control of larvae in Test 1; however, in Test 2 thiodicarb did not significantly reduce the numbers of beet armyworm compared with the untreated control. The microbial insecticide Spod-X provided inadequate larval control in both tests.

Effects of a Nuclear Polyhedrosis Virus and a Fluorescent Brightener on Colonies of Spodoptera exigua (Hübner)

The beet armyworm, Spodoptera exigua (Hübner), is an important pest which is difficult to control because it is resistant to nearly all registered insecticides. A new commercial formulation of a nuclear polyhedrosis virus that is pathogenic to beet armyworm larvae, SPOD-X®, was tested with and without a fluorescent brightener, Tinopal LPW. The effects on larvae from six colonies of the beet armyworm which had recently been established from field collections in Georgia, Alabama and Mississippi were compared with a laboratory colony which had been maintained in the laboratory for 2 years. The LC50 was lower in all bioassays with SPOD-X in 0.25% Tinopal LPW than with SPOD-X in water, although in 3 of 12 bioassays the difference was not significant based on overlapping 95% confidence intervals. The mean LC50 for SPOD-X in water was 376 polyhedral occlusion bodies per cup (surface area 800 mm2). The mean LC50 for SPOD-X in 0.25% Tinopal LPW was 30 polyhedral occlusion bodies per cup. The LC50 for SPOD-X in water was not significantly different between the laboratory colony and 5 of 6 field-collected colonies when bioassayed concurrently. There was no significant difference in LC50 for SPOD-X in 0.25% Tinopal LPW between the laboratory colony and any of the field-collected colonies. Thus, Tinopal LPW enhanced the infectivity of SPOD-X for beet armyworm larvae in laboratory tests and reduced the variability of response of the beet armyworm colonies to the virus.

Phagocytosis of lectin-opsonized fungal cells and endocytosis of the ligand by insect Spodoptera exigua granular hemocytes: an ultrastructural and immunocytochemical study

Phagocytosis of blastospores of the fungal entomopathogen Paecilomyces farinosus by granular hemocytes from larvae of Spodoptera exigua (beet armyworm) was studied. Blastospores were opsonized with a galactose-specific lectin purified from S. exigua hemolymph or with peanut agglutinin prior to incubation with hemocytes. Observations of thin sections revealed that pseudopodia extending from granulocytes attached to ligands (lectins, lectin conjugates) on the blastospores, and that the ligands became detached from the fungal surfaces and were endocytosed by granulocytes via coated pits on the plasma membrane. Coated vesicles bearing the endocytosed molecules appeared to be transported to the hemocytic granules. In other cases, ligand still coated the blastospores after phagocytosis and may have later concentrated within the phagosome along with digested fungal cell wall components. Phagocytosis of blastospores and clustering of a biotinylated lectin conjugate on or within the granulocytes were inhibited by drugs targeting cytoskeletal elements. Actin was concentrated in the pseudopodia of phagocytic granulocytes and may be directly associated with lectin receptor(s). Microtubules were abundant in the granulocytes, sometimes in specific regions.

Characterization of induced resistance in tomato plants

AbstractWe have characterized, using several types of bioassays, the resistance induced in young tomato plants by feeding of the corn earworm, Helicoverpa zea. Beet armyworm larvae, Spodoptera exigua, and leafminers, Liriomyza trifolii, were used to assay the induced resistance. In whole‐plant experiments, damage localized to a single leaflet of four‐leaf tomato plants induced a systemic increase in resistance such that beet armyworm larvae confined to previously damaged (induced) plants grew at a rate about half that of larvae raised on control plants and consumed less leaf tissue from induced plants than from control plants. In experiments using excised leaves, beet armyworm larvae suffered increased mortality when reared on leaves from induced plants. The strength of this induced resistance varied spatially relative to the damaged position; moreover, the spatial distribution of induced resistance changed over a three‐week period following damage. Other experiments demonstrated that the mechanism of induced resistance in tomato foliage involves both a decrease in larval preference for and a decrease in the nutritional value of induced foliage. Induction also retarded the oviposition and/or early development of leafminers. Thus, induced resistance has relatively severe effects on the biology of subsequent herbivores. These data should allow us to begin to elucidate cause‐effect relationships between induced resistance and induced chemistry in tomato plants.

Baculovirus infection of Spodoptera exigua larvae: lacZ expression driven by promoters of early genes pe38 and me53 in larval tissue.

To follow the progression of infection of Autographa californica multicapsid nuclear polyhedrosis virus (AcMNPV) within tissues of its larval host, we have constructed AcMNPV recombinants carrying lacZ reporter genes under the control of the early virus promoters pe38 and me53, in addition to the authentic genes. The early promoter-lacZ gene cassettes were located upstream of the very late polyhedrin gene. In infected insect cell lines, pe38 transcription is initiated at an early promoter, while me53 transcripts start from both early and late sites. Transcriptional mapping of the duplicated me53 and pe38 promoters driving lacZ expression showed that they initiated at the same start sites as in the authentic genes. Expression of lacZ by these recombinants was compared to a recombinant driving beta-glucuronidase expression from the very late p10 promoter and lacZ expression from the constitutive heat shock protein 70 promoter of Drosophila melanogaster. After infection of Spodoptera exigua larvae with the different recombinants, we followed reporter gene expression and polyhedron formation in different tissues using immunohistochemistry and electron microscopy. LacZ expression, indicative of early viral transcriptional activity, was detected in nearly all larval tissues during the course of infection. In most tissues these early events were followed by pathophysiological changes associated with late and very late gene expression. However, p10 transcription and polyhedron formation were not observed in midgut goblet cells, Malpighian tubules and salivary glands. These results suggest that expression of early virus genes, such as me53 and pe38, is not restricted to larval tissues that are permissive for AcMNPV replication.

Effects of the fungal pathogen, Beauveria bassiana on protein biosynthesis of infected Spodoptera exigua larvae

Vegetative development of Beauveria bassiana in the hemocoel of the beet armyworm, Spodoptera exigua did not cause significant alterations in the profile of hemolymph proteins. Pulselabeling tissue expiants revealed that vegetative growth of B. bassiana hyphal bodies did not impact the biosynthetic capability of either the fat body or cuticle epidermis, both major sites of host protein synthesis. Even at the late stage of hyphal body development, when concentrations reached 3 × 104 fungal cells per μl of hemolymph, both fat body and cuticle expiants were capable of synthesizing and secreting the majority of proteins detected in naive samples. Hemocyte cultures were found to secrete significantly fewer labeled proteins than either fat body or cuticle expiants. Replication of hyphal bodies in hemocyte cultures established from infected larvae induced the synthesis and secretion of 3 peptides having Mr of 31, 32 and 40 kDa. Interestingly, peptides having identical Mrs were detected in infected cell free hemolymph samples. These peptides did not correspond to proteins induced in response to heat shock suggesting that they may represent in vivo produced fungal metabolites. At the very late vegetative growth stage, the hyphal bodies produced germ tubes which invaded host tissues. Unlike the hyphal bodies, the mycelial tissue invasion phase inhibited host protein biosynthesis and produced a range of exocellular peptides.

Cytokinin-containing Seaweed Extract Does Not Reduce Damage by an Insect Herbivore

We examined two aspects of treating plants with a cytokinin-containing seaweed extract (SWE). In the first series of experiments, we tested the hypothesis that immature lima bean (Phaseolus lunatus L.) and tomato (Lycopersicon esculentum Mill.) plants provided with exogenous cytokinins could recover from defoliation by a generalist insect herbivore, Spodoptera exigua (Hübner), more rapidly than plants without cytokinin supplements. However, the SWE inhibited growth of lima beans at all levels of herbivore damage. The SWE neither inhibited nor stimulated growth of tomatoes following defoliation. Because SWE effects largely were neutral for tomato growth, we conducted a second series of experiments to test the hypothesis that SWE treatments alter the attractiveness of tomato foliage to S. exigua larvae. In these experiments, we determined consumption of, and preference for, SWE-treated tomato foliage by S. exigua larvae. Repeated root applications of SWE led to increased consumption and preference by S. exigua. Repeated foliar applications did not alter consumption or preference compared with controls. Spodoptera exigua larvae gained significantly more mass when feeding on SWE-treated foliage compared with controls. While these data indicate that plant responses to exogenous cytokinin-containing materials depend on taxa and application method, the practical uses of SWE appear limited given the negative effects on plant growth and increased attractiveness of treated foliage to herbivores.

Insect Management on Bell Pepper in West-Central Florida, Fall 1994

Abstract Transplants were set 8 Aug, 12 inches apart on 8-inch-high and 32-inch-wide beds of fumigated EauGallie fine sand covered with white polyethylene mulch. Each plot consisted of a single row of 12 plants with rows on 5 ft centers. Treatments were replicated 4 times in a RCB design and sprays were applied with a 2.5 gal, hand-held CO2-powered sprayer on 16, 21, 29 Sept, 7, 13, 20, 27 Oct, 3, 10, 16, 23, 29 Nov, 6 and 13 Dec. The sprayer was outfitted with a single nozzle with a D-5 disk and #45 core and delivered 100 gpa at 60 psi. Granular applications were made just prior to soil fumigation (about 2 weeks prior to planting) in two narrow bands 10 inches on either side of bed centers. On 5-6 Oct, each plant in each plot was inspected for small (≤0.5 inch long) and large (0.5 inch long) beet armyworm larvae. On 3 Nov, each plot was rated by two persons for increasing percentage of defoliation by beet armyworm larvae using the Horsfall-Barratt system. With this system, ratings of 1-12 corresponded to 1-100% defoliation. The ratings were averaged prior to analysis. Fruit were harvested on 2, 21 Nov, 14 and 19 Dec and the number and weight of undamaged fruit and the number of fruit damaged by beet armyworm larvae were determined. Fruit with slight feeding damage only on the stem or calyx were considered marketable. Fruit with either slight or severe damage on the fruit wall were considered unmarketable. Fruit also were examined for the presence of oviposition scars on the outside of the fruit and for the presence of larval feeding damage on the inside of the fruit caused by the pepper weevil. On 16 Dec, each plot was sampled by dislodging the insects from the tops of five plants with a 12 inch garden stake into the bottom of a rectangular cake pan painted black and coated with a thin film of vegetable oil. The numbers of pepper weevil adults, armyworm larvae, predator adults and immatures, and aphids were counted. The numbers of predators were totaled over all species since few of any one species were present.

Efficacy of Selective Insecticides on Beet Armyworm Larvae in Lettuce, 1995

Abstract Lettuce was direct seeded into double-row beds on 8 Sep at the Yuma Valley Agricultural Center, Yuma, Az. Each plot consisted of four, 30 ft long beds spaced 42 inches apart and bordered on each side by an untreated bed. Plots were arranged in a RCB design with 4 replicates. Foliar application was made on 20 Sep and 5 Oct with a hand-held CO2 sprayer operated at 60 psi, delivering 20 gal/acre. Spreader-sticker (Triton-X) was included in all spray treatments at a rate of 0.25% of the total volume. Insecticide efficacy was determined by counting the total number of BAW larvae on 20 randomly selected plants per replicate. Insect counts were conducted the day of application and at 1,3, and 7 days following each application.

Armyworm and Pepper Weevil Control on Bell Pepper in West-Central Florida, Spring 1995

Abstract Transplants were set 14 Mar, 12 inches apart on 8-inch-high and 32-inch-wide beds of EauGallie fine sand covered with white polyethylene mulch. Each plot consisted of a single row of 10 plants with rows on 5 ft centers. Treatments were replicated 4 times in a RCB design and were applied with a 2.5 gal, hand-held CO2-powered sprayer on 7, 13, 20 Apr, 4, 11, 18, 25 May, 1, 9, 14, 21, 29 Jun and 6 July. The sprayer was outfitted with a single nozzle with a D-5 disk and #45 core and delivered 100 gpa at 60 psi. The Neemix 4.5% formulation was inadvertently substituted for the 0.25% formulation for the first three applications. On 16 May, each plot was rated 1 to 12 for increasing defoliation due to armyworm feeding using the Horsfall-Barratt scale. Fruit were harvested on 24 May, 12, 26 Jun and 10 July and the number and weight of undamaged fruit and the number of fruit damaged by beet armyworm larvae were determined. Fruit with slight feeding damage only on the stem or calyx were considered marketable. Fruit with either slight or severe damage on the fruit wall were considered unmarketable. Fruit also were examined for the presence of oviposition scars on the outsides of the fruit and for the presence of larval feeding damage on the insides of the fruit caused by the pepper weevil.

Host-specific recognition kairomone for the parasitoidMicroplitis croceipes (Cresson)

A water-extractable host recognition kairomone in frass of corn earworm,Helicoverpa zea Boddie (Lepidoptera: Noctuidae), host larvae stimulates antennation by females of the parasitoidMicroplitis croceipes Cresson (Braconidae: Hymenoptera). In addition, when the wasps contact water extracts of host frass they will subsequently fly in a flight tunnel to odor associated with the extract. Contact with water extracts of cowpea leaves or with water extracts of frass from larvae of nonhost beet armyworm, fall armyworm, or cabbage looper that were fed cowpea leaves does not stimulate antennation, nor do wasps fly to associated odors after contact with these substances. However, contact with the water extract of host frass in association with hexane extract of cowpea-fed nonhost frass will induce the wasps to subsequently fly to the hexane extract of the nonhost frass when it is used as an odor source in a flight tunnel. Thus the host-specific kairomone by whichM. croceipes recognizes the frass of its host is extractable with water. This substance plays a crucial role in the foraging behavior of this parasitoid by allowing it to recognize host frass and to learn to search for odors originating from plants on which the host is feeding.

Effect of nonsteroidal ecdysteroid agonists on ecdysteroid titer in Spodoptera exigua and Leptinotarsa decemlineata

In control last-instar larvae of Spodoptera exigua, and Leptinotarsa decemlineata, major hemolymph ecdysteroid peaks appeared around day 3–4, and 8–9, respectively, which is correlated with normal apolysis. Later on, hormone titers declined to a basal level. In Colorado potato beetle last-instars, a small rise was noted around day 4, which represents the time of digging. In last-instar larvae of S. exigua treated with either RH-5849 or tebufenozide, the ecdysteroid titer remained at a basal level without any elevation. Such larvae showed signs of untimely apolysis within 12–24 h after treatment followed by cessation of fresh weight gain. Likewise, hemolymph ecdysteroid levels and larval weight gain were reduced in last-instar larvae of L. decemlineata treated with RH-5849 as compared with controls. Otherwise, treatment of Colorado potato beetle larvae with tebufenozide caused no hormonal and physiological abnormalities as compared with controls. It is suggested that both nonsteroidal ecdysteroid agonists act via ecdysteroid receptor binding without an increase in ecdysteroid titer.