Kairomones and their use for management of entomophagous insects: III. Stimulation ofTrichogramma achaeae,T. pretiosum,andMicroplitis croceipes with host-seeking stimuli at time of release to improve their efficiency

Frass from larvae of the corn earworm,Heliothis zea (Boddie) and scales fromH. zea moths (that are known to contain the host-seeking stimulus, tricosane) stimulate and orient host-seeking activity in femaleMicroplitis croceipes (Cresson), a larval parasite ofH. zea, andTrichogramma spp., egg parasites ofH. zea. When larval frass, moth scales, and tricosane were used as sign stimuli (releasers) forM. croceipes, T. pretiosum (Riley), andT. achaeae Nagaraji and Nagarkatti, respectively, at time of their release from laboratory containers, parasite performance improved, resulting in significantly increased rates of parasitization over that of unstimulated parasites. Stimulation ofM. croceipes with larval frass had an overriding effect on this parasite's innate tendency to disperse upon release, thereby increasing the numbers remaining and prolonging their retention in the target area. Supplying the appropriate host-seeking stimuli to these 3 hymenopterous parasites ofH. zea at time of their release to improve their efficiency greatly increases the probability of their effective utilization in pest management systems.     

Differential effect of tomatine and its alleviation by cholesterol on larval growth and efficiency of food utilization inHeliothis zea andSpodoptera exigua

The effect of tomatine on larval growth ofHeliothis zea andSpodoptera exigua was assessed by rearing larvae on diets with different concentrations of the chemical added. When reared from neonates, linear dose-response relationships were obtained for both species, withS. exigua being three times more sensitive to tomatine thanH. zea. Tomatine toxicity was completely alleviated inH. zea by the addition of equimolar cholesterol into the diet; however, inS. exigua some toxicity was maintained. Larvae ofS. exigua that were started on control diet were insensitive to tomatine after five days; larvae started on diet with an EC₅₀ of tomatine and then switched to control diet after five days failed to recover from toxicosis. Larval growth ofH. zea, on the other hand, was affected both at the neonate and third-instar stage, but normal growth resumed when the larvae were transferred to control diet. Tomatine had little or no affect on food consumption, assimilation, or dietary utilization of the food by third-instar larvae ofS. exigua, except at a concentration 10 times the EC₅₀. In contrast, the efficiency of food utilization ofH. zea larvae decreased with increasing tomatine concentrations. Assimilation of the food tended to increase, although not significantly, as tomatine levels increased. Food consumption ofH. zea larvae also increased when the tomatine concentration was greater than an EC₅₀. The addition of equimolar cholesterol to diets with an EC₅₀ of tomatine restored weight gain and nutritional indices values to control values. These results are related to the utility of using tomatine in host-plant resistance programs.     

Examination of Different Tobacco (Nicotiana spp.) Types Under- and Overproducing Tobacco Anionic Peroxidase for Their Leaf Resistance to Helicoverpa zea

First-instar larvae of the false tobacco budworm (corn earworm, Helicoverpa zea) that fed on either intact plants, leaf disks from undamaged plants, or leaf disks from insect-damaged plants of Nicotiana sylvestris and N. tabacum Coker plants overproducing a tobacco anionic peroxidase generally caused significantly less damage than those caged with corresponding material from wild-type plants. In some cases mortality was significantly higher and weights significantly less for caterpillars feeding on leaf material from overproducing vs. wild-type plants. First-instar H. zea fed on the same type of leaf material from N. tabacum Xanthi underproducing tobacco anionic peroxidase generally caused significantly more damage than those fed leaf material from wild-type plants. However, first-instar H. zea fed on underexpressing leaf material from N. sylvestris did not cause significantly greater damage compared to wild-type material. In cases where peroxidase enzyme activity was determined, significantly higher mean peroxidase activity was seen in leaves of plant types that also had significantly less mean feeding ratings. This information suggests that peroxidase activity can contribute to leaf resistance to chewing insects. However, the context of the peroxidase (cooccurring substrates, additional inducible factors) can mediate the degree of influence seen by changes in individual peroxidase isozyme levels.     

Constituents of osmeterial secretion of pre-final instar larvae of citrus swallowtail,Papilio demodocus (Esper) (Lepidoptera: Papilionidae)

The defensive osmeterial secretion of pre-final instar larvae of the citrus swallowtail,Papilio demodocus (Lepidoptera: Papilionidae) was found to contain methyl 3-hydroxybutanoate, 3-hydroxybutanoic acid, α-pinene, myrcene, limonene, β-phellandrene, (Z)-ocimene, (E)-ocimene, β-caryophyllene, (E)-β-farnesene, and germacrene-A, as well as a further number of unidentified sesquiterpenoid constituents. The presence of germacrene-A in the secretion was inferred from the formation of β-elemene under certain GC conditions. Larvae of the second, third, and fourth instars produce qualitatively similar secretions. Remarkable quantitative differences were found between the secretions of individual larvae. These variations could not be correlated with the diet on which the larvae were fed, their sex, instar, or color form. However, in a number of larvae the two prongs of the osmeterium were found to produce quantitatively different secretions.     

Effects of cotton condensed tannin,maysin (Corn) and pinitol (soybeans) onHeliothis zea growth and development

Maysin, a flavone glycoside from corn silks, inhibits ingestion, and thus growth, ofHeliothis zea (Boddie) larvae. Pinitol from soybeans inhibitedH. zea growth by the same mechanism. Despite the widely held assumption that tannins inhibit growth by inhibiting assimilation, cotton condensed tannin inhibitedH. zea growth by reducing ingestion; no evidence was found for a reduction in assimilation. Neonate larvae are shown to be much more sensitive to allelochemics than larvae that have fed on control diet before being transferred to diet containing plant allelochemics.Reference to a company and/or product named by the department is only for purposes of information and does not imply approval or recommendation of the product to the exclusion of others which may also be suitable.Published with the approval of the director of the Delaware Agricultural Experiment Station as Miscellaneous Paper No. 968, Contribution No. 514 of the Department of Entomology and Applied Ecology, University of Delaware, Newark, Delaware 19711.     

Ovipositional response of threeHeliothis species (Lepidoptera: Noctuidae) to allelochemicals from cultivated and wild host plants

The role of plant allelochemicals on the oviposition behavior ofHeliothis virescens (F.),H. subflexa (Guenee), andH. zea (Boddie) was investigated in the laboratory using a “choice” bioassay system. Fresh young leaves of tobacco,Desmodium tortuosum (Swartz) de Candolle, groundcherry (Physalis angulata L.), and cotton (Gossypium hirsutum L.) squares (flower buds) were washed in methylene chloride or methanol, concentrated to 1 g equivalent of washed material, and applied to a cloth oviposition substrate. Each of the extracts—including groundcherry, a nonhost—stimulated oviposition byH. virescens. H. subflexa were stimulated to oviposit by groundcherry extract, its normal host, and extract from cotton squares, a nonhost. None of the extracts stimulated oviposition byH. zea, although all except groundcherry were from reported hosts. The sensitivity of the bioassay was confirmed by givingH. virescens andH. subflexa an opportunity to choose between extracts that showed stimulant qualities when tested independently versus only solvent-treated controls. In these tests, tobacco showed the highest level of stimulant activity forH. virescens; groundcherry exhibited the highest level of stimulation forH. subflexa.     

Waxes and volatile oils inHypericum ericoides (Guttiferae)

A wax isolated from an hexane extract ofHypericum ericoides L. was shown to contain only an, aldehydic and an alcoholic fraction. The aldehydic fraction was found to be largelyn-octacosanal (≈77%), with minor amounts of other linear homologous aldehydes, whereas the alcoholic fraction was almost puren-octacosanol. From the same hexane extract, a volatile oil was also isolated and studied by combined gas chromatography-mass spectrometry (GC-MS). Monoterpene, sesquiterpene and aliphatic straight chain (C₈–C₁₁) hydrocarbons, sesquiterpene alcohols and aliphatic long-chain acids (C₈, C₉, C₁₀, C₁₁, C₁₂, C₁₄, C₁₆ and C₁₈) were found. Biogenetic relationships are discussed.     

Effect of host sterols on the sterol composition and virulence of a nuclear polyhedrosis virus ofHeliothis zea

The type of sterol in the diet ofHeliothis zea affected not only the sterol composition of the insect larva but also the virulence and/or sterol composition of a single-nucleocapsid nuclear polyhedrosis virus (HzSNPV). This baculovirus, which was purified by differential and sucrose density gradient centrifugation, had a sterol content of 40 ng per 10⁶ polyhedra. When the sterol composition of HzSNPV was characterized by gas liquid chromatography, reversed phase-high performance liquid chromatography, mass spectrometry, proton nuclear magnetic resonance spectrometry and/or ultraviolet spectroscopy, the sterols in the virus were similar to those of the host. The HzSNPV isolated from larvae fed Δ_{5_}, Δ_{0_} or Δ_5,7-sterols contained primarily cholesterol, cholestanol or 7-dehydrocholesterol, respectively. Changes in the sterol composition of HzSNPV affected its LD₅₀, but not LT₅₀, in larvae containing Δ₅-sterols. The LD₅₀ of virus isolated from larvae containing Δ_{0_}, Δ_{5_} and Δ₇-sterols decreased from 275,423 to 32,359 to 5,012 polyhedra/larva, respectively. The latter virus was also more virulent than the one that was isolated from larvae containing Δ_5,7-sterol and had an LD₅₀ of 58,884 polyhedra/larva. In contrast, the LD₅₀ of an HzSNPV (Sandoz, Inc.) containing Δ₅-sterol was not affected by the presence of Δ_{5_}, Δ_{0_} or Δ_5,7-sterols in the tissues of the host (1,413; 1,288 and 355 polyhedra/larva, respectively). The results of this study indicate that the sterol composition ofH. zea can affect the sterol composition of HzSNPV and therefore may affect the ability of this biological control agent to control its economically important insect host.     

Growth inhibitors in tomato (Lycopersicon) to tomato fruitworm (Heliothis zea)

Several compounds that retard the larval growth of the tomato fruitworm,Heliothis zea (Boddie) have been isolated and identified from tomato leaves,Lycopersicon esculentum Mill. The major allelochemics are -tomatine (I), chlorogenic acid (II), rutin (III), and a new caffeyl derivative of an aldaric acid (IV). The isolation, analyses, and toxicity of these compounds toH. zea are presented.Reference to a company and/or product named by the department is only for purposes of information and does not imply approval or recommendation of the product to the exclusion of others which may also be suitable     

Antifouling agents from marine spongeLissodendoryx isodictyalis carter

The spongeLissodendoryx isodictyalis is an odorous, encrusting, blue-gray sponge found on subtidal flats in North Carolina waters. The strong odor ofL. isodictyalis, coupled with the observation that it is rarely overgrown by fouling organisms, suggested that this sponge may produce metabolites with potent antifouling activity. Ethyl acetate extracts ofL. isodictyalis inhibit larval settlement of the barnacleBalanus amphitrite in laboratory assays at 10 ng/ml. Barnacle settlement bioassays of isolated preparative TLC fractions show thatL. isodictyalis produces at least two pungently scented, antifouling agents with EC₅₀ values of less than 85 μg/ml and less than 250 μg/ml, respectively. The most potent agent inhibits settlement at or below a concentration of 400 ng/ml and kills approximately 25 % of settlement-stage barnacle larvae at 400 μg/ml. The other agent causes 100% mortality of larvae at concentrations greater than 400 μg/ml and inhibits settlement at approximately 40 μg/ml. These metabolites ofL. isodictyalis may inhibit overgrowth of the sponge in nature.     

Interaction of nuclear polyhedrosis virus with catechols: Potential incompatibility for host-plant resistance against noctuid larvae

Two major orthodihydroxy phenolics ofLycopersicon esculentum, rutin and chlorogenic acid, have previously been identified as potential sources of host-plant resistance against the tomato fruitwormHeliothis zea. We report here the possible incompatibility of these chemically based resistance factors with viral control ofH, zea. We have found that both rutin and chlorogenic acid significantly inhibited the infectivity of nuclear polyhedrosis viruses. Chlorogenic acid, when added to tissue culture medium containing TN-368 ovarian cells, inhibited the infectivity of a multiply embedded virus (AcMNPV) by over 86%. Rutin or chlorogenic acid, when fed toH. zea, inhibited the infectivity of a singly embedded nuclear polyhedrosis virus (HzSNPV), with the greatest degree of inhibition occurring at low doses of viral inoculum. Additionally, the ingestion of these phytochemicals significantly prolonged the survival time of virally infectedH. zea larvae. These results suggest that the effectiveness of nuclear polyhedrosis viruses in controllingH. zea populations may be adversely affected by varieties ofL. esculentum with significant levels (eg. 3.5 mol/g wet weight) of rutin or chlorogenic acid.     

Comparative Toxicity of Mycotoxins to Navel Orangeworm (<Emphasis Type="Italic">Amyelois transitella</Emphasis>) and Corn Earworm <Emphasis Type="Italic">(Helicoverpa zea)</Emphasis>

Mycotoxins, such as aflatoxins and ochratoxins, are widely distributed in nature and are frequently problematic crop contaminants that cause millions of dollars of annual losses in the United States. Insect infestations of crop plants significantly exacerbate mycotoxin contamination. Damage to a variety of nut species by Amyelois transitella Walker (navel orangeworm, NOW) is associated with infection by Aspergillus species and concomitant production of aflatoxins and ochratoxins. Resistance to aflatoxins in this lepidopteran is compared here with the levels of resistance in Helicoverpa zea (corn earworm, CEW), another lepidopteran that routinely encounters aflatoxins in its diet, albeit at lower levels. Measured as the developmental delay caused by aflatoxin B1 (AFB1), it is apparent that the LC₅₀ (defined as the concentration preventing 50% of newly hatched larvae from entering the 2nd instar within 48 h) for AFB1 is 100 times greater for A. transitella than for H. zea. Similarly, A. transitella 1st instars display substantially higher tolerance to ochratoxin A, another mycotoxin contaminant produced by Aspergillus species, than do H. zea. Our studies indicate that A. transitella, although a hostplant generalist, may well be highly specialized for mycotoxin detoxification.     

Synergistic Interactions Between Cry1Ac and Natural Cotton Defenses Limit Survival of Cry1Ac-resistant Helicoverpa Zea (Lepidoptera: Noctuidae) on Bt Cotton

Larvae of the bollworm Helicoverpa zea (Boddie) show some tolerance to Bacillus thuringiensis (Bt) Cry1Ac, and can survive on Cry1Ac-expressing Bt cotton, which should increase resistance development concerns. However, field-evolved resistance has not yet been observed. In a previous study, a population of H. zea was selected for stable resistance to Cry1Ac toxin. In the present study, we determined in laboratory bioassays if larvae of the Cry1Ac toxin-resistant H. zea population show higher survival rates on field-cultivated Bt cotton squares (= flower buds) collected prebloom—bloom than susceptible H. zea. Our results show that Cry1Ac toxin-resistant H. zea cannot complete larval development on Cry1Ac-expressing Bt cotton, despite being more than 150-fold resistant to Cry1Ac toxin and able to survive until pupation on Cry1Ac toxin concentrations greater than present in Bt cotton squares. Since mortality observed for Cry1Ac-resistant H. zea on Bt cotton was higher than expected, we investigated whether Cry1Ac interacts with gossypol and or other compounds offered with cotton powder in artificial diet. Diet incorporation bioassays were conducted with Cry1Ac toxin alone, and with gossypol and 4% cotton powder in the presence and absence of Cry1Ac. Cry1Ac toxin was significantly more lethal to susceptible H. zea than to resistant H. zea, but no difference in susceptibility to gossypol was observed between strains. However, combinations of Cry1Ac with gossypol or cotton powder were synergistic against resistant, but not against susceptible H. zea. Gossypol concentrations in individual larvae showed no significant differences between insect strains, or between larvae fed gossypol alone vs. those fed gossypol plus Cry1Ac. These results may help explain the inability of Cry1Ac-resistant H. zea to complete development on Bt cotton, and the absence of field-evolved resistance to Bt cotton by this pest.     

Alleviation of α-tomatine-induced toxicity to the parasitoid,Hyposoter exiguae,by phytosterols in the diet of the host,Heliothis zea

The solitary, endoparasitic ichneumonid,Hyposoter exiguae (Viereck) is a parasitoid of the tomato fruitworm,Heliothis zea (Boddie). However, the parasitoid is deleteriously affected by the tomato glycoalkaloid, -tomatine, ingested from hosts (H. zea) fed on artificial diets or semipurified extracts of tomato plants that contained -tomatine. -Tomatine causes prolonged larval development; disruption or prevention of pupal eclosion; deformation of antennal, abdominal, and genital structures; and reduction in adult weight and longevity of the parasitoid. These toxic effects are exacerbated when the dietary dose of -tomatine is increased from 12 mol to 20 mol/g dry wt of diet. However, the toxicity of -tomatine is attenuated in parasitoids reared from hosts fed on artificial diets that contain equimolar or supramolar amounts of 3-OH-sterols admixed with -tomatine. Further, the toxicity of extracts from the foliage of different cultivars of tomatoes toH. exiguae is contingent upon the composite levels of -tomatine and total phytosterol (free and esterified). Cultivars with a low total sterol-tomatine ratio are more toxic toH. exiguae. The possible mode of action of -tomatine toxicity toH. exiguae by disruption of sterol metabolism is discussed.     

Chemical ecology and the search for marine antifoulants

The gorgonian octocoralLeptogorgia virgulata (Phylum Coelenterata, Class Anthozoa) is rarely overgrown by fouling organisms and is avoided by most predators. Laboratory experiments suggest that secondary metabolites and calcium carbonate spicules interact synergistically to provideL. virgulata with an effective defense against predatory fish. In spite of these defenses,L. virgulata is consumed by the symbiotic, trophically specialized gastropodNeosimnia uniplicata, which closely mimics the appearance of the gorgonian.Neosimnia uniplicata is readily eaten by fish and appears not to acquire an effective antipredator defense from its gorgonian host. Extracts ofLeptogorgia virgulata andNeosimnia uniplicata strongly inhibited the settlement of the barnacleBalanus atnphitrite. Bioassay-directed purification of the more potent antifouling agents fromL. virgulata led to the isolation of two previously described, diterpenoid hydrocarbons, known as pukalide and epoxypukalide. A third inhibitor of barnacle settlement, whose structure is presently unknown, was obtained from bothL. virgulata andN. uniplicata. When assayed for ability to inhibit barnacle settlement, these three compounds possessed EC₅₀ values ranging from 19 to 55 ng/ml. These secondary metabolites may prevent the overgrowth ofL. virgulata by fouling organisms in nature. The allelochemicals ofL. virgulata, N. uniplicata, and other marine organisms may provide nonpolluting alternatives to existing, commercial antifoulants based on derivatives of tri-n-butyltin.     

Beneficial arthropod behavior mediated by airborne semiochemicals

Heliothis zea (Boddie) larvae fed cowpea seedlings produced volatile semiochemicals to whichMicroplitis demolitor Wilkinson responded in a wind tunnel. However, mostM. demolitor females reared fromH. zea larvae fed an artificial diet were not responsive at emergence to the same volatile semiochemicals. A preflight contact with frass fromH. zea fed cowpea was needed to stimulate a response of sustained flight in a wind tunnel. The most consistent flight response was 7–10 days postemergence. Response resulting from both antennal and ovipositor contact with host frass during preflight stimulation was no better than from antennal contact alone. Chilling the parasitoid pupae rendered most of the emerging females unresponsive to volatile semiochemicals.Hymenoptera: Braconidae.     

Fusaric acid

The ability of naturally occurring levels of theFusarium spp. fungal metabolite fusaric acid to synergize the toxicity of the allelochemicals gossypol, a saponin, and 6-methoxy-2-benzoxazolinone to larvae ofHeliothis zea (Boddie) was tested. Levels of fusaric acid comparable to those found near the fungus increased mortality ofH. zea to gossypol, the saponin, and 6-methoxy-2-benzoxazolinone, and decreased the development rate of surviving larvae exposed to gossypol and 6-methoxy-2-benzoxazolinone. Some effect was also noted for levels of fusaric acid found generally distributed throughout infected plants. The chemical properties of fusaric acid suggest that it synergizes the toxicity of the allelochemicals by inhibiting oxidative enzymes responsible for detoxification. Production of the biosynthetically simple fusaric acid may be a fungal strategy for conserving resources as compared to those fungi that produce biosynthetically complex toxins of their own.The mention of firm names or trade products does not imply that they are endorsed or recommended by the U.S. Department of Agriculture over other firms or similar products not mentioned.