The surface hydrocarbons of larval Heliothis virescens and Helicoverpa zea

Third instar larvae of Heliothis virescens and Helicoverpa zea could be distinguished based on the hydrocarbons of their surface lipids. Hydrocarbons were the major components of the surface lipids and a distinctive capillary gas chromatographic profile could be obtained from a hexane extract of the surface lipids of a single larva. Analysis of hexane extracts of the surface lipids by capillary gas chromatography-mass spectrometry (CGC-MS) showed several obvious differences between the two species: (1) in their gas chromatographic profiles; (2) in the presence of a major alkene, hentriacontene, only in H. zea; (3) in H. virescens the CGC-MS peak with a KI of approximately 2860 was 2-methyloctacosane, but in H. zea it was a mixture of 4-methyloctacosane plus 9,13- and 8,12-dimethyloctacosanes; and (4) in the methyl branch positions of dimethyl-branched alkanes with carbon backbones of C₃₁, C₃₃, C₃₅, C₄₅, C₄₇, C₄₉ and C₅₁. The methyl branch points of H. virescens dimethylalkanes were separated by seven or nine methylenes, while in H. zea the methyl branch points of the dimethylalkanes were separated by three and sometimes five methylenes.     

Populations of Predaceous Natural Enemies Developing on Insect-Resistant and Susceptible Tomato in North Carolina

Naturally occurring populations of immature and adultGeocoris punctipes,adultColeomegilla maculataand immature coccinellids were monitored on field-grown tomato lines susceptible and resistant toManduca sextaandHelicoverpa zea. Helicoverpa zeaandHeliothis virescenseggs and small larvae that serve as prey for these predators also were monitored. MoreH. zeaandH. virescenseggs and small larvae were found on resistant than on susceptible plant lines. However, similar populations of largeH. zeaandH. virescenslarvae were found on resistant and susceptible plants. The number of adultGeocoris punctipes,adultColeomegilla maculataand immature coccinellids on resistant plants was always as high or higher than the number on susceptible plants. The data demonstrate no incompatibility of host-plant resistance with biological control provided by these predaceous insects, but indicate that the number ofG. punctipesand coccinellids required to provide effective biological control may develop too late in the season to be of practical value. Large populations of stilt bugs (Jalysus wickhami,Hemiptera: Berytidae) and spiders were observed to occur earlier in the growing season than eitherG. punctipesor coccinellids and may be a significant source of mortality forH. zeaeggs and small larvae.     

Discovery of novel trimethylalkanes in the internal hydrocarbons of developing pupae of Heliothis virescens and Helicoverpa zea

Novel trimethyl-branched alkanes which eluted with the monomethylalkanes were identified in the internal lipids of Helicoverpa zea but were not present in Heliothis virescens. Their structures were unique in that the first methyl branch occurred on carbon 2 and the 2nd and 3rd methyl branch points were separated by a single methylene. Novel trimethylalkanes identified from their chemical ionization and electron impact mass spectra were 2,18,20-trimethyltetratriacontane, 2,18,20-trimethylhexatriacontane, and 2,24,26-trimethyldotetracontane. Previous reports did not find these trimethylalkanes in the cuticular surface lipids of larvae, pupae or adults of either species. The internal pupal hydrocarbons of H. virescens and H. zea amounted to 123 μg and 304 μg per pupa, respectively. They consisted of n-alkanes (8 and 4%, respectively) and methyl-branched alkanes (88 and 94%, respectively). The n-alkanes ranged in chain length from approximately 21 to 35 carbons and the methyl-branched alkanes from approximately 26 to 55 carbons vs. methyl-branched alkanes from 28 to 37 carbons previously reported for hydrocarbons from the pupal cuticular surface. The major n-alkane was heptacosane (3.3 and 1.2%, respectively, in H. virescens and H. zea). The major methyl-branched alkanes in H. virescens were methylhentriacontane (15%), methyltritriacontane (12%) and dimethyltritriacontane (10%), and in H. zea were methylnonacosane (17%), dimethylnonacosane (9%) and methylhentriacontane (20%). Except for the novel trimethylalkanes, the methylalkane branch points were predominantly on odd-numbered carbons as has been reported for these and other species.     

Toxicity effect of the acaricide fipronil in semi-engorged females of the tick Rhipicephalus sanguineus (Latreille, 1806) (Acari: Ixodidae): preliminary determination of the minimum lethal concentration and LC(50)

Chemical acaricides, especially fipronil (active ingredient of Frontline®), are still the most effective method to control tick populations. In this study, the effectiveness of fipronil was assessed in semi-engorged females of the tick Rhipicephalus sanguineus. A protocol for an in vitro bioassay (AIT) was developed, and the LC₅₀ (lethal concentration 50%) and 95% confidence interval were determined. Ticks were immersed in Petri dishes with different concentrations of fipronil or distilled water for 2 min, dried, and placed in an incubator for 7 days. Dead R. sanguineus females treated with the 14 concentrations of fipronil were counted daily. Mortality results were compared with the Probit analysis, and the LC₅₀ and 95% confidence interval were calculated, g (95): LC₅₀ = 9.647 (4.711 to 13.470). This study was aimed at developing a more appropriate and updated protocol for an in vitro bioassay (AIT – adult immersion test), and providing information on the toxic potential of fipronil (elimination of ectoparasites with lower concentrations) and sensitivity of ticks, especially R. sanguineus, a pest of great interest, due to its occurrence in urban environments.     

Fecundity and oviposition ofEucelatoria bryani, a gregarious parasitoid ofHelicoverpa zea andHeliothis virescens

We examined longevity, fecundity, and oviposition strategies ofEucelatoria bryani Sabrosky (Diptera: Tachinidae), a gregarious endoparasitoid ofHelicoverpa zea (Boddie) andHeliothis virescens (F.) (Lepidoptera: Noctuidae). Longevity of adult femaleE. bryani was not related to body size. In contrast to longevity, largerE. bryani females had greater potential fecundity than smaller females, as determined by the number of embryonated eggs present in the common oviduct. However, female parasitoid size did not affect primary clutch size (number of eggs deposited in a host). Because embryos in eggs located in the ovisac were larger than those located elsewhere in the common oviduct, maximum primary clutch size may be physiologically limited by the number of fully mature eggs a female has available at one time.E. bryani females adjusted primary clutch size in response to host size, for bothH. zea andH. virescens. This adjustment appears to be adaptive because females did not overexploit hosts by depositing more larvae than a host could support. Adult emergence was not related to host size. Although host weight positively influencedE. bryani progeny weight, increases in progeny size with host size were counterbalanced by increases in primary clutch size with host size.     

Sweetpotato whitefly resistance to insecticides in Hawaii: Intra-island variation is related to insecticide use

Susceptibility to acephate, methomyl, and permethrin was determined with laboratory bioassays of field-collected adults from 15 populations of the B biotype of sweetpotato whitefly,Bemisia tabaci (Gennadius) (Homoptera:Aleyrodidae), from Hawaii. Comparisons at the LC₅₀ showed up to 24-fold resistance to acephate, 18-fold resistance to methomyl, and 4-fold resistance to permethrin. Analysis of variance showed significant intra-island variation in susceptibility to each insecticide, but no significant variation among islands. Insecticide use varied from 4 to 103 insecticide sprays per site per season. Acephate and methomyl were used more often than permethrin. The frequency of application and LC₅₀ for each insecticide were positively correlated across sites. These results suggest that local variation in insecticide use was a primary cause of variation in susceptibility. If local insecticide use is a key determinant of resistance, as our results suggest, growers can retard resistance development locally by reducing their own insecticide use.     

Hymenopteran specificity of Bacillus thuringiensis strain PS86Q3

The biological activity of Bacillus thuringiensis (Bt) strain PS86Q3 against five Hymenopteran species was determined by means of bioassays adapted to each species. Four species of sawfly that are important pests of conifers (Diprion pini, Gilpinia hercyniae and Pristiphora abietina) or ornamental plants (Arge rosae), as well as the non-target honeybee, Apis mellifera, were studied. Two out of the four sawfly species tested were found to be sensitive to PS86Q3 crystals or spore/crystal suspensions. A sporulated culture of this strain was moderately active on D. pini, and a complete bioassay with solubilized crystals was performed to estimate the LC₅₀ of 4.9 mg/ml. Pristiphora abietina was also found to be sensitive to PS86Q3, with an LC₅₀ of 1.6 mg/ml. By contrast, at the concentrations tested, PS86Q3 did not prove active on the remaining sawflies, G. hercyniae and A. rosae. The strain was administered orally to check its effects on honeybees which were fed sucrose solutions supplemented with a PS86Q3 sporulated suspension, in a field assay using commercial beehives. No significant differences in larval mortality (as deduced by comparing the number of larvae, pupae and empty cells) were found between the Bt and control treatments. On the basis of the results presented here, the suitability of PS86Q3 for the control of Hymenopteran pests, particularly sawflies, in terms of both potency and environmental safety, is discussed.     

Effectiveness of Heterohabditis bacteriophora strain GPS11 applications targeted against different instars of the Japanese beetle Popillia japonica

Field and laboratory tests were conducted from 2001 through 2007 to assess the effectiveness of entomopathogenic nematode Heterorhabditis bacteriophora strain GPS11 applications targeted against different instars of the Japanese beetle, Popillia japonica. During summer flight, P. japonica adults were trapped and caged on turfgrass plots for oviposition. Larval development was monitored for the occurrence of each instar. Nematodes were applied in the field against each developing instar at 2.5 × 10⁹ infective juveniles/ha. In 2001, field data obtained in October resulted in 75%, 53%, and 33% control with the applications targeted against the first, second, and third instars, 69, 28, and 9 days after treatment (DAT), respectively. In 2002 field trial, data obtained in October indicated 97%, 88%, and 0% control when the applications were targeted against the first, second, and third instars at 66, 43, and 14 DAT, respectively. Additional plots established in 2002 to determine efficacy against each instar at 14 DAT showed control of the first, second, and third instars to be 55%, 53%, and 0%, respectively. In laboratory tests conducted in 2002, 2004, and 2007, P. japonica collected from the field at the occurrence of each instar were exposed to H. bacteriophora at concentrations of 0, 10, 33, 100, 330, or 1000 infective juveniles/grub. Probit analysis of the mortality from three of the four sets of tests conducted showed the first instar to be significantly more susceptible to H. bacteriophora than the third instar at the LC₅₀ level and all tests showed the first instar to be significantly more susceptible than the third instar at the LC₉₀ level. In addition to the observed decrease in the third instar susceptibility to H. bacteriophora, soil temperatures in the mid-western United States during late September and October rapidly decline often reaching below 15 °C by the beginning of October when grubs are in the third instar stage of development. Therefore, we conclude that the applications of the nematodes made in August or September will provide higher control than those made in October, due to the more appropriate temperature for nematode activity and the presence of more susceptible larval stages. Early nematode applications may also provide an opportunity for nematodes to recycle and cause secondary infections.     

Specific binding of activated Vip3Aa10 to Helicoverpa armigera brush border membrane vesicles results in pore formation

Helicoverpa armigera is one of the most harmful pests in China. Although it had been successfully controlled by Cry1A toxins, some H. armigera populations are building up resistance to Cry1A toxins in the laboratory. Vip3A, secreted by Bacillus thuringiensis, is another potential toxin against H. armigera. Previous reports showed that activated Vip3A performs its function by inserting into the midgut brush border membrane vesicles (BBMV) of susceptible insects. To further investigate the binding of Vip3A to BBMV of H. armigera, the full-length Vip3Aa10 toxin expressed in Escherichia coli was digested by trypsin or midgut juice extract, respectively. Among the fragments of digested Vip3Aa10, only a 62 kDa fragment (Vip3Aa10-T) exhibited binding to BBMV of H. armigera and has insecticidal activity. Moreover, this interaction was specific and was not affected by the presence of Cry1Ab toxin. Binding of Vip3Aa10-T to BBMV resulted in the formation of an ion channel. Unlike Cry1A toxins, Vip3Aa10-T was just slightly associated with lipid rafts of BBMV. These data suggest that although activated Vip3Aa10 specifically interacts with BBMV of H. armigera and forms an ion channel, the mode of action of it may be different from that of Cry1A toxins.     

Chemical composition and larvicidal effects of essential oil of Dendropanax morbifera against Aedes aegypti L.

Essential oils obtained from the flowers of Dendropanax morbifera were extracted and the chemical composition and larvicidal effects were studied. The analyses were conducted by gas chromatography and mass spectroscopy (GC–MS) revealed that the essential oil of D. morbifera contained 27 compounds. The major chemical components identified were γ-elemene (18.59%), tetramethyltricyclohydrocarbon (10.82%), β-selinene (10.41%), α-zingibirene (10.52%), 2-isopropyl-5-methylbicylodecen (4.2%), β-cubebene (4.19), and 2,6-bis(1,1-Dimethylethyl)-4-phenol (4.01%). The essential oil had a significant toxic effect against early fourth-stage larvae of Aedes aegypti L. with an LC₅₀ value of 62.32 ppm and an LC₉₀ value of 131.21 ppm. The results could be useful in search for newer, safer, and more effective natural larvicidal agents against A. aegypti.     

Immunological Detection of Hymenopteran Parasitism inHelicoverpa zeaandHeliothis virescens

We have developed a monoclonal antibody that recognizes the larval and adult stages ofMicroplitis croceipes(Cresson) (Hymenoptera: Braconidae) andCotesia marginiventris(Cresson) (Hymenoptera: Braconidae), two principal endoparasitoids of the polyphagous pestsHelicoverpa zea(Boddie) (Lepidoptera: Noctuidae) andHeliothis virescens(F.) (Lepidoptera: Noctuidae). The antibody has been incorporated into an indirect enzyme-linked immunosorbent assay that can be used to distinguish parasitized from unparasitized pests. The antibody cross-reacts with several different hymenopteran parasitoids, but not with any of the noctuid pests we have assayed. An immunoassay based on a broadly reactive antibody such as this one enables comprehensive detection of hymenopteran parasitism with a single antibody reagent.     

Effects of cuticle source and concentration on germination of conidia of two isolates of Nomuraea rileyi

The effects of cuticle from larvae of Trichoplusia ni, Heliothis zea and H. virescens on rate and extent of germination of conidia of a Mississippian isolate (MS) and an Ecuadoran (EC) isolate of Nomuraea rileyi were studied. Solid substrates generally stimulated more germination than submerged substrates. There was little or no effect of cuticle source (H. zea or H. virescens) on germination of either the EC isolate or the MS isolate cultured on a solid substrate, however, differences in patterns of germination were obtained in submerged substrates. Addition of cuticle of H. zea or H. virescens generally increased the germination time for the MS isolate. Germination time for the EC isolate was significantly increased when H. virescens cuticle was used.This article reports the results of research only. Mention of a proprietary product in this paper does not constitute a recommendation for use by U.S. Department of Agriculture.     

Steinernema scarabaei, an entomopathogenic nematode for control of the European chafer

A new entomopathogenic nematode species, Steinernema scarabaei, was evaluated for efficacy against two white grub species, the European chafer, Rhizotrogus majalis, and the Japanese beetle, Popillia japonica, in laboratory, greenhouse, and field trials. In laboratory assays, S. scarabaei caused greater mortality than Heterorhabditis bacteriophora. S. scarabaei was highly virulent with an LC₅₀ of 5.5–6.0 and 5.7 infective juveniles (IJs) per third-instar larva in R. majalis and P. japonica, respectively. In a greenhouse trial, S. scarabaei provided greater mortality of R. majalis at all application rates (0.156–1.25 × 10⁹ IJs/ha) than Steinernema glaseri and H. bacteriophora (both at 1.25 × 10⁹ IJs/ha). Combination of imidacloprid and S. scarabaei resulted in an antagonistic interaction. In a fall field trial, S. scarabaei provided 88 and 75% control of R. majalis at 2.5 × 10⁹ and 10⁹ IJs/ha, respectively, and 54% control of P. japonica at 10⁹ IJs/ha; H. bacteriophora had no effect on mortality of either white grub species. In a spring field trial, unusually cool temperatures impeded nematode activity. Against R. majalis, S. scarabaei provided moderate control (56–59%), whereas Heterorhabditis marelatus provided no control. Mortality of P. japonica was moderate (49–66%) in both S. scarabaei and H. marelatus treatments. Overwinter persistence of S. scarabaei activity was demonstrated in a spring assay of soil from fall treated plots in which nematode infection was absent from control plots and present in treated plots.     

Virulence of entomopathogenic nematodes to larvae of the guava weevil, Conotrachelus psidii (Coleoptera: Curculionidae), in laboratory and greenhouse experiments

The guava weevil, Conotrachelus psidii, is a major pest of guava in Brazil and causes severe reduction in fruit quality. This weevil is difficult to control with insecticides because adults emerge over a long period, and larvae develop to the fourth-instar inside the fruit and move to the soil for pupation. We assessed the virulence of entomopathogenic nematodes to fourth-instar larvae in soil by comparing their susceptibility to nine species or strains: Heterorhabditis bacteriophora HP88, H. baujardi LPP7, and LPP1, H. indica Hom1, Steinernema carpocapsae All and Mexican, S. feltiae SN, S. glaseri NC, and S. riobrave 355. In petri dish assays with sterile sand at a concentration of 100 infective juveniles (IJs) of a given nematode species/strain, larval mortality ranged from 33.5 to 84.5%, with the heterorhabditids being the most virulent. In sand column assays with H. baujardi LPP7, H. indica Hom1, or S. riobrave 355 at concentrations of 100, 200, and 500 IJs, mortality was greater than the control only for H. baujardi (62.7%) and H. indica (68.3%) at the highest concentration. For H. baujardi LPP7 in a petri dish assay, the time required to kill 50 and 90% of the larvae (LT₅₀ and LT₉₀) for 100 IJs was 6.3 and 9.9 days, whereas the lethal concentration required to kill 50 and 90% of the larvae (LC₅₀ and LC₉₀) over 7 days was 52 and 122.2 IJs. In a greenhouse study with guava trees in 20-L pots, 10 weevil larvae per pot, and concentrations of 500, 1000 or 2000 IJs, H. baujardi LPP7 caused 30 and 58% mortality at the two highest concentrations. These results show that H. baujardi is virulent to fourth-instar larvae and has potential as a biological control agent in IPM programs.     

Rearing of two predators,Thanasimus dubius andTemnochila virescens, for the biological control ofIps grandicollis in Australia

Rearing methods for two coleopterous predators,Thanasimus dubius andTemnochila virescens, imported into Australia for the biological control ofIps grandicollis, were developed. Bionomic data obtained from laboratory rearings between 1982–1987 showed thatT. dubius eggs took about 7 days to hatch and that duration of the larval stage was about 42 days. Observations showed thatT. dubius had a prolonged prepupal stage (x=56.4 days, range 14–274 days), which was probably non-diapausal in nature. Mean adult longevity was 50 days (range 1–358 days).Temnochila virescens eggs took almost 9 days to hatch, and a lengthy larval stage (x=155.4 days, range 73–333 days) was observed. Mean duration of the pupal stage was 14 days (range 7–28 days). A long preoviposition period (x=141 days, range 47–206 days) was observed, and adults were very long-lived (x=232.7 days, range 14–667 days). Capacity for increase (r_c) calculated from rearing data suggested that numbers ofT. dubius could be increased faster thanT. virescens. Mortality between 1982–1987 averaged about 70% for both species. However, mortality ofT. dubius in 1987 increased significantly, suggesting that inbreeding or other methodological factors could be responsible. A mass-rearing method usingIps-infested pine billets was developed as a cheaper alternative to laboratory rearing, and was shown to be effective in producing large numbers of insects for release.     

Effect of lectins from Opuntia ficus indica cladodes and Moringa oleifera seeds on survival of Nasutitermes corniger

Biodegradation by termites is a serious problem for wood and crop industries worldwide, and new environmentally friendly alternatives for termite control have been developed. This work investigated the effects of crude and purified preparations containing lectins from Opuntia ficus indica cladodes (OfiL) and Moringa oleifera seeds (WSMoL and cMoL) on Nasutitermes corniger workers and soldiers. Purified OfiL was more active than cladode extracts, showing a stronger termiticidal activity against workers (LC₅₀ of 0.116 mg ml⁻¹) than against soldiers. OfiL was active against soldiers only at 1.5 mg ml⁻¹. All preparations containing WSMoL and cMoL were active only at concentrations of 1.0 and 1.5 mg ml⁻¹. The tested preparations did not exert repellent activity against N. corniger. OfiL was able to kill workers and therefore is potentially a new tool for N. corniger control; as a consequence, this lectin could disturb organization, structure, and maintenance of termite colonies.     

Reproductive Isolation and Genetic Variation between Two “Strains” ofBracon hebetor(Hymenoptera: Braconidae)

Bracon hebetorSay(Hymenoptera: Braconidae) is known primarily as a parasitoid of pyralid moth larvae infesting stored grain. In the 1970s, a parasitoid identified asB. hebetorwas released for control ofHeliothis/Helicoverpaspp. (Lepidoptera: Noctuidae) on the island of Barbados. Because life-history traits of this parasitoid differed from those reported forB. hebetorfrom the United States, we conducted a series of laboratory experiments to determine whether this parasitoid was (i) a population ofB. hebetorthat attacks noctuids in the field or (ii) a different species fromB. hebetor.We confirmed thatHeliothis virescens(F.) was a more suitable host for the Barbados strain than forB. hebetor.However, a stored-grain infesting pyralid,Plodia interpunctella(Hübner), was a more suitable host for the Barbados strain than wasH. virescens.Reciprocal crosses between the Barbados strain andB. hebetorshowed that the two populations were reproductively isolated. No mating was observed during a series of 30-min observations of reciprocal crosses, and the crosses produced only male offspring. Examination of each female's spermatheca confirmed that females were not fertilized. Sequence analysis of a 517-bp fragment of the mitochondrial 16S rRNA gene revealed that two populations ofB. hebetorfrom our laboratory were identical but differed in sequence by 2% from the Barbados strain. Collectively, our results indicate that the Barbados strain is a distinct species fromB. hebetor.     

Effects of different Beauveria bassiana isolates on field populations of Lygus lineolaris in pigweed (Amaranthus spp.)

The tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), is a pest of various fruit, vegetable, fiber, and seed crops; including cotton. Lygus spp. populations often build on alternate host plants before moving to cotton, and in the midsouthern U.S. wild host plants, such as pigweed (Amaranthus spp.), play a major role in L. lineolaris population development. Three isolates of the entomopathogenic fungus Beauveria bassiana (Balsamo) were evaluated for L. lineolaris control in redroot pigweed (Amaranthus retroflexus L.): one from L. lineolaris in Mississippi (TPB3); one from Lygus hesperus (Knight) in California (WTPB2); and one commercial isolate from Mycotrol^® (GHA). Fungal applications resulted in moderate to high mycosis in adults (33 to 80%) and moderate mycosis in nymphs (36 to 53%) that were collected from field plots at 2 days post-treatment and incubated under laboratory conditions. Although TPB3 was previously found to be more pathogenic in laboratory bioassays, there was not a consistent separation of this isolate from the other two isolates in field trials. Where differences in adult mycosis or mortality were observed, TPB3 was the most pathogenic. However, in one field trial 7 day mortality for nymphs treated with GHA was higher than those treated with TPB3 or WTPB2. Infection rates at 2, 7, and 14 days post-treatment from caged and non-caged adults suggested that movement of adults among plots occurred, which could have masked some treatment effects. Fungal treatments did not significantly reduce populations relative to controls. This may have been caused by delayed mortality rates under field conditions and/or difficulties with estimating population change under field conditions characteristic of wild host plant populations (e.g., heterogeneous populations, adult movement, and small plot size). Further work evaluating time–dose–mortality over dynamic temperatures, spring and fall field trials on this and other wild hosts, and improved methods for estimating populations on wild hosts are needed.     

Efficacy of Beauveria bassiana (Blas.) Vuill. against cabbage aphid Brevicoryne brassicae L. (Hem.: Aphididae) in laboratory condition

In order to replace the conventional chemical pesticides, extensive researches have been done on entomopathogenic fungi. Entomopathogenic fungus Beauveria bassiana is an important biocontrol agent against major economic pests and is being employed in Integrated pest management (IPM) along with synthetic pesticides. Cabbage aphid Brevicoryne brassicae L. is one of the important pests of Brassicaceae family. Therefore, in this research, the virulence isolate of B. brassicae (IRAN 429C) was investigated on adults of cabbage aphid under laboratory conditions. The experiments were conducted at 25 ± 2 °C, 60 ± 10 R. H. and a photoperiod of 16:8 (L: D). After preliminary experiments, the adult aphids were treated with fungal concentrations of 1 × 10³ to 1 × 10⁷ spores/ml. Probit analysis was conducted to calculate LC₅₀ and LC₉₅ values for the isolate. Positive correlation was observed between concentrations and pest mortality. LC₅₀ and LC₉₅ values calculated for IRAN 429C isolate are 2.04 × 10⁵ and 1.82 × 10⁸, respectively. The mortality was counted one day after the treatment and then continued for 14 days. Cumulative mortality for 14 days after treatment varied from 54% for IRAN 429C at low concentration (10³ conidia/ml) to 83% at high concentration (10⁷ conidia/ml). The lowest LT₅₀ was obtained at 7.67 days for IRAN 429C isolate at concentration 1 × 10⁷ spore/ml. According to the insecticidal activity of mentioned fungi on cabbage aphid, it can be used in biocontrol programmes of B. brassicae.     

Cytolytic differences among lepidopteran cell lines exposed to toxins ofBacillus thuringiensis subst.Kurstaki. (HD-263) andAizawai (HD-112): Effect of aminosugars and N-glycosylation

Summary Comparison of lytic-dose response behavior of seven lepidopteran cell lines to the activated delta-endotoxin polypeptides ofBacillus thuringiensis subspecieskurstaki (HD-263) andaizawai (HD-112) indicated distinct differences among the lines. The lines derived fromSpodoptera speciesS. exigua (URC-SE-1A) andS. littoralis (UIV-SL-575) were more susceptible to lysis byaizawai towin (Bta) thankurstaki toxin (Btk) as were cells from theLymantria dispar line (IPLB-LD652Y). However, the concentrations of Bta required for lysis of 50% of URC-SE-1A and IPLB-LD652Y cells (LC₅₀) were 0.2 to 0.8 μg/ml compared to 5 to 9 μg/ml for UIV-SL-575 cells. In comparison, Btk LC₅₀ concentrations for the three lines were similar (14 to 19 μg/ml). Cells fromS. frugiperda (IPLB-SF-21AE) andTrichoplusia ni (TN368) were similar in their response to Bta (LC₅₀=2.5 to 3.7 μg/ml) and Btk (LC₅₀=1.0 to 2.8 μg/ml) whereas the lines derived fromHeliothis spp. were the least susceptible to both toxins. The LC₅₀ concentrations for Bta with theH. zea line (IPLB-HA-1075) andH. virescens line (BCIRL-HV-AM1) were >50 μg/ml and for Btk were >50 μg/ml and 42 to 50 μg/ml, respectively, yet for both lines Btk was the more cytolytic. Cytolysis of TN368 cells could be inhibited to varying extents by preincubation of the toxins with the aminosugars of galactose, mannose, and glucose and theirN-acetyl derivatives. The unsubstituted hexoses were not inhibitory. The order of decreasing inhibitory effectiveness was the same for both toxins regardless of the derivative species and followed the order galactose, mannose, and glucose. Also, inhibition of cytolysis could be achieved to varying extents by assaying cells grown in medium with tunicamycin. Lysis with Btk was inhibited 68 and 37% using treated cells of TN368 and IPLB-LD652Y, respectively; however, no inhibition was observed with URC-SE-1A cells. Further, no inhibition of Bta-mediated lysis was obtained with tunicamycin-grown cells of the three lines.