Mortality Bioassays Research Articles

Fumigant toxicity of cassia and cinnamon oils and cinnamaldehyde and structurally related compounds to Dermanyssus gallinae (Acari: Dermanyssidae)

The toxicity of two cassia oils, four cinnamon oils and ( E)-cinnamaldehyde and ( E)-cinnamic acid and 34 structurally related compounds to adult Dermanyssus gallinae (De Geer) collected from a poultry house was examined using a vapour-phase mortality bioassay. Results were compared with those of dichlorvos, a conventional acaricide. The cassia and cinnamon oils (cinnamon technical, cinnamon #500, cassia especial, cassia true, cinnamon bark and cinnamon green leaf) exhibited good fumigant toxicity (LD 50, 11.79–26.40 μg cm −3). α-Methyl-( E)-cinnamaldehyde (LD 50, 0.45 μg cm −3) and ( E)-cinnamaldehyde (0.54 μg cm −3) were the most toxic compounds and the toxicity of these compounds was comparable to that of dichlorvos (0.30 μg cm −3). Potent fumigant toxicity was also observed in allyl cinnamate, ethyl-α-cyanocinnamate, ( E)-2-methoxylcinnamic acid and ( Z)-2-methoxylcinnamic acid (LD 50, 0.81–0.92 μg cm −3). Structure–activity relationships indicate that structural characteristics, such as types of functional groups and carbon skeleton rather than vapour pressure parameter, appear to play a role in determining toxicity. The essential oils and compounds described merit further study as potential acaricides for the control of D. gallinae populations as fumigants with contact action due to global efforts to reduce the level of highly toxic synthetic acaricides in the agricultural environment.

Toxicity of Kaempferia galanga rhizome constituents to Meloidogyne incognita juveniles and eggs

AbstractThe toxicity of Kaempferia galanga rhizome constituents to second-stage juveniles (J2) and eggs of Meloidogyne incognita was examined in vitro and in container experiments. Results were compared with those of three nematicides: carbofuran, fosthiazate and metam sodium. Ethyl cinnamate (EC) and ethyl p-methoxycinnamate (EMC) were the nematicidal and hatch inhibitory principles. In direct-contact mortality bioassays, EC 0.037 mg ml–1) and EMC (0.041 mg ml–1) were more toxic than carbofuran (0.092 mg ml–1) but less toxic than fosthiazate (0.002 mg ml–1) towards J2 based upon 48 h LC50 values. EC and EMC treatments resulted in 100% and 93 and 81% inhibition of hatch at 125.0 and 62.5 μg ml–1, respectively. Inhibition of these compounds was higher than carbofuran and metam sodium but significantly lower than fosthiazate. In contact +fumigant mortality bioassays with J2, EC and EMC applied at 0.25 and 0.125 mg (g soil)–1resulted in 81 and 80% and 77 and 73% mortality, respectively, while carbofuran and metam sodium treatments resulted in 86 and 96% and 57 and 73% mortality, respectively. Fosthiazate resulted in 92% mortality at 0.063 mg (g soil)–1. In vapour-phase mortality bioassays with J2, EC and EMC were more effective in a closed container than in an open one, indicating that mode of delivery was, in part, a result of vapour action. Global efforts to reduce the level of highly toxic synthetic nematicides in the agricultural environment justify further studies on K. galanga rhizome-derived materials, particularly ethyl cinnamate and ethyl p-methoxycinnamate, as potential nematicides and hatching inhibitors for the control of M. incognita as fumigants with contact action.

TOXIC PROPERTIES OF CERTAIN BOTANICAL EXTRACTS AGAINST THREE MAJOR STORED PRODUCT PESTS

ABSTRACT Acetonic extracts of melon pumpkin, Cucurbita maxima (Duchesne), Sweet Orange, Citrus sinensis (L.) and Sour Orange, Citrus aurantium (L.), were evaluated for insecticidal activity against adults of three stored product pests viz., Sitophilus oryzae (L.), Rhyzopertha dominica (Fabricius) and Tribolium castaneum (Herbst), by filter paper diffusion method (direct contact application) and fumigation methods. The insect responses towards the treatment depended on the type of plant, the time of exposure and also the mode of application. In a test with the filter paper diffusion method (contact application), C. maxima leaf extract showed 100% mortality to S. oryzae and R. dominica within three days after treatment (DAT) at the rate of 8.5 mg/cm2, whereas, only 65% mortality was observed against T. castaneum at this dosage. The application of the crude plant extracts, C. sinensis and C. aurantium in the same concentrations, caused 89% and 76% mortality to S. oryzae and R. dominica respectively 72 hrs post treatment. Both the extracts produced comparatively less toxicity to T. castaneum and C. sinensis within the same duration of time. Among the 3 insects tested T. castaneum was the most tolerant having least mortality against all the phytochemicals. The plant compounds lack volatile toxic chemicals as indicated by the absence of significant mortality in fumigation bioassays.

Production of cuticle-degrading proteases by Nomuraea rileyi and its virulence against Anticarsia gemmatalis

Nomuraea rileyi represents an important natural control agent of Anticarsia gemmatalis preventing populations from reaching economic threshold levels in soybean. During the processes of host infection, entomopathogenic fungi produce extracellular proteases, which degrade the host cuticle and are suggested to be virulence determinants. It was examined the production of subtilisin-like (Pr1) and trypsin-like (Pr2) proteases in two strains (NR458 and CG434) of N. rileyi and its possible role in the process of pathogenicity to this caterpillar. Fungal growth was performed in a mineral medium containing nitrate, and supplemented with the cuticle or exuviae from A. gemmatalis, or with the non-cuticular substrate casein. In medium containing nitrate as sole nitrogen source, no detectable Pr1-like activity occurred in the culture supernatants of the two fungal strains. However, both strains of N. rileyi produced Pr1-like protease in all medium amended with exogenous nitrogen source, and it was highly expressed in the presence of insect cuticle. Pr2-like activity was significantly inferior to Pr1-like activity and it was detected only in some of the media culture and incubation periods tested. In the NR458 culture supernatant the highest activity was observed in medium containing nitrate as nitrogen source. Correlation analysis between the percentage of A. gemmatalis mortality in bioassays and Pr1-like protease activity of strain NR458 suggests a positive correlation for these variables.

Biological activity of recombinant Spodoptera exigua multicapsid nucleopolyhedrovirus against Spodoptera exigua larvae

In this study the potency and efficacy of recombinant Spodoptera exigua multicapsid nucleopolyhedrovirus (SeXD1) were compared with that of the wild-type S. exigua virus (wt-SeMNPV). Time–dose–mortality bioassays of SeXD1 and wt-SeMNPV were conducted on 2nd to 5th instars of S. exiuga larvae. The results show that the recombinant SeXD1 killed insects significantly faster than wt-SeMNPV. At high dosages, the LT 50 values for SeXD1-infected 2nd to 5th instars were 1.3, 1.3, 1.0 and 0.4 days shorter than those for wt-SeMNPV, respectively. LD 50 values also decreased with increases in infection time. LD 50 of SeXD1 occurred 1 day earlier than that of wt-SeMNPV at the same instar, but no significant difference between those for SeXD1 and wt-SeMNPV was observed. In addition, the effect of SeXD1 on feeding was evaluated in 5th instar S. exigua larvae. While nutritional indices, such as consumption index (CI) and relative growth rate (RGR), were significantly reduced by SeXD1 infection, digestibility and food conversion efficiency showed a slight increase. As a 50% overall reduction in consumption and lower CI and RGR values were found for larvae infected with the recombinant SeXD1 virus, these findings show that SeXD1 may provide better protection than wt-SeMNPV.

Toxicity of Plant Essential Oils to Acaricide-Susceptible and -Resistant <I>Tetranychus urticae</I> (Acari: Tetranychidae) and <I>Neoseiulus californicus</I> (Acari: Phytoseiidae)

The toxicity of 10 plant essential oils to adults of acaricide-susceptible, chlorfenapyr-resistant (CRT-53), fenpropathrin-resistant (FRT-53), pyridaben-resistant (PRT-53), and abamectin-resistant (ART-53) strains of Tetranychus urticae Koch (Acari: Tetranychidae) and to female Neoseiulus californicus McGregor (Acari: Phytoseiidae) was examined using spray or vapor-phase mortality bioassays. In bioassay with the susceptible adults, lemon eucalyptus (19.3 microg/cm3) was the most toxic oil, followed by peppermint, citronella Java, thyme red, caraway seed, clove leaf, and pennyroyal oils (LC50, 20.6-23.7 microg/cm3). The toxicity of these oils was almost identical against adults from either of the susceptible and resistant strains, even though CRT-53, FRT-53, PRT-53, and ART-53 adults exhibited high levels of resistance to chlorfenapyr (resistance ratio [RR], > 9,140), fenpropathrin (RR, 94), pyridaben (RR, > 390), and abamectin (RR, 85), respectively. Against female N. californicus, lemon eucalyptus (LC50, 21.4 microg/cm3) was the most toxic oil, whereas the LC50 values of the other nine oils ranged from 23.2 to 72.6 microg/cm3. N. californicus was 1-2 times more tolerant than T. urticae to the test essential oils. Thus, these essential oils merit further study as potential acaricides for the control of acaricide-resistant T. urticae populations as fumigants.

Field evaluation of systemic imidacloprid for the management of avocado thrips and avocado lace bug in California avocado groves

The efficacy of systemic applications of imidacloprid for the management of avocado thrips and avocado lace bug was determined in field trials. Following insecticide treatment by chemigation, leaves of appropriate age for each insect were sampled over a 6 month period and used for bioassays. Imidacloprid residues were measured by ELISA in leaves used for bioassays to determine concentrations of insecticide that were toxic to both pests. The uptake of imidacloprid into treated trees was extremely slow, peaking in the current year's leaf flush at only 8 ng cm(-2) leaf tissue after 15 weeks. Avocado thrips mortality in bioassays with young flush leaves, the preferred feeding substrate for this insect, was minimal, indicating that imidacloprid concentrations were below threshold levels needed for effective control. Residues present in older leaves, which are preferred by the avocado lace bug, were higher than in young flush leaves, and provided good control of this pest. Probit analysis of bioassay data showed that the avocado lace bug (LC(50) = 6.1 ng imidacloprid cm(-2) leaf tissue) was more susceptible to imidacloprid than the avocado thrips (LC(50) = 73 ng imidacloprid cm(-2) leaf tissue). In spite of the slow uptake of imidacloprid into avocado trees, the levels of imidacloprid would be sufficient to control avocado lace bug infestations. In contrast, the slow uptake would be problematic for avocado thrips control because inadequate levels of insecticide accumulate in new flush foliage and would allow avocado thrips populations to build to levels that would subsequently damage developing avocado fruit.

SEDIAAN BIJI BARRINGTONIA ASIATICA: AKTIVITAS PADA HAMA KUBIS CROCIDOLOMIA PAVONANA DI LABORATORIUM DAN KEEFEKTIFAN DI LAPANGAN

Preparation of Barringtonia asiatica: insecticidal activity against Crocidolomia pavonana on laboratory and effectiveness on field. The objectives of this study were to evaluate the insecticidal and anti-oviposition activity of ethanol seed extract of Barringtonia asiatica against Crocidolomia pavonana in the laboratory, and to determine the effectiveness of a simple preparation of B. asiatica seeds in supressing oviposition and population of C. pavonana in the field. The mortality bioassays were conducted by a leaf-feeding method. Anti-oviposition activity was assessed by a choice-test in the nursery. The results showed that the ethanol seed extract of B. asiatica possessed strong insecticidal activity against C. pavonana larvae with LC50 of 0.14%. The extract at concentrations of 0.14-1.00% reduced oviposition by C. pavonana female as much as 65.7-95.6%. B. asiatica seeds ground in water for 5 seconds and then immersed for 1 hour at a concentration of 50 g l-1 yielded a simple preparation which was active against C. pavoana larvae. Such simple preparation at a concentration of 75 g l-1 sprayed on cabbage crop effectively suppressed population of C. pavonana larvae in the field.

Efficacy of Spray Formulations Containing Binary Mixtures of Clove and Eucalyptus Oils Against Susceptible and Pyrethroid/Malathion-Resistant Head Lice (Anoplura: Pediculidae)

The control efficacy of clove, Eugenia caryophyllata, and eucalyptus, Eucalyptus globulus, essential oils and 15 formulations containing these essential oils alone (8, 12, and 15% sprays) and their binary mixtures (7:3, 5:5, and 3:7 by weight) against adult females of insecticide-susceptible KR-HL and dual malathion- and permethrin-resistant BR-HL strains of head louse, Pediculus humanus capitis (De Geer), was examined by using contact plus fumigant and human hair wig (placed over the head of mannequin) mortality bioassays. In contact plus fumigant mortality bioassay, essential oils from eucalyptus (0.225 mg/cm2) and clove (1.149 mg/cm2) were less effective than either d-phenothrin (0.0029 mg/cm2) or pyrethrum (0.0025 mg/cm2) based on 6-h median lethal concentration values. However, the efficacies of eucalyptus and clove oils were almost identical against females fromn both strains, despite high levels of resistance of the BR-HL females to d-phenothrin (resistance ratio, 667) and pyrethrum (resistance ratio, 754). In human hair wig mortality bioassay, eucalyptus oil spray treatment gave better control efficacy than either spray treatment with clove oil alone or their binary mixtures. Thus, eucalyptus applied as 8% sprays (15 or 20 ml) appears to provide effective protection against pediculosis even to insecticide-resistant head louse populations. Once the safety issues resolved, covering the treated hair and scalp with bath shower cap or hat would ensure the fumigant action of the essential oil.

Laboratory Screening of Insecticidal Activities ofBeauveria bassianaandPaecilomyces lilacinusAgainst Larval and Adult House Fly (Musca domesticaL.)

Thirty-four fungal isolates of Beauveria bassiana (Balsamo) Vuillemin (Hyphomycete: Deuteromycetes) and two isolates of Paecilomyces lilacinus were evaluated in vitro for their entomopathogenic activity against larval and adult house fly, Musca domestica L. (Diptera: Muscidae). Of the fungal isolates tested, B. bassiana isolates were pathogenic to adult flies, causing mortality levels of 30–100 % within six days. The P. lilacinus isolates were non-pathogenic towards adult flies. All the fungal isolates were marginally effective in controlling house fly larvae except isolates of P.lilacinus. Four B. bassiana isolates that caused mortality of 90 % or more within two days were subjected to dose-response mortality bioassays. The lethal concentration of B. bassiana isolates that caused 50 % mortality (LC50) ranged between 103–105 conidia/ml. The lethal time to 50 % mortality (LT50) values ranged between 0.44–1.3 days.

Bivariate Stochastic Modeling of Functional Response With Natural Mortality

A correction due to Abbott (1925) is the standard method of dealing with control mortality in insect bioassay to estimate the mortality of an insect conditional on control mortality not having occurred. In this article a bivariate stochastic process for overall mortality is developed in which natural mortality and predation are jointly modeled to take account of the competing-risks associated with prey loss. The total mortality estimate from this model is essentially identical with that from more classical modeling. However, when predation loss is estimated in the absence of control mortality the results are somewhat different, with the estimate from the bivariate model being lower than that from using Abbott’s formula in conjunction with the classical model. It is argued that overdispersion in observed mortality data corresponds to correlated outcomes (death or survival) for the prey initially present, while Abbott’s correction relies implicitly on independence.

Toxicity of Kaempferia galanga rhizome-derived extract and steam distillate to Meloidogyne incognita juveniles and eggs, and their effects on Lycopersicon esculentum germination and growth

Abstract The toxicity of Kaempferia galanga rhizome-derived methanol extract (RME), powder (RP) and steam distillate (RSD) to Meloidogyne incognita second-stage juveniles (J2) and eggs, and their effects on Lycopersicon esculentum germination and growth were examined in vitro and in pot experiments. Results were compared with those of three nematicides: carbofuran, fosthiazate and metam sodium. In contact + fumigant bioassays with J2, RME applied at 1, 0.5 and 0.25 mg (g soil)–1 resulted in 92, 88 and 73% mortality, respectively. The lethality of RME was almost the same as carbofuran but lower than that of either fosthiazate or metam sodium. RSD and RP were less active than RME. In vapour-phase mortality bioassays with J2, the test materials were more effective in a closed container than in an open one, indicating that mode of delivery was, in part, a result of vapour action. In direct-contact mortality bioassays with M. incognita eggs, RME, RSD and fosthiazate treatments resulted in 91, 100 and 95% inhibition of hatch at 250 μg ml–1 and 82, 88 and 81% inhibition of hatch at 100 μg ml–1, respectively. In filter paper bioassays with L. esculentum seed, 8.8 μg cm–2 RME and RP did not cause germination inhibition, while RSD and fosthiazate treatments resulted in 84 and 13% germination inhibition. In pot tests, RME and RSD applied at 8 mg (g soil)–1 reduced galling caused by M. incognita significantly, and fosthiazate at 0.02 mg (g soil)–1 stopped galling completely. Kaempferia galanga rhizome-derived materials, particularly a methanol extract, merit further study as potential nematicides and hatching inhibitors for the control of M. incognita as fumigants with contact action.

Bivariate Stochastic Modeling of Functional Response With Natural Mortality

A correction due to Abbott (1925) is the standard method of dealing with control mortality in insect bioassay to estimate the mortality of an insect conditional on control mortality not having occurred. In this article a bivariate stochastic process for overall mortality is developed in which natural mortality and predation are jointly modeled to take account of the competing-risks associated with prey loss. The total mortality estimate from this model is essentially identical with that from more classical modeling. However, when predation loss is estimated in the absence of control mortality the results are somewhat different, with the estimate from the bivariate model being lower than that from using Abbott’s formula in conjunction with the classical model. It is argued that overdispersion in observed mortality data corresponds to correlated outcomes (death or survival) for the prey initially present, while Abbott’s correction relies implicitly on independence.

Pyrethroid resistance and esterase activity in three strains of the cotton bollworm, Helicoverpa armigera (Hübner)

Microplate assay technique for estimation of esterase activity in a single insect was used in combination with dose mortality bioassays to detect pyrethroid resistance in three strains of Helicoverpa armigera and to study the frequency of pyrethroid resistant individuals within the population of the same strain at two larval stages, third and fifth instar. The third and fifth instar larvae of the field strains i.e., Nagpur strain and Delhi strain that displayed high degree of resistance towards deltamethrin, had higher esterase activity compared to a susceptible laboratory strain. The frequency distribution of individuals with elevated esterase activity above 1.00 absorbance unit was correlated with the resistance level of the strains. The frequency of resistant individuals in the third instar larvae of Nagpur strain and Delhi strain were 29% and 23%, respectively compared to 4% in the susceptible strain. The resistant individuals in the resistant strains have markedly increased in the fifth instar larvae with a frequency distribution of 63% and 90% in Delhi strain and Nagpur strain, respectively, while only 14% of individuals was found to have elevated esterase activity in the susceptible strain. The results demonstrated the role of esterase in pyrethroid resistance in H. armigera. Microplate assay proved to be a rapid and reliable biochemical technique for monitoring of pyrethroid resistance in H. armigera.

Larvicidal Activity of Compounds Isolated FromAsarum heterotropoidesAgainstCulex pipiens pallens,Aedes aegypti, andOchlerotatus togoi(Diptera: Culicidae)

The toxicity of several compounds isolated from Asarum heterotropoides root steam distillate to third-instar larvae of Culex pipiens pallens Coquillett, Aedes aegypti (L.), and Ochlerotatus togoi Theobald was examined using a direct contact mortality bioassay. Safrole was the most toxic constituent to Cx. p. pallens and Ae. aegypti larvae, whereas terpinolene was most toxic to Oc. togoi. However, LC50 values of these three mosquito larvae to both essential oils as well as the remainder of the 26 compounds identified in A. heterotropoides were considerably greater than for fenthion or temephos. However, we suggest that constituents of A. heterotropoides root steam distillate merit further study as potential mosquito larvicides due to global efforts to reduce the level of highly toxic synthetic pesticides in the aquatic environment.

Is K-O Tab 1-2-3 ® long lasting on non-polyester mosquito nets?

Many societies use locally sourced mosquito nets made from a variety of materials. For protecting against malaria these require regular re-treatment with insecticide. K-O Tab 1-2-3 is a ‘dip-it-yourself’ long-lasting formulation with time-limited interim recommendation from WHO for treatment of washed white and coloured polyester nets for up to 15 washes. To determine wash-resistance on different fabrics, nets made of polyester, polyethylene, cotton or nylon were treated with K-O Tab 1-2-3 and washed up to 20 times using standard WHO washing procedures. Efficacy was assessed using cone and cylinder bioassays and tunnel tests, and deltamethrin content using high-pressure liquid chromatography. Polyethylene and cotton nets treated with K-O Tab 1-2-3 and washed 20 times achieved the WHO threshold of >80% mortality in tunnel tests. Polyethylene matched the performance of polyester in all bioassays in contrast to cotton and nylon which produced low mortality and knock-down in cone and cylinder bioassays. After 20 washes 16.5% of the loading dose of deltamethrin remained on the polyester nets compared with 28.7% on polyethylene, 38.9% on cotton and 2.2% on nylon. Cotton nets retained a high concentration of insecticide but the relatively poor performance in terms of knock-down and mortality suggest most insecticide is bound within the cotton fibres rather than on the surface. K-O Tab 1-2-3 renders insecticide wash fast on polyethylene nets, less so on cotton and nylon. Nets made from polyethylene can be treated in the home to render the insecticide long lasting.

Chemical Composition and Biological Activities of Two Angelica Essential Oils from China

Chinese herbal medicine is an interesting subject for medicinal plant research. The root of Angelica dahurica (Baizhi in Chinese) and Angelica pubescentis (Duhuo in Chinese) are well known in Traditional Chinese Medicine [1]. The pharmacological activities associated with A. dahurica and A. pubescentis include antibacterial, anti-febrile, antalgic, anti-spastic actions [2]. Angelica dahurica and A. pubescentis (Umbelliferae) were fragmented and hydrodistilled to obtain the volatile compounds, and were then identified using gas chromatography and gas chromatography-mass spectrometry. Main Angelica oil constituents were found as follows: A.’dahurica: 46.3% a-pinene, 9.3% sabinene, 5.5% myrcene, 5.2% dodecanol and 4.9% terpinen-4-ol and A. pubescentis: 37.6% a-pinene, 11.6% p-cymene, 8.7% limonene and 6.7% cryptone. Angelica essential oils were examined for antimalarial, antimicrobial, antifungal and insecticidal activity. Antifungal activity of the essential oils from both Angelica species was non-selective at inhibiting growth and development of reproductive stroma of the plant pathogens Colletotrichum acutatum, C. fragariae and C. gloeosporioides. Angelica pubescentis oil resulted in 40% mortality at 62.5 ppm to 1st instar larvae of Aedes aegypti at 24 h. Angelica dahurica oil at 1% concentration exhibited an 86.67% mortality in laboratory bioassays with azalea lace bugs, Stephanitis pyrioides, in comparison with A.’pubescentis oil at 44.0%.

Bioactivity of 54 Essential Oil Extracts Topically Applied to Adult Azalea Lacebugs Stephanitis pyrioides (Scott) [Tingidae:Hemiptera]: A Rapid Bio-Pesticide Discovery Program

Concern about genetic pest resistance and poisoning of non-target organisms are spurring the search for “softer” insecticides with greater selectivity and multiple modes of action. Essential oils are blends of secondary metabolites that serve plants as deterrents against insect herbivores, but remain relatively safe and even beneficial to vertebrates [1]. We used serial-time mortality bioassays to screen the essential oils from 54 representative plant species from 30 genera comprising 13 families of gymnosperms and angiosperms for bioactivity to laboratory-cultured azalea lace bugs, Stephanitis pyrioides (Scott). The principal developmental stages of bugs exposed to the essential oils were the adults-long-lived individuals that provide parental care to their leaf-infesting brood. Clevenger-type distillation extracted essential oils from dried plant material and lead components were purified and identified with gas chromatography-mass spectrometry (GC-MS). Oils were mixed with de-ionized water and a non-toxic emulsifier 0.9–9.0% dimethylsulfoxide (DMSO). All oil emulsions and sometimes their fractionated components were topically applied to adult bugs in randomized blocks at concentrations of 0, 650, 1300, 2500, 5000, and 10000 ppm. Overall bug mortality, as well as LD50, LD95 and LD99 values were calculated after 1, 2, 3, 4 and 5 hours of exposure. Mortality data were analyzed using multivariate probits [1] and preliminary data show that 1% emulsions derived from oil of Pelargonium (94.5% bug-mortality), Cinnamomum (91.4%), Hedychium (85.9%) and Tagetes (81.8%) were more efficacious than the malathion-DMSO emulsions (66.1%) and are four promising botanical sources from which to isolate compounds useful for developing new biorational crop protectants. Acknowledgements: We thank the many generous colleagues who supplied us with plant material and extracts: Ikhlas A. Khan (USA), K. Husnu Can Baser (Turkey), Betul Demirci (Turkey), Gulmira Ozek (Turkey), Temek Ozek (Turkey), Aruna Weerasooriya, (USA), Zengping Gao (China), Sui Zhang (China), Jian Zhang (China), Peng Nan (China), Zhijun Liu (USA), Hamidou Sakhanokho (USA), Cecil Pounders (USA), Sandra Gray (USA), Christine Murphy (USA), Eugene K. Blythe (USA).

Ovicidal and Adulticidal Activities ofOriganum majoranaEssential Oil Constituents against Insecticide-Susceptible and Pyrethroid/Malathion-ResistantPediculus humanus capitis(Anoplura: Pediculidae)

The toxicity of essential oil constituents from marjoram, Origanum majorana, to eggs and adult females of the susceptible KR-HL and dual malathion- and permethrin-resistant BR-HL strains of human head louse, Pediculus humanus capitis, was examined using contact + fumigant mortality bioassay. Results were compared with those following treatment with two pyrethroid pediculicides, d-phenothrin or pyrethrum. As judged by the lethal time to 50% mortality (LT(50)) values at the exposure rate of 0.25 mg/cm(2), 1,8-cineole (14.1 min) was the most toxic compound, followed by linalool (15.4 min) to KR-HL females. These compounds were faster acting than either d-phenothrin (24.1 min) or pyrethrum (33.4 min). Based on the lethal concentration causing 50% mortality (LC(50)) values, (-)-camphor (0.022 mg/cm(2)) was the most toxic compound, followed by linalool (0.035 mg/cm(2)), (-)-terpinen-4-ol (0.040 mg/cm(2)), alpha-terpineol (0.045 mg/cm(2)), and 1,8-cineole (0.068 mg/cm(2)) against KR-HL females. These monoterpenoids were less toxic than either d-phenothrin (LC(50), 0.0015 mg/cm(2)) or pyrethrum (0.0013 mg/cm(2)). However, the toxicities of these monoterpenoids were almost identical against females from either of the two strains, even though the BR-HL females exhibited high levels of resistance to d-phenothrin [resistance ratio (RR), 667] and pyrethrum (RR, 754). After a 24 h exposure to linalool, BR-HL egg hatch was inhibited 100 and 84% at 0.25 or 0.125 mg/cm(2), respectively, while (-)-terpinen-4-ol caused 94 and 69% inhibition of egg hatch at 0.25 and 0.125 mg/cm(2). alpha-Terpineol caused 88 and 76% inhibition of egg hatch at 0.5 and 0.25 mg/cm(2), respectively. Thus, certain monoterpenoids from O. majorana essential oil, particularly linalool, (-)-terpinen-4-ol and alpha-terpineol, merit further study as potential pediculicides and ovicides for the control of insecticide-resistant P. h. capitis populations as fumigants with contact action.

Design of a <I>Bacillus thuringiensis</I>-Based Formulation That Increases Feeding Preference on <I>Spodoptera exigua</I> (Lepidoptera: Noctuidae) Larvae

A Bacillus thuringiensis (Bt)-based formulation intended to increase feeding response in Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae) was developed. Eight matrices were prepared from natural ingredients and confronted with fresh maize leaves to select one highly palatable to larvae. The selected matrix was combined with Bt HD-125 strain at three different concentrations (30, 70, and 100 g/kg) of the spore-crystal complex to elaborate three insecticidal formulations. Effects caused by the matrix, including palatability, any adverse effect, and reduction in toxic activity of the strain, were tested on the formulations. Results indicated that the blend of modified cornstarch, porcine gelatin, and dried corncob was the most preferred by larvae. Formulations obtained were evaluated in mortality bioassays with neonate larvae in laboratory, using artificial diet, and in the greenhouse, with maize, Zea mays L., plants to compare their effectiveness when applied to natural food. In laboratory tests, all formulations, including a commercial formulation, were ingested by larvae causing high mortality in neonate larvae; in the greenhouse tests, formulations were also ingested causing mortality in larvae, overcoming commercial formulation effectiveness. Results suggest that the selected matrix combined with Bt 70 g/kg is the most suitable formulation to achieve effective control because this concentration acts faster than the lower concentration and is equal than the higher concentration. This formulation, designed specifically against a particular pest, is highly effective and offers a high potential for effective pest control.