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PubMed2004

CYP15A1, the cytochrome P450 that catalyzes epoxidation of methyl farnesoate to juvenile hormone III in cockroach corpora allata.

The molecular analysis of insect hormone biosynthesis has long been hampered by the minute size of the endocrine glands producing them. Expressed sequence tags from the corpora allata of the cockroach Diploptera punctata yielded a new cytochrome P450, CYP15A1. Its full-length cDNA encoded a 493-aa protein that has only 34% amino acid identity with CYP4C7, a terpenoid omega-hydroxylase previously cloned from this tissue. Heterologous expression of the cDNA in Escherichia coli produced >300 nmol of CYP15A1 per liter of culture. After purification, its catalytic activity was reconstituted by using phospholipids and house fly P450 reductase. CYP15A1 metabolizes methyl (2E,6E)-3,7,11-trimethyl-2,6-dodecatrienoate (methyl farnesoate) to methyl (2E,6E)-(10R)-10,11-epoxy-3,7,11-trimethyl-2,6-dodecadienoate [juvenile hormone III, JH III] with a turnover of 3-5 nmol/min/nmol P450. The enzyme produces JH III with a ratio of approximately 98:2 in favor of the natural (10R)-epoxide enantiomer. This result is in contrast to other insect P450s, such as CYP6A1, that epoxidize methyl farnesoate with lower regio- and stereoselectivity. RT-PCR experiments show that the CYP15A1 gene is expressed selectively in the corpora allata of D. punctata, at the time of maximal JH production by the glands. We thus report the cloning and functional expression of a gene involved in an insect-specific step of juvenile hormone biosynthesis. Heterologously expressed CYP15A1 from D. punctata or its ortholog from economically important species may be useful in the design and screening of selective insect control agents.

Animals↗
PubMed2003

Three cadherin alleles associated with resistance to Bacillus thuringiensis in pink bollworm.

Evolution of resistance by pests is the main threat to long-term insect control by transgenic crops that produce Bacillus thuringiensis (Bt) toxins. Because inheritance of resistance to the Bt toxins in transgenic crops is typically recessive, DNA-based screening for resistance alleles in heterozygotes is potentially much more efficient than detection of resistant homozygotes with bioassays. Such screening, however, requires knowledge of the resistance alleles in field populations of pests that are associated with survival on Bt crops. Here we report that field populations of pink bollworm (Pectinophora gossypiella), a major cotton pest, harbored three mutant alleles of a cadherin-encoding gene linked with resistance to Bt toxin Cry1Ac and survival on transgenic Bt cotton. Each of the three resistance alleles has a deletion expected to eliminate at least eight amino acids upstream of the putative toxin-binding region of the cadherin protein. Larvae with two resistance alleles in any combination were resistant, whereas those with one or none were susceptible to Cry1Ac. Together with previous evidence, the results reported here identify the cadherin gene as a leading target for DNA-based screening of resistance to Bt crops in lepidopteran pests.

Alleles↗
PubMed1997

Proteinase-mediated insect resistance to Bacillus thuringiensis toxins.

Two Bacillus thuringiensis (Bt)-resistant strains of the Indianmeal moth, Plodia interpunctella, lack a major gut proteinase that activates Bt protoxins. The absence of this enzyme is genetically linked to larval survival on Bt-treated diets. When considered with previous data supporting the existence of receptor-mediated insect resistance to Bt, these results provide evidence that insect adaptation to these toxins occurs through multiple physiological mechanisms, which complicate efforts to prevent or manage resistance to Bt toxins in insect control programs.

Animals↗
PubMed1999

Photorhabdus luminescens W-14 insecticidal activity consists of at least two similar but distinct proteins. Purification and characterization of toxin A and toxin B.

Both the bacterium Photorhabdus luminescens alone and its symbiotic Photorhabdus-nematode complex are known to be highly pathogenic to insects. The nature of the insecticidal activity of Photorhabdus bacteria was investigated for its potential application as an insect control agent. It was found that in the fermentation broth of P. luminescens strain W-14, at least two proteins, toxin A and toxin B, independently contributed to the oral insecticidal activity against Southern corn rootworm. Purified toxin A and toxin B exhibited single bands on native polyacrylamide gel electrophoresis and two peptides of 208 and 63 kDa on SDS-polyacrylamide gel electrophoresis. The native molecular weight of both the toxin A and toxin B was determined to be approximately 860 kDa, suggesting that they are tetrameric. NH2-terminal amino acid sequencing and Western analysis using monospecific antibodies to each toxin demonstrated that the two toxins were distinct but homologous. The oral potency (LD50) of toxin A and toxin B against Southern corn rootworm larvae was determined to be similar to that observed with highly potent Bt toxins against lepidopteran pests. In addition, it was found that the two peptides present in toxin B could be processed in vitro from a 281-kDa protoxin by endogenous P. luminescens proteases. Proteolytic processing was shown to enhance insecticidal activity.

Amino Acid Sequence↗
PubMed1994

Knock down and survival of tsetse flies fed on cattle and pigs dipped in deltamethrin.

Glossina morsitans, G. pallidipes and G. fuscipes fuscipes were fed on cattle or pigs that had been dipped in 0.00375% deltamethrin in water, 0-31 days previously. The knock down and survival of the tsetse were then followed in the laboratory. Although mortality was generally less the longer after the dip the flies were fed, all those that fed on the animals within 7 days of the dipping were killed and all those that fed within 21 days were at least knocked down. Glossina morsitans was slightly more susceptible than the other two species tested.

Animals↗
PubMed1979

Carbofuran residues in organic soils in Southwestern Ontario, 1977.

Organic soils from 22 farms with a history of carbofuran use for soil insect control were sampled in November, 1977. Analysis for carbofuran was by electron capture gas chromatography of the heptaflurobutyric derivative. Nineteen of the 22 soils contained detectable (sensitivity 0.02 ppm) carbofuran residues. However only 8 of the soils contained greater than 0.5 ppm total carbofuran. The highest total carbofuran residue was 1.5 ppm, of which 0.31 ppm was 3-ketocarbofuran. In other soil samples 3-ketocarbofuran comprised 7-50% of the total carbofuran residue. No 3-hydroxycarbofuran was detected. The order of persistence of granular application of 3 insecticides as seed-furrow treatments was ethion greater than fonofos greater than carbofuran.

Carbofuran↗
PubMed1984

Dieldrin, heptachlor, and chlordane residues in soybeans in Illinois 1974, 1980.

The Illinois soybean crop was monitored in 1974 and 1980 for dieldrin, heptachlor, and chlordane residues resulting from the use of these compounds for corn soil insect control in the years before extensive soybean cultivation. Residue levels were compared with past published amounts. Dieldrin residue levels in soybeans declined between 1974 and 1980. Heptachlor and heptachlor epoxide levels remained level between 1974 and 1980. Chlorinated hydrocarbon residues were lower in the southern third of Illinois than for the remainder of the state.

Chlordan↗
PubMed1990

Characteristics of applicator exposure to synthetic pyrethroid in ULV-handheld and ULV-ULA spray applications.

The technique of ultra-low volume by ultra-light aircraft for pesticide spray application has been discussed for some time in North America, mainly due to the air worthiness of such an aircraft which was not designed to carry appreciable amounts of payload. The risk factor of such application in insect control has not been determined, while applicator exposure to insecticide in ULV application by manual sprayer was assessed. An attempt was made to produce, by a series of field exposure measurements, a set of applicator exposure data for ULV-ULA and to compare the results with the data produced in synthetic pyrethroid application by using a hand-held ULV applicator. The applicator exposure of hand-held operation resulted in as high as 1000 times the exposure of aerial applicators indicating the effect of work practices and man-machine relationships. A delineation of toxic dose for these two types of applications shows that the aerial application could provide some benefits in reducing applicator exposure potential.

Aerosols↗
PubMed2001

Movement and deposition of two organophosphorus pesticides within a residence after interior and exterior applications.

Post-application temporal and spatial distributions of two organophosphorus pesticides, diazinon (O,O-diethyl O-[6-methyl-2-(1-methylethyl)-4-pyrimidinyl] phosphorothioate, CAS No. 333-41-5) and chlorpyrifos [O,O-diethyl-O-(2-isopropyl-6-methyl-4-pyrimidinyl) phosphorothioate, CAS No. 2921-88-2], were monitored after homeowner applications for indoor and outdoor insect control. Samples of indoor air, vacuumable carpet dust, carpet dislodgeable residues, deposits on bare floors, table tops and dinnerware, surrogate food, and residues on children's hands and toys were taken before and up to 12 days after treatments in the family room, kitchen, and child's bedroom. Results from the study demonstrate the nature and magnitude of translocation of pesticides from the areas of application to surfaces accessible for human contact and permit comparisons of potential exposures via respiration and dermal contact/oral ingestion. Potential indoor inhalation exposures were estimated to be as high as 0.5 microg/kg/day for diazinon applied indoors and 0.05 microg/kg/day for chlorpyrifos applied to the outside perimeter of the house. While ingestion of carpet dust at the rate of 100 microg/day would have added a maximum of only approximately 0.01 microg/kg/day to the daily dose, residues found on the children's hands suggest that repeated mouthing could have contributed as much as 1-1.5 microg/kg/day. These estimates are below the U.S. Environmental Protection Agency (EPA) reference dose for chlorpyrifos, but exceed those for diazinon.

Administration, Cutaneous↗
PubMed1987

Respiratory exposure of grain inspection workers to carbon tetrachloride fumigant.

Carbon tetrachloride (often mixed with carbon disulfide or ethylene dichloride) is a common constituent of liquid grain fumigants. Applied as liquids, these mixtures volatilize and achieve vapor concentrations sufficient to control insect infestations in stored grains. Absorbed grain desorbs fumigant components after the fumigation period, and it then becomes a source of exposure to workers who handle fumigated grain. Carbon tetrachloride meets the EPA's risk criteria for hepatotoxicity, nephrotoxicity and oncogenicity, and it has been under regulatory review since 15 October 1980. Present OSHA standards for CCl4 are a time-weighted average (TWA) of 10 ppm and an acceptable ceiling of 25 ppm. ACGIH and NIOSH have recommended lowering the OSHA standard. The point at which peak exposure occurs during the grain inspection process has been identified as the off odor test in which the inspector smells the grain sample for rancidity, sourness, etc. Ambient concentrations of CCl4 in 7750 grain samples submitted for inspection were determined by colorimetric tube, and these concentrations were an estimate of peak grain inspector exposure to CCl4. The average ambient concentration of CCl4 per grain sample was 1.69 ppm +/- 8.35. Approximately 380 TWA CCl4 exposures for grain inspection workers were determined by using passive dosimeters. All TWA exposures were less than 2 ppm. Variables are examined, such as location of work, grain type, time of year and grain transportation vehicle--all of which are known to the sampler or inspector before performing their job functions and which affect potential exposure.

Agricultural Workers' Diseases↗
PubMed2005

Healthcare-associated myiasis: prevention and intervention.

Healthcare-associated myiasis (maggot infestation) can have complications that go well beyond the medical consequences of the infestation for patients, their families, and facilities. Prevention of healthcare-associated myiasis requires effort on two fronts: minimizing patient risk factors and reducing fly populations in the healthcare environment. If myiasis occurs, intervention must be swift, thorough, and interdisciplinary. The first priority always is the well-being of the patient. Preservation and identification of the maggots can help determine the likely timing and circumstances that led to the infestation. Conditions favoring the infestation must be identified and then corrected. Free and rapid communication must be promoted. A single designated knowledgeable spokesperson to communicate with the patient, employees, and, as needed, the media will reduce miscommunication and hasten mitigation. Following the guidelines presented in this document, healthcare facilities should be able to reduce the likelihood of healthcare-associated myiasis and effectively intervene when such events occur.

Animals↗
PubMed2001

Issues in public health entomology.

Public health entomology focuses on the population biology of vector-borne infections, seeking to understand how such pathogens perpetuate over time and attempting to devise methods for reducing the burden that they impose on human health. As public health entomology passes its centennial, a series of pervasive research themes and spirited debates characterize the discipline, many reflecting a tension between field and laboratory research. In particular, institutional support for population-based research and training programs has fallen behind that for those using modern lab-based approaches. Discussion of modes of intervention against vector-borne infections (such as deployment of genetically modified vectors, the role of DDT in malaria control, host-targeted acaricides for Lyme disease risk reduction, and truck-mounted aerosol spraying against West Nile virus transmission) illustrates the discipline's need for strengthening population-based research programs. Even with the advent of molecular methods for describing population structure, the basis for anophelism without malaria (or its eastern North American counterpart, ixodism without borreliosis) remains elusive. Such methods have not yet been extensively used to examine the phylogeography and geographical origins of zoonoses such as Lyme disease. Basic ecological questions remain poorly explored: What regulates vector populations? How may mixtures of pathogens be maintained by a single vector? What factors might limit the invasion of Asian mosquitoes into North American sites? Putative effects of "global warming" remain speculative given our relative inability to answer such questions. Finally, policy and administrative issues such as the "no-nits" dictum in American schools, the Roll Back Malaria program, and legal liability for risk due to vector-borne infections serve to demonstrate further the nature of the crossroads that the discipline of public health entomology faces at the start of the 21st Century.

Animals↗
PubMed2006

In vitro asymbiotic germination of immature seed and formation of protocorm by Cephalanthera falcata (Orchidaceae).

BACKGROUND AND AIMS: Many Orchidaceous species are threatened globally by development and over-collection from their natural habitats for horticultural purposes. Artificial propagation from seeds is difficult in most terrestrial orchids native to temperate regions. Seed production is another limiting factor in the artificial propagation for these species because of the lessened probability of pollination and the destruction of fruit by insect larvae. Members of the genus Cephalanthera are distributed across Europe, Asia and North America. C. falcata is a temperate species of East Asia and an endangered species in Japan. As successful propagation from seeds of this species has never been reported, a reproducible method is described here for seed production in situ and propagation using immature seeds in asymbiotic culture in vitro. METHODS: Effects of hand-pollination and bagging treatment of ovaries were examined. Young capsules were collected every 10 d from 50 d after pollination until 120 d after pollination. Immature seeds obtained from these capsules were cultured asymbiotically on modified Kano medium and ND medium. Seed viability was examined within TTC (2,3,5-triphenyl tetrazolium chloride) test solution and histological observations were made on viable seeds by paraffin embedding at each collection stage. KEY RESULTS AND CONCLUSIONS: Hand-pollination followed by bagging treatment of ovaries with aluminium foil was effective for insect control during fruit development, and successfully yielded capsules. Of the capsules, 74.5 % survived to full maturity. The highest frequency (39.8 %) of seed germination was obtained with seeds harvested 70 d after pollination. The frequency declined with progress of seed maturity on the mother plant. Minimal germination was observed with seeds harvested 100 d or later after pollination. Histological observation suggests that accumulation of such substances as lignin in the inner integument surrounding the embryo during seed maturation plays an important role in induction of dormancy.

Germination↗