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PubMed2000

Determination of spinosad and its metabolites in food and environmental matrices. 3. Immunoassay methods.

Spinosad is an insect control agent that is derived from a naturally occurring soil bacterium and is effective on several classes of insects, especially Lepidopteran larvae. Spinosad is registered in many countries for use on a variety of crops, including cotton, corn, soybeans, fruits, and vegetables. Residue methods utilizing a magnetic particle-based immunoassay (IA) test kit have been developed and validated for determining spinosad in environmental and food matrices. These methods involve an extraction of the residues from the matrices with appropriate solvents. For some matrices, the sample extracts can be diluted and measured directly by IA without any cleanup. For other matrices, sample extracts are purified using liquid-liquid partitioning and/or solid phase extraction prior to measurement by IA. The methods determine the total residue of spinosad, which includes the active ingredients (spinosyns A and D) and several minor metabolites, including spinosyn B, spinosyn K, and N-demethylspinosyn D. The methods have validated limits of quantitation of 0.0001 microgram/mL in water, 0.05 microgram/g in sediment, and 0.010 microgram/g in crops, crop processed commodities, and animal tissues. This paper briefly summarizes the residue methodology and method validation data for spinosad in 34 food, feed, and environmental matrices.

Animals↗
PubMed2005

Genetic analysis of citrus leafminer susceptibility.

Damage caused by the citrus leafminer (CLM), Phyllocnistis citrella, is highly dependent on the citrus flushing pattern. Chemical control is only required in young trees, both in nurseries and in newly established orchards. However, this situation is completely different in countries where the causal agent of citrus canker, the bacterium Xanthomonas axonopodis pv. citri exists. CLM infestation results in a higher incidence of citrus canker infection. Among preventive control strategies that provide environmentally sound and sustainable solutions, resistant or tolerant varieties remain the most economical means of insect control. The objective of the present study is to genetically analyse the resistance/susceptibility to CLM and two other traits that might be related, the deciduous behaviour and leaf area of the tree, in a progeny of citradias derived from the cross between two species with different CLM susceptibility--C. aurantium L. and Poncirus trifoliata--using linkage maps of each parent that include several resistance gene analogues. We detected two antibiosis and six antixenosis putative quantitative trait loci (QTLs) in a random sample of forty-two of those citradias. An important antibiosis QTL (R2=18.8-26.7%) affecting both percentage of infested leaves and number of pupal casts per leaf has been detected in P. trifoliata linkage group Pa7, which is in agreement with the CLM antibiotic character shown by this species, and independent from any segregating QTL involved in its deciduous behaviour. The maximum value for the Kruskal-Wallis statistic of the other putative antibiosis QTL coincides with marker S2-AS4_800 in sour orange linkage map. Given that the sequence of this marker is highly similar to several nucleotide binding site-leucine-rich repeat (NBS-LRR)-type resistance genes, it might be considered as a candidate gene for insect resistance in citrus.

Animals↗
PubMed2000

Residues of spinosad in meat, milk, and eggs.

Spinosad is an insect control agent that is derived from a naturally occurring soil bacterium and has a high level of activity against insects that infest a variety of crops. Dairy and poultry feeding studies were conducted to determine the magnitude of spinosad residues in animal products that would result from the consumption of typical feed commodities containing residues of spinosad. Dairy cows were dosed for 28 days with spinosad at rates equivalent to 0, 1, 3, and 10 microg/g in the diet. Chicken hens were dosed for 42 days with spinosad at rates equivalent to 0, 0.1, 0.3, 1, and 5 microg/g in the diet. Milk, eggs, and tissue samples were analyzed by high-performance liquid chromatography and/or immunoassay methods. Spinosad residues occurred in all of the sample types but were lowest in eggs, skim milk, and lean meat and were highest in the fat.

Animals↗
PubMed2006

Modulation of insect Ca(v) channels by peptidic spider toxins.

Insects have a much smaller repertoire of voltage-gated calcium (Ca(V)) channels than vertebrates. Drosophila melanogaster harbors only a single ortholog of each of the vertebrate Ca(V)1, Ca(V)2, and Ca(V)3 subtypes, although its basal inventory is expanded by alternative splicing and editing of Ca(V) channel transcripts. Nevertheless, there appears to be little functional plasticity within this limited panel of insect Ca(V) channels, since severe loss-of-function mutations in genes encoding the pore-forming alpha1 subunits in Drosophila are embryonic lethal. Since the primary role of spider venom is to paralyze or kill insect prey, it is not surprising that most, if not all, spider venoms contain peptides that potently modify the activity of these functionally critical insect Ca(V) channels. Unfortunately, it has proven difficult to determine the precise ion channel subtypes recognized by these peptide toxins since insect Ca(V) channels have significantly different pharmacology to their vertebrate counterparts, and cloned insect Ca(V) channels are not available for electrophysiological studies. However, biochemical and genetic studies indicate that some of these spider toxins might ultimately become the defining pharmacology for certain subtypes of insect Ca(V) channels. This review focuses on peptidic spider toxins that specifically target insect Ca(V) channels. In addition to providing novel molecular tools for ion channel characterization, some of these toxins are being used as leads to develop new methods for controlling insect pests.

Amino Acid Sequence↗
PubMed2005

Is the mature endotoxin Cry1Ac from Bacillus thuringiensis inactivated by a coagulation reaction in the gut lumen of resistant Helicoverpa armigera larvae?

Bacillus thuringiensis endotoxins (Bt-toxins) are the most important biopesticides used in controlling insect pests and vectors of diseases. The emergence of widespread resistance to Bt in some insect species is a serious threat to agricultural production. Analysis of Bt-resistant and susceptible laboratory strains of Helicoverpa armigera revealed elevated immune responses involving increased melanization and the presence of a soluble toxin-binding glycoprotein in the hemolymph and gut lumen of the resistant strain. We propose a resistance mechanism against toxins based on a systemic immune-induction that can be transmitted to the next generation by a maternal effect.

Amino Acid Sequence↗
PubMed2003

[Cloning and sequencing of chitinase gene from Bacillus thuringiensis subsp israelensis].

Chitin, a linear homopolymer of N-acetyl-D-glucosamine, is a common constituent of fungal cell walls, exoskeletons of insects, and shells of invertebrates. Thus, chitinase, a chitin hydrolytic enzyme, has become of interest for potential use as biopesticides for controlling insect pests. Using a pair of specific primers, chitinase gene (ichi) was amplified by touchdown PCR from Bacillus thuringiensis subsp israelensis chromosomal DNA, and then subcloned into pGEM-T easy vector. ichi sequence (GenBank Accession Number: AF526379) with a length of 2570 bp included an open reading frame (ORF) of 2067 bp, which contained 688 amino acids with Mr = 75.79 kDa and pI = 5.90. The amino acid sequence of ichi gene shows 97.24%, 97.18%, 97.63% and 63.07% identity to that of Bacillus cereus strain 28-9 chitinase CW, Bacillus cereus CH chitinase B, Bt subsp Mexican chitinase, and Bt subsp pakistani chitinase A71, respectively. It was demonstrated that Ichi contains a signal peptide (46 amino acid residues) and three functional domains: an N-terminal catalytic domain (105 amino acid residues), a fibronectin type III like domain (74 amino acid residues), and a C-terminal chitin-binding domain (40 amino acid residues).

Amino Acid Sequence↗
PubMed2005

Isolation, cloning and expression of DNA fragments reflecting open reading frames of 1.8 and 4.6 kb RNAs of the I-18 C gene of Chironomus tentans.

This study, based on the genetic engineering approach, concerns the regulation of the insect gene expression, but it has also a strong significance for plant protection, which is associated with the future possibility to control insect development more effectively, especially in those species that are pests of cultivated plants. The I-18 C gene of Chironomus tentans is activated by heat-shock and the steroid hormone--ecdysone. This gene produces different transcripts (at least four) by alternative splicing. Two different open reading frames, i.e. ORFs I and II of the two main transcripts of this gene, i.e. the 1.8 and 4.6 kb RNA, had been isolated, at the DNA level, as the ORFs reflecting DNA fragments, using the polymerase chain reaction, then were cloned into the bluescript vector and finally were cloned into the pET-3a vector to be translated in the T7 RNA polymerase/promoter system of E. coli. As the preliminary outcome of these experiments it was possible to obtain ORF I overexpressed as the polypeptide, whereas ORF II was expressed as the polypeptide that was strongly visible on SDS-polyacrylamide gel. This could facilitate further studies regarding the mechanisms of expression of this gene, including the level of expression of this gene during the C. tentans development.

Amino Acid Sequence↗
PubMed2003

Comparison of gene representation in midguts from two phytophagous insects, Bombyx mori and Ips pini, using expressed sequence tags.

Midgut proteins may provide new molecular targets for insect control. This could be particularly important for some pests, such as pine bark beetles, which are difficult to control by conventional methods. Expressed sequence tags (ESTs) provide information about the activity of a particular tissue, and, in the case of pest insects, may quickly identify potential targets. We present here an EST project representing 574 tentative unique genes (TUGs) expressed in the midgut of the male pine engraver beetle, Ips pini. This tissue uses the mevalonate pathway to produce the monoterpenoid pheromone component, ipsdienol, de novo in response to juvenile hormone (JH) III. Comparison of our ESTs with those previously isolated from larval silkmoth (Bombyx mori) midguts revealed interesting similarities and differences in gene representation that correlate with the conserved and divergent functions of these two tissues. For example, seven mevalonate pathway genes were represented in the I. pini ESTs, while none were found from B. mori. This type of comparison may assist the identification of species-specific targets for future pest control strategies.

Animals↗
PubMedDate not supplied

United States Department of Agriculture-Agricultural Research Service research on managing insect resistance to insecticides.

Insecticide resistance has developed within many classes of pesticide, and over 500 species of insects and mites are resistant to one or more insecticides. Insecticide resistance and the consequent losses of food and fiber caused by failure to control insect and mite pests causes economic losses of several billion dollars worldwide each year. It is the goal of insect resistance management (IRM) to preserve useful pesticides by slowing, preventing or reversing development of resistance in pests. Important aspects of this goal are understanding the development of resistance and monitoring to determine ways to prevent its development. We describe programs specific to missions of the US Department of Agriculture, Agricultural Research Service, which are designed to characterize insecticide resistance in insects and mites with the goal of managing pests in an ecologically acceptable manner. Resistance management of cotton, potatoes, vegetables, melons, ornamentals, greenhouse crops, corn, stored grains, livestock, honeybees and mites, as well as management of transgenic crops are evaluated. We conclude that IRM is a vital part of stewardship of any pest management product and must be a combined effort of manufacturers, growers, consultants, extension services and grower organizations, working closely with regulators, to achieve logistically and economically feasible systems that prolong the effectiveness of all pest-control products.

Agriculture↗
PubMed2002

Factors affecting the field performance of an attracticide against the codling moth Cydia pomonella.

Factors affecting the efficacy of an attracticide strategy for the control of the codling moth Cydia pomonella L (Lepidoptera: Tortricidae) were investigated using laboratory and field experiments. The sex-pheromone-based insect-control strategy utilises 100-microliters droplets of a sticky, paste-like formulation containing 1 mg g-1 (E,E)-8,10-dodecadien-1-ol (codlemone) as an attractant for male moths and 40 mg g-1 cyfluthrin, a contact insecticide, applied to branches in the upper parts of the tree crown. The longevity of the treatment under field conditions was assessed in the laboratory by biological testing of variously aged samples of the attracticide formulation which had been applied to the bark of apple trees growing in commercial orchards. Electroantennogram responses of male moth antennae were used to compare codlemone release from the attracticide after different lengths of environmental exposure. Changes in insecticidal efficacy of the same samples were assessed with reference to the speed of knockdown (KT50) and the mortalities after 48 h among populations of male moths confined in cages containing samples of fresh and field-aged formulations. Gradual declines in both the amount of pheromone released and insecticidal activity were observed over the 10-week period of the experiments. Various factors associated with the behaviour of codling moths in the field which might influence the attracticide strategy were also investigated. Although the vertical position of attracticide sources within apple trees had a strong influence on their attractiveness, their horizontal position had none. Results of field trials showed that efficacy of the attracticide depends on the population density of the pest. Under the conditions of the current study a density of three or more sources per tree (= 4500 sources per ha) was required to attain satisfactory levels of codling moth control.

Agriculture↗
PubMed2000

Field evaluation of deet and a piperidine repellent against Aedes communis (Diptera: Culicidae) and Simulium venustum (Diptera: Simuliidae) in the Adirondack Mountains of New York.

Repellent efficacy of N,N-diethyl-3-methyl-benzamide (deet), the piperidine, 1-[3-cyclohexen-1-ylcarbonyl]-2-methylpiperidine (AI3-37220), and a 1:1 ratio of deet + AI3-37220 were evaluated topically (0.25 mg/cm2 applied in ethanol solution) on human volunteers against the mosquito Aedes communis (DeGeer) and the black fly Simulium venustum Say. The average repellency of all three formulations was > 95% at 4 h. For both mosquitoes and black flies, deet alone provided < 90% protection at 6 h, whereas AI3-37220 provided > 95% protection. Although repellent treatments were not significantly different overall, the contrasts between AI3-3720 versus deet were significant at 6 and 8 h. The 95% confidence interval on percent repellency at 6 h ranged from 90.1 to 98.9% for AI3-37220 versus 64.3 to 82.2% for deet, and at 8 h ranged 76.1 to 88.5% for AI3-37220 versus 47.8 to 64.0% for deet. Similarly, the confidence interval for protection against black flies at 6 h by (AI3-37220 ranged from 86.3 to 99.5% and did not overlap with the confidence interval provided by deet alone (51.2 to 78.8%). There was no evidence of synergistic repellency from a combination of the two compounds; i.e., protection from combined compounds was no better than either repellent used alone.

Aedes↗
PubMed1999

Bacillus sphaericus interferes with the development of Brugia malayi in Aedes aegypti.

Aedes aegypti (black-eyed Liverpool strain) were exposed to a sublethal dose (LD25) of Bacillus sphaericus and were fed to Mastomys coucha infected with Brugia malayi. The development of the filarial parasite was found to be arrested mostly at the second larval stage. The infection (P < 0.05), infectivity rates (P < 0.001) and L3 load (P < 0.001) were found to be reduced significantly in the treated group.

Aedes↗
PubMed2001

[The prescription of repellents].

Repellents are chemical products designed to ward off insects. They are effective against a wide range of arthropods including mosquitoes and flies but not against bees and wasps. Choosing the proper repellent can be difficult because no single product repels all pests. This article compares the performance and toxicity of various repellents based on reports describing systemic, topical, or physical repellents made from natural or synthetic ingredients. Essential oils are the most common natural ingredient. Synthetic ingredients range from dimethyphtalate, ethylexanediol, and diethyltoluamide (DEET) to new molecules such as 35/35, piperidine, bayerepel, and KBR 3023. Our findings indicate that DEET, used as the gold standard in most studies, is still the most effective repellent. There is no synergy between any of these products but combinations (e.g. ethylhexanediol and DEET) can optimize protection. In conclusion we propose guidelines for prescribing repellents to achieve the required level of protection in function of the duration of exposure and benefit-to-risk ratio. Several recommendations are made on the safe use repellents for adults and children.

Animals↗
PubMed2001

Insect neuropeptide antagonists.

The development of a new integrated approach to the generation of a novel type of insect neuropeptide (Np) antagonists and putative insect control agents based on backbone cyclic compounds is described. The approach, termed the backbone cyclic neuropeptide-based antagonist (BBC-NBA), was applied to the insect pyrokinin (PK)/pheromone biosynthesis activating neuropeptide (PBAN) family as a model, and led to the discovery of a potent linear lead antagonist and several highly potent, metabolically stable BBC antagonists, devoid of agonistic activity, which inhibited PBAN-mediated activities in moths in vivo. This review briefly summarizes our knowledge of insect Nps, describes the PK/PBAN Np family, presents the basic concepts behind the BBC-NBA approach, and introduces the advantages of this method for generation of Np agonists, antagonists and insecticide prototype molecules.

Amino Acid Sequence↗
PubMed2006

Improved efficacy of ethyl formate against stored grain insects by combination with carbon dioxide in a 'dynamic' application.

Ethyl formate is being evaluated as a fumigant for stored grain as it is a potential alternative to the ozone-depleting fumigant methyl bromide and to phosphine, which is under pressure owing to the development of strong resistance in stored grain insects. However, use of ethyl formate faces significant challenges, such as poor penetration through grain, significant losses to grain sorption, high concentrations of fumigant required to control insects, and flammability risks, which have limited its further development. In this study it was found that the combination of carbon dioxide (5-20%) with ethyl formate significantly enhanced efficacy of the fumigant against external living stages of the rice weevil, Sitophilus oryzae (L.), the lesser grain borer, Rhyzopertha dominica F., and the flour beetle, Tribolium castaneum (Herbst). Dynamic application of ethyl formate and carbon dioxide mixture (100 mg litre-1 ethyl formate, 20% CO2) pumped through a model silo containing wheat (50 kg) for one gas exchange was also investigated. A flow rate of 6 litres min-1 gave a relatively even distribution of fumigant throughout the grain column and similar mortality levels among cultures of S. oryzae and T. castaneum placed at three positions, the top, middle and bottom of the column. Mortality of 99.8% of mixed stage cultures of T. castaneum and 95.1% of S. oryzae was achieved in 3 h exposures to 111 and 185 mg ethyl formate h litre-1 respectively applied by the dynamic method. It is concluded that the combination of carbon dioxide with ethyl formate and dynamic application enhances distribution and efficacy of the fumigant against stored grain insects.

Animals↗