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PubMed2003

Comparative effects of vetiver oil, nootkatone and disodium octaborate tetrahydrate on Coptotermes formosanus and its symbiotic fauna.

The potential of vetiver oil and nootkatone as wood treatments against Coptotermes formosanus Shiraki was examined by assessing the effects on termite tunneling, feeding activity and survival, and the consequences on the symbiont protozoa responsible for wood digestion. Comparisons were made with non-treated wood (control), wood treated with the borate compound Tim-Bor (a commonly used lumber preservative) and absence of a food source (starved termites), using choice and no-choice tests. All wood slices were prepared at the same time using a 10 g liter(-1) solution of each substance and were tested in four different sessions over one year to investigate longevity of the effects. Termites had to tunnel through sand to exploit the food sources, consisting of two wood slices, placed on opposite sides of the experimental enclosure. No-choice tests showed that in the presence of vetiver oil or nootkatone, tunneling activity was always the lowest; wood consumption, termite survival and flagellate numbers and species distribution were significantly different from the control and similar to the results obtained for starved termites and with Tim-Bor-treated wood. Nootkatone negatively affected termites for 12 months and was longer lasting than vetiver oil. In choice tests, when vetiver oil or nootkatone were present, termites exhibited a significant preference for non-treated wood. Our results confirmed both the toxicity and absence of repellency of Tim-Bor. Vetiver oil and especially nootkatone affected Formosan subterranean termites and their protozoa, acting as arrestants, repellents and feeding deterrents, and represent a promising natural alternative for the control of this invasive pest.

Animals↗
PubMed1998

Serum composition of Aedes aegypti (Diptera: Culicidae) larvae and the production of an oviposition repellent are influenced by infection with the entomopathogenic digenean Plagiorchis elegans (Trematoda: Plagiorchiidae), starvation, and crowding.

Subjecting Aedes aegypti (L.) larvae to conditions that induced the production of oviposition repellency also reduced their wet and dry weights and the concentration of total serum carbohydrates, amino acids, and proteins. Thus, infection with metacercariae of the entomopathogenic digenean Plagiorchis elegans (Rudolphi), starvation for 7 d, or crowding for 2 d reduced larval dry weights by as much as 32, 20, and 23%, respectively, and wet weights by 20, 14, and 11%, respectively. Total serum carbohydrates declined by as much as 36, 21, and 29% for infected, starved, and crowded larvae, respectively, amino acids by 39, 48, and 44%, and protein concentrations by 72, 63, and 62%, respectively. Repellency dilution titers were correlated inversely with movement of the mouth parts and gut. Incubation of infected, starved, and crowded larvae in 0.01 g/liter glucose greatly reduced the level of repellency of their waters, whereas adding glucose to repellent waters had only minor effects. Results indicate that the induction of repellency is associated strongly with nutritional depletion effects.

Aedes↗
PubMed2001

Roundabout signalling, cell contact and trophic support confine longitudinal glia and axons in the Drosophila CNS.

Contrary to our knowledge of the genetic control of midline crossing, the mechanisms that generate and maintain the longitudinal axon pathways of the Drosophila CNS are largely unknown. The longitudinal pathways are formed by ipsilateral pioneer axons and the longitudinal glia. The longitudinal glia dictate these axonal trajectories and provide trophic support to later projecting follower neurons. Follower interneuron axons cross the midline once and join these pathways to form the longitudinal connectives. Once on the contralateral side, longitudinal axons are repelled from recrossing the midline by the midline repulsive signal Slit and its axonal receptor Roundabout. We show that longitudinal glia also transiently express roundabout, which halts their ventral migration short of the midline. Once in contact with axons, glia cease to express roundabout and become dependent on neurons for their survival. Trophic support and cell-cell contact restrict glial movement and axonal trajectories. The significance of this relationship is revealed when neuron-glia interactions are disrupted by neuronal ablation or mutation in the glial cells missing gene, which eliminates glia, when axons and glia cross the midline despite continued midline repellent signalling.

Animals↗
PubMed1997

Defensive production of quinoline by a phasmid insect (Oreophoetes peruana).

Adults and nymphs of the Peruvian stick insect Oreophoetes peruana (order Phasmatodea) have a pair of thoracic glands from which they discharge a malodorous fluid when disturbed. The secretion contains a single volatile component, quinoline. Quinoline has not been reported previously from an animal source. The compound proved repellent or topically irritant in assays with ants, spiders, cockroaches and frogs. O. peruana nymphs, at molting, do not extricate the shed cuticular lining of the glands, thereby managing not to lose their secretory supply when they cast their skin. They are able, as a consequence, to discharge secretion even while still teneral after molting.

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PubMed2000

Botanical biocides. 4. Mosquitocidal activity of certain Thymus capitatus constituents.

Successive extraction of Thyme plant, Thymus capitatus (L.) Hoffm. and Link (Lamiaceae), by different solvents of increasing polarity, showed that potency was highly attributed to the non-polar fraction (e.g., petroleum ether) when tests were carried out against the larvae and adults of Culex pipiens (L). Of special concern to the mosquitocidal activity, the following fractions and isolates were recognized: the volatile oil, unsaponifiable portion, and certain compounds isolated from the unsaponifiable portion (e.g., Thymol, alpha-Amyrin, Carvacrol + beta-Caryophyllene). The volatile oil, Thymol, and the unsaponifiable portion proved high larvicidal potency against the tested insect (LC50 = 49.0, 58.0, and 100.0 ppm, respectively). Non-lethal concentrations of these substances synergized the toxicity of Malathion, while induced additive or antagonistic effects when mixed with Permethrin or Pirimiphos-methyl. The unsaponifiable portion and volatile oil showed the highest adulticidal potency (LC50 = 0.0070 and 0.0076 mg/cm2, respectively). The efficacy of the tested candidates as repellent agents was found in the following order: unsaponifiable portion > alpha-Amyrin > Thymol > volatile oil > Carvacrol + beta-Caryophyllene. Thymol as well as volatile oil affected egg hatchability, causing Sterility Indices accounting for 0.70 and 0.74, respectively, while the unsaponifiable portion showed lower degree of sterility (0.81). The results obtained in this study may shed light on the importance of T. capitatus as a probable source of some biologically active agents for mosquito control in the future.

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PubMed2003

West Nile virus in the United States: an update on an emerging infectious disease.

West Nile virus is a mosquito-borne flavivirus and human neuropathogen. Since the virus was recognized in New York City in 1999, it has spread rapidly across the United States, with human disease documented in 39 states and the District of Columbia. West Nile virus can cause a broad range of clinical syndromes, including fever, meningitis, encephalitis, and a flaccid paralysis characteristic of a poliomyelitis-like syndrome. Approximately one in 150 infections results in severe neurologic illness. Advanced age is the greatest risk factor for severe neurologic disease, long-term sequelae, and death. Physicians should consider West Nile virus infection when evaluating febrile patients who have unexplained neurologic symptoms, muscle weakness, or erythematous rash during late spring through early fall, or throughout the year in warm climates. West Nile virus infection has no characteristic findings on routine laboratory tests, although anemia, leukocytosis, or lymphopenia may be present. Testing for IgM antibody to West Nile virus in serum or cerebrospinal fluid (samples from the acute and convalescent phases, submitted at least two weeks apart) is the most common diagnostic method. Local or state health departments usually can perform the test within 24 to 36 hours of submission. Treatment is supportive. Prevention relies on comprehensive mosquito-control programs and measures to avoid mosquito bites, including the use of mosquito repellents containing N,N-diethyl-m-toluamide.

Animals↗
PubMed1989

Susceptibility status of Anopheles maculatus Theobald (Diptera: Culicidae) to DDT in Peninsular Malaysia.

Susceptibility tests were carried between 1987-1989 on Anopheles maculatus female adults collected from twelve different localities in Peninsular Malaysia to DDT. Mosquitoes collected from all localities except those from Kuala Berang, Trengganu state were found to be susceptible to DDT when tested with 4% impregnated paper. Several factors contributing to the lack of development of resistance despite many years of residual spraying in Peninsular Malaysia include exophily, exophagic and excito-repellency behaviour of An. maculatus and the inadequate spraying coverage of houses.

Animals↗
PubMed1989

Repellency of two controlled-release formulations of deet against Anopheles quadrimaculatus and Aedes taeniorhynchus mosquitoes.

Two experimental controlled-release repellent formulations containing 35% (3M) and 44% (Biotek) deet, respectively, were compared with a 75% standard formulation of deet used by the military. The military repellent was equal to or significantly better than the formulations in duration of protection against 2 mosquito species in laboratory and field tests, but the formulations contained only 47-59% the amount of deet in the military repellent. In all cases high levels of protection (greater than 95%) were measured, but because of high densities of biting mosquitoes in field tests, this level did not necessarily indicate few bites. In terms of mean bites/test/day by Anopheles quadrimaculatus in caged tests, the military repellent had fewest (2) and Biotek had most (41).

Aedes↗
PubMed1964

STUDIES ON THE KINETIC RESPONSE OF MOSQUITOS TO CHEMICALS.

An apparatus is described for study of the activity of mosquitos either with or without stimulation by exposure to insecticides or other chemicals such as repellents. Batches of up to 30 mosquitos can be used and they can be studied for a longer time than is possible with, for instance, the method put forward in 1960 by the WHO Expert Committee on Insecticides. Random activity by the test insects, in the absence of directional stimuli due to light or chemicals, is converted to progress through baffles in the partitions separating a series of four boxes and is expressed as a percentage of the total possible activity that would be shown if all the insects passed all the baffles. Exposure to chemicals, by exposure to impregnated papers, can take place before the mosquitos are put in the apparatus, or in the first box. In the experiments described, the activity of recently fed female Anopheles was studied over periods of up to 20 hours.Comparison of the method described with other methods shows that it shares the high variance characteristic of all current procedures for studying mosquito behaviour, although the use of large numbers of insects over long periods has some advantages. The method does, however, give information on mortality under conditions of facultative contact that may be a valuable supplement to the results of conventional susceptibility tests.

Animals↗
PubMed2002

Advantages of larval control for African malaria vectors: low mobility and behavioural responsiveness of immature mosquito stages allow high effective coverage.

BACKGROUND: Based on sensitivity analysis of the MacDonald-Ross model, it has long been argued that the best way to reduce malaria transmission is to target adult female mosquitoes with insecticides that can reduce the longevity and human-feeding frequency of vectors. However, these analyses have ignored a fundamental biological difference between mosquito adults and the immature stages that precede them: adults are highly mobile flying insects that can readily detect and avoid many intervention measures whereas mosquito eggs, larvae and pupae are confined within relatively small aquatic habitats and cannot readily escape control measures. PRESENTATION OF THE HYPOTHESIS: We hypothesize that the control of adult but not immature mosquitoes is compromised by their ability to avoid interventions such as excito-repellant insecticides. TESTING THE HYPOTHESIS: We apply a simple model of intervention avoidance by mosquitoes and demonstrate that this can substantially reduce effective coverage, in terms of the proportion of the vector population that is covered, and overall impact on malaria transmission. We review historical evidence that larval control of African malaria vectors can be effective and conclude that the only limitations to the effective coverage of larval control are practical rather than fundamental. IMPLICATIONS OF THE HYPOTHESIS: Larval control strategies against the vectors of malaria in sub-Saharan Africa could be highly effective, complementary to adult control interventions, and should be prioritized for further development, evaluation and implementation as an integral part of Rolling Back Malaria.

Animals↗
PubMed2005

Potential of oil-based formulations of Beauveria bassiana to control Triatoma infestans.

The in vitro development of Beauveria bassiana conidia was monitored when immersed in six concentrations of seven non-ionic (MP 6400, MP 600, Renex 60, Renex 95, Span 80, Tween 20 and Tween 80) and three anionic (DOS 75, Hostapaval BVQ 9 and Surfax 220) surfactants and 11 vegetable oils (linseed, soybean, groundnut, rapeseed, thistle, sunflower, olive, sesame, corn, castor, and babassu). The influence of the oils on the settling behavior of Triatoma infestans nymphs and the activity of an oil-water formulation of the fungus against this vector under laboratory and simulated field conditions were also determined. With exception of DOS 75 and Surfax 220 germination of conidia on complete medium was >98% at 24 h after exposure to surfactants up to 10%. Elevated rates of germination (>25%) were observed in 10% corn, thistle and linseed oil 8 days after incubation. Pure oils had a significant repellent effect to T. infestans. Repellency decreased generally at 10% of the oil and some oils showed some attractiveness for nymphs when tested at 1%. Nymphs were highly susceptible to oil-water formulated conidia, even at unfavorable moisture for extra-tegumental development of the fungus on the insect cuticle.

Animals↗
PubMed1998

Control experiments with yellow jacket wasps (Hymenoptera: Vespidae) injuring cattle in Israel.

Injuries caused by the German yellow jacket Vespula germanica F. to dry and lactating dairy cows (Bos tourus) in 5 herds in Israel were monitored and adversely affected < or = 65% of the cows. Elimination of large alternative protein sources (placentas, sewage containing milk from the milking parlor), and prebaiting with high-quality minced meat (or fish) in adequate numbers of baiting cages around the dairy farm for several days, are necessary for successful control. Significant control was achieved after a shorter period of time when the dairy farm was surrounded by a smaller area of uncultivated land than by a larger area. At some dairy farms there were significant differences among numbers of wasps visiting the various cage sites and significant variability between baiting days. Efficient and significant control was achieved by minced meat bait containing 1.5% acephate (orthene) and 2% microencapsulated diazinon (Antikan). Wasps were totally repelled by minced meat bait containing 2.25% of a plant-derived bioinsecticide derived from Meliaceae (Ag1000). The potential of using Ag 1000 for repelling yellow jackets from teats and udders of dairy cows is discussed.

Animals↗
PubMed2005

Reduced response of insecticide-resistant aphids and attraction of parasitoids to aphid alarm pheromone; a potential fitness trade-off.

Response to the alarm pheromone, (E)-beta-farnesene, produced by many species of aphids, was assessed in laboratory bioassays using an aphid pest, Myzus persicae (Sulzer), and its primary endoparasitoid, Diaeretiella rapae (McIntosh). This was done in three separate studies, the first investigating responses of a large number of M. persicae clones carrying different combinations of metabolic (carboxylesterase) and target site (kdr) insecticide resistance mechanisms, and the other two investigating the responses of young virgin female adult parasitoids. In M. persicae, both insecticide resistance mechanisms were associated with reduced repellence suggesting that each has a pleiotropic effect on aphid behaviour. In contrast, D. rapae females were attracted to the alarm pheromone source. The implications of this apparent fitness trade-off for the evolution and dynamics of insecticide resistance, and the potential for using beneficial insects to combat resistance development are discussed.

Animals↗
PubMedDate not supplied

[Variation of anopheles density with deltamethrin-impregnated mosquito nets in an endemic malaria area of the Brazilian Amazon].

In 1992 a survey on the use of deltamethrin-impregnated mosquito nets was conducted in the municipality of Costa Marques, Rondonia. In the intradomicile, impregnated nets decreased the vector density at rates similar to those for non-impregnated nets during low-transmission periods; during high anopheline density periods, they led to a significant reduction in vector density, while in the non-impregnated net group there was an increase in the number of anophelines captured. There was no change in vector density in the peridomicile. In the impregnated net group, the most frequently captured species was Anopheles darlingi (63.2%), found mostly in the peridomicile, while Anopheles deaneorum (35.3%) was most frequent indoors. The impregnated mosquito nets' excitatory-repellent effect decreased the intradomiciliary vector density but did not alter density in the peridomicile.

Animals↗
PubMed2005

Behavioral responses to DDT and pyrethroids between Anopheles minimus species A and C, malaria vectors in Thailand.

Behavioral responses of two field populations of Anopheles minimus complex species A and C for contact and non-contact actions of chemicals were compared during and after exposure to operational field concentrations of DDT (2 g/m2), deltamethrin (0.02 g/m2), and lambdacyhalothrin (0.03 g/m2) using an excito-repellency escape chamber. The two populations were collected from the Mae Sot District in Tak Province (species A) and the Tri Yok District in Kanchanaburi Province (species C) in western Thailand. Female mosquitoes of both populations rapidly escaped from chambers after direct contact with DDT, deltamethrin, and lambdacyhalothrin. The non-contact repellency response to DDT and the two synthetic pyrethroids was pronounced with An. minimus species A; however, non-contact repellency was relatively weak with An. minimus species C, but remained significantly greater than the paired controls (P < 0.05). We conclude that strong contact irritancy was present in both test populations, whereas non-contact repellency also played a significant role in the escape response of An. minimus species A.

Animals↗
PubMed2006

Transgenic tobacco plants producing caffeine: a potential new strategy for insect pest control.

Caffeine (1,3,7-trimethylxanthine) is one of the most widely used plant secondary metabolites, primarily as a stimulant and an ingredient in drugs. In nature, caffeine is believed to function in chemical defense, acting as an antiherbivory and allelopathic agent, and therefore it might be employed to protect agriculturally important crop plants. In coffee plants, caffeine is synthesized from the precursor xanthosine in four steps, three N-methylations and removal of ribose. We had previously isolated genes encoding three distinct N-methyltransferases, and we demonstrated production of recombinant enzymes that yielded caffeine in in vitro reconstitution experiments. When these caffeine biosynthetic pathway genes were simultaneously expressed in tobacco plants (Nicotiana tabacum), caffeine was successfully produced up to 5 microg/g fresh weight in leaves. The leaves were unpalatable to tobacco cutworms (Spodoptera litura). This repellent action appeared to be more widely applicable to lepidopteran caterpillars as observed with small white (Pieris rapae) fed on Chinese cabbages that had been top-treated with caffeine. Our recent results suggest a novel approach to strengthen anti-herbivore traits by producing caffeine in crop plants.

Animals↗
PubMed2004

Piperitenone oxide as toxic, repellent, and reproduction retardant toward malarial vector Anopheles stephensi (Diptera: Anophelinae).

Anopheles stephensi (Liston) is a well-known vector of malarial parasite in tropical countries. The developing trend of resistance in mosquitoes toward synthetic mosquitocidal agents makes their management extremely difficult. Effectiveness of essential oils with aroma therapeutic values seems to be an emerging tool to combat this vector. Piperitenone oxide isolated from essential oil of a new genotype, Mentha spicata L. variety viridis, has been evaluated for larvicidal, ovicidal, oviposition-deterrent, developmental toxicity, and repellent properties against various stages of A. stephensi. The results indicated the higher efficacy of piperitenone oxide than the crude essential oil of M. spicata variety viridis in all the bioassay experiments. The lethal response of piperitenone oxide and the oil toward fourth instar larvae showed LD50 values of 61.64 and 82.95 microg/ml, respectively. Female adults of A. stephensi exposed to the oil laid approximately 42 times less number of eggs at the dose of 60.0 microg/ml as compared with control, whereas exposure of piperitenone oxide at the same dose completely inhibited the oviposition. Furthermore, piperitenone oxide also completely inhibited egg hatching at the dose of 75.0 microg/ml in ovicidal assay. Developmental toxicity studies showed the significant developmental inhibition potential of the compound and oil. Additionally, piperitenone oxide was found to be highly toxic and repellent toward adults of A. stephensi as compared with oil.

Animals↗
PubMed1999

Effects of roundabout on growth cone dynamics, filopodial length, and growth cone morphology at the midline and throughout the neuropile.

roundabout (robo) encodes an axon guidance receptor that controls midline crossing in the Drosophila CNS. In robo mutants, axons that normally project ipsilaterally can cross and recross the midline. Growth cones expressing Robo are believed to be repelled from the midline by the interaction of Robo and its ligand Slit, an extracellular protein expressed by the midline glia. To help understand the cellular basis for the midline repulsion mediated by Robo, we used time-lapse observations to compare the growth cone behavior of the ipsilaterally projecting motorneuron RP2 in robo and wild-type embyros. In wild-type embryos, filopodia can project across the midline but are quickly retracted. In robo mutants, medial filopodia can remain extended for longer periods and can develop into contralateral branches. In many cases RP2 produces both ipsilateral and contralateral branches, both of which can extend into the periphery. The growth cone also exhibits longer filopodia and more extensive branching both at the midline and throughout the neuropile. Cell injections in fixed stage 13 embryos confirmed and quantified these results for both RP2 and the interneuron pCC. The results suggest that Robo both repels growth cones at the midline and inhibits branching throughout the neuropile by promoting filopodial retraction.

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