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PubMed2004

Genomic hardwiring and phenotypic plasticity of terpenoid-based defenses in conifers.

Over evolutionary history, conifers have faced a myriad of threats from phloem- and xylem-feeding insects, defoliating insects, and fungal pathogens. Among the trees' defenses, terpenoids appear to play a major role by harming, disabling, deterring, repelling, or otherwise reducing the fitness of potential invaders. Each of the three classes of terpenoids in conifers, monoterpenes, sesquiterpenes, and diterpenes, are composed of a large number of representative compounds. In most cases, the presence of a particular terpenoid compound in the oleoresin or volatile emissions from a specific conifer can be accounted for by the expression of one of many committed terpene synthase (TPS) genes. However, while each TPS may produce one or a few major products, many produce a variety of minor products with relatively constant component ratios in the product blends. TPS genes exist in conifers in large and functionally diverse, yet monophyletic, gene families. Within these gene families, new biochemical functions of TPS appear to have evolved by gene duplication and changes in the amino acid sequence of the enzyme's active site. In addition, TPS genes may be differentially expressed prior to, during, and following attack by insects or pathogens. Thus, while the production of any particular terpenoid is hardwired into a conifer's genome, these trees have the capacity to change the mixture of terpenoids in oleoresin secretions and volatile emissions. Anatomical changes may also accompany induced terpenoid production, supplementing the plasticity of the molecular and biochemical events.

Alkyl and Aryl Transferases↗
PubMed2005

Effect of volatile constituents from Securidaca longepedunculata on insect pests of stored grain.

Securidaca longepedunculata Fers (Polygalaceae) is commonly used as a traditional medicine in many parts of Africa as well as against a number of invertebrate pests, including insects infesting stored grain. The present study showed that S. longepedunculata root powder, its methanol extract, and the main volatile component, methyl salicylate, exhibit repellent and toxic properties to Sitophilus zeamais adults. Adult S. zeamais that were given a choice between untreated maize and maize treated with root powder, extract, or synthetic methyl salicylate in a four-way choice olfactometer significantly preferred the control maize. Methyl salicylate vapor also had a dose-dependant fumigant effect against S. zeamais, Rhyzopertha dominica, and Prostephanus truncates, with a LD100 achieved with a 60microl dose in a 1-l container against all three insect species after 24 hr of exposure. Probit analyses estimated LD50 values between 34 and 36 microl (95% CI) for all insect species. Furthermore, prolonged exposure for 6 days showed that lower amounts (30 microl) of methyl salicylate vapor were able to induce 100% adult mortality of the three insect species. The implications are discussed in the context of improving stored product pest control by small-scale subsistence farmers in Africa.

Animals↗
PubMed2001

Effect of food plants on the volume of repellent secretion obtained in adult Zonocerus variegatus (Orthoptera: Pyrgomorphidae).

The volume of secretion obtained from adult Zonocerus variegatus (Orthoptera: Pyrgomorphidae) was influenced by the type of food plants. Insects fed on leaves of cassava Manihot esculenta, bitter leaves Vernonia amygdalina, and a mixture of M. esculenta and Acalypha wilkesiana gave a good volume of secretion while Chromolaena odorata, Elaeis guinensis, Aspilia africana and Citrus sinensis did not favour secretion production. No significant difference was recorded in the volume of secretion obtained from Z. variegatus from the two seasons irrespective of the food plant. Similarly, food plants gave no significant difference on the volume of secretion between the two seasons.

Animals↗
PubMed1971

2,5-Dichlorophenol (from ingested herbicide?) in defensive secretion of grasshopper.

The defensive froth emitted by the grasshopper Romalea microptera contains several odorous compounds (phenols, terpenes, benzoquinone), including a chlorinated aromatic compound, 2,5-dichlorophenol. This compound, which is repellent to ants and therefore defensively useful to the grasshopper, probably stems from herbicide or herbicide derivative ingested by the insect with its diet. Although there is precedent for the defensive employ by one species of chemical agents produced by another, no instance was known involving secondary utilization of a pesticide dispensed by man.

Animals↗
PubMedDate not supplied

Vectors control importance on leishmaniasis transmission.

We reviewed the control of transmission of leishmaniasis regarding chemotherapy, reservoirs elimination, vaccination and insect control through the use of chemical insecticides. We also discussed complementary measures like monitoring traps, impregnated bednets and curtains, repelents, pheromones, biological control, etc. A cost comparison of insecticide interventions through the use of products belonging to the four main chemical groups was also done, comparing together conventional formulations versus a slow-release insecticide developed by the Núcleo de Pesquisas de Produtos Naturais, Universidade Federal do Rio de Janeiro. We finally did recommendations on the situation that would justify an insecticide intervention to control sandflies.

Animals↗
PubMedDate not supplied

Induction and regulation of antimicrobial peptides in Drosophila.

Activation of the innate immune response involves recognition of the infectious agent and the subsequent activation of cellular and humoral reactions. In insects, a number of immunity genes are activated at the level of transcription leading to the synthesis of antimicrobial peptides. Genetic analyses in Drosophila have identified several signal transduction pathways that promote activation of these immunity genes. Recent data suggest that the insect immune system is able to discriminate between a bacterial and a fungal infection, and responds by higher levels of activation of the appropriate peptides to repel the infection. These and other recent data on transcription factors and regulation of antimicrobial genes are integrated into a model to suggest how differential activation of antifungal and antibacterial peptides can occur in response to fungal and bacterial infection.

Animals↗
PubMed1999

[Habitat of the allergic child: theory and practice].

Control of the asthmatic child's environment forms an integral part of therapeutic care. This requires knowing what the main allergens in the child's habitat are and how they arise: eg, acarids, animal teguments, insects and fungi. The overall measures for reducing them chiefly entail controlling humidity: regular airing, or even ventilation, and eliminating sources of humidity can be recommended. Control of acarids will require modifying furnishings (no mats or carpeting, non hangings or heavy curtains, a slatted not interior spring bed base). Acarid-repellent loose covers seem to be more effective than acaricides, which give conflicting results. Physical processes, although necessary, are seldom sufficient. Animals should be evicted. If this is impossible, certain measures have proved effective, however. Insects and moulds are controlled by specific sanitary measures. A practical approach is proposed that takes into account both theoretical demands and everyday realities.

Acari↗
PubMed2006

Aphid alarm pheromone produced by transgenic plants affects aphid and parasitoid behavior.

The alarm pheromone for many species of aphids, which causes dispersion in response to attack by predators or parasitoids, consists of the sesquiterpene (E)-beta-farnesene (Ebetaf). We used high levels of expression in Arabidopsis thaliana plants of an Ebetaf synthase gene cloned from Mentha x piperita to cause emission of pure Ebetaf. These plants elicited potent effects on behavior of the aphid Myzus persicae (alarm and repellent responses) and its parasitoid Diaeretiella rapae (an arrestant response). Here, we report the transformation of a plant to produce an insect pheromone and demonstrate that the resulting emission affects behavioral responses at two trophic levels.

Animals↗
PubMed2000

The transmembrane protein semaphorin 6A repels embryonic sympathetic axons.

Semaphorin 6A (Sema6A) (previously named Semaphorin VIa) is the originally described member of the vertebrate semaphorin class 6, a group of transmembrane semaphorins homologous to the insect semaphorin class 1. Although Sema-1a (previously named semaphorin I) has been implicated in axon guidance in insects, the function of Sema6A is currently unknown. We have expressed the extracellular domain of Sema6A in mammalian cells as either a monomeric or a dimeric fusion protein and tested for potential axon guidance effects on two populations of embryonic neurons in growth cone collapse and collagen matrix chemorepulsion assays. Sema6A was observed to induce growth cone collapse of sympathetic neurons with an EC50 of approximately 200 pM, although a 10-fold higher (EC50 of approximately 2 nM) concentration was necessary to induce growth cone collapse of dorsal root ganglion neurons. The activity of Sema6A is likely to depend on protein dimerization or oligomerization. Although Sema6A mRNA is expressed in complex patterns during embryonic development, it is strikingly absent from sympathetic ganglia. Sema6A is, however, expressed in areas avoided by sympathetic axons and in areas innervated by sympathetics, but before their arrival. Our results demonstrate that transmembrane semaphorins, like the secreted ones, can act as repulsive axon guidance cues. Our findings are consistent with a role for Sema6A in channeling sympathetic axons into the sympathetic chains and controlling the temporal sequence of sympathetic target innervation.

Animals↗
PubMedDate not supplied

West Nile virus in the United States (1999-2005).

The accidental introduction of West Nile Virus into New York City from the Old World in 1999 resulted in an epidemic in humans, horses, and birds that swept to the west coast in just 3 years. The virus is transmitted by infective mosquitoes among susceptible native birds, which serve as amplifying hosts. Clinical disease occurs in humans and horses, but not enough virus is produced in their blood to infect other mosquitoes; therefore, humans and horses are considered dead-end hosts. Humans can best protect themselves by remaining indoors during periods of high mosquito activity and/or by using recommended repellents. Effective vaccines are available for horses.

Animals↗
PubMed1976

Toxicity and health effects of selected organotin compounds: a review.

The toxicity of selected tin compounds is reviewed. Over the years, a variety of uses has been found for organic and inorganic tin compounds, as fungicides, as stablizers in plastics, moluscicides, and miticides; they have also been suggested as insect chemosterilants and for other industrial uses. Many of these products are unpalatable when mixed into diets and have been suggested as rodent repellents. Inhaling tin as dust or fumes may cause a benign pneumoconiosis in exposed workers. The organotin compounds can be divided into alkyltin and aryltin compounds. The trimethyl and triethyltin compounds are well absorbed from the gastrointestinal tract and are the most toxic in this group. Triethyltin particularly produces status spongiosus of the white matter of the central nervous system. Most of the other alkyl and aryl tin compounds are poorly absorbed from the gastrointestinal tract, and are less toxic when given orally than when given parentally. Only one compound, tricyclohexyltin hydroxide, is now registered by the Environmental Protection Agency as a miticide. This product produces skin irritation in rabbits. Studies should be conducted to determine whether it causes contact dermatitis in humans.

Animals↗
PubMed2004

The divergent Robo family protein rig-1/Robo3 is a negative regulator of slit responsiveness required for midline crossing by commissural axons.

Commissural axons in vertebrates and insects are initially attracted to the nervous system midline, but once they reach this intermediate target they undergo a dramatic switch, becoming responsive to repellent Slit proteins at the midline, which expel them onto the next leg of their trajectory. We have unexpectedly implicated a divergent member of the Robo family, Rig-1 (or Robo3), in preventing premature Slit sensitivity in mammals. Expression of Rig-1 protein by commissural axons is inversely correlated with Slit sensitivity. Removal of Rig-1 results in a total failure of commissural axons to cross. Genetic and in vitro analyses indicate that Rig-1 functions to repress Slit responsiveness similarly to Commissureless (Comm) in Drosophila. Unlike Comm, however, Rig-1 does not produce its effect by downregulating Robo receptors on precrossing commissural axon membranes. These results identify a mechanism for regulating Slit repulsion that helps choreograph the precise switch from attraction to repulsion at a key intermediate axonal target.

Animals↗
PubMed2001

Insecticide-induced behavioral responses of Anopheles minimus, a malaria vector in Thailand.

This study was designed to determine the behavioral responses of 2 test populations of Anopheles minimus females to DDT at 2 g/m2, deltamethrin at 0.0625 g/m2, and lambdacyhalothrin at 0.0369 g/m2 using an improved excito-repellency escape chamber. One test population was colonized in 1993 and referred to as a young colony. The 2nd field test population was collected from Ta-Soa County, Tri-Yok District, Kanchanaburi Province. in western Thailand and referred to as a wild population. Results showed that females of both young and wild test populations rapidly escaped from direct contact with DDT, deltamethrin, and lambdacyhalothrin. Lambdacyhalothrin exhibited the strongest irritant effect on female mosquitoes, followed by DDT and deltamethrin. Fewer females escaped from test chambers without direct contact with treated surfaces but the response was significantly different from that of the controls (P < 0.05). The noncontact response is indicative of a noncontact repellent action. Both contact irritancy and noncontact repellency are involved in An. minimus escape responses. Experimental hut studies that include monitoring of house-entering populations of An. minimus are needed for a meaningful assessment of noncontact repellent actions.

Animals↗
PubMed2005

Insect communication: 'no entry' signal in ant foraging.

Forager ants lay attractive trail pheromones to guide nestmates to food, but the effectiveness of foraging networks might be improved if pheromones could also be used to repel foragers from unrewarding routes. Here we present empirical evidence for such a negative trail pheromone, deployed by Pharaoh's ants (Monomorium pharaonis) as a 'no entry' signal to mark an unrewarding foraging path. This finding constitutes another example of the sophisticated control mechanisms used in self-organized ant colonies.

Animal Communication↗
PubMed1999

Evaluation of conventional odour attractants for Glossina brevipalpis and Glossina austeni (Diptera: Glossinidae) in South Africa.

The components of the synthetic ox-odour used in Zimbabwe against Glossina pallidipes and G. m. morsitans were evaluated for the attraction of G. brevipalpis and G. austeni in South Africa. The Zim babwe mixture (Zim-mix), which consisted or acetone and a 1:4:8 mixture of 3-n-propyl phenol, 4-methyl phenol and 1-octen-3-ol, increased the catches of G. brevipalpis by c. 2.1-4.4 times compared to when no odours were used. One of the odour components, namely 3-n-propyl phenol, did not significantly increase the size of the catches. Acetone was an essential component for G. brevipalpis, especially during the warm and wet season when it acted synergistically with high doses of 1-octen-3-ol and 4-methyl phenol. The most attractive odour combination for G. brevipalpis was 1-octen-3-ol released at 2.3-9.1 mg/h with 4-methyl phenol at c. 15.5 mg/h and acetone at c. 350 mg/h. This combination increased the catches by another 2.3-2.8 times when compared to the Zim-mix and 10.1-12.3 times compared to 'no odour'. None of the odour components was attractive for G. austeni. None of the components was repellent for either species.

Acetone↗