Breeding sites of Culicoides paraensis and options for control by environmental management.
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Biological combat of schistosomiasis Ambrosia maritima (Damsissa) for snail control.
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Animals↗
Cyanide production by rhizobacteria and potential for suppression of weed seedling growth.
Rhizobacteria strains were characterized for ability to synthesize hydrogen cyanide and for effects on seedling root growth of various plants. Approximately 32% of bacteria from a collection of over 2000 isolates were cyanogenic, evolving HCN from trace concentrations to > 30 nmoles/mg cellular protein. Cyanogenesis was predominantly associated with pseudomonads and was enhanced when glycine was provided in the culture medium. Concentrations of HCN produced by rhizobacteria were similar to exogenous concentrations inhibiting seedling growth in bioassays, suggesting that cyanogenesis by rhizobacteria in the rhizosphere can adversely affect plant growth. Growth inhibition of lettuce and barnyardgrass by volatile metabolites of the cyanogenic rhizobacteria confirmed that HCN was the major inhibitory compound produced. Our results suggest that HCN produced in the rhizospheres of seedlings by selected rhizobacteria is a potential and environmentally compatible mechanism for biological control of weeds.
Culture Media↗
Biological control of the snail hosts of schistosomiasis in areas of low transmission: the example of the Caribbean area.
The biological control of schistosomiasis has already proven its efficiency in several habitats in the Caribbean area. Two main types of biological control agents, either trematode parasites or competitor snails have been studied and tested against the snail hosts of schistosomiasis in this region. The first one, Ribeiroia guadeloupensis, a trematode sterilizing Biomphalaria glabrata was successfully tested in a Guadeloupean pond housing a natural population of B. glabrata. The second agent involves several species of competitor snails belonging to the Ampullariidae (Pomacea glauca, Marisa cornuarietis) and Thiaridae (Tarebia granifera, Melanoides tuberculata) families. Ampullarid snails were tested with success in several West Indian islands such as Guadeloupe. Thiarid snails have also proven their efficiency but also their limits in several types of habitats in Guadeloupe, Martinique, St. Lucia and Venezuela. Competitor snails have also proven to be useful in preventing the recolonization by the snail hosts after molluscicide treatments. The case of the rivers of the littoral central part of Venezuela is particularly relevant to this issue. The island of Martinique also constitutes a good example of the importance of competitor snails in a post-transmission phase of schistosomiasis control. This island is a well-developed country where schistosomiasis transmission was interrupted in the 1970s. However, the reactivation of some transmission sites was observed in the 1980s. The introduction of M. tuberculata into these sites resulted in the interruption of transmission and the near total disappearance of the snail hosts. Presently, the thiarid snails have colonized the whole Martinican hydrographic system and maintain dense populations preventing an eventual recolonization by the planorbid snails and thus are maintaining a sustainable control.
Animals↗
Movement of simazine in runoff water and weed control from citrus orchard as affected by reduced rate of herbicide application.
Simazine (6-chloro-N,N'-diethyl-1,3,5-triazine-2,4-diamine) and diuron (N'-(3,4-dichlorophenyl)-N,N-dimethylurea) are applied as pre-emergence herbicides to control weeds in over 45,000 hectare of citrus in the San Joaquin Valley of California. Growers usually apply 2.0 kg active ingredient (ai) ha(-1) simazine and 2.0 kg ai ha(-1) diuron together in the fall and winter seasons. Surface water and groundwater contamination, ecological, and health damage have led to increased regulatory attention and a search for changes in current weed management practices. Reduced application rate of simazine on runoff losses generated by simulated rainfall was studied in experiment 1. Treatments included a control without herbicide application and application of herbicides at 0.5, 1.0, 1.25 and 2.0 kg ai ha(-1). Three generated runoff events were produced using simulated rainfall with 540 l water. For each simulated rainfall event, the simazine concentration in runoff water was greatest at the first volumetric sampling interval, decreasing gradually in subsequent samples. Simazine concentration in runoff water for the three runoff events was undetectable for the control treatment. For the first simulated rainfall event, simazine concentrations in runoff water averaged 0.55, 1.07, 1.27, and 2.12 mg l(-1) for treatments receiving 0.5, 1.0, 1.25 and 2.0 kg ai ha(-1) herbicide application, respectively; simazine concentration in runoff water from the second event one week later averaged 0.16, 0.27, 0.36, and 0.58 kg ai ha(-1) and two weeks later the concentration was reduced to 0.05, 0.10, 0.14 and 0.22 mg l(-1), respectively. Total simazine mass recovered in runoff water from the three simulated rainfall events was estimated approximately 13.8, 26.3, 32.3 and 53.8 g ha(-1) for the treatments receiving herbicide application at 0.5, 1.0, 1.25 and 2.0 kg ai ha(-1), respectively. Field evaluation of weed density showed that pre-emergence herbicides applied at reduced rates (1.0 and 1.25 kg ai ha(-1)) were as effective as the standard rate (2.0 kg ai ha(-1)) for weed control in experiment 2.
Agriculture↗
Entomogenous fungi as promising biopesticides for tick control.
When ticks were sealed in nylon tetrapacks and infected with the entomogenous fungi, Beauveria bassiana and Metarizium anisopliae and maintained in potted grass in the field, the fungal oil formulations (10(9) conidia per ml) induced 100% mortality in larvae of Rhipicephalus appendiculatus and Amblyomma variegatum, whereas mortalities in nymphs varied between 80-100% and in adults 80-90%. The aqueous formulations (10(9) conidia per ml) induced mortalities of 40-50% and reductions in egg hatchability of 68% (B. bassiana) and 48% (M. anisopliae) when sprayed on Boophilus decoloratus engorging on cattle. The strains of B. bassiana and M. anisopliae isolated from naturally infected ticks were also found to induce high mortalities in both R. appendiculatus and A. variegatum in tetrapacks placed in potted grass. Both aqueous and oil-based formulations were found to be effective, although the latter induced higher mortalities. These fungal strains in aqueous formulation (10(8) conidia per ml) suppressed on-host populations of adult R. appendiculatus by 80% (B. bassiana) and 92% (M. anisopliae) when sprayed on tick-infested grass once per month for a period of 6 months. The feasibility of using entomogenous fungi for tick control in the field is discussed.
Animals↗
Wolbachia as a potential tool for suppressing filarial transmission.
There is currently a great deal of interest in Wolbachia because of their wide distribution in arthropods and filarial nematodes and their striking effects on the biology of their hosts, including a possible role in speciation. They manipulate the reproduction of arthropod hosts through various effects on their hosts' biology, particularly cytoplasmic incompatibility (CI), to increase the proportion of infected individuals in the population, often to the point of fixation. This ability of Wolbachia to sweep through host populations indicates several potential applications of Wolbachia in the control of mosquito-borne disease. One uses Wolbachia-induced CI as a form of sterile-insect technique, to suppress mosquito populations. Another envisages the application of CI for population replacement, with the intention of preventing the transmission of human pathogens, by substituting desirable genotypes, including those carried in transgenes. A third possibility is to use Wolbachia to reduce the survival of mosquito populations and thereby reduce their ability to transmit the infection. This article provides an overview of the biological effects of Wolbachia on arthropod hosts, with discussion of the possible future exploitation of these effects in the control of filariasis.
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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↗
Potential for outbreaks of leafrollers (Lepidoptera: Tortricidae) in California apple orchards using mating disruption for codling moth suppression.
Two species of leafrollers, Argyrotaenia citrana (Fernald) and Pandemis pyrusana Kearfott, represent serious obstacles to the implementation of mating disruption for control of codling moth in coastal California apple orchards. Larval and adult densities of A. citrana and P. pyrusana and subsequent fruit damage were compared under different codling moth control treatments. Leafroller larval counts and levels of fruit damage were significantly higher in most plots that were untreated or treated only with codling moth pheromone. Leafroller fruit damage levels in these plots were commonly between 10 and 15% at harvest. As summer larval counts were good predictors of fruit damage levels, larval sampling could be a useful tool for predicting leafroller outbreaks. Use of pheromone trapping for A. citrana to detect localized outbreaks within an orchard was not useful and failed to correlate with larval numbers, whereas adult monitoring for P. pyrusana appears more promising. Efforts to implement a codling moth mating-disruption program in California must include changes in strategies for monitoring and controlling leafroller species.
Animals↗
The penetration of three simuliid species by the nematode Reesimermis nielseni.
After 4 h of exposure to the preparasitic stage of R. nielseni first, second, and third instar Simulium venustum, S. decorum and S. vittatum were found to be harbouring the nematodes in the haemocoel and/or the gut. The possible use of R. nielseni in the biological control of simuliid species is discussed.
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The use of the copepod Mesocyclops longisetus as a biological control agent for Aedes aegypti in Cali, Colombia.
We present data on the efficacy of Mesocyclops longisetus as a biocontrol agent in controlling Aedes aegypti larvae in catch basins in Cali, Colombia. Additionally, we determined some of the features that facilitated the establishment of the copepods in catch basins. Between June 1999 and February 2000, 201 catch basins were treated with an average of 500 adult copepods. The copepods had established in 49.2% of all the basins and they maintained Ae. aegypti larvae at low densities until the end of the 8-month study. The corrected efficacy percent was 90.4%. The copepods established in basins located in a flat area as opposed to those in steep areas, exposed to sunlight and with 0-10% of floating organic matter. When the catch basins were contaminated with synthetic washing agents, like detergents, the copepods did not survive. The copepod M. longisetus could be incorporated as a biological control agent in an integrated Ae. aegypti control program.
Aedes↗
Evaluation of a microgel droplet formulation of Bacillus sphaericus 1593 M (Biocide-S) for control of mosquito larvae in rice fields in southern India.
A new microgel droplet formulation of Bacillus sphaericus 1593 M (Biocide-S) was tested at 2 rates against culicine vectors of Japanese encephalitis and Anopheles subpictus. A single application just after transplantation of rice seedlings prevented the buildup of anopheline as well as culicine populations, and gave 83-100% reduction of pupal density at the lower rate (2.2 kg/ha) and 87-100% reduction at the higher dosage (4.3 kg/ha) for at least 5 weeks. During the last 3 wk before harvest, density was naturally very low and the efficacy of the treatment could not be assessed. This formulation has a potential for control of riceland mosquitoes, but a suitable delivery system is required before it can be considered for practical control.
Agriculture↗
Sex ratio, emergence and infection rates of Heterotylenchus-exposed Musca autumnalis (Diptera: Muscidae).
Experimental infections were produced with the host-specific nematode Heterotylenchus autumnalis, which sterilizes its host, the face fly (Musca autumnalis). The high infection rate achieved (means = 82.5%) was similar for male and female flies. The pupal emergence rate was significantly lower for fly larvae exposed to the nematodes than for unexposed controls. Heterotylenchus-exposed flies had a sex ratio skewed in favor of males. This indicates that in addition to sterilization, H. autumnalis has other deleterious effects on its host. Heterotylenchus autumnalis is therefore a candidate for use as a potential biological control agent of the face fly.
Animals↗
The prehatch period and larval survival of Boophilus decoloratus (Koch, 1844) (Acarina: Ixodidae) under natural conditions in the Transvaal, South Africa.
Studies were made on the duration of the prehatch period of Boophilus decoloratus and on the subsequent survival and viability of larvae under natural conditions. The length of the prehatch and larval survival periods was found to be inversely dependent on increased temperature. A high initial temperature at the time of female drop decreased the prehatch period further, resulting in synchronous hatching of eggs laid at different times. Oviposition occurred but no eggs hatched during mid-winter months with mean temperatures below 10 degrees C. Eggs laid after mid-winter hatched because of the higher temperatures during subsequent months. Diapause occurs at the egg stage in areas with mean winter temperatures below 10 degrees C. Larvae survived for 10-35 weeks during periods of high and low seasonal temperatures respectively. Larval viability decreased concomitantly with larval survival. The results suggest that pasture spelling alone would be impractical as a control measure for this tick species.
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Use of Agrobacterium radiobacter in agricultural ecosystems.
Agrobacterium tumefaciens is a soil inhabitant that infects many dicotyledonous plants, causing crown gall disease. The success of Agrobacterium radiobacter K84 to control this disease in agroecosystems throughout the world has been impressive. This review describes the attributes of K84, its mechanism of control, its failures, and other alternative biocontrol agents.
Adenine Nucleotides↗
[Mermithids as biological control agents of blackflies].
About 80 species of mermithids parasitic in blackflies have been recorded from the Ethiopian and Holarctic regions. Species of three genera, Mesomermis, Gastromermis and Isomermis, are most common parasites of blackflies. Critical periods during the ontogenesis of all mermithids are associated with the penetration of infective larvae into the host and protective reactions of the later. Intraspecific hybridization of the parasites is recommended in order to increase the effectiveness of mermithids as agents of biological control of blackflies.
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Biological control of malaria vectors.
A comprehensive review is presented of the potentiality of biocontrol agents viz. entomophagus bacteria (Bacillus thuringiensis var. israelensis and Bacillus sphaericus), fungi, microsporidians, predators and parasites against malaria vectors in the field condition. Unlike insecticides, these control agents are host specific and safer to the environment. However, barring fishes which are being used in certain situations, other biocontrol agents have not yet reached the operational stage. Two spore forming bacteria B. thuringiensis var. israelensis and B. sphaericus have been extensively tested against malaria vectors in the field. Though they are effective in suppressing anopheline larval population, their recycling capacity and availability of toxin hearing spores on the water surface are limited. Therefore, there is a need for developing improved formulations through bio-engineering techniques for enhancing their residual activity and availability of spores for anopheline larvae which feed mostly on the water surface. The biocontrol potentiality of other agents in the field condition is yet to be explored fully. The use of biocontrol agents for malaria control also poses certain operational constraints in view of the vastness of the anopheline breeding habitats and less acceptance for their use in domestic environments. However, there is a scope for using these biocontrol agents in conjunction with other control methods in integrated control programmes.
Animals↗
The safety of Bacillus species as insect vector control agents.
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