Biological control by trematode antagonism. I. A successful field trial to control Schistosoma spindale in northeast Thailand.
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Host range tests with Edhazardia aedis (Microsporida: Culicosporidae) against northern Nearctic mosquitoes.
Twelve species of northern Nearctic mosquitoes representing five genera (Aedes, Anopheles, Culex, Culiseta, and Psorphora) were bioassayed for susceptibility to Edhazardia aedis, an exotic, heterosporous, microsporidian parasite of the yellow fever mosquito, Aedes aegypti. Infections were achieved in Aedes atropalpus, Aedes triseriatus, and Aedes vexans following oral ingestion of uninucleate spores obtained from patently infected Ae. aegypti larvae. The microsporidium underwent normal vegetative growth and development in each unnatural mosquito host; the only differences observed were in the degree of infection. With the exception of adult oenocytes, the predominant sites of infection in Ae. triseriatus were generally similar to those in Ae. aegypti. These included the gastric caeca and muscle tissue in larvae and fat body tissue in adult females. Binucleate spores, which are normally responsible for ovarian infection and transovarial transmission in Ae. aegypti, were produced in all but one (Ae. atropalpus) susceptible host. However, E. aedis was not transmitted transovarially to larvae of the filial generation by these alternate female hosts thus indicating a high level of specificity for Ae. aegypti. Since E. aedis can not complete its normal life cycle through two successive host generations in alternate host mosquitoes, its potential as a biological control agent would appear to be limited to Ae. aegypti.
Aedes↗
Reduction of Haemonchus contortus infective larvae by Harposporium anguillulae in sheep faecal cultures.
Harposporium anguillulae is a common nematophagous fungus which colonizes cattle pats deposited in Brachiaria decumbens pasture in Brazil. To assess its possible effect on free living stages of trichostrongylid nematodes, the reduction of Haemonchus contortus infective stages in sheep faecal culture was evaluated in vitro. Addition of 300,000 conidia per gram of faeces caused a reduction of 99.5% compared to the control group. This result indicates that H. anguillulae could be a candidate for the development of strategies for the biological control of trichostrongylid nematodes.
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Toxicological assessment of biological pesticides.
The majority of pesticides are based on synthetic chemicals. Regulatory assessments are performed by comparing the findings in a range of routine toxicity studies, designed for testing chemicals, with estimates of exposures. Recently there have been significant moves towards developing natural/biological alternatives. Biological pesticides (those based on viable organisms) present the regulator with a different set of challenges to those raised by most chemical pesticides. The concerns associated with biological pesticides can vary greatly from one organism to another, requiring an almost case-by-case approach. The known toxicity of certain bio-molecules and the pathogenicity of certain organisms underlines the need for a risk assessment of biological pesticides. The main aspects of a health risk assessment are characterisation of the organism, infectivity, pathogenicity, sensitisation and production of toxic secondary metabolites. Obtaining information or data on these areas is not always easy as there are no widely accepted test schemes or protocols for organisms, though guidelines are being developed for the European Commission (EC). Predicting exposure following pesticidal use of an organism is made more complex if it multiplies or secretes toxic metabolites. Reliable data on effects (lack of) associated with naturally occurring (background) exposures can sometimes provide considerable reassurance. This paper describes the background to the proposed EC scheme, which has much in common with current UK practices, and presents three examples of biological pesticides which have been assessed under the existing UK procedures.
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Tuberculina-Thanatophytum/Rhizoctonia crocorum-Helicobasidium: a unique mycoparasitic-phytoparasitic life strategy.
Tuberculina species are mitosporic parasites of rust fungi. Phylogenetically they belong to the Urediniomycetidae, therefore being closely related to their rust fungal hosts. We reveal by means of molecular analyses, ultrastructural and morphological features, observations in the field, and infection experiments that species of the genus Tuberculina and the violet root rot (Helicobasidium/Rhizoctonia crocorum) are stages of the life-cycle of one holomorph. This opens up new perspectives on parasitic life strategies as the resulting life-cycle is based on interkingdom host jumping between rusts and spermatophytes. In addition, we point at the consequences for any practical application dealing with Helicobasidium as an economically important plant pathogen and Tuberculina as a biological agent in rust control.
Basidiomycota↗
The Tsetse Research Laboratory.
The Tsetse Research Laboratory in Bristol was opened in December 1962, with the initial objective of developing techniques for rearing tsetse flies on a large scale outside Africa. Its work has, however, extended greatly since then. This article highlights the research undertaken at the Laboratory, not only on the breeding of tsetse flies but also on various aspects of their biology and control.
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Effects of larval density and predation by Toxorhynchites amboinensis on Aedes polynesiensis (Diptera: Culicidae) developing in coconuts.
Organisms manipulated as biological control agents of disease vectors should tolerate ranges of developmental conditions exploited by their target species. Furthermore, they should reduce numbers of host-seeking vector adults without providing fitness benefits to larval survivors developing among fewer competitors. We studied electrochemistry in rat-chewed coconuts, an important developmental habitat used by Aedes polynesiensis, a vector of lymphatic filariasis. We also studied the effects of larval density and predation by the mosquito Toxorhynchites amboinensis as predators of Ae. polynesiensis. The predators significantly reduced survival rates of Ae. polynesiensis and numbers of males and females developing in coconut husks. Adults from cohorts of Ae. polynesiensis exposed to predators emerged at the same time and were equal in size to adults emerging from predator-free cohorts. No differences were detected in the numbers or sizes of Ae. polynesiensis reaching adulthood among the densities tested. At least for this common natural habitat, Tx. amboinensis gave a good level of biological control of the vector Ae. polynesiensis.
Aedes↗
Impact of the entomophilic digenean Plagiorchis noblei (Trematoda: Plagiorchiidae) on the survival of Aedes provocans under field conditions.
Under field conditions, exposure of Aedes provocans to Plagiorchis noblei cercariae reduced the number of pupae produced to about one-third of control values. Larvae bearing more than 2 metacercariae rarely survived, and pupal mortality was almost 3 times higher among exposed individuals than controls. Adult females exposed to cercariae as pre-imagos experienced a 32% reduction in longevity. The life span of males was not affected. The potential of entomophilic digeneans as biological agents in the control of mosquitoes is discussed.
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Population genetics of autocidal control and strain replacement.
The concept that an insect species' genome could be altered in a manner that would result in the control of that species (i.e., autocidal control) or in the replacement of a pestiferous strain of the species with a more benign genotype was first proposed in the mid-twentieth century. A major research effort in population genetics and ecology followed and led to the development of a set of classical genetic control approaches that included use of sterile males, conditional lethal genes, translocations, compound chromosomes, and microbe-mediated infertility. Although there have been a number of major successes in application of classical genetic control, research in this area has declined in the past 20 years for technical and societal reasons. Recent advances in molecular biology and transgenesis research have renewed interest in genetically based control methods because these advances may remove some major technical problems that have constrained effective genetic manipulation of pest species. Population genetic analyses suggest that transgenic manipulations may enable development of strains that would be 10 to over 100 times more efficient than strains developed by classical methods. Some of the proposed molecular approaches to genetic control involve modifications of classical approaches such as conditional lethality, whereas others are novel. Experience from the classical era of genetic control research indicates that the population structure and population dynamics of the target population will determine which, if any, genetic control approaches would be appropriate for addressing a specific problem. As such, there continues to be a need for ongoing communication between scientists who are developing strains and those who study the native pest populations.
Animals↗
Trichogramma releases in North Carolina cotton: why releases fail to suppress heliothine pests.
Field studies were conducted in 1996 and 1997 to determine the fate of naturally oviposited F3 heliothine eggs in cotton plots treated with augmentative releases of Trichogramma exiguum Pinto & Platner and nontreated plots. Four cohorts of newly oviposited eggs (< 24 h old) were followed in 1996 and two cohorts in 1997. In 1996, mean +/- SD percent parasitism, estimated by in-field studies following the fate of naturally oviposited eggs, ranged from 7 +/- 7 to 61 +/- 8% in T. exiguum release plots and 0 +/- 0 to 35 +/- 13% in control plots. The mean +/- SD percent of eggs hatched in T. exiguum release plots ranged from 1 +/- 2 to 11 +/- 4% and 7 +/- 4 to 28 +/- 10% in control plots. In 1997, mean +/- SD percent egg parasitism ranged from 27 +/- 4 to 40 +/- 3% in T. exiguum release plots and 15 +/- 18 to 25 +/- 8% in control plots. The mean +/- SD percent of eggs hatched in T. exiguum release plots ranged from 7 +/- 3 to 12 +/- 2% and 18 +/- 6 to 28 +/- 8% in control plots. Despite increased parasitism and reduced egg hatch in T. exiguum release plots, overall, there was no significant difference in larval density (all instars combined) between T. exiguum release and control plots. Combined analysis of the heliothine larval populations and egg fate data revealed that the additional egg mortality produced by released T. exiguum was offset by lower larval mortality in release plots. Because of the occurrence of compensatory mortality, the egg stage of heliothines is not an appropriate target for biological control using Trichogramma wasp releases.
Animals↗
Biological control by trematode antagonism. II. Failure to control Schistosoma spindale in a field trial in northeast Thailand.
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Animals↗
The journal of infection control nursing. The biology, importance and control of pharaoh's ant (Monomorium pharaonis L.) infestations in hospitals.
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Animals↗
Considerations and proposed experimental design for the safety evaluation of biological pesticides in nontarget species.
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Animals↗
Delphastus catalinae and Coleomegilla maculata lengi (Coleoptera: Coccinellidae) as biological control agents of the greenhouse whitefly, trialeurodes vaporariorum (Homoptera: Aleyrodidae).
Predation efficacy and compatibility of the predatory lady beetles Coleomegilla maculata lengi Timberlake and Delphastus catalinae (Horn) against the greenhouse whitefly, Trialeurodes vaporariorum (Westwood) were studied in laboratory on glabrous fuchsia (Fuchsia hybrida Voss cv Lena Corolla) and pubescent poinsettia plants (Euphorbia pulcherrima Willd ex Klotzch cv Dark Red Annette Hegg). On glabrous plants (fuchsia), fourth-instar and adults of C maculata were the most efficient, both against whitefly eggs and pupae. On pubescent plants (poinsettia), the larger stages of C maculata were negatively affected and less efficient than adults of D catalinae. The presence of plant structure did not affect the voracity of either predator species. Finally, the simultaneous use of both predator species generated inter-specific competition. These results provide recommendations for biological control of whitefly in horticultural greenhouses.
Agriculture↗
The potential of nematophagous fungi to control the free-living stages of nematode parasites of sheep: towards the development of a fungal controlled release device.
Studies showed that chlamydospores of the nematophagous fungus, Duddingtonia flagrans, are capable of surviving pressures of several tonnes when incorporated into matrices and pressed into tablets for the manufacture of prototype intraruminal controlled release devices (CRDs). They remain viable in this tabletted form for at least 9 months when stored at 4 degrees C. In vitro studies demonstrated that there was no effect on spore viability of prolonged exposure to either room or elevated temperature (40 degrees C) in air, or under an atmosphere of either of the major ruminal gases, carbon dioxide and methane. In vivo, studies showed that viable chlamydospores could be detected at the erosion surface of prototype CRDs recovered from the rumen and also in faeces of fistulated sheep, for up to 3 weeks after administration. Further studies have shown that chlamydospores released from such devices can substantially reduce the number of infective larvae that develop in cultures of faeces collected from sheep infected with the nematode parasite, Haemonchus contortus. This work demonstrates, in principle, that the deployment of chlamydospores of D. flagrans in intraruminal CRDs, is another possibility in the development of a range of methods for the biological control of parasites in livestock.
Animals↗
Evaluation of Mesocyclops annulatus (Copepoda: Cyclopoidea) as a control agent of Aedes aegypti (Diptera: Culicidae) in Argentina.
We evaluated the potential of Mesocyclops annulatus as a control agent of Aedes aegypti in La Plata city (Argentina). Mosquito larval survivorship due to predation by these copepods was estimated at weekly intervals during the oviposition period of A. aegypti. Mean weekly A. aegypti larval survivorship in cylindrical plastic containers (12 cm height and 11 cm diameter) with copepods was significantly lower than in control containers. Furthermore, weekly larval survival was negatively correlated with M. annulatus adult density, and approximately 23 adult copepods/container would be a threshold density over which the weekly mosquito larval survivorship approached zero. The copepods were able to persist in all containers during approximately 100 days (in three of them until the end of the experiment: 155 days) without the resource represented by A. aegypti larvae. The predation and persistence observed suggest that M. annulatus is a potential control agent to be considered in biological control programs.
Aedes↗
Susceptibility of Diatraea saccharalis (Lepidoptera: Crambidae) to tebufenozide.
Dosage-mortality baselines were determined for first and newly molted third instars of the sugarcane borer, Diatraea saccharalis (F.), with tebufenozide incorporated into an artificial diet. Using death as an endpoint for these assays, LC50 and LC90 values were estimated to be 0.17 and 0.41 ppm for the first and 0.87 and 3.67 ppm for third instars, respectively. Developmental effects also were observed and were defined to include mortality as well as physical impairment and retarded or prolonged development with absence of feeding. Concentrations causing developmental effects in treated larvae (EC50 and EC90) were 5.8- and 3.8-fold lower than the LC50 and LC90, respectively. The critical time of exposure to tebufenozide was determined for developmentally synchronous third instars to be less than 12 h postecdysis. Mortality through adult emergence significantly decreased from 92% (treatment at 0 h postecdysis) to 30% (treatment at 12 h postecdysis), when exposed to tebufenozide at the EC50. For surviving larvae, length of development time until pupation was significantly increased and female pupal weight significantly decreased when larvae were treated at 0 h postecdysis into the third instar. In addition, to modifying the traditional ways of assessing mortality 0-3 d postapplication, this study points out the value of using other approaches to pesticide assessment, especially where insect growth regulators are involved.
Age Factors↗
Toxicity of commonly used insecticides in sweet corn and soybean to multicolored Asian lady beetle (Coleoptera: Coccinellidae).
Use of insecticides with low toxicity to natural enemies is an important component of conservation biological control. In this study, we evaluated the toxicity of insecticides used in sweet corn, Zea mays L., and soybean, Glycine max (L.) Merr., to the multicolored Asian lady beetle, Harmonia axyridis (Pallas), under laboratory and field conditions. Field experiments conducted in sweet corn in 2003 and 2004 and in soybean in 2003, showed that H. axyridis was the most abundant predator. In sweet corn, densities of H. axyridis larvae in plots treated with spinosad or indoxacarb were generally higher than in plots treated with chlorpyrifos, carbaryl, bifenthrin, and A-cyhalothrin. In soybean, densities of H. axyridis larvae in plots treated with chlorpyrifos were higher than in plots treated with lambda-cyhalothrin. Laboratory experiments were conducted to evaluate the acute toxicity of insecticides to eggs, first and third instars, pupae, and adults. Spinosad, followed by indoxacarb, were the least toxic insecticides for all life stages of H. axyridis. Conventional insecticides showed high toxicity to H. axyridis when applied at field rates under laboratory conditions. Overall, first instars were most susceptible to the insecticides tested, followed by third instars and adults, eggs, and pupae. Our results suggest that spinosad, and to a lesser extent indoxacarb, offer reduced toxicity to H. axyridis and would be beneficial for conservation biological control in agricultural systems where H. axyridis is abundant.
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