Workshop summary: biological control of nematode parasites of livestock.
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Animals↗
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Ascosphaera aggregata contamination on alfalfa leafcutting bees in a loose cell incubation system.
The alfalfa leafcutting bee, a solitary bee used to pollinate alfalfa seed crops, is seriously affected by chalkbrood, a larval disease caused by the fungus Ascosphaera aggregata. One attempt to control the disease includes removing nests from the nesting boards (the "loose cell" system). We report here that adults emerging from the loose cells are heavily contaminated with A. aggregata spores. The contamination levels are not as high as previously reported for bees emerging directly from the boards, but they are still a likely focus for disease spread and may need to be targeted in chalkbrood control strategies.
Animals↗
Yeasts as biological agents to control Botrytis cinerea.
Yeasts, isolated from different sources, were identified and tested for inhibition using YMA-MB plates seeded with Botrytis cinerea strains. A total of 42 yeast strains of 20 different species were tested in vitro for antagonism against 18 pathogenic B. cinerea strains. Pichia membranifaciens, P. anomala and Debaryomyces hansenii displayed the most important inhibitory effect against Botrytis strains. In small-scale trials, post-harvest application of P. membranifaciens CYC 1106 to apple wounds inhibited B. cinerea CYC 20010. Purified killer toxin from P. membronifaciens CYC 1106 inhibited B. cinerea CYC 20010. Results indicated that certain yeasts, or their toxins such us P. membranifaciens CYC 1106 killer toxin, might have potential as novel agents to control B. cinerea.
Antibiosis↗
Effects of virulence, sporulation, and temperature on Metarhizium anisopliae and Beauveria bassiana laboratory transmission in Coptotermes formosanus.
Sporulation characteristics and virulence of Metarhizium anisopliae and Beauveria bassiana were examined in relation to laboratory transmission in Coptotermes formosanus. Fungal isolates significantly affected disease prevalence in termite populations. Sporulation of M. anisopliae played a more important role than virulence in producing epizootics within small groups of termites, but this was not the case for B. bassiana. Isolates characterized by quick sporulation (day 2 after death) did not exhibit better transmission in termites than those with high total sporulation (day 11 after death) in either fungal species. An isolate of M. anisopliae ranking highly in all three categories (virulence, quick sporulation, and total sporulation) produced better epizootics than an isolate that was inferior in all three characteristics. High temperatures (35 degrees C) significantly reduced fungal germination rates, leading to significant reduction of epizootics. M. anisopliae was better than B. bassiana in producing epizootics at 27 degrees C. Thus, fungal characteristics other than virulence should be considered for the seasonal colonization approach to termite microbial control.
Animals↗
Re-assessing the infection strategies of the entomopathogenic nematode Steinernema feltiae (Rhabditidae; Steinernematidae).
Previous studies have indicated that between 60 and 80% of a population of entomopathogenic nematodes do not infect their insect hosts at any one period in time. Two hypotheses explain this behaviour: the first that there is a subpopulation of non-infectious nematodes and the second that the non-infectious group is created by inhibitory cues derived from infected insects. Through an experimental approach with the Galleria mellonella-Steinernema feltiae system we show that both mechanisms operate together. When conditions for infection were optimized, the sum of individual infection behaviours was similar to the number infecting as a population, implying observed infection rates are driven by intrinsic mechanisms. In addition, there was evidence that an infected host released a chemical cue into the environment which inhibited subsequent levels of infection. This degree of inhibition was independent of the number of infecting nematodes. Both these mechanisms are dynamic, so the observed proportion of infectious nematodes depended heavily on the time of exposure. The implications of these findings for both the design of laboratory trials and the use of entomopathogenic nematodes in biological control are discussed.
Animals↗
Population control in snails by natural inhibitors.
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Animals↗
Tritrophic interactions between cabbage cultivars with different resistance and fertilizer levels, cruciferous aphids and parasitoids under field conditions.
Tritrophic interactions involving cabbage Brassica oleracea var. capitata cultivars +/- fertilizer, Brevicoryne brassicae (Linnaeus) and Myzus persicae (Sulzer), and the parasitoids Diaeretiella rapae (M'cIntosh) and Aphidius sp. were conducted in 1998 and 1999. Brevicorne brassicae was the dominant aphid species on all cultivars +/- fertilizer, except for some treatments in late season 1998. Ruby Ball (red-leaved with antixenosis factors for B. brassicae alates) +/- fertilizer was consistently less colonized by aphids in early stages of plant growth, although only significantly so compared with Derby Day (green-leaved, susceptible to aphids) without fertilizer for B. brassicae and Minicole (green-leaved with antibiosis factors for B. brassicae) with fertilizer for M. persicae. In early 1999, only B. brassicae was present and no significant differences between cultivars were seen. In the mid to late season 1998, the highest aphid infestations were usually found on Derby Day, although only significantly so for B. brassicae, in some treatments. In 1999, higher aphid infestations were observed on Derby Day in mid to late season and some significant differences were found for M. persicae as well as for B. brassicae. In both years, Ruby Ball had the greatest mummy:aphid ratios early season, with no consistent difference between the other cultivars. Later in the season, mummy:aphid ratios were generally highest on Minicole. Parasitism differed in seasonal occurrence and relative abundance. Diaeretiella rapae mummies were found earlier than Aphidius sp. There was evidence of a beneficial interaction between the degree of plant resistance and biological control in early to mid season.
Animals↗
Predation and control of laboratory populations of the snail Biomphalaria glabrata by the freshwater prawn Macrobrachium rosenbergii.
Laboratory experiments were conducted on predation by the giant freshwater prawn, Macrobrachium rosenbergii, on Biomphalaria glabrata, a snail intermediate host of human schistosomiasis. Prawns greater than 22 mm carapace length could consume snails of any size. Smaller prawns exhibited a size-specific upper limit on the size of snail they could kill. Below the maximum size of prey consumed, little selectivity for prey size was demonstrated. All prawns heavier than 2.5 g killed the largest size of snail offered (16 mm diameter). Consumption, in terms of the numbers of snails killed, and the snails' wet weight and percentage of prawn body weight eaten per day, increased with prawn size. Large prawns consumed snails at a high rate (39% of body weight per day). Population experiments demonstrated that a prawn of 25 mm carapace length could eliminate 95% of a population of 80 snails in a 20-1 aquarium within 20 days and all snails by day 40. A prawn of 15 mm carapace length could not eliminate all snails. Large snails (24% of the initial population) had some protection from predation because of their size. Although the snails bred continuously, no snails were able to recruit to these populations in the presence of small prawns. In contrast, snail populations in control aquaria without prawns expanded to a mean of 919 snails by the end of the experiment (day 70). Since M. rosenbergii are voracious predators on B. glabrata, exhibit considerable habitat overlap with the snail prey, and are likely to treat snails as highly preferred food, further experimentation on these prawns in the context of biological control of schistosomiasis is warranted. The ready availability of prawns through established prawn hatcheries and the synergistic use of these prawns in aquaculture may ensure the reliability of stocking procedures and meet the standards of availability and cost-effectiveness required of a biological control agent. Polyculture of Macrobrachium with fin fish (Tilapia) indicates that these prawns may be a particularly useful control agent in aquacultural environments.
Animals↗
Sex pheromones of Lepidoptera. Development of a method for pheromonal control of Pectinophora gossypiella in cotton.
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Animals↗
Differential susceptibility of Dysmicoccus vaccinii (Homoptera: Pseudococcidae) to entomopathogenic nematodes (Rhabditida: Heterorhabditidae and Steinernematidae).
The susceptibility of the mealy bug, Dysmicoccus vaccinii Miller & Polavarapu, to infection by various species and strains of entomopathogenic nematodes was investigated in laboratory sand-dish and sand-column assays. Steinernemo carpocapsae (Weiser) (All strain), S. feltiae (Filipjev) (AB [Australia] strain), and S. glaseri (Steiner) (NC strain) were ineffective against individual mealybugs in sand-dish assays conducted in small petri dishes (1 cm high by 3.5 cm diameter) at 25 degrees C with doses of infective juvenile nematodes ranging up to 500 or 1,000 infective juveniles and exposure periods up to 5 d. However, Heterorhabditis bacteriophora Poinar (HP88 strain and 2 New Jersey isolates). H. hawaiiensis Gardner, Stock & Kaya (MG-13 strain), and H. indicus Poinar, Karunakar & David (EMS-13 strain) induced significant mortality (65.0-90.0%) at doses as low as 100 infective juveniles and an exposure of 5 d. H. bacteriophora (HBNJ strain) was effective at doses of 500 and 1,000 infective juveniles but, together with H. zealandica Poinar (V16 strain) and 4 other H. bacteriophora isolates from New Jersey, was ineffective at doses of 100 infective juveniles. Removal of the waxy coating from the mealybugs did not influence susceptibility to H. bacteriophora (HP88 strain). In the sand-column assay (5.5 cm high by 5 cm diameter, 5-d exposure, 25 degrees C), which more closely resembles host-finding in the field, H. bacteriophora (HP88 strain) induced no significant mortality against individual mealybugs at doses of 100 infective juveniles but produced 93.8% mortality at 500 infective juveniles, whereas H. indicus (EMS-13 strain) induced 56.3 and 100% mortality at 100 and 500 infective juveniles, respectively. H. bacteriophora (HP88 strain and some New Jersey isolates), H. hawaiiensis (MG-13 strain), and H. indicus (EMS-13 strain) successfully reproduced in and emerged from mealybug cadavers. This study demonstrates strong variability in the susceptibility of D. vaccinii to different species and strains of entomopathogenic nematodes, and implicates certain heterorhabditids as promising candidates for the biological control of this insect.
Animals↗
Effects of Toxorhynchites moctezuma larval predation on Aedes aegypti populations: experimental evaluation.
Predatory larvae of the mosquito Toxorhynchites moctezuma were used experimentally to control a standing crop of larvae of the dengue vector mosquito Ae.aegypti. Each week, fifty Ae.aegypti first instar larvae were introduced to each of five water-filled drums (220 litres) of the type commonly used for domestic water storage in Caribbean dwellings. At the beginning of the fourth week, a certain number (0, 1, 2, 5 or 10) of first instar Tx.moctezuma larvae were introduced to each drum and the daily yield of Ae.aegypti adults from each drum was monitored thereafter. The experiment was repeated three times. With only one or two Tx.moctezuma larvae, predation on Ae.aegypti larvae stopped the output of Ae.aegypti adults for 1 week. Five or ten Tx.moctezuma prevented any Ae.aegypti emergence for up to 16 weeks. Cannibalism among Tx.moctezuma larvae was seldom observed and appeared not to be a hindrance in using this species against Ae.aegypti. Thus Tx.moctezuma is regarded as a good candidate for the biological control of Ae.aegypti by augmentative releases.
Aedes↗
Environmental control of schistosomiasis through community participation in a Moroccan oasis.
Summary Akka oasis, in the province of Tata, southern Morocco, is one of the oldest foci of urinary schistosomiasis in Morocco where transmission is still taking place. We report the results of two studies: a cross-sectional snail survey investigated the distribution of Bulinus truncatus in relation to habitat factors in the Akka traditional irrigation system. The presence of aquatic vegetation, especially Potamogeton sp. was identified as a key factor determining snail occurrence and abundance in canals, impoundments and isolated small puddles and streamlets in the Akka riverbed. In a participatory rapid appraisal, the community identified snail control as a way to reduce transmission of schistosomiasis. Without any further outside incentives, the local irrigation committee implemented repeated cleaning and vegetation removal in canals. A longitudinal study evaluated the effect of these measures on populations of B. truncatus. Snail and egg mass densities showed significant reductions after repeated vegetation clearing in the study sites. The participatory approach led to low-cost, environment-friendly schistosomiasis control measures that were effective and sustainable.
Animals↗
In vitro studies on the potential for biological control on Aspergillus section Flavi by Kluyveromyces spp.
AIMS: Antagonist activity of Kluyveromyces spp. isolates on Aspergillus section Flavi was studied. METHODS AND RESULTS: The screening of isolates were made through studies of growth at different water activities and temperatures, index of dominance (I(D)), ecological similarity, antifungal activity and impact on aflatoxin B1 accumulation. High optical density was obtained at 25 and 30 degrees C and 48 h of incubation. Cell growth decreases with decrease in water activity. The predominant interaction was mutual intermingling at a(w) = 0.982 and 0.955, while at a(w) = 0.999 and 0.937 mutual inhibition for contact was exhibited. All isolates were catabolically identical to Aspergillus section Flavi and compete by nutritional source. At high water activities yeasts showed inhibitory activity on Aspergillus strains, inhibition percentages varied between 75 and 100%. The isolates Y9, Y14, Y16, Y22, Y25 and Y33 showed antifungal activity and inhibitory activity on aflatoxin B1 accumulation at all water activities assayed from all Aspergillus section Flavi strains. CONCLUSIONS: The data show that the isolates selected in a wide range of environmental conditions could exert their roll like biological control agents for Aspergillus section Flavi in storage maize ecosystem. SIGNIFICANCE AND IMPACT OF THE STUDY: Isolates of Kluyveromyces spp. may have practical value in the postharvest control of storage maize.
Aflatoxin B1↗
Industry viewpoint on thresholds for genotoxic carcinogens.
Modern chemical control of pests has contributed to a dramatic improvement in public welfare since its introduction 50 years ago. Millions of lives have been saved through the control of disease vectors, and millions more have been improved by the use of chemicals to produce an inexpensive and abundant food supply. Hundreds of pesticidally active ingredients are in commercial use today, and among these are found genotoxic and nongenotoxic carcinogens. In the United States, the Environmental Protection Agency regulates carcinogens using threshold and nonthreshold approaches depending upon the outcome of a weight-of-evidence determination. More than one-half of all pesticides with some evidence of carcinogenic potential are regulated by the nonthreshold approach. The limitations on product use imposed by this approach have restricted the number of products available to growers and to the public. This restriction has had a direct impact on industry with respect to commercial success and financial returns on investment as well as an indirect impact on the industry's ability to fund the discovery and development of new compounds. This paper explores the question of how well regulation by the nonthreshold approach has achieved the goal of protecting public health, whether it does this better than the alternative use of the threshold approach, and whether the incremental protection it affords is a meaningful public benefit that justifies the aforementioned impacts on industry.
Carcinogenicity Tests↗
Trapping effect of synthetic sex pheromone of Acleris fimbriana (Lepidoptera: Tortricidae) in Chinese northern orchard.
The yellow tortrix, Acleris fimbriana Merick (Lepidoptera: Tortricidae), is an economically important insect pest on fruit trees with four generations a year in North China. In order to develop a new and effective method for forecasting and controlling the pest, the sex pheromone was studied. We have identified the female sex pheromone as (E)-11,13-tetradecadienal (E11,13-14:Ald), (E)-11,13-tetradecadienyl acetate (E11,13-14:Ac) and (E)-11-tetradecenyl acetate (E11-14:Ac). Trapping effect of synthetic chemicals E11,13-14:Ald, alone and in combination with E11,13-14:Ac or/and E11-14:Ac to A. fimbriana males was tested in Beijing Xishan Orchard (2001). E11,13-14:Ald on its own was much attractive to A. fimbriana males. Neither E11,13-14:Ac nor E11-14:Ac alone caught any moths. The catches markedly increased by adding E11,13-14:Ac to E11,13-14:Ald. The optimum ratio of E11,13-14:Ald and E11,13-14:Ac was 6:4 to 5:5. This attractiveness was apparently enhanced when 5% to 10% of E11-14:Ac was added. The best field activity was in the lure baited with a 6:4:1 ratio of E11,13-14:Ald, E11,13-14:Ac and E11-14:Ac at a dosage of 1000 microg/septum. The effect of antioxidant, 2,6-di-tert-butyl-4-methylphenol [butylated hydroxyluene (BHT)], to the synthetic pheromone blends on its duration and catching efficacy was also tested. Addition of 5-10% BHT to the synthetic pheromone could prolong the life-span of pheromone chemicals for 6-8 weeks, thereby increased its catching efficacy.
Animals↗
[A control program for an outbreak of the scorpion Tityus serrulatus, Lutz and Mello 1922 in the town of Aparecida, São Paulo state (Scorpiones, Buthidae)].
A scorpion control program was proposed for the town of Aparecida (SP), an endemic region of Tityus serrulatus. Clusters of scorpions in urban and rural areas, environmental degradation of the town's outskirts and new scorpion procreation and dispersal habitats were studied. In addition, infrastructure problems such as the disposal and collection of residential and municipal refuse, sanitation (sewage and storm sewer), condition of vacant lots and constructions in the urban area were evaluated. After an epidemiological study, educational measures such as the distribution of pamphlets, cleaning group work, visits to residences and cooperation from High School teachers and students were also suggested. Chemical control was indicated in high-risk sites, especially those of near-school buildings. Furthermore, the use of natural predators was also mentioned within the present sanitation regulations for urban areas. The authors assert that these procedures must be integrated and continued uninterruptedly for several years. They also suggest a collaborative work with those responsible for the dengue eradication program, as well as the institution of the "scorpion study week", which would greatly contribute to the education of the population, to preventive programs and to scorpion control.
Animals↗
Effect of combining imidacloprid and diatomaceous earth with Beauveria bassiana on mole cricket (Orthoptera: Gryllotalpidae) mortality.
Sublethal doses of three orthopteran-derived strains of Beauveria bassiana (Balsamo) Vuillemin were topically applied to adult southern mole crickets, Scapteriscus borellii Giglio-Tos (Orthoptera: Gryllotalpidae), and tested in combination with substrate treatments of diatomaceous earth (DE) and imidacloprid. Crickets treated only with the high doses (10(8) conidia per cricket) of each of the three B. bassiana strains exhibited the shortest survival times as well as the highest percentage mortality at 28 d after treatment. However, these treatments did.not differ significantly from any of the diatomaceous earth combination treatments. Two of the strains tested, 5977 and 3622, exhibited synergistic interactions with DE, whereas the third strain, GHA, was not significant for synergy. Mortality caused by the combination treatment was still greater than the expected additive effect. DE abrades the insect cuticle and absorbs cuticular lipids, aiding the entry of germinating conidia into the mole cricket hemocoel. None of the three strains exhibited synergy when combined with imidacloprid, and mortality of all combination treatments was less than additive. For strain 5977, there was an antagonistic interaction with imidacloprid. It was difficult to obtain <30% mortality for imidacloprid only treatments, which was considered the upper limit for sublethal doses. The mean percentage mortality caused by imidacloprid was 37.5%, and this high percentage made it difficult for any combination treatment to cause significantly more mortality than the expected additive effect. These results clarify the interactions of other control products with B. bassiana and provide a basis for a reduced pesticide approach to mole cricket control.
Animals↗
The economics of vector control strategies for controlling tropical diseases.
This paper describes the techniques of economic evaluation and how they can help improve the efficiency of vector control strategies for controlling tropical diseases. The differences among the techniques are clarified, and the main components of each analytical approach are presented, as well as some of the major problems in their application. The historic evolution of the application of economics to vector control in developing countries is summarized, before analyzing some more recent studies that have explored some of the choices concerning vector control. The paper concludes with some recommendations for improving the quality and, therefore, the usefulness of studies.
Animals↗