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PubMed2005

Extinction and permanence of one-prey multi-predators of Holling type II function response system with impulsive biological control.

In this paper, one investigates the dynamic behaviors of one-prey multi-predator model with Holling type II functional response by introducing impulsive biological control strategy (periodic releasing natural enemies at different fixed time). By using Floquet theorem and small amplitude perturbation method, it is proved that there exists an asymptotically stable pest-eradication periodic solution when the impulsive period is less than some critical value and permanence condition is established via the method of comparison involving multiple Liapunov functions. It is shown that multi-predator impulsive control strategy is more effective than the classical and single one.

Animals↗
PubMed1989

Managing resistance with multiple pesticide tactics: theory, evidence, and recommendations.

Sequences, mixtures, rotations, and mosaics are potential strategies for using more than one pesticide to manage pest populations and for slowing the evolution of pesticide resistance. Results from theoretical models suggest that, under certain conditions, mixtures might be especially effective for resistance management. The assumptions of such models, however, are probably not widely applicable. Potential disadvantages associated with mixtures that are usually not considered in modeling studies include disruption of biological control, promotion of resistance in secondary pests, and intense selection for cross-resistance. Results from limited experimental work suggest that pesticide combinations do not consistently suppress resistance development. More thorough evaluation of tactics that seek to optimize benefits of more than one insecticide will require rigorous experiments with the particular pest and pesticide combinations. Because of the difficulty in generalizing results across systems and the potential negative effects of multiple insecticide use, emphasis on minimizing insecticide use is recommended.

Animals↗
PubMed1991

A host-host-pathogen model with free-living infective stages, applicable to microbial pest control.

A model has been investigated of the dynamics of the interaction between two hosts which are both attacked by a common pathogen, where the pathogen has free-living infective stages the population size of which must itself be modelled explicitly, and where the host species do not interact with one another except through their shared pathogen. If either host interacted with the pathogen alone, three broad classes of dynamics would be possible: host regulation, pathogen persistence and pathogen extinction. Here, all possible types of combinations of hosts are examined: regulation-regulation (both hosts would be regulated if they interacted with the pathogen alone), regulation-persistence, regulation-extinction, persistence-persistence persistence-extinction and extinction-extinction. A wide range of dynamics is generated, including a number of patterns quite unlike those found in the one-host pathogen case (e.g. persistence in one host, elimination of the other host) and behaviour contingent on initial densities in the system. For clarity and pertinence, attention is focused on the case where one host is a pest, the pathogen is a potential microbial control agent, and the other host is a non-target species which it is undesirable to harm. The model suggests, broadly, that non-targets are unlikely to be seriously threatened in such cases, and also that non-targets, far from undermining pest control, are quite likely to contribute to its efficacy.

Animals↗
PubMed2003

The effect of temperature on the functional response of Phytoseiulus persimilis (Acari: Phytoseiidae).

Environmental variables, such as temperature, are important in determining the efficiency of biological control in ornamental crops. This paper examines the effect of temperature on the functional response of adult female Phytoseiulus persimilis to eggs of the spider mite, Tetranychus urticae. The functional response was determined using a new functional response assay technique with plant stems as an arena, rather than leaf discs. The use of plant stems allows the influence that plant structure has on predation to be incorporated into the assay. Control assays were also used (without predators) to estimate natural losses of prey. The data were analysed using a binomial model, with the use of Abbot's formula to correct for the losses in the controls. A combined equation to describe the effect of temperature and prey density on the predation rate of Phytoseiulus persimilis was derived. The results showed that more prey are eaten as the temperature increases from 15 degrees C to 25 degrees C, but the number of prey eaten then declines at 30 degrees C, although not to the levels seen at 20 degrees C. The implication of these results for biological control in ornamental crops, where the temperature can often exceed 30 degrees C, is discussed.

Acari↗
PubMed2004

Biological control of sciarid and phorid pests of mushroom with predatory mites from the genus Hypoaspis(Acari: Hypoaspidae) and the entomopathogenic nematode Steinernema feltiae.

In small-scale experiments, the predatory mites, Hypoaspis aculeifer (Canestrini) and H. miles Berlese, applied at 700 mites m(-2), and the entomopathogenic nematode, Steinernema feltiae (Filipjev) applied at 3 x 10(-6) nematodes m(-2) controlled sciarids and phorids in mushroom compost and casing substrates. For both mite species, earliest application to the growing substrate following sciarid infestation reduced sciarid emergence. In contrast, later application of each biological control agent provided more effective control of phorid emergence. The behaviour of adult mites suggested that H. aculeifer were more positively geotactic than H. miles although both species could penetrate compost and casing substrates to a depth of 2-12 cm. A majority of S. feltiae nematodes resided at a depth of 2-4 cm in both substrate types. Independent application of H. aculeifer provided more comprehensive control of sciarids and phorids than the other biological agents studied, owing to its better dispersal within compost and casing, and ability to attack larvae of differing ages.

Agaricales↗
PubMed2005

Influence of Bacillus thuringiensis var. israelensis on oviposition of Aedes albopictus (Skuse).

The effect of Bacillus thuringiensis var israelensis (B.t.i.) on the oviposition behavior of Aedes albopictus was evaluated in the field and laboratory in Clemson, SC, U.S.A. In the field, water taken from containers in which mosquito larvae were reared (conditioned water) was placed in 16 containers. Eight containers received 50 jld of B.t.i., and eight with water only were kept as controls. In the laboratory, field-collected females of Ae. albopictus were placed in rearing chambers and provided two containers for oviposition, one with 50 microl of B.t.i and one a control with water only. Eight cage experiments were conducted, five using filtered tap water and three with conditioned water. In the field over the 13 trials, more eggs were laid in the containers with B.t.i. although no significant difference was found in the number of eggs between the treatment and controls over 72 h. In the laboratory, more eggs were laid in the containers with B.t.i. versus the controls. The containers had filtered tap water and B.t.i. had significantly more eggs laid in them compared to the controls.

Aedes↗
PubMed2005

Integrated pest management models and their dynamical behaviour.

Two impulsive models of integrated pest management (IPM) strategies are proposed, one with fixed intervention times and the other with these unfixed. The first model allows natural enemies to survive but under some conditions may lead to extinction of the pest. We use a simple prey-dependent consumption model with fixed impulsive effects and show that there exists a globally stable pest-eradication periodic solution when the impulsive period is less than certain critical values. The effects of pest resistance to pesticides are also studied. The second model is constructed in the light of IPM practice such that when the pest population reaches the economic injury level (EIL), a combination of biological, cultural, and chemical tactics that reduce pests to tolerable levels is invoked. Using analytical methods, we show that there exists an orbitally asymptotically stable periodic solution with a maximum value no larger than the given Economic Threshold (ET). The complete expression for this periodic solution is given and the ET is evaluated for given parameters. We also show that in some cases control costs can be reduced by replacing IPM interventions at unfixed times with periodic interventions. Further, we show that small perturbations of the system do not affect the existence and stability of the periodic solution. Thus, we provide the first demonstration using mathematical models that an IPM strategy is more effective than classical control methods.

Agriculture↗
PubMedDate not supplied

United States Department of Agriculture-Agricultural Research Service research on natural products for pest management.

Recent research of the Agricultural Research Service of USDA on the use of natural products to manage pests is summarized. Studies of the use of both phytochemicals and diatomaceous earth to manage insect pests are discussed. Chemically characterized compounds, such as a saponin from pepper (Capsicum frutescens L), benzaldehyde, chitosan and 2-deoxy-D-glucose are being studied as natural fungicides. Resin glycosides for pathogen resistance in sweet potato and residues of semi-tropical leguminous plants for nematode control are also under investigation. Bioassay-guided isolation of compounds with potential use as herbicides or herbicide leads is underway at several locations. New natural phytotoxin molecular target sites (asparagine synthetase and fructose-1,6-bisphosphate aldolase) have been discovered. Weed control in sweet potato and rice by allelopathy is under investigation. Molecular approaches to enhance allelopathy in sorghum are also being undertaken. The genes for polyketide synthases involved in production of pesticidal polyketide compounds in fungi are found to provide clues for pesticide discovery. Gene expression profiles in response to fungicides and herbicides are being generated as tools to understand more fully the mode of action and to rapidly determine the molecular target site of new, natural fungicides and herbicides.

Agriculture↗
PubMedDate not supplied

[Long-term results of biological control by predation. Experimental study of population development of several species of snails (author's transl)].

The evolution of malacological fauna, which is subject to prediation of Zonitidae snails, is studied on two types of habitats of Lymnaea truncatula: swampy meadows and banks of river maintained by a periodical grass-mowing. Two years are necessary for obtaining an entire elimination of Lymnaea truncatula. Then other species of Lymanaeidae and Succinea are affected by predation, but Succinea snails do not pass away completely. The other snails are not affected or little by predation.

Animals↗
PubMed2000

Insect population control using a dominant, repressible, lethal genetic system.

A major modification to the sterile insect technique is described, in which transgenic insects homozygous for a dominant, repressible, female-specific lethal gene system are used. We demonstrate two methods that give the required genetic characteristics in an otherwise wild-type genetic background. The first system uses a sex-specific promoter or enhancer to drive the expression of a repressible transcription factor, which in turn controls the expression of a toxic gene product. The second system uses non-sex-specific expression of the repressible transcription factor to regulate a selectively lethal gene product. Both methods work efficiently in Drosophila melanogaster, and we expect these principles to be widely applicable to more economically important organisms.

Animals↗
PubMed1992

Performance of an aquatic multispecies system in evaluating the effects of a model microbial pest control agent on nontarget organisms.

A recirculating multispecies test system was developed in conjunction with a study of the fate and persistence of a model microbial pest control agent on non-target marine and freshwater organisms. The basic unit of the system was a 113-I glass aquarium with vertical biological filters in the center of the aquarium, such that two compartments were formed. This allowed the sequestration of predator and prey species within the same system. Organisms from six phyletic groups were subjected to a genetically altered strain of Pseudomonas putida for 15-29 d in either artificial seawater or fresh water. The system was able to maintain the animals for these periods with a minimum of maintenance. Additionally, the system design lent itself to disinfection, dismantling, and rebuilding between experiments with a minimum of labor, and has potential for longer-term studies.

Animals↗
PubMed2006

Potential for classical biological control of the potato bug Closterotomus norwegicus (Hemiptera: Miridae): description, parasitism and host specificity of Peristenus closterotomae sp. n. (Hymenoptera: Braconidae).

The potato bug, Closterotomus norwegicus (Gmelin) (Hemiptera: Miridae) is an introduced pest of lucerne, white clover and lotus seed crops in New Zealand and a key pest of pistachios in California, USA. Efforts were made to identify potential biological control agents of C. norwegicus in Europe. A total of eight parasitoids, including six primary parasitoids from the genus Peristenus (Hymenoptera: Braconidae) and two hyperparasitoids from the genus Mesochorus (Hymenoptera: Ichneumonidae), were reared from C. norwegicus nymphs collected in various habitats in northern Germany. With a proportion of more than 85% of all C. norwegicus parasitoids, Peristenus closterotomae (Hymenoptera: Braconidae), a new species, was the most dominant parasitoid, whereas other parasitoid species only occurred sporadically. Peristenus closterotomae did not fit in the keys to any described species and is described as new to science. Parasitism caused by P. closterotomae was on average 24% (maximum 77%). To assess the host specificity of parasitoids associated with C. norwegicus, the parasitoid complexes of various Miridae occurring simultaneously with C. norwegicus were studied. Peristenus closterotomae was frequently reared from Calocoris affinis (Herrich-Schaeffer), and a few specimens were reared from Calocoris roseomaculatus (De Geer) and the meadow plant bug, Leptopterna dolobrata (Linnaeus) (all Hemiptera: Miridae). The remaining primary parasitoids associated with C. norwegicus were found to be dominant in hosts other than C. norwegicus. Whether nymphal parasitoids may potentially be used in a classical biological control initiative against the potato bug in countries where it is introduced and considered to be a pest is discussed.

Animals↗
PubMed2001

First steps to improve cotton crop management in Thailand.

Thai cotton growers yearly face serious pest problems consisting of heavy infestation associated with resistance to pesticides leading to expensive and harmful pest control practices. Thanks to a multi discipline research work carried out from 1991 to 1996, a decision-oriented model for cotton crop management was developed and compared to farmers' practices during the 1988 cotton growing season 1998 in Klang Hat district, Thailand. This model, based on plant monitoring, involved a new cotton cultivar (DORA 11 as a replacement for Sri Samrong 60), seed treatment with imidacloprid (at 3.5 g of a.i./kg of seeds), a threshold-based spray of mepiquat chloride, a cotton growth regulator (Pix at 1.5 l/ha) and a set of rules to selectively control with chemical and biological insecticides the major pests the American bollworm (Helicoverpa armigera Hübner) and the cotton leafhopper (Amrasca biguttula biguttula Ishida). This package was more friendly towards environment than farmers' practices since seed treatment does not harm beneficials at the beginning of cotton growing season while 1 and 5 sprays were saved against respectively the American bollworm and sucking pests and more than 50% of the sprays directed against American bollworms involved biological insecticides (Bacillus thuringiensis toxins potentialized by a low dosage of endosulfan). Threshold-based sprays against the main pests, the use of a cotton growth regulator, earliness of cotton cultivar and seed treatment were accountable for savings in pesticide sprays. Involving a biological insecticide and endosulfan at the beginning of cotton growing season and using the same quantity of active ingredient at each spray during the cotton growing season also improved the management of pyrethroid resistance in American bollworm populations was also. There was no significant difference between yields inside farmers' fields and innovation plots. However, thanks to cheaper pest control practices economic results were better. Lastly few improvements of this package are proposed.

Agriculture↗
PubMed2000

Assessment of microencapsulated formulations for improved residual activity of Bacillus thuringiensis.

Bacillus thuringiensis Berliner is a highly efficacious bioinsecticide used to control lepidopteran pests in the field. Unfortunately, it has limited residual activity on plants because sunlight inactivates spores and crystals and they can be washed off by rain. To minimize loss of activity, formulations must contain UV protectants, stickers, or both. We tested approximately 80 formulations and determined optimal combinations of ingredients and spray drying conditions for improving B. thuringiensis residual activity after simulated rain and simulated sunlight. B. thuringiensis stability, after simulated sunlight (xenon light/8 h) and rain (5 cm/50 min), was improved using formulations based on lignin, corn flours, or both, with up to 20% of the active ingredient, when compared with technical powder or Dipel 2x in laboratory assays. Two formulations, made with corn flours or lignin + pregelatinized corn flour (PCF), killed 51.6 and 75.3% of Ostrinia nubilalis (Hübner) neonates after rain, respectively, versus 27% for technical powder. When the insecticidal activity was tested after simulated sunlight, corn flour-based formulations killed 78.5% of test larvae, and the lignin + PCF formulation killed 70.4%, in contrast to technical powder which caused an average of 29% mortality. Formulations made with Dipel 2x rather than technical powder, caused 62.5% mortality (corn flour-based formulations), and 72.3% mortality (lignin + PCF), versus 53.4% for Dipel 2x after rain. When tested after simulated sunlight, formulations killed 95% of the larvae (average of both formulations) versus 82% for Dipel 2x. In a field test, formulations were applied to cabbage and insecticidal activity was determined against Trichoplusia ni (Hübner) neonates exposed to treated leaves. Insecticidal activity of the corn flour-based formulations was comparable to Dipel 2x for 4 d after treatment, but was significantly better than Dipel 2x 7 d after application. A lignin and PCF-based formulation showed significantly higher residual activity than Dipel 2x, 4 and 7 d after application.

Animals↗
PubMed1998

Potency of products based on Bacillus thuringiensis var. israelensis: interlaboratory variations.

Six quality-control laboratories in 4 countries independently bioassayed aliquots of a flowable formulation of Bacillus thuringiensis var. israelensis (B.t.i.) against the international standard powder IPS-82. All laboratories substantially followed World Health Organization or U.S. Department of Agriculture standard protocols. Significant differences were found in resulting potency values between laboratories. Factors that may have influenced results, such as age, stage, and strain of larvae used, amount and type of food provided to larvae, and processing of samples were examined. Use of different rearing temperatures, different strains of Aedes aegypti L., or late 3rd instars vs. the recommended early 4th instars did not explain the inconsistencies. The slope of the dose-response curve of the IPS-82 powder was influenced by particle size, which varied with the nature and duration of sample homogenization. Laboratories using low-intensity processing obtained a greater slope in the dose-response curve for the flowable product than for the powder standard. The type and quantity of food provided to larvae affected susceptibility. Larvae fed an excess of protein-rich food became 4th instars in 3 days and were less susceptible to B.t.i. than those fed smaller quantities of carbohydrate-rich food that became 4th instars in 5-7 days. Overall, deviations from standard protocols with regard to larval stage, holding temperature, and lighting regime may not be as important as differences in sample processing and pretest rearing conditions. The need to improve standardization in these areas, which are not clearly specified in current protocols, is discussed.

Aedes↗
PubMed2004

Evaluating the impacts of refuge width on source-sink dynamics between transgenic and non-transgenic cotton.

Resistance management for Bt-transgenic crops relies in part on the production of sufficient numbers of susceptible insects in non-toxic refuges. Simulation models suggested that source-sink dynamics could interact with the structure of refuges to impact the production of insects in these areas. We tested the hypothesis that altering isolation between refuges and transgenic cotton by manipulating the width of refuges embedded within cotton fields would alter the density of Heliothis virescens and Helicoverpa zea eggs oviposited in refuges. Three categories of refuge widths were tested over two years: they included narrow (16-24 m wide), medium (32-48 m wide) and wide (80-96 m wide) refuges. Isolation between the two habitats increased as refuge width increased. In 1996, eggs of H. virescens from H. zea were not distinguished, but a significant increase in the density of eggs and a significant decrease in relative yield (refuge yield compared to the yield from immediately surrounding Bt-cotton) was found as refuge width increased. In 1997, eggs from H. virescens were analyzed separately from H. zea using an ELISA test. The density of H. virescens eggs increased with increasing refuge width, and there was a significant decline in density of H. virescens eggs with increasing distance from the refuge. In contrast, there was no impact of refuge width on the density of H. zea eggs, nor was the slope of a regression of egg density and distance from the refuge significantly different from zero. We suggest that these differences reflect differences in the biology of the two insects.

Animals↗