R. A. J. Taylor

Aggregation, migration and population mechanics.

A concept is developed for the regulation of populations by density-dependent movement, rather than by overt competition alone. Fitness is seen as maximising the reproductive advantage of a balance between migratory and congregatory behaviours. Population density is shown to be spatially, as well as temporally dynamic and a mechanism is proposed that accounts for observed spatial behaviour.

The relationship between density and distance of dispersing insects

Abstract. 1. The data for dispersal of Drosophila pseudoobscura of Dobzhansky & Wright (1943) were re‐examined and an improved description found for them.

Deposit structure and efficacy of pesticide application. 1: Interactions between deposit size, toxicant concentration and deposit number

Application of pesticides through a hydraulic nozzle produces deposits on a plant surface which have a spatial structure with elements of deposit size, number per area, and toxin per deposit. To investigate the relative contributions of these elements to the interaction of deposit structure and toxicant efficacy, we used a stochastic cellular automaton model of diamondback moth feeding on Bacillus thuringiensis (Bt)-treated cabbage – the Pesticide Dose Simulator (PDS) model. Data were analyzed using a specialized response surface approach called a mixture design. The advantage of this design was that it integrated the effects of deposit size, number per area and toxin per deposit on toxicant efficacy. Results from PDS simulations led to the following conclusions: (1) Deposit structure plays a major role in toxin efficacy. (2) Small deposits are not always the most efficacious. (3) Uniform coverage is not the best deposit structure if one is forced to limit application rates and field persistence. (4) Since uniform deposit structures allow an insect to live longer, uniform deposit structures should result in more insects acquiring sub-lethal doses. This may result in an interaction between ‘uniform coverage’ and the development of pesticide resistance in insect populations. (5) Percentage mortality and the level of crop protection are not necessarily correlated. Overall, these results help reconcile laboratory observations that small droplets are more efficacious with field observations that application of small droplets (eg from spinning disk sprayers) does not necessarily increase field efficacy. © 1999 Society of Chemical Industry

Effects of vascular endothelial growth factor on wound closure rates in the genetically diabetic mouse model.

Impaired wound healing is characteristic of diabetic patients. Potential reasons include poor inflammatory response, granulation tissue formation, and abnormal patterns of cytokine release and response. Vascular endothelial growth factor, abnormally regulated during healing in diabetics, is the major factor stimulating angiogenesis during normal wound healing. We tested our hypothesis that topically applied vascular endothelial growth factor would improve wound closure rates in diabetic animals in a full‐thickness wound model in genetically diabetic mice (C57 BL/KsJ db/db). Animals received either 1.0 µg of vascular endothelial growth factor165 or polyethylene glycol alone topically to wounds daily between days 0 and 4 postwounding. Wound area was measured at days 0, 5, 10, 15, and 21. Data were analyzed using probit analysis and expressed as length‐of‐time (LT) to 50, 90, and 95% wound closure. Among untreated animals, nondiabetics had an LT50 of 8.5 days (fiducial limits 8.3–8.7), while diabetics had an LT50 of 15.8 days (15.6–16.1). Vascular endothelial growth factor‐treated animals had LT50 values of 7.8 (7.6–8.1) and 11.8 days (11.6–12.0) for nondiabetics and diabetics, respectively, representing a 25% improvement in time to 50% closure in treated diabetics. We conclude that topically applied vascular endothelial growth factor improves time to wound closure in the genetically diabetic mouse model.

Efficiency of insect exclusion screens for preventing whitefly transmission of tomato yellow leaf curl virus of tomatoes in Israel

Tomato yellow leaf curl virus (TYLCV) is the most frequently occurring virus in tomatoes in the Middle East, and the most harmful one. It is transmitted solely by the whitefly Bemisia tabaci (Gennadius). Within 4-6h of inoculative feeding, a whitefly can transmit TYLCV to a healthy plant with 80% probability. The symptoms are apparent after two to three weeks whereupon fruit-set is effectively terminated. The only means of controlling TYLCV is by controlling the whitefly. Until 1990 this was exclusively by insecticides. Starting in 1990, growers of greenhouse tomatoes in Israel began adopting insect exclusion screens to prevent inoculation of TYLCV. This article reports on the methods used in the search for efficient screening materials and presents data on their relative efficiencies in excluding B. tabaci and several other greenhouse pests. Ten materials were tested, of which five were found to be effective in excluding B. tabaci under laboratory conditions. This number was reduced to three following field trials and trials in commercial tomato greenhouses. These materials are now in widespread use in Israel: by 2000 practically all table tomatoes in Israel were grown under exclusion screens. The use of exclusion screens has been shown to be an economically viable pest management method.

A Simulation Model of Locust Migratory Behaviour

(1) A computer simulation model was developed for a migration of Schistocerca gregaria: the locusts were reported to have reached the United Kingdom in 1954 and were described by Rainey (1963) who concluded from meteorological evidence and current locust reports that they originated in N.W. Africa. (2) The model follows the same basic assumptions that, whilst migratory motion in locusts is maintained behaviourally, displacement is attributed almost entirely to transport in wind systems (Rainey 1951). (3) Laboratory estimates of flight performance from the literature were found to be inadequate to define the distribution of performance in the field. (4) A dummy variable, equivalent to ground speed, was used to compare the effects of different distributions of flight performance. (5) Response surfaces were defined for combinations of parameters and were found to vary qualitatively and quantitatively with different distributions of flight performance. (6) The effect of down-wind orientation was investigated and found to affect the flight performance but in no simple way.

Deposit structure and efficacy of pesticide application. 2 : Trichoplusia ni control on cabbage with fipronil

Pesticide deposits have a spatial structure having elements of size, number per area and toxicant per deposit. To investigate the relative contributions of these elements to the efficacy of the deposit structure, we developed a bioassay using the cabbage looper (Trichoplusia ni), cabbage, and a soluble concentrate formulation of fipronil [(±)-5-amino-1-(2,6-dichloro-α,α,α-trifluoro-p-tolyl)-4-trifluoromethylsulfinylpyrazole-3-carbonitrile]. The bioassay manipulated deposit structure by changing the number, toxicant concentration of the solution, and size of droplets used in creating deposits. The bioassay methodology was developed as an extension from standard industrial mixture experimental designs. Results from the bioassay led to the following conclusions: (1) Deposit structure plays a major role in toxicant efficacy. (2) The effect of droplet size is roughly equal to the effect of concentration, while both these factors may have a greater effect than droplet number. (3) The interactions between the factors of deposit size, deposit number, and concentration are more important than any single component. (4) Uniform coverage is not the most efficacious deposit structure if one is forced to limit application rates, and field persistence. (5) Uniform deposit structures have less variability in their biological effect than do more heterogeneous structures-though the relationship is not linear. These bioassay data corroborate the predictions of an earlier paper.

Use of nozzle-induced air-entrainment to reduce active ingredient requirements for pest control

Abstract A simple nozzle design/modification is presented which takes advantage of the known effect of the increasing biological efficacy of a pesticide with decreasing drop size for insecticides and perhaps fungicides. However, applying active ingredient (AI) in unassisted fine sprays leads to poor canopy penetration and increased drift hazard. Therefore, the air entrained by medium-coarse nozzles spraying water is utilised to impart kinetic energy to a finer spray containing AI. A fine nozzle is sprayed into a medium-coarse spray at an angle of approximately 15 ° from vertical approximately 10 cm below the medium-coarse nozzle, spraying into the direction of travel of the sprayer. The subsequent spray cloud consists of: small drops, typically The atomisation characteristics and potential drift problems of such a nozzle system were investigated. The results show that the velocity characteristics of the carrier (medium) spray were imparted to the fine spray, removing the problem of low spray cloud kinetic energy. Coalescence of drops in-flight was approximately 50%. Drift measurements in a large wind tunnel showed that drift increased four-fold at 4 m/s windspeed and approximately two-fold at 2 m/s. Taking into account the expected reduction in AI requirements, at 2 m/s, drift was quantitatively approximately the same as that of the medium nozzle.

The application of biological pesticides: Limitations and a practical solution

Biopesticides and agrichemicals are applied using basically the same equipment. The limitations imposed on biological or conventional chemical pesticides by current application systems are discussed. In general, any pesticide must be applied into a crop using the commonly used application system in that crop. This will normally be the hydraulic nozzle. Researchers attempting to increase the efficacy of a biopesticide by changing application system should bear in mind the constraints set by farmers on altering their usual spraying practices. These constraints are considered along with the criteria required for the successful market introduction of a novel application system. A novel application system, the “double nozzle” is introduced, which fulfils the criteria discussed, in particular the reduction in terms of amount of active ingredient required for pest control. The scientific rationale for this new system is explained, and its performance discussed.RésuméEn principe, biopesticides et produits agrochimiques sont pulvérisés à l’aide du même équipement. Les limitations imposées aux pesticides biologiques aussi bien qu’aux produits chimiques conventionnels par les systèmes d’application couramment utilisés sont discutées. Quels que soient les pesticides utilisés, ils seront généralement appliqués sur une certaine culture à l’aide du même matériel d’épandage, le plus communément employé pour ce type de culture, c’est-à-dire normalement des buses hydrauliques. Les chercheurs qui tentent d’augmenter l’efficacité d’un biopesticide en modifiant le système de pulvérisation devraient garder à l’esprit les réticences des cultivateurs à l’égard de tout changement dans leurs pratiques d’épandage. Ces contraintes sont examinées en détail, ainsi que les critères requis pour commercialiser avec succès tout nouveau système d’application. Un système nouveau de pulvérisation appelé la ’double buse’ est présenté, lequel satisfait aux critères discutés ci-dessus, en particulier en termes de réduction des quantités d’ingrédients actifs utilisés pour lutter contre les nuisibles. Les arguments scientifiques qui plaident en faveur de ce nouveau système sont expliqués et ses performances discutées

Dose transfer of Bacillus thuringiensis from cabbage to the diamondback moth: A graphical simulator

Abstract The application of agrichemicals is a highly inefficient process and one of the main causes of the environmental and health risks currently associated with pesticide usage. Efforts to mitigate this inefficiency have largely been unsuccessful, due principally to the poor understanding of the processes involved in the spray application of pesticides, from atomization to biological effect. A generalized model of the application system for pesticides from atomization to biological result is described in this overview. The model allows the investigation of the biological consequences of altering the application parameters for the bacterial insecticide Bacillus thuringiensis when used against the diamondback moth (Plutella xylostella L.) with cabbage as the substrate. Parameters input into the model include the in‐flight droplet size frequency distribution of the spray cloud, spatial distribution of the deposit, spread and subsequent environmental degradation of the deposit, and behavioral and toxicolo...