PEST MODELS FOR DECISION SUPPORT – DEVELOPMENT AND APPLICATIONS

Introduction                                                                Back to Table of contents

In cotton crop management, there are many solutions to problems relating to insects, weeds, irrigation, fertilization, harvest, etc.  Almost every expert has a different solution.  How can we know which solution or recommendation is best?  One way is to evaluate the objectivity of the decision–making process.   Is there any conflict of interest?  Did the process fairly evaluate several, rational, crop management solutions to determine which is best for the farmer, the environment, and the decision–maker?  The advice of experts is important, but objectivity may be enhanced using complex, crop systems models…

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ASSESSING POPULATION STRUCTURE IN THE COTTON BOLLWORM, HELICOVERPA ARMIGERA (LEPIDOPTERA: NOCTUIDAE), USING VARIATION IN THE A+T-RICH REGION OF MITOCHONDRIAL DNA

Abstract                                                                         Back to Table of contents

Helicoverpa armigera is an introduced pest that attacks a wide variety of agricultural crops in Australia, especially cotton.  Genetic variation in mitochondrial DNA (mtDNA) is being examined amongst individuals from different geographical locations to assess population structure.  A 630 bp mtDNA fragment is amplified using primers in conserved genes that span the hyper variable A+T-rich region. Using one of the same primers, direct sequencing of the amplified product yields 260 bp of sequence from individual moths.  To date twenty-two polymorphic nucleotide positions within this sequence has allowed identification of 33 different haplotypes among 119 moths.  The relatively high degree of haplotype diversity suggests a large effective population size and/or a high mutation rate.  Some haplotypes appear to be relatively common and occur in most regions while other, usually rarer, haplotypes are unique to a particular region.  Chi-squared analysis shows Australia-wide heterogeneity that indicates some degree of population differentiation.  Further sampling is underway to test the consistency of this observation, and to assess the value of this marker for determining moth movement patterns.

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MANAGEMENT OF THE COTTON BOLL WEEVIL WITH ATTRACT-AND-KILL-DEVICES

Abstract                                                                         Back to Table of contents

Poison baits such as molasses laced with arsenic were employed against the cotton boll weevil, Anthonomus grandis grandis Boheman, soon after the pest entered the United States in 1893 but were never effective. The search for an effective attracticide continued for nearly a century. New interest in attracticide research was spurred by the discovery and synthesis of Grandlure®, the boll weevil pheromone, in 1969. Grandlure® has been employed in traps for monitoring boll weevil populations and is highly attractive to both sexes early and late in the growing season. Scientists at the Boll Weevil Research Unit, ARS, USDA, Mississippi State, Mississippi, have developed an attract-and-kill device that incorporates Grandlure®, feeding stimulants and a toxicant. Laboratory and field tests with the device, the Boll Weevil Bait Stick (BWBS), have been carried out for the last four years. Area-wide field tests in Tennessee and Georgia have demonstrated significant suppression. Improvements in the BWBS and the methods of use are ongoing. The technology has been granted a U.S. Patent and is registered for commercial use by the Environmental Protection Agency. The attract-and-kill concept may prove to be an economical, effective and environmentally sound approach to a major pest problem.

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MODELLING PHEROMONE USE FOR PINK BOLLWORM CONTROL IN EGYPT

Abstract                                                                         Back to Table of contents

In 1994 Egypt will use artificial pheromones for pink bollworm control on 150,000 ha of cotton, 45% of the national crop.  The COT plant and insect simulation model has been initialised for the main long staple cotton varieties (Giza’75 and Giza’80) and for the release rate characteristics of several pheromone formulations and dispenser types.  When primed with the magnitude of the spring bollworm emergence and certain agronomic data, the system will generate plant and bollworm populations for given field management scenarios.  Simulations have proved accurate and useful but have demonstrated problems with the use of pheromone traps as control decision tools.  The Ministry of Agriculture intends to use the model to schedule pink bollworm pheromone and insecticide applications on significant areas of commercial cotton in forthcoming seasons.

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PROBLEMS AND PROSPECTS OF MANAGEMENT OF INSECTICIDE RESISTANCE IN HELICOVERPA ARMIGERA (HÜBNER) IN INDIA

Abstract                                                                         Back to Table of contents

Insecticide resistance in Helicoverpa armigera (Hübner) is a major threat to crop production in India.  Critical gaps in the knowledge base for management of resistant H. armigera in India are identified.  The status, need and constraints to utilisation of Insecticide Resistance Management (IRM) technologies such as scouting, resistance monitoring, temporal and spatial restrictions on the use of pesticides, regulation of application rate, application technology and use of biocontrol agents are discussed in relation to conditions prevailing in India.  A simple IRM strategy for improved control of H. armigera in cotton is suggested.  The need for adopting Integrated Pest Management (IPM) in other host H. armigera crops is emphasised.

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IMPACT OF THE INTRODUCTION OF THE COTTON BOLL WEEVIL IN BRAZIL

Abstract                                                                         Back to Table of contents

The populations of Anthonomus grandis Boheman that were first reported in Brazil in the state of São Paulo in February 1983, and in the state of the Paraíba in the northeastern region in August 1983, are morphologically similar to the southeastern boll weevil of the United States. All of the principal cotton-growing states in the southern region (São Paulo, Paraná, Minas Gerais, Mato Grosso and Mato Grosso do Sul) and in the northern region (Paraíba, Pernambuco, Rio Grande do Norte, Ceará, Bahia, Piauí, Maranhão and Alagoas) are now infested by the boll weevil.

The losses caused by the boll weevil in the northern region are both direct and indirect, and extend throughout the entire social, financial and economic structure of the region. It is impossible to estimate the losses due to depreciated land value, closing down of cotton gins and oil mills, and other indirect results of the boll weevil introduction.

An estimate of the magnitude of yield loss is afforded by the gains which have been recorded from recent field studies in which boll weevil injury has been eliminated. In the states of the Paraíba and Pernambuco where the boll weevil originally caused yield losses of 54 to 87%, increases in yield of seed-cotton over control (untreated plots) varied from 116 to 657% in tests. We believe that Integrated Pest Management technology using selective insecticides, natural mortality (high temperatures and low humidity and soil moisture, predators, parasitoids and pathogens), short season cotton and stalk destruction will collectively constitute the best management approach for production of a profitable cotton crop.

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INSECTICIDE RESISTANCE IN MAJOR COTTON PESTS WORLDWIDE: INCIDENCE, MECHANISMS AND MANAGEMENT

Abstract                                                                         Back to Table of contents

Management of insect pests is required for successful cotton production in most of the world’s cotton producing areas.  For many years insecticides have played the primary role in management programs.  The occurrence of resistance is now limiting their effectiveness.  In this presentation we will review the major mechanisms of insect resistance to insecticides and describe the principles determining which mechanisms of resistance are likely to occur in various insect pests.  In addition we report on which resistance mechanisms are likely to occur with each of the different types of conventional insecticides.

Resistance monitoring techniques and restricted insecticide use strategies have become major components of successful resistance management programs.  New strategies involving use of Bacillus thuringiensis and other less toxic chemicals as pest management agents are being developed.  Future successful pest management programs may involve primary reliance on Bacillus thuringiensis as an insect growth regulator with conventional insecticides as important, but secondary components.

Conclusions

  1. The development of restricted insecticide use strategies in conjunction with resistance monitoring has greatly extended the useful life of pyrethroid insecticides in cotton production.
  2. Occasional failures in the strategy might have resulted from the use of highly toxic pure isomer pyrethroids in place of mixed isomer pyrethroids rather than from inadequacies in the strategy.
  3. A strategy based on the use of a low dose mixture of insecticides may be an effective way to continue insecticide use and lessen selection for resistance.
  4. Alternate strategies based on the use of noninsecticidal controls such as Bacillus thuringiensis, juvenile hormone analogs and crop oils may significantly reduce the need to control cotton insect pests with insecticides in the future.
  5. The cotton ecosystem normally contains beneficial insect predators and parasites in numbers that frequently provide partial to satisfactory pest control. The use of soft strategies which maximize the effectiveness of beneficials seems to be the most effective way to manage insect pest populations in cotton.

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STATUS OF TOBACCO BUDWORM PYRETHROID RESISTANCE IN MEXICO

Abstract                                                                         Back to Table of contents

The tobacco budworm (TBW) Heliothis virescens (F.) is a common insect pest of cotton in Mexico. Since the early 1980s pyrethroids have been used successfully for control of this and other insect pests of cotton. In order to evaluate the resistance levels in northwestern Mexico, a monitoring program was initiated in 1984.

The topical application technique was used on third instar larvae and since 1989 was complemented with the adult vial technique (AVT). In 1989 a strategy to reduce pyrethroid selection pressure was implemented in the Yaqui Valley which restricted the use of pyrethroids to one month during the middle of the cotton season. In 1992 the AVT was expanded to the main cotton production areas in Mexico. Results of the resistance monitoring program  showed an increase in pyrethroid resistance in TBW larvae reaching a peak in 1987, decreased in 1988 and 1989, remaining stable since 1990. The decrease in resistance levels in the Yaqui Valley is an indication that the strategy implemented in the area has worked well. However, the cotton area has decreased drastically and may have influenced the decline in resistance levels. Data obtained in 1992 through the AVT in nine cotton production areas of Mexico, showed that the northeastern area has higher levels of pyrethroid resistance than the northwestern area. The high survivorship (80%) at the discriminating 10 µg/vial dosage indicates that problems to control TBW can be expected in northeastern Mexico.

Conclusions

Results of the monitoring program indicate that TBW larvae populations from northwestern Mexico are less susceptible to pyrethroids than 10 years ago when these products started to be used in cotton for insect control. In the last few years resistance ratios have lowered compared to those observed in 1987 and 1988. This is the result of less use of insecticides and reduction of the cotton area. The AVT showed that in northeastern Mexico, TBW populations have more pyrethroid resistance problems than those of northwestern Mexico. The implementation of insecticide resistance management programs in Mexico is required in order to reduce production costs and increase the useful life of pyrethroids and other insecticides used in cotton.

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EFFECTIVE SPRAY COVERAGE MEASURING PROCEDURES

Abstract                                                                         Back to Table of contents

A computer vision system was developed to analyse spray coverage on leaves and target paper strips.  The rapid computer analysis of the captured image gives the size distribution of the droplets and the relative area of the target that was covered by different effective radial distances.  The effective radial distance is defined by the distance from a droplet on a leaf that is affected by the chemical.

Conclusions

The definition of the Effective Radial Distance (ERD) as a measure of the distance from a droplet that a chemical has the desired effect on disease or insect control allows the ability for the comparison of the coverage efficiency by droplets of varying size deposited in a non-uniform manner.  The computer vision system described was able to give rapid analysis of spray droplet size distribution and the uniformity of coverage in a better method than conventionally used.  The results will allow chemical developers and farmers to make better decisions in developing and using chemicals and machinery for controlling diseases and insects.

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INCREASED DEPOSITION OF INSECTICIDE USING TURBULENT AIR ASSISTANCE

Abstract                                                                         Back to Table of contents

A canopy turbulent air jet sprayer was evaluated and found to achieve better coverage of both sides of cotton leaves. This opens up the possibility for the use of lower rates of conventional insecticides and perhaps also non-toxic crop oils etc. for the control of cotton whitefly Bemisia tabaci  (Gennadius).

Conclusions

The turbulent air jet canopy sprayer can cover both sides of all the leaves of cotton plants and control cotton whitefly without polluting the environment.  The turbulent air jet spraying technology can be adapted to other row and orchard crops to achieve better spray penetration and coverage, and to save chemicals with less pollution.

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