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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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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