Distribuição espacial e plano de amostragem sequencial de Conotrachelus psidii (Marshall, 1922) (Coleoptera: Curculionidae) na cultura da goiabeira

Abstract

Brazil is the largest producer of tropical fruits and the third largest producer of guava (Psidium guajava L.) in the world. Many insect pests act by limiting guava productivity, being Conotrachelus psidii (Marshall, 1922), popularly known as guava weevil, one of the main pests because, that in large population densities, causes serious damage to guava culture. The guava weevil has sampling and control difficult to perform because of its subterranean habit during the pre-pupae phase. Thus, the work aimed to study population dynamics, the distribution pattern and develop a sequential sampling plan of C. psidii in guava culture. Two sampling areas were used: the first area consisted of an organic orchard with the cultivar Pedro Sato, located in the municipality of Itaporã, State of Mato Grosso do Sul, central western region of Brazil, the second sample area used consists of conventional cultivation, located in the municipality of São Roque do Canaã, State of Espírito Santo, Southeastern Brazil. Evaluations were performed weekly in three agricultural years, starting 120 days after pruning. For samplings, a beating choth was placed underneath the plants, covering every dimension of the crown. The branches were agitated for the adult insects to fall on the beating choth and be identified and counted. In the agricultural year of 2014/2015 15 samples were taken from the emergence period of C. psidii of the soil to reach the crown of the plants (approximately 120 days after pruning), until the end of the infestation period. In the State of Espírito Santo, the sample area consisted of 70 plants, each plot being represented by one plant. Samplings were carried out in the agricultural years of 2015/2016 and 2016/2017, and also occurred since the emergence of C. psidii from the soil until the end of the period of occurrence, in a total of 17 samplings in each agricultural evaluation year. The obtained results allow the realization that, in relation to the presence of adults and thefruits attacked by oviposition and feeding in the guava crop, the dispersion indices studied, whatever, variance / mean ratio, Morisita index, and exponent k of the negative binomial distribution, indicated that the weevil guava and its damages are added. This result was confirmed by the best fit to the probabilistic negative binomial distribution model by the chi-square test. As for the sequential sampling plan. The values adopted for type I and type II errors were α = β = 0.05. The parallel lines for decision making for occurrence of adults of C. psidii were represented by S1 = 9.0256+0.6681n, indicating the upper limit and rejecting H0, that is, controlling and S0 = -9.0256+0.6681n , indicating the lower limit and accepting H0, ie not controlling. The sequential sampling plan developed for C. psidii indicated that the maximum number of sample units expected for decision making is 45 samples and the minimum number is 15 samples. The parallel lines for decision making for the presence of oviposition were represented for S1 = 7.6062+0.7327n, indicating the upper limit and rejecting H0, ie, controlling S0 = -7.6062+0.7327n, indicating the lower limit and accepting H0, ie not controlling. For power supply S1 = 16.1704+1.8028n, indicated the upper limit and therefore, rejecting H0, ie control and S0 = -16.1704+1.8028n. According to the sampling plans prepared, determined the maximum number of 29 samples for fruits attacked with ovipositions and 82 samples for fruits attacked by feed.