Aspectos espaço – temporais de infestações de Brevipalpus phoenicis (Geijskes, 1939) (Acari: Tenuipalpidae) em citros na Bahia

Abstract

Citrus agribusiness occupies 59,330 ha and produces around 970 000 tons, giving to Bahia State 2nd place in the national production ranking. Together, Recôncavo of Bahia (RB) and Litoral Norte (LN) produce 80% of the citrus production in Bahia. Polyphagous and cosmopolitan, the mite Brevipalpus phoenicis (Geijskes, 1939) has highlighted because transmits important plant viruses to fruit cultivation and ornamental species. Around the world, the most important and studied is the citrus leprosis (CiLV), it triggers economic damages, and requires an annual cost of US$ 75 million of the production chain for the vector control. Although prevalent in 100% of the citrus orchards of Bahia, the mite has been categorized as a pest, only in the regions that CiLV occurs (in LN and West) and no work has been developed in the state about its involvement in the transmission of viruses to ornamental species. This study aimed to determine the minimum sample size to quantify the prevalence and incidence of Brevipalpus mites in the BR, a free area of CiLV; understand the spatio-temporal dynamics of mite infestation in RB and LN, by an ecological approach to study the probability of mite infestation in plants and fruits. The minimum sample size was 18 and 89 orchards to quantify the incidence of vector in plants and fruits, respectively. The incidence of B. phoenicis was 74% and 63% in plants and 41% and 34% in fruits in samples collected in April and September of 2008, respectively. The spatial pattern was aggregated for orchards. The average proportion of infested plants ranged from 0.38 to 1.0. In fruits, the minimum infestation was 10% to a maximum of 66% in LN and 73% in the RB. The seasonal trend showed a higher number of infested units in the spring-summer (Nemenyi, p <0.05). The spectral density analysis showed the occurrence of two cycles in the pattern of infestation, one of nearly two months and another, annual. These, possibly related to biology and vector-host - environment interactions, respectively. The pattern of infection within and between orchards was random. The likelihood of infestation was positively correlated with temperature and photoperiod, and negatively with days of rain, precipitation, relative humidity and water soil available fraction (Spearman, p <0.01). Using the Quantile-Quantile technique, thresholds were determinated and associated with changes in the rate of infestation (Ri): 24.5 º C, 14 days of rain, 70 mm of rain, 81% RH, 50% of available water in soil, 71 mm evapotranspiration, the average insolation 6h/day and 12h photoperiod. The combination of longer days, higher temperatures, lower rates of evapotranspiration and low relative humidity increased the likelihood of infestation of plants by B. phoenicis, while successive rainfall events decreased this risk. Infestation rates were influenced negatively by relative humidity exceeding 83% and positively by decreasing the fraction of available soil water by sunlight and photoperiod.