No abstract

The dispersal of plant-feeding mites can occur involuntarily, through transportation of infested plant parts, or voluntarily, by walking to new plant parts or to suitable spots where biotic (phoresis) or abiotic (wind, agricultural tools, etc.) factors carry them over long distances. Elucidating the dispersal mechanisms of the coconut mite, Aceria guerreronis Keifer, is important for understanding the process of colonization of new fruits of a same or different plants, essential for the improvement of control strategies of this serious coconut pest. Thus, the objective of this work was to investigate the voluntary dispersal mechanisms of this mite. The hypothesis that the coconut mite disperses by walking, phoresis or wind were tested. The coconut mite was shown to be able to walk short distances between fruits of the same bunch or between bunches of the same plant. Phoresis on insects of the orders Hymenoptera (Apidae), Coleoptera (Curculionidae) and Lepidoptera (Phycitidae) was evaluated in the laboratory and in the field. Although in the laboratory mites were shown to be able to climb onto honeybees, field investigations failed to show these insects as important carriers of the pest, corroborating findings of previous works; however, both laboratory and field investigations suggested the curculionid Parisoschoenus obesulus Casey to be able to transport the coconut mite between plants. Similarly, laboratory and field investigations suggested wind to be important in the dispersal of the coconut mite between plants.

In the Lower Middle São Francisco Valley, Tetranychus urticae Koch is controlled by the application of acaricides; however, the intensive use of these products in this region has caused control failures in the field. In the present study, concentrationeresponse curves were constructed periodically to monitor the toxicity of abamectin to T. urticae in two vineyards over two years. Diagnostic concentrations of 1 mg and 9 mg of abamectin/L water were established based on the monitoring period to detect T. urticae resistance in different vineyards in the region. Concentration-response curves were obtained for abamectin, bifenthrin and carbosulfan for the populations considered resistant to abamectin. T. urticae were confined in arenas on cotyledonary leaf discs from jack bean (Canavalia ensiformis L.) that had been immersed in acaricide solution. Mite mortality was assessed after 48 h of exposure to the acaricides. The lethal concentration (LC) values varied over time in both of the vineyards studied, which was most likely a result of crop management. An additional 35 vineyards were sampled, and 20 additional populations were established. The results indicated that 45% of the populations exposed to the 9 mg/L abamectin diagnostic concentration experienced less than 80% mortality and were considered resistant to abamectin. The frequency of resistant mites ranged from 4.1% to 80.4%. The resistance ratio ranged from 2406-fold to 8272-fold compared to susceptible populations in the laboratory. Resistance to bifenthrin was also confirmed in the present study, though resistance to carbosulfan was not. No cross-resistance between abamectin and bifenthrin was observed though this requires further investigation.

Aceria guerreronis Keifer (Acari: Eriophyidae) is considered a major pest of the coconut (Cocos nucifera L.), and the use of pesticides is the current method to control it. However, no standard toxicological tests exist to select and assess the efficiency of molecules against the coconut mite. The aim of this study was to develop a methodology that allows for the evaluation of the relative toxicity of acaricides to A. guerreronis through rapid laboratory procedures. We confined A. guerreronis on arenas made out of coconut leaflets and tested two application methods: immersing the leaf fragments in acaricides and spraying acaricides on the leaf fragments under a Potter spray tower. In the latter application method, we sprayed leaf fragments both populated with and devoid of mites. We evaluated the comparative toxicity of two populations (Itamaracá and Petrolina, Pernambuco, Brazil) by spraying on leaflets without mites and submitted the mortality data to probit analysis after 24 h of exposure. No difference was observed in the LC50, regardless of whether the leaflets were immersed or sprayed with acaricide (abamectin, chlorfenapyr or fenpyroximate). The toxicity of chlorfenapyr and fenpyroximate did not differ, irrespective of whether it was applied directly to the leaflet or to the mite; however, the toxicity of abamectin was higher when applied directly to the mite. Chlorpyrifos and abamectin toxicities were lower for the Petrolina population than for the Itamaracá population. Immersing and spraying coconut leaflets can be used to assess the mortality of A. guerreronis under laboratory conditions.

Predictive models based on diagrammatic scales of damage have been developed to estimate the population density of Aceria guerreronis, an important coconut pest. Steneotarsonemus concavuscutum colonizes the same habitat as A. guerreronis and causes similar lesions on fruits. The present study aims to evaluate the possibility of using predictive models developed for A. guerreronis to estimate S. concavuscutum populations. Fruits infested by S. concavuscutum were collected and evaluated according to the diagrammatic scales developed by Galvão et al. (2008) and by Sousa et al. (2017). All active forms of S. concavuscutum were accounted for. Graphical and statistical analyzes were performed to evaluate the adequacy of the predictive models. Both the models proved to be inadequate to estimate the population of S. concavuscutum, both statistically and graphically. New predictive models were proposed using the grades of the diagrammatic scales and the mean numbers of S. concavuscutum/fruit. To validate the models, new fruits were collected and evaluated by 10 examiners with both the diagrammatic scales. All active forms of S. concavuscutum were accounted for. The new predictive model based on the grades of Galvão et al. (2008) underestimated the populations of S. concavuscutum, while the model obtained from the grades of Sousa et al. (2017) generated values close to the expected, proving itself to be adequate statistically and graphically, to estimate the populations of S. concavuscutum.