Rainfalls may affect the efficiency of pesticides due to a decreased deposit of active ingredient on plants. This should be considered in spraying with acaricides, the main strategy used for the management of citrus leprosis, the main viral disease of the Brazilian citrus culture. Citrus leprosis disease is transmitted by Brevipalpus mites, mainly B. yothersi. The objective of this study was to evaluate the effects of artificial rains on the efficiency of the acaricide propargite in combination or not with adjuvants for the control of the mite B. yothersi. The experiment was conducted using orange plants grown in pots kept under greenhouse conditions. The acaricide propargite was evaluated isolated and with addition of the adjuvants polydimethylsiloxane (20mL cp/100 L of water) and a mixture of phosphatidylcholine (lecithin) and propionic acid (500 mL cp/100 L of water). After the application of the acaricide with and without the adjuvants, the plants were subjected to a 10-mm artificial rainfall at different time intervals: 5 minutes, and 1 and 12 hours after application. Thereafter, B. yothersi mites were transferred to plants for survival evaluation. The artificial rainfall affected negatively the efficiency of propargite isolated and in mixture. The addition of the adjuvant phosphatidylcholine and propionic acid impaired the efficiency of propargite due to an increased runoff of the broth and a decrease in the deposit of active ingredients on plants. We conclude that the acaricide propargite should not be used in combination with the adjuvants polydimethylsiloxane and mixture of phosphatidylcholine and propionic acid in rainy conditions.
Acromyrmex subterraneus molestans (Hymenoptera: Formicidae) is a leaf-cutting ant species found in the Brazilian Cerrado and the Atlantic Forest and causes serious damages to cultivated plants. Knowledge about its foraging activity could help to improve the integrated pest management of this species and to better understand its ecology. The relationship between ambient temperature and the biomass collected by individuals of one Ac. subterraneus molestans colony was studied in the laboratory. The colony remained in an experimental room at 24 C and its foragers had access to an arena in an incubator set at six different temperatures (10, 16, 22, 28, 34 or 40 C). Fresh leaves of Hibiscus sp. were put in the arena and the flow of ants leaving and returning to the nest, the proportion of ants returning to the nest with a leaf fragment, as well as the dry mass of these fragments, were evaluated during 1 h for each temperature. The head width of foraging ants (laden and unladen) and their running speed were also measured. The rate of biomass collected was almost null at 10 C, increased from 16 to 34 C, and decreased abruptly at 40 C. The size of the workers did not vary across temperatures, and the running speed increased with increasing temperatures but more rapidly for unloaded ants than for loaded ones. The lower flow intensity at 28 and 40 C was somewhat compensated at the individual level by the selection of larger leaf fragments or by an increase in the probability to return loaded to the nest, respectively. The results obtained in this study could improve the management of these ants, allowing to target the most favourable meteorological conditions to apply toxic baits, increase the probability for the baits to be carried to the nest, in addition to reducing their availability to nontarget organisms. Furthermore, they could be used to make predictions on the effects of global warming on the foraging activity of this species.
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