The biology and control of the big-headed ant and its associated mealybugs in Hawaiian pineapple fields

Abstract

This study was undertaken to (1) obtain a better understanding of the interrelationship of ants, mealybug, and mealybug wilt disease of pineapple in Hawaii, and (2) to develop alternative methods of ant control. The study was in three parts: 1) a follow-up study of the epidemiology of mealybug wilt in a pineapple field at Poamoho, Oahu, Hawaii, Which was previously used for a study on the biology and ecology of big-headed ant, Pheido1e megacephala (Fabricius), and the gray pineapple mealybug, Dysmicoccus neobrevipes Beardsley, the two most important insects associated with the mealybug wilt of pineapple; 2) laboratory screening of potentially useful insecticide compounds for possible use as ant baits or as broadcast spray; and 3) field tests of promising ant baits and broadcast spray for ant control on the Island of Molokai. The population density of the big-headed ant was higher during the second crop than during the first crop of pineapple at both Poamoho and Molokai. No mealybug wilt plants were found in plots with excellent ant control, while the number of mealybug wilt plants increased sharply during the second crop in blocks where ants were not controlled. The incidence of mealybug wilt was higher at the edge of the plot than toward the middle of the field. Infestation of the Mo10kai experimental planting (20.3 ha divided into 102 0.2-ha plots) by big-headed ants started at the edge of the planting adjacent to an abandoned field and along a waste area. The ant dispersal and percentage of ant infested plots increased progressively with the age of the pineapples. A baited stake technique is described for use of evaluation of big-headed ant populations. Soybean oil mixed with peanut butter (50:50) was the most attractive bait material of all those tested for the big-headed ant workers. The greatest foraging activity of the ant occurred after sunset. Sixteen pesticides were selected from laboratory screening tests and tested as baits. Baits of AC 217300 (2(1H)-Pyrimidinone, tetrahydro-5,5-dimethyl-, [3-4-(trifluoromethyl)phenyl]-1-[2-[4( trifluoromethyl)phenyl]=ethenyl]-2-propenylidene]hydrazone) were acceptable to the ant and were more effective than any of the other pesticides studied. Field tests were conducted with baits of AC 217300 (85% corncob grits, 15% soybean oil, and AC 217300 at concentration of 1500 to 7500 ppm) at a rate of 2.24 kg bait per hectare. Results showed that the baits at 7500 ppm were as effective as mirex baits (0.3%) for controlling ~. megacephala. Broadcast sprays of 8 insecticides were applied for control of P. megacephala in the pineapple field at Molokai. Carbofuran, chlordane, diazinon, fonofos, heptachlor, and acephate all gave a high initial kill of the ants one day after the treatment. However, five months after the treatment, only heptachlor and chlordane continued to give good control of the ants. Tests with diazinon and acephate showed that their effectiveness was affected by the size of the pineapple plants. Additional tests with acephate indicated it has some promise for ant control. Pest management strategies for control of pineapple mealybug wilt disease are discussed. Information of ant movement would be useful in ant control programs. Destroying ants and mealybugs along edges of pineapple plantings may prevent pest migrations into newly planted fields. Use of insecticides only at the periphery of the fields and in uncultivated areas contiguous with new plantings may effectively control the ants, thus minimizing the overall use of insecticides.