PREDATION ON NEONATE LARVAE OF DIAPREPES ABBREVIATUS (COLEOPTERA: CURCULIONIDAE) IN FLORIDA CITRUS: TESTING FOR DAILY PATTERNS OF NEONATE DROP, ANT PREDATORS AND CHEMICAL REPELLENCY

Robin J. Stuart, Ian W. Jackson and Clayton W. McCoy

Abstract


The root weevil, Diaprepes abbreviatus (L.), is a major pest of Florida citrus. When neonate larvae hatch from egg masses in the citrus canopy and drop to the soil surface before burrowing down to the roots for feeding, they are vulnerable to ant predation. However, neonates are reported to produce a chemical repellent that lasts up to four days and reduces ant predation by about 40&percnt;. We assessed the daily pattern of neonate drop from egg masses under laboratory conditions (24°C, 70&percnt; RH, L:D &equals; 12:12), examined the role of ants as predators of neonates (<48 h post hatch) on the soil surface in three citrus groves in central Florida, and tested for chemical repellency in the field by comparing predation rates on 5-day versus 1-2 h old neonates. Neonate drop was not well synchronized within or among egg masses, occurred during all hours of the light and dark phases, and extended over 5 to 23 h (mean &equals; 11.97, SE &equals; 0.866) for individual egg masses (n &equals; 29). However, the drop rate was highest during the second half of the light phase (52.4&percnt;) and lowest during the second half of the dark phase (8.0&percnt;). Predation occurred in 104 of 199 replicates (52.3&percnt;) in the three groves with a total of 475 of the 3980 larvae (11.9&percnt;) removed by predators within 20 mins. Predation pressure varied within and among groves, and involved eight ant species (Hymenoptera: Formicidae) and a single predation event by a nymph of the big-eyed bug, Geocoris floridanus Blatchley (Hemiptera: Lygaeidae). For data pooled among groves, the red imported fire ant, Solenopsis invicta Buren, was responsible for 29.5&percnt; of the predation, Pheidole moerens Wheeler 27.8&percnt;, Dorymyrmex reginicula (Trager) 9.7&percnt;, Brachymyrmex obscurior Forel 8.8&percnt;, Dorymyrmex bureni (Trager) 8.6&percnt;, Cardiocondyla emeryi Forel 8.0&percnt;, Paratrechina bourbonica Forel 4.8&percnt;, and Pheidole morrisi Forel 2.5&percnt;. In our test for age-dependent chemical repellency, a total of 2620 of the 3840 neonates (68.2&percnt;) were preyed upon within 30 mins but the predation rate on old versus young neonates did not differ at 68.8&percnt; and 67.7&percnt;, respectively. In this experiment, 368 of the predation events (14.0&percnt;) were observed directly with P. moerens responsible for 62.5&percnt;, S. invicta 25.3&percnt;, C. emeryi 10.1&percnt;, B. obscurior 1.4&percnt;, Cardiocondyla wroughtonii (Forel) 0.5&percnt;, and D. bureni 0.3&percnt;. We conclude that ants are important predators of Diaprepes neonates in central Florida citrus groves and have potential for a conservation biological control program.

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