Effectiveness of mass trapping by bottle traps baited with salt sardines to control Bactrocera oleae (Gmelin)

Abstract

Various substances are known as attractants of tephritid flies; the putrescine and other compounds coming from animal decay have been positively tested for attraction of Bactrocera cucurbitae (Coquillett) and other tephritids. In Sicilian coastal areas, usually heavily infested by Bactrocera oleae (Gmelin), few organic farmers producing high quality olive oil apply mass trapping by using bottle traps baited with salt sardines. The aim of this paper is to test the effectiveness of this kind of mass trapping to control the olive fruit fly. In 2005 and 2006 mass trapping was tested in an organic olive grove (Cerasuola cultivar) located in Trapani. In 2005 two plots were delineated: 189 untreated plants and 190 plants bearing bottle traps. In this year compared theses were three: untreated trees, central and marginal trees bearing bottle traps. In 2006 another plot and the relating thesis were added: 131 trees twice treated with copper hydroxide. The attractive device consists of a transparent 2-l polythene bottle with 2 holes (diameter 2 cm) in the upper third; it is filled two thirds full with water and one salt sardine. Previous to put the sardine in the bottle the salt is rinsed off it. When the solution dries and its level is below one third of the bottle, water is added to reach the initial level. At the beginning of August (5th in 2005, 2nd in 2006) baited bottles were positioned: one every tree along the margin and one every two trees in the rest. The infestation due to B. oleae was monitored by sampling 100 olives from ten trees per each thesis (ten fruits per sampled tree). Samplings were performed every two weeks until total infestation reached 5% and, subsequently, they were weekly. In both years olive oil has been extracted from olives exclusively collected from the ten sampled trees of each plot, to relate oil quality to infestation and treatments. To monitor olive fruit fly captures done by mass trapping, the content of 10 bottles along the margin and 10 bottles in the central part of mass trapping area was sieved at two (2005) or six (2006) samplings. In 2005 total infestation levels due to B. oleae of the three theses recorded statistically significant differences in the whole period, reaching at harvest 39% of infested drupes in the central trees bearing bottle traps with sardines, 64% in the marginal trees with bottle traps and 80% in the untreated trees; on the other hand, in the same period, the harmful infestation (3rd instar larvae, pupae and exit holes) between the marginal and untreated trees did not statistically differ; the oil quality was excellent in all theses and it resulted more related to the harmful infestation rather than the total one. In 2006 both total and harmful infestation levels of the four theses recorded three statistically homogeneous groups: once again the best result was achieved by the central trees bearing bottle traps (total infestation at harvest 23%), the second group consists of marginal trees with bottle traps and those treated with copper hydroxide (36% and 53% of total infestation at harvest, respectively); the worst result was achieved by untreated trees (68% of tot. infestation at harvest). In this year the oil quality was good in all theses, with few differences. Arthropods caught in the bottle traps were almost exclusively Diptera Brachycera (98% in 2005, 95% in 2006). B. oleae adults represented 42% of caught arthropods in 2005 and 71% in 2006. In both years B. oleae captures by bottle traps showed no significantly statistical differences between central and marginal trees, or between B. oleae males and females. Ceratitis capitata (Wiedemann) was also caught in bottle traps (6% of total in 2005, 14% in 2006).