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Fruit Notes |
Toward Traps Alternative to Black
Pyramids for Capturing Plum Curculios |
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Fruit Notes |
Ronald Prokopy, Bonnie Dixon, and Tracy Leskey |
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Fruit Notes |
In the two preceding articles, we concluded that unbaited black pyramid traps (and probably all other unbaited traps) aimed at capturing plum curculios intent on entering host trees by crawling or flying onto tree trunks are unsatisfactory for monitoring curculios in a way that reflects accurately the potential for curculio damage to fruit. In the 1997 Winter issue of Fruit Notes, we presented results of a preliminary test in 1996 showing that sticky-coated squares of clear Plexiglas positioned just outside of apple tree canopies captured about as many plum curculio adults as black pyramid traps next to tree trunks. Here, we report on a 1997 study further comparing these two trap types. We also report preliminary results on a potentially useful third trap type. Materials and Methods The first study was carried out in a small block of unmanaged semi-dwarf apple trees at Hampshire College in South Amherst. The Plexiglas traps were designed to capture plum curculios flying toward tree canopies from overwintering sites or from other host trees. Each trap was constructed of clear Plexiglas (2 feet by 2 feet) attached vertically on a wooden pole positioned 2 feet away from the edge of the tree canopy. The outer-facing but not the inner-facing surface of the Plexiglas was coated with Tangletrap to capture curculios flying toward the tree canopy. Two such traps were attached to each pole, one opposite the lowermost foliage and the other opposite the uppermost foliage. Two poles with traps were placed on opposite sides of each of six trees. Two unbaited black pyramid traps were placed on opposite sides of and immediately next to the trunks of each of six other trees. All traps were emplaced at the beginning of apple tree bloom (May 24) and were examined daily thereafter for 22 days for captured curculios. Each day, 16 fruitlets on each of the 12 trees were examined for evidence of plum curculio damage. Each day, temperature, relative humidity, and wind speed were recorded. The second study was carried out in two unmanaged apple trees, one in Amherst and one in Conway. Traps were designed to capture plum curculios that had already arrived in tree canopies and were searching for resources of fruit borne on twigs or resting sites on twigs. Each trap, constructed of cardboard, was cylindrical in shape (8 inches tall and either 1 or 3 inches in diameter), coated with yellow or black latex paint, and capped with an inverted screen funnel developed originally to capture boll weevils. The yellow cylinders were intended to mimic foliage and fruit borne by twigs and were similar in appearance to yellow-green plastic traps used commercially to capture cotton boll weevils. The black cylinders were intended to mimic twigs themselves. Each cylinder was positioned vertically on a branch over an upright clipped twig, used as support. For each trial, we collected curculios (by branch tapping) from nearby trees, placed ten in a vial, and attached the vial in horizontal position to a branch about 9 inches from a cylinder. The curculios could crawl or fly directly from the vial opening toward the cylinder. Of the curculios that left vials, we recorded proportions that arrived on a cylinder during a 30-minute trial period. Results There were no significant differences in numbers of curculios captured per trap among sticky-coated Plexiglas traps in low position, sticky-coated Plexiglas traps in high position, and black pyramid traps (Table 1). These results confirm and are remarkably similar to those of the 1996 study reported in the 1997 Winter issue of Fruit Notes. Importantly, we found here that increases in captures by sticky Plexiglas traps but not by black pyramid traps were significantly positively correlated with increases in fruit damage caused by plum curculios the following day. Also, captures by sticky Plexiglas traps as well as fruit damage were significantly positively correlated with temperature, with the former also significantly negatively correlated with wind speed. Among plum curculios that left vials in which they were released on apple tree branches, 22-24% arrived on upright test twigs or on 1-inch-diameter or 3-inch-diameter upright yellow cylinders (Table 2). Significantly greater proportions (41-48%) arrived on upright black cylinders (Table 2). All observed curculios arrived on twigs and cylinders by crawling. None arrived by flight. Conclusions The findings reported here, though still preliminary, encourage us to believe that improved variants of the sticky Plexiglas squares and tall black cylinders studied here could be more suitable than black pyramids for monitoring curculios, because captures by these traps better coincide with periods of curculio damage to fruit than captures by black pyramid traps. Sticky Plexiglas squares placed adjacent to tree canopies are much too cumbersome for widespread use by growers, but a simplified non-sticky version (possibly incorporating attractive canopy-mimicking stimuli) might be an effective substitute. Similarly, an improved version of a black twig-mimicking trap could be of considerable value in monitoring within-canopy activity of curculios. We are planning further studies on these alternative trap types. Acknowledgments This work was supported by grants from the USDA Northeast Regional IPM Competitive Grants program and the New England Tree Fruit Research Committee. |
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