Treating Mexican grapefruit with gibberellic acid (GA3) before color break, significantly delayed peel color change and increased peel puncture resistance, but it did not reduce grapefruit susceptibility to Mexican fruit fly, Anastrepha ludens (Loew) attack under natural conditions. Despite GA3 treatments, larval infestation levels increased with higher fruit fly populations, which also increased as the season progressed. Late in the season, infestation levels were even higher in GA3-treated fruit compared with untreated fruit, possibly because treated fruit were in better condition at that stage. Egg clutch size was significantly greater in very unripe, hard, GA3-treated fruit at the beginning of the harvest season and in December, compared with control fruit. Under laboratory conditions, egg injection into different regions of the fruit suggested that A. ludens eggs are intoxicated by peel oil content in the flavedo region. However, A. ludens' long aculeus allows females to oviposit eggs deeper into the peel (i.e., albedo), avoiding toxic essential oils in the flavedo. This makes A. ludens a particularly difficult species to control compared with other citrus-infesting species such as Anastrepha suspensa (Loew), Anastrepha fraterculus (Wiedemann), and Ceratitis capitata (Wiedemann) (fly species with significantly shorter aculei), which can be effectively managed with GA3 sprays. We discuss our findings in light of their practical implications and with respect to the oviposition behavior of various fruit flies attacking citrus.

Previously, the distances between odor-baited spheres deployed on perimeter trees of apple orchards for behavioral control of apple maggot flies, Rhagoletis pomonella (Walsh) (Diptera: Tephritidae), have been assigned largely arbitrarily. Here, we report a new approach for assigning distances that employs an index incorporating the state of four environmental variables: the size of orchard trees, quality of pruning, cultivar composition, and nature of bordering habitat. The deployment of odorbaited spheres on the perimeters of 12 plots of apple trees (each ∼ 0.4 ha) in commercial orchards in 2003 resulted in an apple maggot control which was no different from that achieved by insecticide sprays in adjacent plots in 2003, and no different from that achieved by an arbitrary assignment of distances between odor-baited spheres on perimeter trees in these same plots in 2001 and 2002. However, only 61-67% of spheres were used under the new index approach compared with the previous arbitrary approach, thereby substantially reducing the cost of behavioral control. Our findings are discussed in relation to use of the index for blocks of trees which are large in size and pruned poorly vs. small in size and pruned well, and in relation to the cost-competitiveness of odor-baited perimeter spheres vs. insecticidal sprays for the control of apple maggots.

Treating Mexican grapefruit with gibberellic acid (GA3) before color break, significantly delayed peel color change and increased peel puncture resistance, but it did not reduce grapefruit susceptibility to Mexican fruit fly, Anastrepha ludens (Loew) attack under natural conditions. Despite GA3 treatments, larval infestation levels increased with higher fruit fly populations, which also increased as the season progressed. Late in the season, infestation levels were even higher in GA3-treated fruit compared with untreated fruit, possibly because treated fruit were in better condition at that stage. Egg clutch size was significantly greater in very unripe, hard, GA3-treated fruit at the beginning of the harvest season and in December, compared with control fruit. Under laboratory conditions, egg injection into different regions of the fruit suggested that A. ludens eggs are intoxicated by peel oil content in the flavedo region. However, A. ludens' long aculeus allows females to oviposit eggs deeper into the peel (i.e., albedo), avoiding toxic essential oils in the flavedo. This makes A. ludens a particularly difficult species to control compared with other citrus-infesting species such as Anastrepha suspensa (Loew), Anastrepha fraterculus (Wiedemann), and Ceratitis capitata (Wiedemann) (fly species with significantly shorter aculei), which can be effectively managed with GA3 sprays. We discuss our findings in light of their practical implications and with respect to the oviposition behavior of various fruit flies attacking citrus.