Olive fruit flies [Bactrocera oleae (Gmelin)] occur at densities in California that can result in intraspecific larval competition within infested fruit. Larval B. oleae densities tracked in the field at six location were found to be highly variable and related to the proportion of fruit infested and adult densities. Egg and larval distribution within the field was generally aggregated early in the season and trended toward random and uniform as the season progressed. To determine whether B. oleae experienced fitness consequences at a range of larval densities observed in the field, olive fruits were infested with one, two, four, and six eggs, and larval and pupal developmental time, pupal weight, and pupal yield were compared. At the highest egg density, all measures of performance were negatively impacted, resulting in fewer and lighter pupae that took longer to pupate and emerge as adults, and even when only two larvae was present per olive, resulting pupae were significantly smaller. Density did not impact the sex ratio of the resulting flies or survive to adults. As field surveys showed, larval densities ranged from 1 to 11 B. oleae per fruit at some sites, and our results suggest that, at high densities, B. oleae do experience competition for larval resources. The impact of intraspecific larval competition North American in field populations of B. oleae is unknown, but the potential for competition is present.

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The data is being used to develop models that will better predict when the adults are active and olives are at risk.

If you as the grower can recognize the different types of scars you can differentiate between symptoms that indicate biological (e.g., insect, mite, disease, or snail), mechanical (e.g., equipment, hail, or wind rubbing), or chemical (e.g., phytotoxic burn) damage. Once you know the causal agent you can take steps to reduce injury to future crops. Orchards should be carefully monitored when fruit are small, the stage at which damage is most likely to occur. As soon as you observe signs of damage, make an immediate search for possible sources of the damage. It is much harder to determine the cause of fruit damage toward the end of the season because the insects or other causal agents are no longer present in the orchard and many types of injuries are by then similar in appearance. PUBLICATION 8090 Most citrus fruit scarring occurs in spring (April through June) when fruit are first developing on the tree. The rind tissue is very tender and easily damaged at this time. If damage is severe, the fruit will often fall off of the tree, either at the time of damage or during June fruit drop. If the damage is less severe, the fruit will remain on the tree and continue to grow, and the scarring will become noticeable. Some of the more common types of fruit damage seen in citrus groves are shown on the pages that follow.