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Abstract
The Argan Argania spinosa (L.) Skeels (Ericales: Sapotaceae) is an endemic and emblematic tree growing in the centre and the southwest of Morocco. Argan fruits are frequently infested by the Mediterranean fruit fly Ceratitis capitata Wied (Diptera: Tephritidae). To date, no control program has been undertaken in the Argan forest. This research is the first investigation of natural mortality factors of C. capitata larvae in the Argan forest. The study was conducted at two localities near the city of Essaouira with different climatic conditions. Observations were conducted using 260 late instar larvae which were individually deposited on the ground, under fruiting host trees, where they naturally fall to find a suitable pupation site. Overall, 42% of the larvae died before being able to burrow into the ground, irrespectively of the location. Larval survival and their likelihood of burrowing decreased with increasing ground temperature, as 53% of all the larvae deaths occurred at temperatures over 48°C. However, at lower ground temperature, predation by ants and spiders accounted for 47% of all mortality. Four species of ants carried out 94% of the captures. Monomorium subopacum Mayr (Hymenoptera: Formicidae), which frequently forages under Argan trees, was by far the most efficient predator, due to a powerful sting that rapidly immobilizes the prey. Our results suggest that the burrowing performance of larvae is constrained by high thermal conditions and the presence of ant predators at lower temperatures.
Acknowledgements
We thank Professor J.H. Delabie (Itabuna, Brazil) and Professor H. Cagniant (Toulouse, France) for ant identification and Dr A. Bakri (Marrakech, Morocco), and the anonymous reviewers for helpful comments on a previous version of this article. We were assisted by Mrs Jacqueline Minett for English editing and by Mr David Aragones for illustrations and figures. This work was funded by Agencia Española de Cooperacion Internacional (AECI – PCI program, Moroccan-Spanish cooperation projects A3478/05 and A/4774/06). It was conducted with the authorization of the Essaouira Directorate of Waters and Forests.