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Ben Halima Kame Monia, Mdellel Lassaad and David Martinez-Torres
Accepted Abstracts: Entomol Ornithol Herpetol
Four aphid species are known to colonize peach and almond in Tunisia: Hyalopterus pruni species complex, Myzus persicae Sulzer, Brachycaudus amygdalinus Shouteden and Pterochloroides persicae Cholodkovsky. Brief information about biology, preferential host, distribution and growth rates are given for each species. The work aimed to study the population behaviour, the distribution, the phylogeny and the efficiency of natural enemies of brown peach aphid P. persicae . Five host plants were identified and two behaviours were observed where aphid can maintain all the year on peach in irrigated orchards and sub humid climate or on four Prunus genus in dry fields and arid climate. Population dynamics showed that aphids first appeared on roots and then move up to cover the collar and the trunks where populations behaved differently. Effects of hosts and temperature on biotic potential were studied under controlled and field conditions. Adults were reared individually at different temperatures (15, 20 and 25�C) on peach, almond, plum and apricot tree branches. Results showed that 20�C is the best temperature for the reproductive potential of P. persicae and peach was the best host for P. persicae in mass rearing. Therefore, the partial sequences from the mitochondrial COI and the nuclear long-wave opsin genes were obtained for approximately 100 P. persicae aphid individuals sampled from 34 colonies collected mainly in Tunisia and other Mediterranean locations. The variability found at the mitochondrial locus revealed the presence of two maternal haplotypes closely related in the studied area. The nuclear gene analysed, however, failed to reveal any variability in this species. The variability found at the COI locus was related to the season of aphid sampling and with the site of feeding, with haplotype I mostly detected in samples collected in spring and summer on trunk and haplotype II only detected in aphids collected in autumn on roots. The presence of two clonal races of P. persicae co-existing in the studied area differentially adapted to conditions prevalent in the alternative seasons and/or to different feeding sites, along with variations in the life-cycle developed by P. persicae in this region could account for the observed pattern of molecular variation. The natural enemies present near colonies of P. persicae were Coccinella algerica Kov�r (Coleoptera, Coccinellidae) and Episyrphus balteatus (Diptera, Syrphidae). Laboratory studies were conducted to determine the efficiency of C. algerica against P. persicae and compared against Acyrthosiphum pisum Harris (Hemiptera: Aphidinae). Feeding on P. persicae had a significant effect on predation rate by either fourth stage larvae or adults of C. algerica . The developmental period of C. algerica reared on P. persicae was significantly shorter than those reared on A. pisum (F = 51.45, d.f. = 1.19, P = 0.05). Larvae and adults of C. algerica reared on P. persicae showed a significantly greater mortality than those on A. pisum (F = 27.29, d.f. = 2, P = 0.05). Furthermore, the aphid species has an effect on body weight and fecundity of C. algerica. These results demonstrated that C. algerica is not recommended as a biological control agent of P. persicae in Tunisia.