Utilisation De Pharoscymnus Ovoideuset Pharoscymnusnumidicus(coleoptera-coccinellidae) Dans Une Tentative De Lutte Biologique Contre Parlatoria Blancharditarg. (homoptera-diaspididae) Dans Les Palmeraies À Ouargla (sud-est Algérien)

Résumé: Use of Pharoscymnus ovoideus and Pharoscymnus numidicus (Coleoptera-Coccinellidae) in an attempt at biological control against Parlatoria blanchardi (Homoptera-Diaspididae) in palm groves of Ouargla (South-eastern Algeria) Abstract Our study on the biological control against white scale Parlatoria blanchardi by the use of two ladybird's coccidiphagousPharoscymnus ovoideus and Pharoscymnus numidicus appealed several steps. The inventory of the flora and fauna composition of the two study sites, the palm grove of Mekhadema (S1) and the exploitation of the University of Ouargla (S2) allowed us to identify 33 floristic species and 47 faunistic species were recorded in (S1), while 12 floristic species and 21 faunistic species were inventoried in (S2). Predominance was noted for phytophagous and zoophagous on both study sites with the existence of detritus chains in (S1). The maintenance and the floristic richness of a biotope contribute to its diversity and its balance. In the region of Ouargla, white scale Parlatoria blanchardi presents three generations, the most important of which is the spring generation. The estimated rate of infestation of this pest, we found that the study site (1) is more infested than site 2 and the cultivar Deglet-Nour has higher infestation rates compared to Ghars. The microclimatic factors characterizing each station contribute to these levels of infestations by the white scale. The study of the effect of the chemical composition (N, Ca, Mg, K, P, Na, total sugars and water content) and the morphological and histological structure of the leaflets on the white scale infestation rate shows that the cultivar Ghars has a higher cationic ratio (K / Ca + Mg) which contributes to this cultivar a resistance against the pest contrary to Deglet-Nour rich in Mg. The histological sections show stiffness of the epidermis of Ghars also promoting resistance against these homopterans. The inventory of the fauna associated with the mealy bug has identified 16 species belonging to 02 classes, 06 orders and 11 families. The ecological analysis of the inventoried species has shown that the highest centesimal frequencies are recorded for Cybocephalus seminillum, Camponotus sp., Pharoscymnus ovoideus and Pharoscymnus numidicus with percentages respectively of 14,97; 13,53; 12,70 and 11,57. The frequency of occurrence of the two species selected for biological control Pharoscymnus ovoideus and Pharoscymnus numidicus are respectively 56,94% and 50,69% on Deglet-Nour and 55,55% and 52,08% on Ghars. These two species are regular. The diversity of the feet of cultivars Deglet-Nour and Ghars by this associated fauna is quite important and it is in a state of equilibrium. The duration of biological cycles of the two coccidiphagous ladybirdsP. ovoideus and P. numidicusunder three degrees of temperature (24 ° C, 26 ° C and 28 ° C) is inversely correlated with this parameter. At 28 ° C, P. ovoideus completed its cycle at 34,5 ± 1,76 days and P. numidicus at 37,4 ± 0,98 days. Both lady birds species have two annual generations, one spring generation (longer) and one autumn generation. The study of voracity shows that P. ovoideus is more voracious than P. numidicus. It devours an average of 26,59 individuals / 24h of Ghars scale and 27,08 individuals of Deglet-Nour cultivar scale. Females are more voracious than males for this species. It should be noted that these species do not have any preference for food with respect to the white scale of the two cultivars studied. The biological control attempt by releases of P. ovoideus and P. numidicus on the Deglet-Nour cultivar by two doses (30 and 120 ladybirds / tree) showed that both ladybirds presented an efficiency that is positively correlated with the number of ladybirds released. P. ovoideus is always more voracious than P. numidicus with a predation rate of 32.40%. The high dose is the most significant from the diminishing of the white scale infestation.

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