Sap beetles (Nitidulidae) of date palms of the Deglet Nour variety in the Ziban region (Algeria): distribution patterns and effectiveness of date bunch bagging

Abstract This study aims to update the list of Nitidulidae species observed on date palms in Algeria (Ziban region), their spatial dynamics according to the development stages (larva, pupa, adult), and the effectiveness of the bagging operation. In 2020, we sampled and examined 1800 dates of the Deglet Nour variety from three palm groves managed with different protection modes: yellow bagging, white bagging, and no bagging. The results obtained mention the presence of nine species of Nitidulidae with five species reported for the first time on dates in Algeria. The highest relative abundance (RA) of Nitidulidae beetles was noted in the southern (28%) direction. However, the variation of infestation rate (IR) according to the direction was not very accentuated. The GLM analysis showed that, except for the adult stage, the direction presented a highly significant effect on the RA variation of the total Nitudilidae, the larva and pupa stages ( p < 0.0001), but there was no significant effect of direction on the IR in all studied cases. The highest RA of total Nitidulidae was found on the white plastic-protected dates (RA = 42%), the IR of the total Nitidulidae was higher on dates protected by yellow plastic (IR = 38%). The unprotected dates recorded the lowest RA and IR for all studied cases and the effect of bagging type on the RA variation of Nitidulidae, in all studied cases, was statistically highly significant ( p < 0.0001). This effect on the IR was very highly significant only for total Nitudilidae, larvae, and adults ( p < 0.0001). So, the southern direction presents the best conditions for sheltering the largest numbers of Nitidulidae. The latter also has a marked preference for bunches covered by plastic bags rather than for those left uncovered. This implies the ineffectiveness of the operation of protecting dates with plastic bags, especially the yellow-coloured ones.