Population dynamics of the cottony cushion scale Icerya purchasi (Homoptera, Monophlebidae) and its natural enemies on citrus fruits in Aoulouz area and contribution to an IPM strategy

The Cottony Cushion Scale Icerya purchasi (Homoptera, Monophlebidae) is a citrus pest whose importance is growing due to the prohibition of broad-spectrum chemical molecules such as Chlorpyrifos Ethyl. Monitoring of the population during the 2022 and 2023 campaigns in the Aoulouz region on Nadorcott plantations revealed that the pest carries out 4 generations per year, like what has been reported in regions with a similar climate (Arizona and Iran). The recorded natural enemies of the pest are lacewings and the ladybug Rodolia cardinalis (Coleoptera, Coccinellidae). The latter is by far the most important aid in limiting infestations. The ladybug comes into activity early in the season around Mid-March. It largely contributes to controlling the pest if the evolution of its population is not disrupted by high temperatures and chemical treatments, especially those targeting thrips, aphids, and California red scale. Incubations carried out on the cottony cushion scale females collected from the same region did not reveal the presence of the parasitoid Cryptochetum iceryae (Diptera, Cryptochetidae) which has demonstrated its effectiveness in the biological control of I. purchasi in California and Israel. Trials were conducted to evaluate the impact of pesticides commonly used on citrus fruits (Spirotetramat, Spinosad, Abamectin, Pirimicarb and Sulfoxaflor) on R. cardinalis to outline an integrated control strategy against this pest on citrus fruits. All these products showed a certain selectivity towards the beneficial, which implies a certain habituation developed by the natural occurring populations of the ladybug. The control of I. purchasi needs the establishment of a monitoring system of the population of both, the pest and R. cardinalis, combined with a continuous follow-up of the climate conditions to avoid any surprises closed to the harvest period. In term of pesticide use possibilities, the tested chemicals are sufficient to achieve the control of other pests by preserving the activity of natural enemies on the cottony cushion scale. The inoculative introduction if the parasitoid C. iceryae into Morocco should reinforce the biological control strategy.