Current status of the scale insect fauna of citrus in Tunisia and biological studies on Parlatoria ziziphi (Lucas)

English. The Tunisian scale insect fauna (Hemiptera: Coccoidea), is among the poorly studied fauna in the world. Actually, populations of some species have increased to pest status in many crops and the black scale Parlatoria ziziphi Lucas (Hemiptera: Diaspididae) is one of the most important insect pests attacking citrus crop in Tunisia. In the current study, a revision of the scale insect fauna occurring on citrus in Tunisia was done based on the results of field surveys and literature review. Moreover, effects of two temperatures (T1=20°C; T2=24°C) and plant substrates (green fruits of lemon and seedling plants of sour orange) on the development, fecundity and life table parameters (the intrinsic rate of increase (rm), the mean generation time (T0) and the net reproduction ratio (R0)) of the black scale were assessed. From surveys conducted in the main citrus growing regions located in the northern part of Tunisia, a total of 84 samples were collected and over 200 slide-mounted specimens were identified. Twenty-one species of scale insects are occurring nowadays on citrus trees in Tunisia; three of them were detected for the first time. An inventory of all species injuring citrus crop in Tunisia and their main characteristics (pest status, change in abundance over time, and distribution) is provided. Results on laboratory studies indicated a consistent influence of the temperature more than the plant substrate on the development and reproductive capacity of P. ziziphi. In fact, this species was well adapted at temperatures mainly 24°C. Survival declines clearly at 20°C (37.8% at female stages); while at 24°C very low mortalities were registered. Temperature significantly affected the durations of the majority of immature and adult stages; and total female development approached globally four months at 20ºC and two months at 24ºC. Sex differentiation showed a strong male-biased sex ratio of about 2:1 at 20°C and 1:2 at 24°C. Low mean fecundities were obtained, 26±3.5 and 47.47±1.5 eggs/female at 20°C and 24°C, respectively. In addition, at each generation, P. ziziphi had the capacity to increase their populations by a mean of 11.0 at 20°C in an average of 161.5 days with an intrinsic rate of increase of 0.015. At 24°C, parameters become better estimated; P. ziziphi populations can multiply meanly 32.35 times in an average of 86 days, with an intrinsic rate of increase of 0.041. As recommendations, the situation of some species is still unclear and it is necessary to continue with prospections in order to have a clearer complete list of species associated with the citrus trees in Tunisia. For life table study, this is a first contribution to assess the biological potential of the black scale under laboratory conditions; studying more temperatures should contribute to a better understanding of the population dynamics of this pest in the field.