Acta agriculturae Slovenica, 119/2, 1–11, Ljubljana 2023 doi:10.14720/aas.2023.119.2.2975 Original research article / izvirni znanstveni članek Use of sugars as alternative to chemical control: trials carried out on thrips associated with olive tree Ilhem BOUHIDEL 1, 2 , Nadia LOMBARKIA 1 , Sabah RAZI 3 Received December 27, 2022; accepted March 21, 2023. Delo je prispelo 27. decembra 2022, sprejeto 21. marca 2023 1 Agronomy Department, Laboratory of Improvement of the Phytosanitary Protection Techniques in Mountanious Agrosystems (LATPPAM), University of Batna 1, Algeria 2 Corresponding author, e-mail: ilhem.bouhidel@univ-batna.dz 3 Department of Agronomic Sciences, Faculty of Sciences, University Mohamed Khieder Biskra, Algeria Use of sugars as alternative to chemical control: trials carried out on thrips associated with olive tree Abstract: Foliar spraying of infradoses of sugars (gluco- se, fructose or sucrose) induces plant resistance to pests that are particularly difficult to combat. These include thrips, which can cause flower abortion, stunting and deformation of olives, resulting in significant crop losses. Randomised block trials were conducted during three years (2017 to 2019), on two cul- tivars Chemlal and Sigoise, in an olive grove in Batna province (Algeria), with the aim of determining the most effective dose and type of sugar on thrips populations, and to evaluate the effectiveness of combining sugar with chemical treatment, as well as the possibility of reducing the dose of the latter. The re- sults showed that sucrose at a concentration of 100 ppm was the most effective and that the efficacy of sucrose was higher than that of glucose and fructose, on both cultivars tested. The combination of sucrose with insecticide resulted in a synergi- stic effect and a higher efficacy gain than sucrose alone, and that the efficacy of the combination sucrose + insecticide at low dose D1 was identical to the combination sucrose + insecticide at recommended dose D2. It is therefore possible to reduce the chemical insecticide dose while maintaining good treatment efficacy for the control of these pests. Key words: thrips; Olea europaea L.; sucrose; fructose; glucose; ‘Sigoise’; ‘Chemlal’ Uporaba sladkorjev kot alternative kemijskemu nadzoru: po- skus zatiranja tripsa na oljkah Izvleček: Pršenje s sladkorji v majhnih koncentracijah (glukoze, fruktozeali saharoze) vzpodbuja odpornost rastlin na škodljivce, ki jih je še posebej težko zatirati. Med njimi so tripsi, ki lahko povzročajo odpadanje cvetov in deformacijo plodov oljk, kar znatno zmanjša pridelek. V obdobju treh let, 2017- 2019, je bil na dveh sortah oljk, Chemlal in Sigoise, izveden naključni bločni poskus v oljčniku v provinci Batna (Alžirija), z namenom določitve najbolj učinkovitega odmerka in vrste slad- korja za uravnavanje populacije tripsa in ovrednotenje učinko- vitosti kombiniranja sladkorja s kemičnimi zaščitnimi sredstvi kot možnosti njihove manjše uporabe. Rezultati so pokazali, da je bila saharoza pri koncentraciji 100 ppm najbolj učinkovita in, da je bila učinkovitost saharoze večja kot glukoze in fruktoze pri obeh preiskušenih sortah. Kombinacija saharoze z insekti- cidi je imela sinergetski učinek in večjo učinkovitost kot samo saharoza. Učinkovitost kombinacije saharoze in insekticida pri majhnem odmerku D1 je bila enaka kot pri kombinaciji saha- roze in priporočenem odmerku insekticida D2. Iz tega sledi, da je mogoče zmanjšati odmerek insekticidov za doseganje dobre učinkovitosti pri uravnavanju teh škodljivcev. Ključne besede: trips; Olea europaea L.; saharoza; frukto- za; glukoza; ‘Sigoise’; ‘Chemlal’ Acta agriculturae Slovenica, 119/2 – 2023 2 I. BOUHIDEL et al. 1 INTRODUCTION The olive tree (Olea europaea L.) is a typical and emblematic tree of the Mediterranean countries where it is of great importance from the economic, social and landscape point of view (Loumou & Giourga, 2003; Pap- palardo et al., 2021). It represents one of the oldest and most widespread crops in Algeria. Thanks to its capacity to adapt to all bioclimatic stages, this species is present in the majority of the Algerian territory (Abdessemed et al., 2018). Nevertheless, the olive tree is susceptible to several insects’ attacks and pathogens that cause a decline in ol- ive production (Hadjou et al., 2013; Canale et al., 2019). Climatic variations in recent years have facilitated the in- troduction, spread and establishment of some pests and diseases in olive production (Ouyang et al., 2020; Vono et al., 2020; Ruggero, 2021). Among these pests, thrips (Thysanoptera), which are tiny sucking biting insects, having a short reproductive cycle with high reproduc- tive potential and have a wide host spectrum includ- ing many weeds (Mound, 2018). The damage caused by food bites and viruses transmitted by certain species of thrips is mainly qualitative (discolouration, necrosis, de- formation, etc.) and leads to a downgrading of the fruit and therefore to significant economic losses (Bournier, 1983). On olive trees, thrips attacks cause abortion of flowers and young fruits or result in stunted, scarred and deformed olives (Spooner-Hart et al., 2007; Phillips et al, 2020). The specific biology and behaviour of thrips makes chemical control difficult. Indeed, thrips tend to hide in flowers and buds, safe from contact insecticides; eggs inserted in the plant, and nymphs located in the soil, are also safe from treatments. In addition, they have the ability to develop resistance to insecticides (Bielza et al., 2007; Funderburk et al. 2016). Wu et al. (2018) and Re- itz et al. (2020), reported that in recent years thrips have been a serious problem for crops, due to their damage and the constraints of pesticide application that make their control difficult. Faced with this situation, the use of alternative methods to chemical control remains neces- sary, such as the use of intercropping (Gombač & Trdan, 2014), biological control by predatory mites Neoseiulus spp., hemipterans Orius spp. (Loomans & Murai, 1997), or by predatory thrips Aeolothrips intermedius Bagnall 1934 (Trdan et al., 2005) A new biocontrol method based on exogenous ap- plications of infra-doses of soluble carbohydrates has been developed to reinforce plant immunity against certain herbivores and pathogens (Arnault et al., 2021). This is the new concept of ‘Sweet Immunity’ or ‘sugar- enhanced defence’ (Bolouri-Moghaddam & Van Den Ende, 2013; Arnault et al., 2021). Soluble carbohydrates, mainly, sucrose, glucose and fructose, are involved in many stress response mechanisms, biotic or abiotic, where they act not only as metabolites, but also as sig- nals capable of activating signalling pathways leading to gene expression changes (Morkunas & Ratajczak. 2014; Formela-Luboińska et al., 2020). Furthermore, soluble carbohydrates sprayed at low doses can penetrate the cu- ticle and end up on the plant surface, constituting signals perceived by the insect through contact, then influencing its behavior and selection of the host plant to lay eggs (Derridj et al., 2011). This method induces physiological and metabolic changes in plant tissues and on the leaf surface, as well as resistance to pests (Smeekens et al., 2010) The action of soluble carbohydrates (glucose, fruc- tose, sucrose, trehalose) sprayed in infra doses (ppm) on the surface of cultivated plants has been studied on different crops for the control of various pests; such as Cydia pomonella (L., 1758) on apple, Thrips tabaci Lin- deman, 1889 on leek, Ostrinia nubilalis (Hübner, 1796) on maize, Tuta absoluta (Meyrick, 1917), Meloidogyne javanica (Treub, 1885) and Botrytis cinerea Pers. on to- mato (Ferré et al., 2008; Derridj et al., 2012; Arnault et al., 2012, 2015, 2017). These studies revealed that sugar alone has interesting effects and when combined with chemical plant protection products, it allows reducing their doses while keeping a good efficiency. Sugars activate defense pathways but not always in the same way (Arnault et al., 2021), it would however be advisable to analyse for each crop and each targeted phytophage, the most active sugar and dose. Derridj (2009), reports that the species, vari- ety and age of the plant at the time of treatment seem to be important factors for successful resistance induction. The judicious choice of varieties and sugar should make it possible to significantly limit phytosanitary interven- tions against one or several pests. As no studies have been carried out on thrips associated with olive trees, this work aims to determine the most effective sugar dose (sucrose tested at different doses of 1, 10, 100 and 1000 ppm); the most effective type of sugar to use (sucrose, fructose or glucose); and whether the use of sugar alone or combined with a phytosanitary treatment (insecticide tested at recommended and reduced doses), could be an effective alternative for the control of thrips populations associated with olive tree, on two cultivars (Sigoise and Chemlal), in an olive grove located in the region of Batna (North-East of Algeria). 2 MATERIAL AND METHODS 2.1 STUDY SITE The study was carried out in an olive grove (Table Acta agriculturae Slovenica, 119/2 – 2023 3 Use of sugars as alternative to chemical control: trials carried out on thrips associated with olive tree 1), located in the region of Oued Chaaba, 10 km South- east of Batna (Northeast Algeria). This region is charac- terized by a semi-arid climate, hot, dry in summer and cool in winter. Table 1: Characteristics of the experimental orchard Geographical coordinates 35° 30′ 17″ N, 6° 4′ 40″ E Age of the plantation Area Number of trees Topography (altitude) Cultivar Plantation density Ploughing Irrigation Fertilisation Weed control 14 years 7 ha 2000 1082 m Chemlal (55 %) Sigoise (45 %) 5 x 7 m in winter drip irrigation livestock manure manual/mechanical Protection programme no treatment Table 2: Characteristics of the studied varieties Cultivar Chemlal Sigoise Origin local (Kabylie, North of Algeria) local (Mascara, Northwest of Algeria) Destination oil dual purpose (oil+table) Tree Port Vigour Foliage density Rooting rate upright high medium very low upright medium medium medium Fruit Mass (g) Form Summit Aspect Colour at maturity 1.05-2.14 (reduced) elongated pointed smooth black 2.74-4.79 (medium) ovoid rounded smooth black Endocarp Mass (g) Form Summit Core surface 0.43-0.45 (small) spherical pointed rough 0.55-0.76 (big) ovoid rounded rough Leaves long (70.19 mm) medium (50.62 mm) Quality (acidity %) very good (0.171 à 0.22) medium(0.177 à 0.34) Oil yield (%) 18 à 24 18 à 22 Maturity end of October November Resistance to drought and cold medium Low 2.2 EXPERIMENTAL DESIGN Six trials were conducted on two olive cultivars (Si- goise and Chemlal), during three years, from 2017 to 2019. Table 2 illustrates the aspects of the two studied varieties. All trials are based on a randomised Fisher block design with four replications (4 blocks). The modalities are randomly distributed within each block and each modality (elementary plot) consists of two trees, its sur- face is 35 m 2 (5 m x 7 m). In the first year of 2017, two trials were carried out on two olive cultivars (Sigoise and Chemlal), the objec- tive was to determine the most effective sugar dose on thrips associated with the olive crop. Once identified, this dose will be used in subsequent trials. A sucrose treatment at different doses, 1, 10, 100 and 1000 ppm (= 0.1, 1, 10 and 100 g 100 l -1 ) was compared to the control (untreated trees) and a reference treatment (insecticide Acetamiprid). Then during 2018, two trials were set up to determine the effect of sugar type on treatment efficacy. The sucrose treatment was compared to fructose and glu- cose, tested at the same concentration (100 ppm =10 g 100 l -1 ), on both cultivars (Sigoise and Chemlal). In 2019, the objective of the trials was to evaluate the effect of the application of infra-doses of sugar (sucrose 100 ppm) as- sociated or not with a chemical treatment (Acetamiprid) and also to study the possibility of reducing the dose of phytosanitary product. Acta agriculturae Slovenica, 119/2 – 2023 4 I. BOUHIDEL et al. Thrips dropped on the Japanese umbrella were preserved in 70 % alcohol, counted and identified in the laboratory. 2.5 STATISTICAL ANALYSIS The results of the average number of thrips per twig and the percentages of effectiveness of the treatments were processed by analysis of variance (ANOVA) with Tukey’s test using the Excel Stat 2014 software. Results were expressed as mean ± S.E. (Standard Error), and con- sidered significantly different at p < 0.05. Treatment efficacy is calculated using formula (1) of Henderson and Tilton 1955 (Valette, 2007), which deter- mines the effectiveness of the different treatments rela- tive to the control and relative to the pre-treatment data (To) (1) Nu(t 0 ): number of thrips before treatment on control; Nu(t): number of thrips after treatment on control; NT(t) number of thrips after treatment on treated plot; NT(t 0 ):number of thrips before treatment on treated plot. 3 RESULTS AND DISCUSSION 3.1 PRESENTATION OF THE RECORDED SPECIES The thrips species collected on olive trees in the study area (Table 3) are phytophagous (F. occidentalis was the dominant species of all species found). Indeed, the females of these species lay their eggs mainly in flower buds and flowers (Lambert, 1999). Upon hatching, the larvae feed on pollen and floral parts, causing prema- ture flower drop. Heavy infestations cause silvering of the fruits, which dry out and fall prematurely. On olive trees, thrips cause damage to olives in the form of scars and wounds on the surface of the fruit, resulting from the sucking action of thrips, which extract the contents of the plant cells. The wounds result in the loss of the original 2.3 APPLICATION OF TREATMENTS The chemical insecticide (Acetamiprid) was ap- plied when the intervention threshold was reached (10 thrips/100 shoots), which was determined by weekly monitoring (scouting) of thrips by the strike method. Shaking on shoots was carried out weekly from the be- ginning of flowering (April-May), on 100 actively grow- ing shoots, selected at random in the study plot (Man- drin & Lichou, 2000, Valette, 2007). According to these authors, the monitoring of the number of thrips trapped allows to know the peak of thrips migration, key date for a chemical intervention. According to Allan and Gillett- Kaufman (2018), the peak of thrips collection on olive trees coincided with flowering. Above 10 thrips per 100 shoots, chemical treatment is justified (Valette, 2007). The chemical insecticide used in this study was Acetami- prid, which was tested at the recommended dose (D2 = 50 ml 100 -1 l) and at a dose reduced by half (D1 = 25 ml 100 -1 l) The sugars (sucrose, fructose and glucose) are sprayed in infra-doses (in the ppm range), obligatorily early in the morning, before the start of photosynthesis, at the time when the intercellular spaces of the apoplast are poor in sugars, according to the method advocated by (Derridj, 2009; Derridj et al., 2011, 2012; Arnault et al., 2015, 2021), using a backpack sprayer and trying to wet the whole foliar surface. The treatment with the chemical insecticide was done just after the sugar spray. 2.4 SAMPLING METHOD Thrips sampling during the 3 years of the study (2017 to 2019) was carried out according to the method recommended by Valette (2007), which consists in ran- domly shaking 25 twigs per elementary plot (2 trees/el- ementary plot), in the five directions (north, south, east, west and center) and from top to bottom. Thus, 100 twigs per modality were shaken during each sampling (each modality is repeated 4 times). Sampling was carried out in the morning between 8 and 10 am, 1 day (24 h) before treatment, and 1, 3, 7, 10, 14 and 20 days after treatment. Table 3: Thrips species encountered in an olive grove in the Batna region Suborder Family Species Terebrantia Thripidae Melanthripidae Frankliniella occidentalis (Pergande, 1895) Odontothrips confusus (Piesner, 1926) Melanthrips fuscus (Sulzer, 1776) Tubulifera Phlaeothripidae Haplothrips aculeatus (Fabricius, 1803) Acta agriculturae Slovenica, 119/2 – 2023 5 Use of sugars as alternative to chemical control: trials carried out on thrips associated with olive tree colour and the acquisition of the characteristic silvery ap- pearance of the wounded olives (Halimi et al., 2022). 3.2 DETERMINATION OF THE SUGAR DOSE The 1, 10, 100 and 1000 ppm sucrose modalities were compared to the reference treatment ‘insecticide’ and to the control. The results revealed, for both cultivars (Figure 1), a decrease in thrips populations on all treat- ed modalities from the day after treatment (T+1). This decrease continued until the end of the experiment for the 1, 10 and 100 ppm sucrose treatments. On the other hand, the number of thrips increased from the third day (T+3) in the plots treated with 1000 ppm sucrose. The in- secticide treatment resulted in a sharp decrease in thrips populations until day 3 (T+3). Then, the population in- creased again to reach the level of the “100 ppm sucrose” modality towards the end of the experiment at T+20 In order to better analyze these data, it appears interesting to evaluate their respective effectiveness (Fig- ure 2) and to compare them statistically. The chemical modality “insecticide” offered a good efficiency from the first day of treatment. The best ef- ficacy was obtained 3 days after treatment (T+3), with 69.64 % ± 2.69 on Sigoise and 81.72 % ± 3.92 on Chemlal, then this efficacy gradually decreased. On the contrary, the efficacy of the sugar treatments, sucrose 1.10 and 100 ppm, increased with time and the best efficiencies were obtained at the end of the experiment at T+20, with re- spectively 38.39 % ± 1.36, 40.46 % ± 1.72, 48.30 % ± 1.16 on Sigoise and 33.14 % ± 1.39, 41.56 % ± 1.26, 52.48 % ± 1.68 on Chemlal. Derridj (2009) and Derridj et al. (2011) reported that foliar spraying of sugars at infra doses (in the range of 1 to 10 g 100 -1 l) on fruit and vegetable plants induces systemic resistances against different pests. These resist- ances occur on the surface and in the leaves as well as in the roots, against insects, fungal pathogens and nema- todes respectively. Indeed, soluble sugars deposited on the plant surface penetrate the plant and can constitute signals that trigger defence cascades within the plant and/or intervene in the plant’s physiological regulation pathways. The same authors added that depending on the plant and the pest, the induction of resistance may vary depending on the sugar and its dose. They showed that only sucrose at 10 ppm, fructose at 0.1 ppm sprayed on maize grown under glass had a significant effect on Ostrinia nubilalis oviposition, and that the sugar that can induce systemic resistance in tomato to the nema- tode Meloidogyne javanica is sucrose at a concentration of 1 ppm. This dose effect was also observed on Botrytis cinerea where the use of 100 ppm sucrose was very ef- fective on tomato against Botrytis (100 % reduction of symptoms) and much less on bean (only 23 %). On their side, Arnault et al. (2015) demonstrated that spraying su- crose or fructose at a concentration of 100 ppm was able to reduce codling moth Cydia pomonella damage by 55 % in apple orchards. In our study, after 20 days, the 100 ppm sucrose treatment appeared to be more effective than the treat- ments at other doses, its efficacy was 48.30 % ± 1.16 on Sigoise and 52.48 % ± 1.68 on Chemlal, and it was even as effective as the treatment with the chemical modality (Figure 2). On the other hand, the least effective treat- ment, on the two cultivars studied, was the 1000 ppm sucrose, with an efficacy that did not exceed 18 %. In- creasing the sugar dose does not increase the effects of Figure 1: Temporal evolution of the number of thrips per twig according to the different treatments, on the cultivar Sigoise (A) and Chemlal (B) in an olive grove located in the Batna region, in 2017. C (control); Ins= Insecticide; Suc1 = sucrose at 1 ppm; Suc10 = sucrose at 10 ppm; Suc100 = sucrose at 100 ppm; Suc1000 = sucrose at 1000 ppm Acta agriculturae Slovenica, 119/2 – 2023 6 I. BOUHIDEL et al. resistance induction and sometimes even cancels them out, and has the disadvantage of having secondary effects (insect feeding, growth and development of epiphytic fungi or bacteria, etc.) on pests on the plant surface (Der- ridj et al., 2010). 3.3 EFFECT OF THE SUGAR TYPE The results obtained from the trials conducted in 2018 (Figure 3), showed that treatments with different types of sugar (sucrose, fructose or glucose) and chemi- cal modality resulted in a significant decrease in thrips populations from the first day of treatment. The popula- tion levels of the different treated modalities remained significantly lower than the control throughout the ex- periment. The results obtained 20 days after treatment (Figure 4) showed that 100 ppm sugar (glucose, fructose or su- crose) sprays on the cultivar Sigoise resulted in a signifi- cant reduction of the thrips population compared to the untreated control (2.6 ± 0.78, 3.18 ± 0.67, 2.1 ± 0.78 vs. 4.9 ± 1.16 respectively). On ‘Chemlal’ , glucose, fructose or sucrose treatments at a dose of 100 ppm also resulted in a significant reduction of the thrips population, with a number of 1.4 ± 0.6, 2.13 ± 0.33 and 1.23 ± 0.44 respec- tively, compared to the untreated control (3.68 ± 0.78) As reported in the literature, the application of very low doses of sugar to the surface of plants could limit pest attacks by two mechanisms; by modifying the chemical composition of the leaf surface, sugars would disrupt the oviposition behaviour of females, which would not rec- ognize the plant as suitable for the development of their larvae, but also by a systemic effect. Sugars are indeed involved in a cascade of plant defence reactions and can therefore have a generalized effect of stimulating natural defences (Derridj et al., 2011; Arnault et al., 2015; Lam- bion et al., 2016). Soluble carbohydrates not only act as Figure 2: Treatment efficacy, calculated according to the Henderson and Tilton method, at 1, 3, 7, 10, 14 and 20 days after treat- ment, for the cultivar Sigoise (A) and Chemlal (B), in an olive grove located in the Batna region in 2017. Values with different letters are significantly different (p < 005; Tukey test) Acta agriculturae Slovenica, 119/2 – 2023 7 Use of sugars as alternative to chemical control: trials carried out on thrips associated with olive tree Figure 3: Temporal evolution of the number of thrips per twig according to the different treatments, on the cultivar Sigoise (A) and Chemlal (B) in an olive grove located in the Batna region in 2018 Figure 4: Number of thrips/twig and treatment efficiency, calculated according to the Henderson and Tilton method, at 20 days after treatments, for the cultivar Sigoise (A) and Chemlal (B), in an olive grove located in the Batna region in 2018. The values with the different letters are significantly different [different lower-case letters indicate significantly different mean thrips/twig numbers and different upper-case letters indicate significantly different percentage efficacy (p < 0.05; Tukey test)] carbon skeleton donors and respiratory substrates, but they can also induce metabolic signals influencing the expression of many genes involved in plant defence (Rol- land et al., 2006; Morkunas & Ratajczak, 2014; Yoon et al., 2021; Choudhary et al., 2022) The results acquired from the trials, conducted in 2018 (Figure 4), revealed that the sucrose treatment at 100 ppm offers a more effective protection against thrips (the efficacy is 56.82 % ± 2.55 on ‘Sigoise’ and 65.14 % ± 2.22 on ‘Chemlal’), compared to the treatments with the chemical modality and the other two sugars (glu- cose or fructose). Indeed, sucrose is the main product of photosynthesis and the main transport carbohydrate in plants (Xu et al., 2018; Aluko et al., 2021). It has been recognized as contributing to various regulatory mecha- nisms in plants, including growth and development, dif- ferential gene expression and stress-related responses (Formela-Luboińska, 2020; Li et al., 2020; Jeandet et al., 2022). High sucrose: hexose ratios can probably trigger a sucrose-specific signal to induce the genes required for the production of a range of protective agents such as an- thocyanins and other secondary metabolites (Y oon et al., 2020). The specificity of sucrose as a signalling molecule was demonstrated by the fact that equimolar applications Acta agriculturae Slovenica, 119/2 – 2023 8 I. BOUHIDEL et al. of glucose and fructose did not result in significant accu- mulation of anthocyanins (Solfanelli et al., 2006). On the other hand, the 100 ppm glucose treatment was found to be satisfactorily effective for both cultivars tested, with 50.30 % ± 1.70 for ‘Sigoise’ and 58.64 % ± 2.48 for ‘Chemlal’ . While fructose at 100 ppm is the least effective sugar, where the efficiency is significantly low compared to the other sugars, which did not exceed 40 % on ‘Sigoise’ and 47 % on ‘Chemlal’ . It has been shown that sucrose, glucose and mannitol are the most abun- dant sugars in olive tree, while fructose is the least pre- sent (Bousaadia et al., 2010; Haouari, 2013; DePascali et al., 2022). Our results are in agreement with those obtained by Valette (2007), who showed that sucrose is the most effective of the three tested sugars (sucrose, glucose and fructose), against thrips on nectarine. Numerous studies have also shown significant protective effects of sucrose at a dose of 100 ppm on different pests such as melon borer and powdery mildew, leek thrips, codling moth, corn borer, tomato leafminer (Derridj, 2009; Derridj et al., 2011, 2012; Arnault et al., 2012, 2015, 2017, 2021) 3.4 EFFECT OF COMBINING SUGAR WITH A PHYTOSANITARY TREATMENT The obtained results in 2019 trials confirmed the ef- ficacy of sucrose foliar spray, 20 days after treatment (Fig- ure 5), in reducing thrips populations associated with olive. The efficacy was 50.93 % ± 2.52 on ‘Sigoise’ and 61.83 % ± 2.53 on ‘Chemlal’ . Sucrose treatment at a con- centration of 100 ppm alone induced effects comparable to those recorded with insecticide treatment alone at the recommended dose on the cultivar Sigoise. However, on the cultivar Chemlal, sucrose treatment was more effec- tive than insecticide alone. Sucrose at 100 ppm improved the efficacy of the chemical modality for both the reference dose (D2) and the halved dose (D1), on both cultivars tested (Figure 5). Indeed, several studies recommend the use of sugars as an additive treatment to phytosanitary treatments. Thus, the work carried out by Derridj et al. (2011), showed that the combination of sucrose at a dose of 100 ppm with a pyrethroid insecticide treatment had a significant effect on the oviposition of the female corn borer Ostrinia nu- bilalis. In plots treated with pyrethroids in combination with 100 ppm sucrose, they observed a 20 % reduction in maize damage compared to maize plots treated with the insecticide alone, where the damage reduction was only 8 %. Similar work by Arnault et al. (2015) also showed that the addition of 100 ppm sucrose to an “organophos- phate” chemical treatment increased its effectiveness by 35 %. Recent experiments (Arnault et al., 2016, 2021; Bouhidel & Lombarkia, 2021), have significantly dem- onstrated that the addition of sugars, such as sucrose or fructose, can reduce the insecticide dose by up to 50 % while maintaining the same level of efficacy against the pests. This was confirmed by the results obtained in this study, in which the treatment combining 100 ppm su- crose with the insecticide in half dose (D1) was as effec- tive as the sucrose treatment combined with the insecti- cide in reference dose (D2), on the two cultivars studied, Figure 5: Number of thrips/twig and treatment efficiency, calculated according to the Henderson and Tilton method, 20 days after treatments, for the cultivar Sigoise (A) and Chemlal (B), in an olive grove located in the Batna region in 2019. The values with the different letters are significantly different [different lower-case letters indicate significantly different mean thrips/twig numbers and different upper-case letters indicate significantly different percentage efficacy (p < 0.05; Tukey test)] Acta agriculturae Slovenica, 119/2 – 2023 9 Use of sugars as alternative to chemical control: trials carried out on thrips associated with olive tree with an efficacy of 65 to 68 % on ‘Sigoise’ and 74 to 76 % on ‘Chemlal’. The addition of 100 ppm sucrose thus increased the efficacy of a reduced dose of insecticide and resulted in similar efficacy to that obtained with a full dose. 4 CONCLUSION The conducted trials in the present study showed very promising results. Foliar spraying of sucrose at a dose of 100 ppm showed an improved efficacy on thrips, both alone and in combination with a chemical insecti- cide. This method reduced the recommended insecticide dose by half while improving the efficacy of the treatment and thus allowing a significant reduction of thrips popu- lations on olive trees. As a consequence, we can affirm that the use of sugars, which are non-toxic and inexpensive substances, could lower pest population levels to more controllable levels or below economic thresholds, and thus contribute to increase the efficiency of integrated pest management or organic farming methods. 5 REFERENCES Abdessemed, S., Abdessemed, A., Boudchicha, R.H. & Benbou- za, H. (2018). Caractérisation et identification de quelques écotypes d’olivier Olea europaea L en Algérie. Agriculture, 8(2), 26-43. Allan, S. & Gillett-Kaufman, J.L. (2018). Attraction des thrips (Thysanoptera) aux pièges collants colorés dans une olive- raie de Floride. Entomologiste de Floride, 101, 61–69. htt- ps://doi.org/10.1653/024.101.0112 Aluko, O.O., Li, C., Wang Q. & Liu H. (2021). Sucrose utiliza- tion for improved crop yields: A review article. Internatio- nal Journal of Molecular Sciences, 22(9), 4704. https://doi. org/10.3390/ijms22094704 Arnault, I., Chovelon, M. & Derridj, S. (2012). Preliminary tests in field conditions of alternatives substances against grape downy mildew in organic farming. Proceedings of the IOBC/ WPRS Working Group “Biological Control of Fungal and Bacterial Plant Pathogens” , Reims, France, 24-27 June 2012. Arnault, I., Bardin, M., Ondet, S., Furet, A., Chovelon, M., Kasprick, A.C., Marchand, P ., Clerc, H., Davy, M., Roy, G., Romet, L., Auger, J., Mançois, A. & Derridj, S. (2015). Uti- lisation de micro-doses de sucres en protection des plantes. Innovations Agronomiques, 46, 1-10. Arnault, I., Lombarkia, N., Joy-Ondet, S., Romet, L., Brahim, I., Meradi, R., Nasri, A., Auger, J. & Derridj, S. (2016). Fo- liar application of microdoses of sucrose to reduce codling moth Cydia pomonella L. (Lepidoptera: Tortricidae) dam- age to apple trees. Pest Management Science, 72(10), 1901- 1909. https://doi.org/10.1002/ps.4228 Arnault, I., Zimmermann, M., Furet, A., Chovelon, M., Thi- bord, J.B., & Derridj, S. (2017). Fructose and sucrose as priming molecules against pathogens and pests? In: Ab- stract book of IOBC-WPRS general assembly Meeting of the WGs Integrated protection in viticulture, Induced resistance in plants against insects and diseases and Multitrophic in- teractions in soil. Riva del Garda, Italy, 15-20 October 2017. Arnault, I., Aveline, N., Bardin, M., Brisset, M.N., Carriere, J., Chovelon, M., Delanoue, G., Furet, A., Frérot, B., Lam- bion, J., Ondet, S., Marchand, P ., Desmoucaux, N., Romet, L., Thibord, J.B. & Trouvelot, S. (2021). Optimisation des stratégies de bio contrôle par la stimulation de l’immuni- té des plantes avec des applications d’infra-doses de sucres simples, Innovations Agronomiques, 82, 411-423. Bielza, P .1., Quinto, V ., Fernandez, E., Grávalos, C. & Contreras, J. (2007). Genetics of spinosad resistance in Frankliniella occidentalis (Thysanoptera: Thripidae). Journal of Economic Entomology, 100(3), 916-20. https://doi.org/10.1603/0022- 0493(2007)100[916:GOSRIF]2.0.CO;2 Bolouri Moghaddam, M.R. &Van den Ende, W . (2012). Sugars and plant innate immunity. Journal of Experimental Botany, 63(11), 3989-98. https://doi.org/10.1093/jxb/ers129 Bouhidel, I. & Lombarkia, N. (2021). Use of infra-doses of sugars to control Cydia pomonella L. (Lepidoptera: Tortri- cidae) on apple trees in Algeria. Journal of Entomological Research, 45(4), 622-627. https://doi.org/10.5958/0974- 4576.2021.00097.9 Bournier, A. (1983). Les Thrips. Biologie-Importance Agrono- mique. Inra, Paris (France), 128p Boussadia, O., Steppe, K., Zgallai, H., Ben El Hadj, S., Braham, M., Lemeur, R. & Van Labeke, M.C. (2010). Effects of ni- trogen deficiency on leaf photosynthesis, carbohydrate sta- tus and biomass production in two olive cultivars ‘Meski’ and ‘Koroneiki’. Scientia Horticulturae, 123(3), 336-342. https://doi.org/10.1016/j.scienta.2009.09.023 Canale, M., Bernardo, U., Milonas, P . & Santos, S. (2019). Pests and diseases of the olive tree. Biological and biotechnical methods for olive pest control. Biological and Biotechnical methods for olive pests control. EIP-AGRI Focus Group, 9p Choudhary, A., Nirmaljit Kaur, A., & Kaur, H. (2022). Molecu- lar cues of sugar signaling in plants. Physiologia Plantarum, 174(1), 1-20. https://doi.org/10.1111/ppl.13630 DePascali, M., Vergine, M., Negro, C., Greco, D, Vita, F., Sa- bella, E., De Bellis, L. & Luvisi, A. (2022). Xylella fastidiosa and drought stress in olive trees: A complex relationship mediated by soluble sugars Biology, 11(1), 112; https://doi. org/10.3390/biology11010112 Derridj, S. (2009). L ’induction de la résistance à des phyto-agres- seurs par des infra dose des sucres : une nouvelle technolo- gie. Journées fruits et légumes. Paris: ITAB, 2009, 9-14. Derridj, S., Arnault, I., Lombakia, N., Ferre, E., Galy, H., Lambi- on, J. & Auger, J. (2011). Les sucres solubles utilisés comme inducteurs de résistance de la plante aux bio-agresseurs. Quatrième conférence internationale sur les méthodes alter- natives en protection des cultures, Lille - 8, 9, 10 mars 2011, 383-388. Derridj, S., Elad, Y . & Birch, A.N.E. (2012). Sugar signaling as a new way for vegetable and fruit induced resistance against Acta agriculturae Slovenica, 119/2 – 2023 10 I. BOUHIDEL et al. insects, pathogens and nematodes. Induced resistance in plants against insects and diseases. IOBC-WPRS Bulletin Vol. 83, 127p. Ferré, E., Galy, H., Moulin, F ., Clement, G. & Derridj, S. (2008). Le saccharose inducteur de résistance du pommier contre Cy- dia pomonella L. 8 ème Conf. Int. Agric. Montpellier, France, 1-8 Formela-Luboińska, M., Remlein-Starosta, D., Waskiewicz, A.,Karolewski, Z., Bocianowski, J., Stepien, L., Labudda, M., Jeandet, P. & Morkunas, I. (2020). The role of saccha- rides in the mechanisms of pathogenicity of Fusarium ox- ysporum f. sp. lupini in yellow lupine (Lupinus luteus L.). In- ternational Journal of Molecular Sciences, 21, 7258. https:// doi.org/10.3390/ijms21197258 Funderburk, J.E., Frantz, G. & Mellinger, C. (2016). Biotic resistance limits theinvasiveness of the western flower thrips, Frankliniella occidentalis (Thysanoptera: Thripi- dae), in Florida. Insect Science, 23,175–182. https://doi. org/10.1111/1744-7917.12250 Gombač, P. & Trdan, S. (2014). The efficacy of intercropping with birdsfoot trefoil and summer savoury in reducing damage inflicted by onion thrips (Thrips tabaci , Thy- sanoptera, Thripidae) on four leek cultivars. Journal of Plant Diseases and Protection, 121(3), 117-124. https://doi. org/10.1007/BF03356499 Hadjou, L., Lamani, O. & Cheriet, F. (2013). Labellisation des huiles d’olive Algériennes contraintes et opportunité de processus. New Médiat, 2, 35-46. Haouari, A. (2013). Influence des modifications de l’équi- libre source-puits sur les paramètres physiologiques et bio- chimiques chez l’ olivier (Olea europaea L.), sous bioclimat se- mi-aride de Tunisie. Thèse de Doctorat, Faculté des sciences en Bio-ingénierie, Université de Gand, Belgique et Faculté des Sciences de Sfax, Tunisie, 186p Jeandet, P., Formela-Luboińska, M., Mateusz Labudda, M. & Morkunas, L. (2022). The role of sugars in plant Mresponses to stress and their regulatory function during development. International Journal of molecular Sciences, 23(9), 51-61. https://doi.org/10.3390/ijms23095161 Lambion, J. & Mazollier, C. (2016). Protection de la tomate en culture biologique sous abris: du sucre contre Tuta absoluta . Maraichage Bio Info, 89, 1-2. Li, C., Liu, Y., Tian, J., Zhu, Y. & Fan, J. (2020). Changes in sucrose metabolism in maize varieties with different cad- mium sensitivities under cadmium stress. PLoS ONE, 15, e0243835. https://doi.org/10.1371/journal.pone.0243835 Loomans, A.J.M. & Murai, T . (1997). Culturing thrips and para- sitoids. In Thrips as Crop Pests; Lewis, T., Ed. CAB Interna- tional Harpenden: Herts, UK, 477–503. Loumou, A. & Giourga, C. (2003). Olive groves: “The life and the identity of the Mediterranean” . Agriculture and Human Va- lues, 20, 87-95. https://doi.org/10.1023/A:1022444005336 Mandrin, J.F . & Lichou, J. (2000). Le thrips californien sur pêches : Nouvelle approche pour la protection des vergers. Infos - Ctifl n°161, 4p. Morkunas, I. & Ratajczak, L. (2014). The role of sugar signal- ing in plant defense responses against fungal pathogens. Acta Physiologiae Plantarum, 36(7), 1607–1619. https://doi. org/10.1007/s11738-014-1559-z Mound, L.A. (2018). Biodiversity of Thysanoptera. In Insect Biodiversity: Science and Society; Foottit, R.G., Adler, P.H., Eds.; Wiley- Blackwell: Chichester UK, V II, 483–499. htt- ps://doi.org/10.1002/9781118945582.ch18 Ouyang, F., Hui, C., Ge. S., Men, X.Y., Zhao, Z.H., Shi, P.J., Zhang, Y.S. & Li, B.L. (2014). Weakening density depend- ence from climate change and agricultural intensification triggers pest outbreaks: A 37-year observation of cotton bollworms. Ecology and Evolution, 4, 3362–3374. https:// doi.org/10.1002/ece3.1190 Pappalardo, S., Villa, M., Santos, S., Benhadi-Marín, J., Pereira, J. A. & V enturino, E. A. (2021). T ritrophic interaction model for an olive tree pest, the olive moth – Pray oleae (Bernard). Ecological Modelling, 462, 1097. https://doi.org/10.1016/j. ecolmodel.2021.109776 Phillips, E.F., Allan, S.A., Griffith, T.B. & Gillett-Kaufman, J.L. (2020). Survey of Thysanoptera using colored sticky card traps in Florida olive groves. Florida Entomologist, 103(2), 264-273. https://doi.org/10.1653/024.103.0218 Rolland, F., Baena-Gonzalez, E. & Sheen, J. (2006). Sugar sens- ing and signaling in plants: Conserved and novel mecha- nisms. Annual Review of Plant Biology, 57, 675–709. https:// doi.org/10.1146/annurev.arplant.57.032905.105441 Ruggero, P. (2021). Climate change and major pests of Medi- terranean olive orchards: Are we ready to face the global heating? Insects, 12(9), 802. https://doi.org/10.3390/in- sects12090802 Smeekens, S., Ma, J., Hanson, J. & Rolland, F. (2010). Sugar signals and molecular networks controlling plant growth. Current Opinion in Plant Biology, 13, 274-7. https://doi. org/10.1016/j.pbi.2009.12.002 Solfanelli, C., Poggi, A., Loreti, E., Alpi, A. & Perata, P . (2006). Sucrose-specific induction of the anthocyanin biosynthetic pathway in Arabidopsis, Plant Physiology, 140, 637–646. https://doi.org/10.1104/pp.105.072579 Spooner-Hart, R., Tesoriero, L. & Hall, B. (2007). Invertebrate pests, 19–37 In Field Guide to Olive Pests, Diseases and Dis- orders in Australia. Publication No. 07/153. Rural Indus- tries Research and Development Corporation, Brisbane, Queensland, Australia. Trdan, S., Andjus, L., Raspudić, E. & Kač, M. (2005). Distribu- tion of Aeolothrips intermedius Bagnall (Thysanoptera: Ae- olothripidae) and its potential prey Thysanoptera species on different cultivated host plants. Journal of Pest Science, 78(4), 217–226. https://doi.org/10.1007/s10340-005-0096- 3 Valette, E. (2007). Le sucre : un allié insoupçonné dans la lutte insecticide contre le thrips. Projet de recherche, Astia Phyto Anadiag France, 50p Vono, G., Bonsignore, C.P., Gullo, G. & Marullo, R. (2020). Olive production threatened by a resurgent pest Liothrips oleae (Costa, 1857) (Thysanoptera: Phlaeothripidae) in Southern Italy. Insects, 11, 887. https://doi.org/10.3390/in- sects11120887 Wu, S., Tang, L., Zhang, X., Xing, Z., Lei, Z. & Gao, Y. (2018). A decade of a thrips invasion in China: lessons learned. Ecotoxicology, 27(7), 1032-1038. https://doi.org/10.1007/ s10646-017-1864-6 Xu, Q., Chen, S., Yunjuan, R., Chen, S. & Liesche, J. (2018). Acta agriculturae Slovenica, 119/2 – 2023 11 Use of sugars as alternative to chemical control: trials carried out on thrips associated with olive tree Regulation of sucrose transporters and phloem loading in response to environmental cues. Plant Physiology, 176, 930–945. https://doi.org/10.1104/pp.17.01088 Yoon, J., Cho, L.H., Tun, W., Jeon, J.S. & An, G. (2021). Su- crose signaling in higher plants. PlantSscience, 302, 110703. https://doi.org/10.1016/j.plantsci.2020.110703