The Whitefly Dialeurodes citri: A New Pest on Citrus in Tunisia?

Whiteflies invaded citrus orchards in Tunisia in the 90’s. Two species: Aleurothixus floccosus and Parabemisia myricae have been recorded successively infesting citrus and causing severe damage in Cap-Bon (North-East of Tunisia). These pests were first controlled by several insecticidal applications but with a relative efficiency. Then two biological control programs have been deployed completing the action of native natural enemies especially for P. myricae. The result was a very satisfactory control of both whitefly species, to a point that they almost disappeared from orchards for about 30 years. In 2017, a third whitefly species, identified as Dialeurodes citri, was observed during a prospection in citrus orchards in Takelsa region (Cap-Bon). It was a common species in Algeria, but never caused damage in Tunisia. In 2020, D. citri was found again with very high population densities in the regions of Menzel Bou Zelfa (Cap-Bon) and Tunis. These observations confirmed its change of status and spread in Tunisia. The main morphological and biological traits to distinguish between D. citri and the other two whitefly species, already recorded in Tunisia, were described and first observations on its infestation were reported. Some recommendations to manage this new pest are given.

Control of Tutaabsoluta using pheromone traps on tomato crops under greenhouse in Algeria

The present study aimed to assess the effectiveness of pheromone traps of adults of Tuta absoluta in 4 potential tomato production areas in Algeria: Tipaza (Center), Mostaganem (West), Jijel (East) and Biskra (South), during the 2012-2014 campaigns. Two tomato greenhouses were considered for each zone in which, one was protected by the setup of pheromone traps and the other as an insecticide sprayed control. Tomato leaf samples were taken from each greenhouse, each month of each year according to the areas of studies to calculate the rates of infestation. Higher infestation rates were recorded in the greenhouses with local agricultural practices (control) compared with those protected by pheromone traps. With the use of the pheromone traps, a remarkable reduction affected the infestation of the greenhouses in the 4 studied areas during the years 2012 to 2014. The southern area seemed to be the most infested and at a least degree the areas of the West, the Center and the East, respectively. The temporal evolution of infestation rates showed an increase since January until July with June and July showing the higher infestation rates. These results showed the efficacy of trapping of T. absoluta males and the importance of their sustainable use in the integrated control system against this devastating insect in Algeria.

Potentials of the Extracts of Algerian Saharan Plant Cotula cinerea for the Management of Two Insect Pests, Aphis fabae and Tribolium castaneum

The insecticidal potential of the Saharan plant Cotula cinerea, was evaluated on two insect species namely Aphis fabae and Tribolium castaneum by topical application (contact toxicity) and repellency test. A crude ethanolic extract of aerial part of the plant was prepared and tested in the laboratory on adults of both species. For contact toxicity, five doses were tested on each of the two species 1.56, 3.12, 6.25, 12.5 and 25 mg/ml for A. fabae and 25, 50, 250, 350 and 500 µg/insect for T. castaneum. The repellency of the extract was studied at the dose 500 μg/insect for T. castaneum and 25 µg/ml for A. fabae. Results showed that the repellency of the extract increased with exposure time and the highest rates were observed after 4 h of exposure (72.33 ± 22% for T. castaneum and 87 ± 3.6% for A. fabae). For insecticidal activity, at the highest doses (25 mg/ml and 500 µg/ml), 100% mortality is obtained 72 h after treatment for A. fabae and after 48 h for T. castaneum. The extract of this plant was found to be more toxic against T. castaneum adults. LD50 calculated 24 h after treatment for the two species is estimated at 1.7 mg/ml for A. fabae and at 30.3 µg/insect for T. castaneum. The extract of this plant inhibited the activity of acetylcholinesterase (AChE) in both insect species. This result suggests that this plant has a neurotoxic effect on A. fabae and T. castaneum. The results of phytochemical study showed that the plant is mainly rich in flavonoids, gallic tannins, alkaloids, saponosides and glucosides. The insecticidal effect obtained in this study could be due to the synergetic action of all constituents of the extract. Results suggest the possibility of using the extracts of this plant in integrated pest management to replace the chemical insecticides.

Effect of Deltamethrin on the Leaf Miner (Liriomyza cicerina) of Chickpea and its Parasitoids

The objective of this work was to investigate the effects of chemical treatments on larvae and adults of the chickpea leaf miner (Liriomyza cicerina) and its parasitoids. The study was conducted according to the split-plot design with three replicates, during the cropping seasons 2016 and 2017 in the northwestern Tunisia. Deltamethrin treatments were applied on winter and spring chickpea varieties (Nour and Amdoun, respectively) when the pest density reached a level of 2-3 larvae/leaf in 50% of plants in the field. The number of emerged parasitoids and pest adults were recorded, and parasitism rates were investigated after treatments. Results revealed that the number of captured pest adults has been reduced in treated plots compared to control ones. Respective reduction rates attained 64.15% and 60.17% for Nour and Amdoun varieties during 2017. Additionally, the highest and the lowest parasitism rates were recorded respectively for Opius monilicornis 26.09% on control samples and for Diaulinopsis arenaria 2.88% on treated samples of Nour variety. In all experiments, L. cicerina larvae adults and parasitoids mortalities were higher for the spring variety. Hence, the use of more selective insecticides should be recommended to reduce the negative side-effects on the chickpea leafminer natural enemies.

Diet Selection of Heteracris littoralis in a Cultivated Environment, Mzab Valley, Septentrional Sahara, Algeria

This paper presents the results of a study on the diet of Heteracris littoralis in an agro-ecosystem at Mzab valley, Ghardaïa Province, Northern Sahara, Algeria. The diet was determined by the analysis of plant fragments in the feces of H. littoralis sampled in the field. The studied grasshopper consumed 12 of the 30 plant species found in the cultivated environment. The results showed that the locust predominantly fed on a few plants, such as Lagenaria siceraria and Solanum lycopersicum, although their diet includes over 12 plant species. Its food niche breadth was narrow (0.51), with a selectivity index of 0.61 for females, 0.52 for males and 0.42 for larvae. The plants consumed by the two sexes and larvae were not significantly different. This study suggests that Eyprepocnemidinae is a polyphagous grasshopper species, in spite of pronounced preference towards Cucurbitaceae and Solanaceae. This property results in a low Berger-Parker index value (0.24). Results are of great significance, increasing the understanding of insect herbivore feeding behavior and how to control the damage caused by this Orthoptera.

Screening Rice Genotypes for Brown Spot Disease Resistance

A field experiment was conducted to screen 20 rice genotypes against brown spot disease caused by Bipolaris oryzae under natural epiphytotic field conditions at Bangaun, Dang, Nepal, from June 2018 to March 2019. The experiment was carried out in a randomized complete block design with 3 replications. Sawa Mansuli was taken as susceptible check and Sabitri as a resistant check in the experiment. Disease assessment was done by calculating disease severity and Area Under the Disease Progress Curve (AUDPC). Among the evaluated genotypes, disease severity and AUDPC varied in the field experiments. Rice genotypes showed the resistance to highly susceptible reactions based on AUDPC value which ranged from 88.51 to 260.65. Among the evalauted rice genotypes in the field experiment, the highest mean AUDPC value was recorded with Basmati (260.65) followed by Radha-13 (172.80) and the lowest was recorded with Kathe Jhinuwa (88.51). Similarly, the highest severity rate was recorded with Basmati (25.91) followed by Radha-13 (21.00) and Tilki (20.75) and the lowest was recorded with Kathe Jhinuwa (11.03) which was at par with Radha-4 (11.11) followed by Sukhadhan-1 (12.02) and Sabitri (12.06). The highest grain yield was recorded with Sarju-52 (4.32 t/ha) followed by Sabitri (4.19 t/ha). Grain yield was negatively correlated with mean AUDPC by 14.77%. Kathe Jhinuwa, Radha-4, and Sabitri can be used for higher grain yield purposes under similar field conditions and also can be utilized as the source of resistance in a plant breeding program.

Defense of Host Plants against Orgyia trigotephras in Northeast of Tunisia

The egg-larval stage of Orgyia trigotephras were observed in shrubs maquis of Jebel Abderrahmane in north-east Tunisia, mainly on Quercus coccifera and Pistacia lentiscus, while only eggs were noticed on Phillyrea media. This kind of observation suggest us to study tree defense against O. trigotephras which will be explored by chemical analysis of P. lentiscus, Q. coccifera and P. media. Two types of analyses were the focus of this study to understand plant defense (i) primary metabolites and (ii) components of essential oils of these tested plants. Kjeldhal method was used for nitrogen and Mrssorr method for potassium, sodium and phosphorus extraction. Essential oils were extracted with the hexane solvent; chemical composition was determined using (GC/MS) methods. Oil compounds were identified by comparison to their retention time. Results of mineral extraction showed that percentage of potassium, sodium, phosphorus and nitrogen were more important in P. lentiscus and P. media than in Q. coccifera. Five major compounds were identified from essential oils of Q. coccifera, four from P. media and four from P. lentiscus. Nitrogen, which is a source of protein for insects, is produced in low concentrations in the foliage, decreasing nitrogen levels strategy for defending the plant against insect larvae. The absence of monoterpens in the foliage at P. media could explain the choice of larvae not to feed upon this host which probably confers resistance against this defoliator.