The Gum Tree Thrips, Thrips australis: Description, Geographical Distribution and Host Plants in Tunisia

The gum tree thrips, Thrips australis, was recorded during 2011 in Tunisia in the Center East coastal region. Moreover, it was encountered during 2012 in many other regions (North and Center West of the country). T. australis was found on different host plants among which Eucalyptus spp., Citrus spp., Chrysanthemum spp., Calendula arvensis, and Tropaeolum majus

Emergence of the apricot seed wasp Eurytoma samsonowi Vassiliev (Hymenoptera: Eurytomidae) as an economic pest of apricots in Tunisia

International audienceMany eurytomid (Eurytomidae) wasps are plant parasites, and some of them are economic agricultural pests. In 2015, a new eurytomid wasp species was detected attacking apricots in the governorate of Gafsa located in the southern west region of Tunisia. Morphological and molecular identifications allowed to identify the pest as the apricot seed wasp Eurytoma samsonowi Vassiliev, a new record in Tunisia and Africa. Besides, field surveys were performed from 2017 to 2021 in order to assess the distribution of E. samsonowi in the main Tunisian apricot production areas, to characterize its symptoms of attack and to assess its damage on different apricot cultivars. The pest has limited distribution in Tunisia as it was found only in the governorates of Gafsa, Sidi Bouzid and Tozeur. Larvae of this pest feed on apricot nucellar tissues. Infested fruits either prematurely fall on the ground or turn black, become 'mummified', and remain attached to the tree. The highest infestation rates were recorded on Bayoudhi cultivar ranging from 64 to 76% depending on the year. Infestation rates registered on Bedri and Amor Leuch cultivars ranged from 24% to 51% and 27 to 53%, respectively. Therefore, this insect should be considered as an economic pest of apricots in Tunisia. Possible management measures and future outlooks are discussed

Medicago sativa and M. tunetana reveal contrasting physiological and metabolic responses to drought

Alfalfa production is frequently constrained by drought, indicating the importance of assessing species biodiversity in endemic close relatives to enhance forage production under future global change conditions. In the present study, plants of two ecotypes of M. tunetana, native to Tunisia, and four commercial cultivars of M. sativa were subjected to two water regimes (control vs drought [15% field capacity]). Physiological, isotopic and metabolic analyses were used to characterize leaf and nodule profiles of the plants. Biomass, gas exchange and the maximum carboxylation rate (Vc) indicated significant decreases in photosynthetic capacity under drought in M. sativa cultivars. However, M. tunetana ecotypes maintained photosynthetic performance and aboveground biomass under drought conditions. Furthermore, nitrogen isotope composition (δN) in nodules and leaves was significantly decreased, which reveals a reduction in the N fixing activity of nodules under drought conditions that was not translated into lower leaf N content but was probably due to lower N demand. Analyses of starch, soluble sugar, and amino acid content in leaves and nodules have clearly proven the ability of Medicago spp. cultivars to increase the accumulation of osmo-protectors under drought. This study demonstrated the genetic variability of the strategy adopted among the studied cultivars in response to drought. In this sense, M. tunetana, and in part the M. sativa cultivar adapted to Mediterranean conditions, seem capable of maintaining adequate biomass, photosynthesis and biological N fixation in comparison to the other M. sativa cultivars

Parasitism rate of Bactericera trigonica hodkinson nymphs by Tamarixia pronomus walker under field and laboratory conditions

International audienceThe carrot psyllid, Bactericera trigonica, is a vector of ‘Candidatus Liberibacter solanacearum’ which infects carrots and many of solanaceous plants. The psyllid was first reported in Spain, then it was rapidly spreading throughout the Mediterranean countries, where it causes considerable damages to carrot crops. To minimize the spread of psyllid species as well as the associated fastidious bacteria, field inspections have been carried out in order to seek for a natural enemies of B. trigonica. Field surveys revealed the presence of a new eulophid parasitoid for the first time in Tunisia attacking larvae of B. trigonica, the main responsible for the significant losses in carrot fields. In order to study the parasitism rate of this parasitoid, a weekly sampling of carrot plants carrying the psyllids and its parasitoids was performed in carrot fields. The parasitism rate and the preferential stage for this parasitoid were also determined under laboratory conditions. The result shows Tamarixia pronomus, preferred late (4th and 5th) instar larvae to early (2nd and 3rd) instar larvae of B. trigonica. There, the parasitism average of late instars was estimated to average 80% and approached 100%. It should be noted that parasitism rates varied by season, with the spring showing the highest averages. Further efforts are warranted to enhance the biological control of B. trigonica and thereby reduce psyllid populations and the spread of ‘Candidatus Liberibacter solanacearum’

Survey of Species of the Genus Orius in the Tunisian Sahel Region

Species of the genus Orius belong to the Anthocoridae family. They are polyphagous predators of small sized insects and they are of great importance in biological control. During an inventory of Orius species on Chrysanthemum coronarium flowers undertaken in 2010 and 2011 in different locations in the Tunisian Sahel region, three species were encountered namely O. laevigatus, O. albidipennis and O. majusculus. These species are predators of mites and small insects such as thrips, aphids, and white. The first species was the most abundant one in all localities (a total of 4358), followed by O. albidipennis and O. majusculus with 51 individuals. Temporal evolution of Orius species showed that activity of the predaceous bugs depends essentially on the flowering period of C. coronairum. Orius species occurred during spring period with various densities, depending on species, and increased considerably in June. O. leavigatus was detected in February and remained active until June. Regarding O. albedipenis and O. majusculus, their activity has begun in April-May but with different densities. Monitoring revealed the abundance of females as compared to males within Orius species which indicated that females occupy a significant importance within population