Toxicity of the active fraction of Pergularia tomentosa and the aggregation pheromone phenylacetonitrile on Schistocerca gregaria fourth-instar nymph: effects on behavior and acetylcholinesterase activity

Chemical insecticides remain the most used approach in locust control although they present a serious menace to human health and the environment. The search for alternative control methods, efficient and environmentally friendly, has become indispensable. The aim of this work is to study the effect of the aggregation pheromone, phenylacetonitrile, alone or in combination with the active fraction of Pergularia tomentosa on Schistocerca gregaria fourth-instar nymph. Toxicity bioassays showed that the combination of phenylacetonitrile with the active fraction of P. tomentosa significantly increased nymph mortality. Results also showed that the aggregation pheromone caused significant mortality especially after 6 hours of exposure. The pheromone also caused neurotoxic effects on S. gregaria nymph due to the disturbance of the acetylcholinesterase activity. We also noted the presence of cannibalism phenomenon. Phenylacetonitrile seems to have an effect on phase ployphenism of S. gregaria imagos that exhibit specific traits to the solitarious phase

Repellency and toxicity of the crude ethanolic extract of Limoniastrum guyonianum against Tribolium castaneum. Acheuk, F., Belaid, M., Lakhdari, W., Abdellaoui, K., Dehliz, A., and Mokrane, K. (Algeria/Tunisia)

In nature, the interaction between plants and insects has led to the production of a set of secondary compounds. Many plant secondary metabolites have significant insecticidal activity. The aim of this study is to evaluate the repellent and insecticidal effect of the crude ethanolic extract of Limoniastrum guyonianum against adults of the red flour beetle Tribolium castaneum. For the insecticidal activity, five doses (100, 200, 400, 600, and 800 µg/insect) were tested and were topically applied onto insect thorax. An area preference method was adopted to assess the repellent activity. A phytochemical study and measurement of two enzymatic biomarkers: acetylcholinesterase (AChE) and gluthatione Stransferase (GST) were made to understand the mechanisms of toxic action of the tested extract. Phytochemical study showed the presence of various groups of natural products. The plant is rich in flavonoids, tannins, alkaloids, and glycosides. Low amount of saponins was noted. The study also showed that this plant does not contain iridoids. For repellent activity, the results showed that the highest dose (800 µg/insect) exhibited obvious repellent effect against T. castaneum. The repellency percentage was 90.14 ± 2.5% after 4 h of exposure. The crude extract was found to be toxic to T. castaneum and the corresponding LD50value was 218.3 μg/insect. Moreover, the extract inhibits the activity of the acetylcholinesterase (IC50: 205.7 µg/insect)

Effects of Latex from Pergularia tomentosa and the Aggregation Pheromone, Phenylacetonitrile, on Locusta migratoria Larvae

Despite being a serious risk to human health and environment, chemical insecticides remain the most used for locust control. Searching for alternative control methods, effective and compatible with the environment, has become of increasing interest. Plant latex is an endogenous fluid secreted from highly specialized laticifer cells and has been suggested to act as a plant defense system. The aim of the present investigation was to study the insecticidal potentialities of Pergularia tomentosa latex at different concentrations, alone or in combination with the penylacetonitrile (PAN), on the 4th instar larvae of Locusta migratoria. The obtained results showed that the latex revealed an interesting insecticidal activity against L. migratoria larvae, resulting in a mortality reaching 96.49 %, 6 days after treatment. Toxicity bioassays revealed that PAN, associated with the latex, is able to accelerate and to increase the mortality rate. Pheromone-based treatment affected the health of treated insects by significantly reducing their respiratory rhythms. PAN was shown able to alter, quantitatively and qualitatively, the larval blood cells as expressed by the significant decrease in the number of the differential haemocyte counts (prohemocyte, plasmatocytes and granulocytes) and the important cell lysis

First Record of Dericorys albidula Serville, 1838 (Orthoptera: Dericorythidae) in Tunisia and Libya

Tlili, Haithem, Abdellaoui, Khemais, Chouikha, Manel Ben, Mhafdhi, Mouna, Jemmazi, Adel, Ammar, Mohamed, Desutter-Grandcolas, Laure (2019): First Record of Dericorys albidula Serville, 1838 (Orthoptera: Dericorythidae) in Tunisia and Libya. Zootaxa 4551 (3): 385-393, DOI: https://doi.org/10.11646/zootaxa.4551.3.

Daily microhabitat shifting of solitarious-phase Desert locust adults: implications for meaningful population monitoring

The Desert locust Schistocerca gregaria is a major world pest that causes substantial agricultural and economic damage. Effective pest control relies on effective monitoring, which requires knowledge of locust microhabitat selection. Yet little is known about microhabitat selection of solitarious adult locusts in the field. We conducted field surveys to investigate fine-scale diel temporal and spatial distributions of solitarious adults in the Sahara Desert in Mauritania, a major breeding and recession area. We found that solitarious adults moved among different, specific microhabitats throughout the 24-h period in a cyclical manner. At night, they roosted in trees, moved to the ground to feed shortly after dawn, sheltered in low vegetation during the hot midday, and returned to the ground in the late afternoon. Hence, they switched microhabitats and plant species throughout each day. These cyclical daily movements among diverse microhabitats and specific plant species were correlated with time of day, light intensity, temperature, humidity, and specific plant species, and may relate to anti-predator defence, thermoregulation, and feeding. The present study suggests that locust monitoring should be adjusted, based on time of day, locust age, phase state and relative abundance of specific plant species. For example, we recommend surveying ground after morning and trees at night, for solitarious adults, when at low density

Effects of water extracts of frass from three locust species and various plants on oviposition and embryonic development in the desert locust, Schistocerca gregaria

The water extract of desert locust, Schistocerca gregaria, frass collected in the wild had an oviposition inhibitory (OI) effect when mixed with sand and presented to adults. Likewise, the leaves of six plant species, as well as frass produced by desert locusts fed with these plants, exerted OI effects when compared with the control sand wetted with water alone. In general, frass extracts had a greater OI effect than the extracts of leaves. The OI effect was also observed when adult desert locusts were exposed to extracts of frass produced by two other locusts, the Bombay locust, Nomadacris succincta, and the migratory locust, Locusta migratoria, fed with rescue grass, Bromus catharticus. Among the three species of locust, desert locust and migratory locust frass exerted a greater OI effect than Bombay locust frass. Frass samples extracted with hot and cool water produced similarly high OI effects, indicating that bacterial involvement during extraction is unlikely. Hatching rates of desert locusts were significantly reduced by extracts of all of the above mentioned frass when the extracts were mixed with sand and used to incubate the eggs. In contrast, the lethal effects of leaf extracts on the hatching rates varied depending on the plant species. The embryos became deformed within four days when three-day-old eggs were incubated in sand containing frass extracts from desert locusts fed with rescue grass, whereas no apparent morphological changes were observed when seven-day-old eggs were similarly tested, although their hatching rate was significantly reduced

Antifeedant and antigonadotropic effects of Ruta chalepensis methanolic extract against Locusta migratoria. Abdellaoui, K., Miladi, M., Ben Marzouk, I., Bahloul, N., Acheuk, F., Chaira, N., and Ben Halima-Kamel, M. (Tunisia / Algeria)

The migratory locust Locusta migratoria is one of the most important pests due to its extensive and serious damage to crops in large parts of Africa and Asia. To identify novel new environment friendly products for the management of the migratory locust, experiments were conducted to assess the effect of a methanolic extract of Ruta chalepensis (ME-Rc) on feeding activity and different reproductive phases of L. migratoria. The results showed that ME-Rc caused a significant decline in food intake and insect digestibility. The treatment applied to adult females caused a significant lengthening of the preoviposition period and a significant reduction in both fecundity and fertility. ME-Rc also affected growth and development of oocytes as evidenced by measurements of ovarian weight, length and volume of terminal oocytes and ovarian index. In addition, ME-Rc based-treatments led to disturbances in the incorporation of haemolymph metabolites (proteins and carbohydrates) in oocytes resulting in a significant decrease in their concentrations in ovaries

FIGURE 1 in First Record of Dericorys albidula Serville, 1838 (Orthoptera: Dericorythidae) in Tunisia and Libya

FIGURE 1. Sampling map showing the Tozeur region in Tunisia