No abstract

Pigment-dispersing factor (PDF) is a neuropeptide widely distributed in insect brains and plays important roles in the circadian system. In this study, we used RNA interference to study the role of the pigment-dispersing factor (pdf) gene in regulating circadian locomotor rhythms in the cricket, Gryllus bimaculatus. Injections of pdf double-stranded RNA (dspdf) effectively knocked down the pdf mRNA and PDF peptide levels. The treated crickets maintained the rhythm both under light-dark cycles (LD) and constant darkness (DD). However, they showed rhythms with reduced nocturnal activity with prominent peaks at lights-on and lights-off. Entrainability of dspdf-injected crickets was higher than control crickets as they required fewer cycles to resynchronize to the LD cycles shifted by 6 h. The free-running periods of the dspdf-injected crickets were shorter than those of control crickets in DD. These results suggest that PDF is not essential for the rhythm generation but involved in control of the nocturnality, photic entrainment, and fine tuning of the free-running period of the circadian clock.

ABSTRACT-The circadian system of hemimetabolous insects is reviewed in respect to the locus of the circadian clock and multioscillatory organization. Because of relatively easy access to the nervous system, the neuronal organization of the clock system in hemimetabolous insects has been studied, yielding identification of the compound eye as the major photoreceptor for entrainment and the optic lobe for the circadian clock locus. The clock site within the optic lobe is inconsistent among reported species; in cockroaches the lobula was previously thought to be a most likely clock locus but accessory medulla is recently stressed to be a clock center, while more distal part of the optic lobe including the lamina and the outer medulla area for the cricket. Identification of the clock cells needs further critical studies. Although each optic lobe clock seems functionally identical, in respect to photic entrainment and generation of the rhythm, the bilaterally paired clocks form a functional unit. They interact to produce a stable time structure within individual insects by exchanging photic and temporal information through neural pathways, in which serotonin and pigment-dispersing factor (PDF) are involved as chemical messengers. The mutual interaction also plays an important role in seasonal adaptation of the rhythm.

Rabbit carcass decomposition was examined in four seasons in Al-Ahsaa Oasis. Decomposition rate was significantly faster in summer compared with other seasons. Fourteen insect species from four orders and seven families were recorded: Calliphoridae, Muscidae, Sarcophagidae, Formicidae, Histeridae, Dermestidae, and Tenebrionidae. Most of the fly maggots collected were Calliphoridae with only one species from both Muscidae and Sarcophagidae. Maggots of Calliphora vicina (R.-D.) and Chrysomya albiceps (Wiedemann) colonized the carcasses in all seasons while both Ch. bezziana (Villeneuve) and Lucilia sericata (Meigen) were found in all seasons except for winter. Maggots of Chrysomya megacephala (F.) and Phormia regina (Meigen) were only collected in the summer and autumn, respectively. Four coleopteran species were collected: Hymenorus sp., Saprinus chacites (Illiger), Dermestes maculatus DeGeer and Blaps sp. One formicidian species, Pheidole megacephala (F.), was observed in all seasons. Insect richness was greater, and decomposition rate was faster in summer compared with other seasons.

No abstract

The red palm weevil, Rhynchophorus ferrugineus, is of great concern worldwide, especially in the Middle East, where dates are a strategic crop. Despite their ecological hazard, insecticides remain the most effective means of control. A bioinsecticide of bacterial origin, spinosad is effective against several pests, and its efficacy against male R. ferrugineus was assessed in the present study. The antioxidative responses of key enzymes including catalase (CAT), superoxide dismutase (SOD), and glutathione-S-transferase (GST) to spinosad were investigated in the midgut and testes, and the effects of this insecticide on the cell ultrastructure of the midgut, Malpighian tubules, and testes were also determined. The lethal concentration 50 of spinosad was measured at 58.8 ppm, and the insecticide inhibited the activities of CAT, SOD, and GST in the midgut. However, no significant changes in the activities of these enzymes were observed in the testes. Spinosad treatment resulted in concentration-dependent changes in the cellular organelles of the midgut, Malpighian tubules, and testes of R. ferrugineus, and some of these effects were similar to those exerted by other xenobiotics. However, specific changes were observed as a result of spinosad treatment, including an increase in the number and size of concretions in Malpighian tubule cells and the occasional absence of the central pair of microtubules in the axonemes of sperm tails. This study introduces spinosad for potential use as an insecticide within an integrated control program against male red palm weevils. Additionally, the study provides biochemical and ultrastructural evidence for use in the development of bioindicators.

No abstract

Red palm weevil, Rhynchophorus ferrugineus, destroys palms almost all over the world, especially in the Middle East, where dates are a strategic crop in arid places. In view of the urgent need to combat this destructive pest, effective pesticides with high environmental safety should be sought. Spinosad is a pesticide of bacterial origin that is presumed to have a high degree of environmental safety and is effective in combating a wide range of insect pests. In this study, the efficacy of spinosad was evaluated in females of R. ferrugineus. The lethal concentration for 50% of the treated females was calculated at 44.3 ppm. The effects of spinosad concentrations of 10, 50 and 200 ppm on the activity of catalase (CAT), glutathione S‐transferase (GST) and superoxide dismutase (SOD) in the ovaries were assessed. In addition, the pathological effects of these concentrations were documented on the ultrastructure of the follicle cells and ooplasm. The results showed a significant increase in CAT activity only in response to treatment with 200 ppm. Treating the females with different spinosad concentrations resulted in varying intensity changes in cell organelles, where the most pronounced sign of programmed cell death was at the concentration 200 ppm. This study demonstrates the possibility of using spinosad as an insecticide against females of R. ferrugineus.