No abstract

Insect chemosensory proteins (CSPs) are supposed to transport hydrophobic chemicals to receptors on sensory neurons. However, CSPs are broadly expressed in various insect tissues, suggesting their involvement in the physiological processes beyond chemoreception. So, the exact physiological roles of CSPs in insects still need to be unraveled. In this study, three full-length of CSP genes from Spodoptera exigua have been cloned and characterized. The deduced amino acid sequences of SexiCSP1, SexiCSP2 and SexiCSP3 revealed open reading frames of 128, 128 and 126 amino acids, respectively, with four conserved cysteine residues. The expression patterns of the three SexiCSPs were further investigated by real-time PCR. Three SexiCSPs were expressed in antennae, heads, legs, wings, thoraxes, abdomens, testes and ovaries, with the highest expression level in female and male antennae. Furthermore, all three SexiCSPs mRNA were distributed extensively in the tested development stages with the highest expression level in pupae. RNAi-based gene silencing study resulted in a dramatic reduction of corresponding mRNA in female S. exigua after injection with dsRNA of all three SexiCSPs. Consequentially, 42.5% of mortalities, 68.3% (compare to DEPC water injected control) and 71.4% (compare to uninjected control) oviposition inhibition, and significantly effected egg hatching were observed in the female S. exigua injected with dsSexiCSP3 as compared to control treatments. On the other hand, dsSexiCSP1 and dsSexiCSP2 injected female adults did not show effects on survival and reproduction. Our study confirms the utility of RNAi approach to functional characterization of CSP genes in S. exigua and provides a starting point for further studies on female survival and reproduction in this insect. It also reveals the potential pest controlling method, as insect behavior regulation agent that disrupts the expression of chemosensory proteins.

No abstract

The entomopathogenic fungal infection of target hosts depends on pathogen fitness and host defence mechanisms. Pathogen-host interactions in red palm weevil, Rhynchophorus ferrugineus larvae are poorly understood. In order to explore this interaction, 4th, 8th, and 12th instar red palm weevil larvae were immersed in conidial suspensions of four isolates of Beauveria bassiana. Significant differences in the virulence of the tested isolates were revealed by LT 50 values. Conidia of B8463, a highly virulent isolate, showed 33.53 % higher relative hydrophobicity and twice as much Pr1 activity than conidia of B8465. Growth indices, calculated after 72 h of incubation, revealed significant differences in the food utilization efficiencies of all studied larval instars infected with different isolates. Conidial infection with B8463 caused 39-45 % reduction in efficacy of consumption of ingested food (ECI) and 55-61 % reduction in digested food (ECD). The least virulent isolate, B8465, caused the smallest reduction in ECI (2-4 %) and ECD (3-9 %). Furthermore, enhanced expression of target antioxidant genes (catalases and peroxidase) was observed in larvae infected with virulent isolates. Similarly, approximate digestibility showed an opposite trend, with the highest values being recorded from samples infected with the most virulent conidia (B8463) at each studied larval instar. In conclusion, isolate B8463 significantly affected the growth and development of red palm weevil larvae and has good potential for use in eco-friendly R. ferrugineus management.

Insects infected with entomopathogenic fungi, experience physiological changes that influence their growth and immune defence. The potential of nine isolates of entomopathogenic fungi was evaluated after determining percent germination and relative conidial hydrophobicity. However, nutritional indices were evaluated after immersing eighth-instar Rhynchophorus ferrugineus larvae into each isolate suspension (1 × 10 7 conidia/mL). The results showed that isolates B6884 and M9374 had 44.51% and 39.02% higher conidial hydrophobicity compared with isolate I03011 (least virulent). The results of nutritional index assays revealed a significant reduction in growth indices after infection with different isolates. Compared with control, B6884 and M9374 greatly decreased larval growth by reducing the efficacy of conversion of ingested food (36%-47%) and Efficacy of conversion of digested food (50%-63%). Furthermore, only isolate B6884 induced 100% mortality within 12 days. Compared with control, isolate I03011, possessing the lowest conidial hydrophobicity, only reduced 0.29% of the efficacy of conversion of ingested food (ECI) and 0.48% of the efficacy of conversion of digested food (ECD). Similarly, transcriptomic analysis of genes related to the Red palm weevil (RPW) immune response, including pathogen recognition receptors (C-type lectin and endo-beta-1,4-glucanse), signal modulator (Serine protease-like protein), signal transductors (Calmodulin-like protein and EF-hand domain containing protein) and effectors (C-type lysozyme, Cathepsin L., Defensin-like protein, Serine carboxypeptidase, and Thaumatin-like protein), was significantly increased in larval samples infected with B6884 and M9374. These results suggest that for an isolate to be virulent, conidial hydrophobicity and germination should also be considered during pathogen selection, as these factors could significantly impact host growth and immune defence mechanisms.

This study aimed to explore the larvicidal and growth-inhibiting activities, and underlying detoxification mechanism of red palm weevil against phenylpropanoids, an important class of plant secondary metabolites. Toxicity of α-asarone, eugenol, isoeugenol, methyl eugenol, methyl isoeugenol, coumarin, coumarin 6, coniferyl aldehyde, diniconazole, ethyl cinnamate, and rosmarinic acid was evaluated by incorporation into the artificial diet. All of the phenylpropanoids exhibited dose- and time-dependent insecticidal activity. Among all the tested phenylpropanoids, coumarin exhibited the highest toxicity by revealing the least LD50 value (0.672 g/L). In addition, the most toxic compound (coumarin) observed in the current study, deteriorated the growth resulting tremendous reduction (78.39%) in efficacy of conversion of digested food (ECD), and (ECI) efficacy of conversion of ingested food (70.04%) of tenth-instar red palm weevil larvae. The energy-deficient red palm weevil larvae through their intrinsic abilities showed enhanced response to their digestibility resulting 27.78% increase in approximate digestibility (AD) compared to control larvae. The detoxification response of Rhynchophorus ferrugineus larvae determined by the quantitative expression of cytochrome P450, esterases, and glutathione S-transferase revealed enhanced expression among moderately toxic and ineffective compounds. These genes especially cytochrome P450 and GST detoxify the target compounds by enhancing their solubility that leads rapid excretion and degradation resulting low toxicity towards red palm weevil larvae. On the other hand, the most toxic (coumarin) silenced the genes involved in the red palm weevil detoxification mechanism. Based on the toxicity, growth retarding, and masking detoxification activities, coumarin could be a useful future natural red palm weevil-controlling agent.

No abstract

Crop damage and consequent loss in productivity associated with arthropod pests represent the most serious threats to the world economy. Different methods have been used in the past to control arthropod pests; however, the increase in incidences of resistance to pesticides, food safety concerns, and concerns related to environmental impact associated with the use of chemical pesticides have led to the recent expansion of biological control agents. Entomopathogenic fungi are important and promising bio-control agents for controlling arthropod pests. This review compiles recent information regarding the potential of entomopathogenic fungi used against arthropod pests, traits responsible for mycoinsecticide virulence, and possible ways to enhance the virulence of entomopathogenic fungi, in order to pave the way for the development of bio-rational and eco-friendly arthropod pest management strategies.