Asma Laarif

Bacillus amyloliquefaciens AG1 biosurfactant: Putative receptor diversity and histopathological effects on Tuta absoluta midgut

The use of biosurfactant in pest management has received much attention for the control of plant pathogens, but few studies reported their insecticidal activity. The present study describes the insecticidal activity of biosurfactant extracted from Bacillus amyloliquefaciens strain AG1. This strain produces a lipopeptide biosurfactant exhibiting an LC50 of about 180ng/cm(2) against Tuta absoluta larvae. Accordingly, the histopathologic effect of this biosurfactant on T. absoluta larvae showed serious damages of the midgut tissues including rupture and disintegration of epithelial layer and cellular vacuolization. By PCR, we showed that this biosurfactant could be formed by several lipopeptides and polyketides including iturin, fengycin, surfactin, bacyllomicin, bacillaene, macrolactin and difficidin. Binding experiment revealed that it recognized five putative receptors located in the BBMV of T. absoluta with sizes of 68, 63, 44, 30 and 19kDa. Therefore, biosurfactant AG1 hold potential for use as an environmentally friendly agent to control the tomato leaf miner.

Involvement of the processing step in the susceptibility/tolerance of two lepidopteran larvae to Bacillus thuringiensis Cry1Aa toxin

Bacillus thuringiensis (Bt) Cry1A toxins are known for their effectiveness against lepidopteran insects. In this study, the entomopathogenic activity of Cry1Aa was investigated against two lepidopteran larvae causing serious threat to various crops, Spodoptera littoralis and Tuta absoluta. Contrarily to S. littoralis, which showed low susceptibility to Cry1Aa (40% mortality with 1μg/cm(2)), T. absoluta was very sensitive to this delta-endotoxin (LC50 of 95.8ng/cm(2)). The different steps in the mode of action of this toxin on the two larvae were studied with the aim to understand the origin of their difference of susceptibility. Activation of the 130kDa Cry1Aa protein by T. absoluta larvae juice generated a 65kDa active toxin, whereas S. littoralis gut juice led to a complete degradation of the protoxin. The study of the interaction of the brush border membrane vesicles (BBMV) with purified biotinylated Cry1Aa toxin revealed six and seven toxin binding proteins in T. absoluta and S. littoralis BBMV, respectively. Midgut histopathology of Cry1Aa fed larvae demonstrated approximately similar damage caused by the toxin in the two larvae midguts. These results suggest that the activation step was strongly involved in the difference of susceptibility of the two larvae to Cry1Aa.

Smanjenje zaraze uskladištenih žitarica kestenjastim brašnarom (Tribolium castaneum) pomoću esencijalnih ulja tuniškog pelina (Artemisia sp.)

Essential oils of three species of Artemisia genus (A. absinthium L., A. campestris L. and A. herba-alba (Asso)) were analyzed by gas chromatography-mass spectrometry (GC-MS) and their potential insecticidal and repellent activities against the stored grain insect Tribolium castaneum (Herbst) was investigated. Fumigant and repellent activity bioassays were investigated in vitro. Chemical characterisation of essential oils showed that the bicyclic monoterpenes were predominant in all Artemisia essential oils, A. absinthium essential oil having the highest content of bicyclic monoterpenes, bicycloheptanes, naphthalenes and cycloalkenes. A. campestris had the highest content of sesquiterpenoids and acyclic monoterpenoids. A. herba-alba was characterised by the highest amounts of menthane monoterpenoids, oxanes, cumenes, oxolanes, ketones, benzenoids and monocyclic monoterpenes. Fumigant bioassay demonstrated that the three types of oil applied separately caused significant insect mortality. The lowest median lethal dose, LC50=142.8 μL/L, was observed with A. herba-alba. In repellency test, essential oil of A. absinthium was more potent with more rapid action than all other species. The mixture of Artemisia sp. essential oils showed an antagonistic effect in all the tested combinations. This study highlighted an important potential of Artemisia sp. especially A. herba-alba and A. absinthium in the control of the pests of stored products.