Efficacy of the entomopathogenic nematode isolate Heterorhabditis taysearae to control the cotton leafworm, Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae)

Background Entomopathogenic nematodes (EPNs) are promising alternatives since they have many characteristics as a biological control agent against insect pests. Results Among indigenous EPN isolated, adapted to local environmental conditions by employing the Galleria baiting strategy, only one sample was positive for the presence of EPNs. The new isolate was identified at the species level using DNA sequencing of the internal transcribed spacer region and the Basic Local Alignment Search Tool search of GenBank showed that the isolate had a high similarity (99%) with that sequence available for Heterorhabditis taysearae. The pathogenicity of the EPN isolate was tested against the cotton leaf worm, Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae), using different concentrations (60, 90, 120 and 150 IJs/larvae). Data showed that 150 IJs/larvae caused 100% mortality rate, followed by 120 IJs/larvae (90%), while 60 IJs/larvae showed the lowest rate (60%) after 72 h. Conclusions The present study indicated that the native isolate of EPN could be recommended against S. littoralis as an efficient tool in its control programs.

Sustainable Production of Bioactive Compounds From Persea indica

In this work we have investigated the accumulation of ryanoids in different plant parts (leaves, stems roots) of aeroponically grown Persea indica cloned trees (one year old cloned individuals) and a selected mature wild tree. We have tested the insect antifeedant (against Spodoptera littoralis, Myzus persicae and Rhopalosiphum padi) and nematicidal (against Meloidogyne javanica) effects of ethanolic extracts from these different plant parts. The HPLC-MS analysis of P. indica extracts showed that the mature tree (wild) leaves had 2 times more chemical diversity than the stems. The aeroponic plants showed lower differences in chemical diversity between leaves and stems, with the lowest diversity found in the roots. The ryanodane epiryanodol (1) was present in all the plant parts, with the mature stems (wild) having the highest amount. The aeroponic stems also accumulated ryanoids including 1, cinnzeylanol 2 and cinnzeylanone 4. The insect Spodoptera littoralis was strongly affected by the stem extracts while the leaf ones were moderately active. Based on the predicted vs. the real antifeedant values we conclude that the ryanoid content (1 or a combination of 2, 4 and 1) explained the antifeedant effects of the stem extracts while addition-al components contributed to the activity of the leaf ones. Therefore, careful individual selection of P. indica seedlings should be carried out prior to proceed with its aeroponic cultivation in or-der to obtain ryanodane-rich stem or leaf extracts with strong antifeedant effects on S. littoralis.

Synthesis and characterization of some new tebufenozide analogues and study their toxicological effect against Spodoptera littoralis (Boisd.)

Many of mimic analogues synthesized before depending on the change in the structure of aromatic rings. In this work, the carbonyl group in the structure of compounds 1-4 converted to thiocarbonyl group, and then studying the toxicological activity due to chemical change in the active center of mimic analogues was performed for compounds N-tert-butyl-2,4-dichloro-N'-(2,4-dichlorobenzoyl)benzohydrazide (2) and N-tert-butyl-2,4-dichloro-N'-[(2,4-dichlorophenyl)carbonothioyl]benzenecarbothiohydrazide (6). The toxicological study was done by using 2nd and 4th instar larvae of the cotton leaf worm, Spodoptera littoralis (Boisd.). Five concentration levels (600, 300, 150, 75 and 37.5 ppm) of compounds (2) and (6) were applied on the fresh plant food to the newly grown (2nd and 4th) instar larvae.

Transgenic plants expressing immunosuppressive dsRNA improve entomopathogen efficacy against Spodoptera littoralis larvae

Transgenic plants that express double-stranded RNA (dsRNA) targeting vital insect genes have recently emerged as a valuable new tool for pest control. In this study, tobacco plants were transformed to produce dsRNA targeting Sl 102 gene that is involved in the immune response of Spodoptera littoralis larvae, a serious lepidopteran pest of several crops. Experimental larvae reared on transgenic tobacco lines showed (1) a strongly reduced level of Sl 102 transcripts, which was positively associated with food consumption; (2) a substantial impairment of the encapsulation response mediated by hemocytes; and (3) a marked increase in the susceptibility to Xentari™, a Bacillus thuringiensis-based insecticide. Importantly, this approach may allow a reduction in the doses of B. thuringiensis used for field applications and enhance its killing activity on mature larvae. The results obtained thus support the use of immunosuppressive RNAi plants to enhance the performance of microbial insecticides on lepidopteran larvae.