Effects of Dipel 2X and littovir bioinsecticides on larvae of the cotton leafworm Spodoptera littoralis (Lepidoptera : Noctuidae)‎

Abstract EN

Bacillus thuringiensis (Bt) and Nuclear Polyhedrosis Virus (NPV) are effective microbial control agent for controlling numerous species from different insect orders.

The cotton leafworm Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae) is a polyphagus insect pest which infests many crops in Egypt.

Toxicity of Dipel 2X (Bacillus thuringiensis Kurstaki) and Littovir (SpliNPV) was evaluated on S.

littoralis 2nd instar larvae in the laboratory.

Larvae were selected by the two bioinsecticides at sublethal concentrations of LC70, LC50, LC25, LC10 and LC5.

All selected larvae were died after seven days of treatment except those of LC5 treatment.

The offspring (F1 progeny) of LC5 treatment was selected with two tested formulations at LC5 concentration.

Dipel 2X treatments caused slight depletion in the total protein content of the treated larvae whole body tissues and their gut tissue compared with untreated larvae.

LC70 and LC50 treatments produced significant decrease (35.7and 27.8%, respectively) in protein of treated parent larvae.

LC70 treatment of Dipel 2X induced a significant elevation (39.7and 27.3%) of body tissues (Na+/K+) ATPases and gut Proteases, respectively.

The vigorous histopathological effects of Dipel 2X on midgut tissue of treated larvae were observed in LC70 and decreased in LC50 and lower in LC25.These effects were hyperplasia of epithelial cell layer, appearance of apoptotic bodies, rupture of the bruch border microvilli, activation of stem cells, contraction of the muscle layer, extensive fragmentation and separation of mucosal epithelium from the basement membrane and the gut lumen was filled with debris of disrupted cells.

Littovir caused insignificant decrease in total proteins of larval tissues with LC70, LC50 and LC25 treatments but LC10 and LC5 induced increase in protein concentration of treated larvae.

This content was increased in gut tissue of all treated larvae.

High concentrations of Littovir produced insignificant reduction in ATPases activity in bodies of treated larvae, while lower concentrations elevated this activity which reaches to significant value (31%) in tissues of LC5 treated larvae.

All treatments inhibited the activity of midgut Protease in treated larvae and this effect was pronounced (40.1 and 32.3%) in LC70and LC50 treatments.

LC70 treatment of littovir caused hyperplasia and destruction of the midgut epithelium, appearance of apoptotic bodies, rupture of the bruch border microvilli and vacuole formation.

These effects decreased with LC50 and LC25 treated larvae.

Dipel 2X at LC5 treatment of 1st generation (F1) larvae caused slight reduction in total proteins and ATPase in larval bodies but Littover increased proteins and significantly elevated (31%) ATPase in treated larvae.

Insignificant increasing in gut proteins and Protease were detected and, slight changes in midgut tissues were observed in larvae treated with the two tested bioinsecticides.

Results of this study concluded that the (Na+/K+) ATPase and Protease played an important role in toxicity of Bacillus thuringiensis subsp.

Kurstaki and Nuclear Polyhedrosis Virus (SpliNPV) and tolerance of S.

littoralis larvae to their effects.