Chemical Treatments for Insect Cell Differentiation: The Effects of 20-Hydroxyecdysone and Veratridine on Cultured Spodoptera frugiperda (Sf21) Insect Cell Ultrastructure

Previous studies have shown that insect cell cultures stop dividing, form clumps, and can be induced to grow processes reminiscent of axons, when the culture medium is supplemented with 20-hydroxyecdysone, insulin, or an agent that mimics their action, such as the ecdysone agonist, methoxyfenozide. Those cell growing processes resemble nerve cells, and the present study evaluates the ultrastructure of these cultures by transmission electron microscopy. Sf21 cells treated with 20-hydroxyecdysone (with or without veratridine amendment) and subjected to ultrastructural analysis had a similar somatic appearance to control cells, with slight changes in organelles and organization, such as a greater number of cytoplasmic vacuoles and mitochondrial granules. Finger-like projections were observed between control and treated cells. However, no structural markers of synaptic contacts (e.g., vesicles or synaptic thickenings) were observed in controls, 20-hydroxyecdysone, or 20-hydroxyecdysone + veratridine treated cells. It is concluded that additional agents would be required to induce functional synaptogenesis in Sf21 cells.

Geometric Morphometrics Approach on Genotoxicity Evaluation of Ecdysone Agonist, Chromafenozide on Corcyra Cephalonica Stainton (Lepidoptera: Pyralidae)

The present investigation attempted to evaluate the genotoxicity effect of ecdysone agonist, on the wing architecture using the land mark based shape analysis through geometric morphometrics. The study revealed that the fore and hind wings of treated male and female showed significant variation in shape. High significance in shape was observed in male fore and hind wings. But, variation in size was not affected. The analysis of symmetry and asymmetry between left and right wings, suggests that the untreated male exhibit shape difference between left and right forewings and similar variation was also found in forewings of treated female. These findings demonstrate that, chromafenozide treated on the egg masses produced genotoxic effect on the adult wing architecture of C. cephalonica. Both the male and female forewing showed high significant shape decomposition at P = 0.0001 level exposed to 1/5 EC50 of chromafenozide. The morphological alteration in wing shape suggests that, it affects the aerodynamics pattern of the insect. In the present study, species diagnosis was performed in laboratory reared F1 generation using multilocus barcoding technique and obtained a sequence of 658bp (CO I) and 563bp (18s) in length.

Effects of nonsteroidal ecdysone agonist RH-5992 and chitin biosynthesis inhibitor lufenuron on Spodoptera littoralis (Boisduval, 1833)

Comparative studies of the effects of two compounds, tebufenozide (an ecdysone agonist) and lufenuron (an insect growth regulator inhibiting chitin synthesis), were conducted on Spodoptera littoralis (Boisduval, 1833). The compounds, orally administered, caused larval mortality proportional to the concentrations in the food source. Tebufenozide initiated precocious molting, and lufenuron, and inhibited chitin synthesis. In both cases, larvae were unable to complete the molting process and died in the old larval cuticle. Larvae contaminated by sublethal doses completed their development to adulthood. Lufenuron is more active than is tebufenozide. LD-50 for lufenuron is 0.0001ppm and for tebufenozide 0.001ppm. Topical application of the test compounds to eggs caused dose- and agedependent inhibition of embryonic development. Application of tebufenozide in the second half of embryogenesis caused precocious molting of eclosed larvae of the 1st instar. Some morphological changes in the process of larval-pupal transformation were also observed. Tested compounds also reduced reproduction in adult individuals that had been treated by the tested compounds in the larval stage.