Studies on the action mechanisms of new type of biorational insecticides
Botancical insecticides and nonsteroidal ecdysone agonists of insect growthregulators (IGRs) are two kinds of important biorational insecticides with novel modesof action, which are less harmful to nontarget organism than conventional chemicalinsecticides. This paper emphasized on the effects of Celangulin Ⅳ and matrine on ionchannel currents in cultured nerve cell of insect by using whole cell of patch clamptechnique. Furthermore, the effects induced by new type nonsteroidal ecdysoneagonist on cuticle structure and moulting process of Helicoverpa armigera werecarried out.This research developed a modified culture medium to improve the attachment ofnerve cells. Furthermore, supplemented with essential ingredients that promote thenerve cell growth. All these improved the number of attachment nerve cells .Theculture medium also adapt to the neuron cells of Spodopteta exigua to grow in vitro.The voltage gated ion channels in central neurons of S. exigua had been characterizedby whole-cell patch champ recording. It exhibits tetrodotoxin-sensitive sodium current,L-type high-voltage activated calcium current, delayed rectifier potassium current (〓)and 〓 sensitive to 4-aminoloyridine. The types of voltage gated ion channels incentral neurons of S. exigua are same as H. armigera.Celangulin Ⅳ is the active ingredient which has narcotic action against someinsects. The effects of Celangulin Ⅳ on inward sodium channel current (〓) incultured nerve cell of cotton bollwom (H. armigera) were studied by patch champtechnique. The recording results showed that Celangulin Ⅳ reduced sodium inwardcurrent in a concentration dependant manner, affected the kinetics of sodium channeland shifted the active and peak current potential to the positive direction. Lidocaine isa clinical local anesthetic. The effects of lidocaine on 〓 in cultured nerve cell ofcotton bollworn were studied comparatively. The results indicated that lidocaine alsohad effects on 〓, but 〓 could be inhibited with more potency of Celangulin Ⅳ thanthat of lidocaine. At same time, the patch clamp recording showed that Celangulin Ⅳinhibited the sodium current in cultured nerve cell of S. exigua. The effects are similarto H. armigera on the whole, but S. exigua has different sensitivity to Celangulin Ⅳcompared with H. armigera.That high-voltage activated calcium current was identified by nifedipine is L-type〓 channel. Moreover, we compare with the calcium current in the external solutionsof 〓 and 〓 as carrier. 〓 displaced 〓 as divalent cation carrier, the peakamplitude of the inward current was bigger, and there was a slower decline of thecurrent during the voltage step. In addition, the effects of Celangulin Ⅳ on inwardcalcium channel current (〓) in cultured nerve cell of H. Armigera were studied.Matrine is another kind of conventional alkaloids from plants against insect pests.Its effects on inward sodium channel current (〓) in cultured nerve cell of H.armigera were studied. The recording results indicated that Matrine inhibited thesodium current in a dose dependent manner and without changing the active potential,peak potential and shape of current-voltage relation curve.The action mode of sulphur-sulphur dibenzoylhydrazine-type nonsteroidalecdysone agonists was studied on the larva of cotton bollworn, H. Armigera(Lepidoptera) by transmission electron microscope. The results revealed thatW200013 was same as dibenzoylhydrazine-type insecticide RH-5992 on the toxicsymptoms, bioassay results and ultrasturctural changes of integument. They allinitiated a precocious and lethal larval moult. It proved that W200013 exhibits itsnematicidal action by bind to ecdysteroid receptors as RH-5992. In conclusion, the research illustrated the narcotic action mechanisms ofCelangulin Ⅳ and effects of Matrine on sodium channel current. Furthermore, theabnormal moult mode induced by new sulphur-sulphur dibenzoylhydrazine-typenonsteroidal ecdysone agonist was explained.