| The beet armyworm, Spodoptera exigua (Hbüner), is a polyphagous noctuid of worldwide importance that feeds on various agricultural crops, including vegetable, cotton and omamental. The heavy dependence on insecticides for control of this pest has resulted in the emergence of resistance to a variety of insecticides. Insect growth regulators (IGRs) including tebufenozide and chitin inhibitors are the major insecticides used to control Spodoptera exigua in the field. They have selective toxicity towards different pests, and have less adverse effects on mammals, birds, fishes and other vertebtrates, as well as various beneficial insects. In order to maintain long effective controlling, we must pay more attention to sensitivity of these insecticides to beet armyworm.The life activities of insect is controlled by its nerve system potential conduction. Nerve potential is the potential difference dues to the different ion concentration of inside and outside neurilemma. ATPase in the neurilemma mostly controls the different ion concentration of inside and outside neurilemma. Na-K-ATPase catalyses the bottom phosphoric acid of ATP to be hydrolyzed, and the high-energy phosphate bond liberatives free energy which can be used to counter-transport Na+,K+ with electrochemistry gradient, in order to maintain the relative invariablenes and balance of osmotic pressure of Na+,K+ concentration of inside and outside neurilemma. Ca2+ plays an important part in neuraxon conduction, synapse neurotransmitters release and neurilemma stability. In normal condition, Ca2+ concentration of outside neurilemma is higher than that inside neurilemma. And the modulation of Ca2+ inside and outside neurilemma mainly depends on Ca-ATPase and Ca-Mg-ATPase. Target sites of pyrethroid insecticides are sodium channel on the neurilemma and Na-K-ATPase,Ca-ATPase and Ca-Mg-ATPase which can maintain the stability of ions inside and outside neurilemma. The variation of sodium channel and the decreased activities of nerve ATPase are main causes to pyrethroid insecticide resistance.Three parts are involved in this thesis: (1) sensitivity of insect growth regulators to resistant strain of beet armyworm, Spodoptera exigua and (2) inhibition of Lambda-cyhalothrin on Nerve Na-K-ATPase, Ca-ATPase and Ca-Mg-ATPase in the Beet Armyworm.(3)active changes of multi-function oxidases in Beet Armyworm.The results are as follows.1. In the same condition in laboratory, LD50 or LC50 of 3rd instar larva of susceptible strain and Lambda-cyhalothrin resistant strain of beet armyworm were determined. The results detected by topical application showed that 3rd instar larva of the resistant strain had 5163.0 fold resistance to Lambda-cyhalothrin compared to the susceptible strain. The results detected by dipping method showed that 3rd instar larva of the resistant strains had 985.2 fold resistance to Lambda-cyhalothrin. Sensitivity of five insect growth regulators to resistant and susceptible stains of beet armyworm was evaluated. The order of sensitivity to 3rd instar larvae of susceptible strain detected by leaf-dipping method was methoxyfenozide﹥tebufenozide﹥hexaflumuron﹥RH-5849﹥diflubenzuron. The resistant stain showed the similar resistant orders to 5 IGRs as susceptible strain. Compared with susceptible strain, the sensitivity of resistant stain to methoxyfenozide, tebufenozide, hexaflumuron, RH-5849 and diflubenzuron decreased 3.81, 5.55, 4.81, 3.85 and 2.61 folds respectively.2. The activities of Na-K-ATPase, Ca-ATPase and Ca-Mg-ATPase in susceptible and Lambda-cyhalothrin resistant strains of beet armyworm, Spodoptera exigua, were determined. The results indicated that there was no significant difference in Na-K-ATPase activity between the two strains, but Ca-ATPase and Ca-Mg-ATPase activities were much lower in resistant strain than in susceptible strain. Lambda-cyhalothrin at concentrations of 10-8-10-3 mol/L inhibited obviously the three above ATPase activities in two strains, and the inhibition was higher in susceptible strain than in resistant strain. For example, At concentration of 10-4 mol/L, the inhibition on Na-K-ATPase, Ca-ATPase and Ca-Mg-ATPase activities was 29.6%, 34.3% and 22.3% in susceptible strain and 21.8%, 21.9% and 16.9% in resistant strain respectively. The results showed that the sensitivity of three above ATPases in resistant strain decreased to Lambda-cyhalothrin.3. Larvae of beet armyworm were reared on artificial diet and evaluated for resistance to Lambda-cyhalothrin for 43 generations under laboratory condition without exposure to any insecticides (for non-selection). Four indices of monoxygenase activities [methoxyresorufin O-demethylase (MROD), ethoxyresorufin O-deethylase (EROD), arylhydrocarbon hydroxylase (AHH) and aldrin epoxidase (AE)] were compared between F2, or F20, or F43 generation and the susceptible strain, respectively. Compared with the susceptible strain, the activities of MROD and AE in midguts in fifth instar larvae of F2 generation showed significant difference, those of F20 and F43 generations showed no significant difference. In the same way, the activities of MROD and AHH of F2, F20 and F43 generation also showed significant difference. This indicated that the resistance of Spodoptera exigua to lambda-cyhalothrin was closely correlated with multi-function oxidase which may play different roles at different resistant levels.
|
PDF Full Text Request