Zhao Zhimo

Development and reproduction of threeEuseius (Acari: Phytoseiidae) species in the presence and absence of supplementary foods

Development duration, mortality and oviposition rate ofEuseius tularensis (Congdon),E. stipulatus (Athias-Henriot) andE. hibisci (Chant) were determined on three basic foods (pollen of iceplant, Pacific spider mite and citrus red mite) in the presence and absence of supplementary foods (honeydew from aphids and whiteflies). The studies were conducted in the laboratory at a constant temperature of 25°C. The mean duration of each development stage and total development time did not differe significantly between treatments with and without supplementary food, regardless of species and basic foods. The mortality of the immature stages of the threeEuseius species was generally higher in the absence of supplementary foods than in the presence of these foods, but differences were not significant (P=0.05). Oviposition rates generally were significantly higher in the presence of supplementary foods. The basic food was the most important factor affecting development, survival and oviposition rate; the most favorable food was pollen and the least favorable was citrus red mite. The development and oviposition rates differed somewhat among the threeEuseis, species on the same food or food combination.

Resistance risk assessment: realized heritability of resistance to methrin, abamectin, pyridaben and their mixtures in the spider mite, Tetranychus cinnabarinus

The heritability of resistance has an important bearing on the management of pest resistance, especially for evaluating the sustainability of a chemical on a particular pest population. The susceptibility of pests to insecticides may change depending on the selection pressure of these compounds on populations. Tetranychus cinnabarinus, a very important mite pest of many crops in China, was continuously selected with methrin, abamectin, pyridaben and mixtures of pyridaben and abamectin (pyidaben:abamectin = 7.4:0.1 m/m), and methrin and abamectin (methrin:abamectin = 8.9:0.1 m/m). After 16 generations, the resistance increased to 25.8-, 3.7-, 1.3-, 4.0- and 2.5-fold to methrin, abamectin, pyridaben, pyridaben + abamectin and methrin + abamectin, respectively. The more generations selected, the higher was the resistance level, except in the case of the strain selected with pyridaben. The realized heritabilities of resistance to methrin, abamectin, pyridabe, pyridaben + abamectin and methrin + abamectin were: 0.20, 0.15, 0.03, 0.18 and 0.08, respectively. Higher values of heritability occurred during the second eight generations selected than through the first eight generations except in the case of the strain selected with the mixture pyridaben + abamectin.

COMPARISON OF ENERGY RESERVES AND UTILIZATION IN LIPOSCELIS BOSTRYCHOPHILA POPULATIONS SELECTED FOR TOLERANCE TO CONTROLLED ATMOSPHERE

Abstract  One population of Liposcelis bostrychophila Badonnel (CA selected) was exposed to a controlled atmosphere (CA) (35% CO2+ 1% O2, balance N2) for 30 generations. Another population (control) was reared under natural atmospheric conditions. Reserves of triacylglycerol, polysaccharides and free amino acids were evaluated in adults of the CA selected and the control populations in generations F15 and F30. The utilization rate of triacylglycerol and polysaccharides in the CA exposure were also determined in generation F30. The results indicate that the reserves of triacylglycerol and polysaccharides increased significantly during selection for CA tolerance; the higher the tolerance level, the greater the reserves. A total of 15 free amino acids constituents were detected in both populations. The total amino acid content in the CA selected population was obviously higher than that in the control population. Exposure of this population to a controlled atmosphere was associated with a steady utilization of reserves. In contrast, the unselected population responded to the controlled atmosphere by accelerated utilization of triacylglycerol and polysachharides. Comparison of utilization rates during CA exposure showed that triacylglycerol is the main energy source, and polysaccharides contribute only a small extent to the metabolic energy supply.

ESTMATION OF REALIZED HERITABILITY OF RESISTANCE TO FENPROPATHRIN,ABAMECTIN,PYRIDABEN AND THEIR MIXTURES IN ACARICIDE-SELECTED STRAINS OF TETRANYCHUS CINNABARINUS (BOIDUVAL)

Abstract Threshold trait analysis was used to estimate realized heritability (h2) of resistance to five acaricides (three single acaricide and two mixtures) and resistance risk in Tetranychus cinnabarinus (Boiduval). Tetranychus cinnabarinus collected from the field of Beibei, Chongqing reared more than 60 generations under pesticide free conditions and considered susceptible. Successively selected for about 30 generations, the strain had a 65.55‐, 5.82‐, 1.23‐, 5.20‐ and 1.42‐fold increase in resistance to fenpropathrin, abamectin, pyridaben, pyridaben‐abamectin (pyridaben: abamectin = 7.4:0.1, m/m) and fenpropathrin‐abamectin (fenpropathrin: abamectin = 8.9:0.1, m/m), respectively. The realized heritability of resistance to fenpropathrin, abamectin, pyridaben, pyridaben‐abamectin (pyridaben: abamectin = 7.4:0.1, m/m) and fenpropathrin‐abamectin (fenpropathrin: abamectin = 8.9:0.1, m/m) is 0.2167, 0.0967, 0.0130, 0.0800 and 0.0172, respectively. Under the selected condition, a 10‐fold increase in resistance would be expected 15 generations for fenpropathrin, 34 generations for abamectin, 333 generations for pyridaben, 42 generations for pyridaben‐abamectin (pyridaben: abamectin = 7.4:0.1, m/m) and 200 generations for fenpropathrin‐abametcin (fenpropathrin: abamectin = 8.9:0.1, m/m). The highest resistance risk of the five acaricides in Tetranychus cinnabarinus was fenpropathrin, then abamection, pyridaben‐abamectin (pyridaben: abamectin = 7.4: 0.1, m/m), fenpropathrin‐ abamectin (fenpropathrin: abamectin = 8.9:0.1, m/m) and that to pyridaben was the lowest. The mixture of pyridaben and abamectin is not useful in delaying development of resistance in the pest to the two single acaricide while the mixture of fenpropathrin and abamectin could do it.

Calculation of developmental duration of mites reared in groups compared to those reared in isolation

Abstract Laboratory studies with the phytoseiid mites, Euseius hibisci (Chant) and E. stipulatus (Athias-Henriot) were conducted to calculate and analyze the mean duration of each developmental stagewhen reared in groups. The results show that the calculation method suggested in this paper is suitable for group rearing. The results calculated by this method are basically identical with that of calculation under conditions of rearing isolated individuals, provided that mortality during development is low.