Effects of juvenile hormone analogue and ecdysteroid on adult eclosion of the fruit fly Bactrocera minax (Diptera: Tephritidae).

The univoltine Bactrocera minax (Enderlein) is a devastating pest of citrus in Nepal, India, Bhutan, and China. To better understand the overwintering pupal diapause, we investigated the juvenile hormone III (JH III) and ecdysteroid 20-hydroxyecdysone (20E) titers across the developmental stages, and the effects of juvenile hormone analog (JHA) and 20E treatments on adult emergence patterns. The results showed that both JH III and 20E levels fluctuated from the late larval stage to the late pupal stage. JHA and 20E treatments at the late larval stage had marginal effect on the adult emergence patterns, with slightly faster adult eclosion and higher eclosion rate. Similarly, JHA treatment at the early pupal stage did not affect the adult emergence. However, 20E treatment at the early pupal stage remarkably shortened the duration of diapause, but lowered the eclosion rate, especially with relatively high dose. These findings demonstrated that 20E treatment at the early pupal stage is a suitable method to hasten the diapause termination of B. minax, which will contribute to the rearing of B. minax in the laboratory as needed for routine experiments.

Infection by Wolbachia bacteria and its influence on the reproduction of the stored-product psocid, Liposcelis tricolor.

Wolbachia are maternally inherited intracellular bacteria that infect a wide range of arthropods and nematodes and are associated with various reproductive abnormalities in their hosts. The infection by Wolbachia of the psocid, Liposcelis tricolor (Psocoptera: Liposcelididae), was investigated using long PCR amplification of the wsp gene that codes for a Wolbachia surface protein. The results showed that L. tricolor was positive for Wolbachia . Phylogenetic analysis showed that the Wolbachia found in L. tricolor was related to the B-group. Wolbachia infection in L. tricolor could be removed through antibiotic treatment. The results of crosses including female(W+) x male(W+), female(W-) x male(W+), female(W+) x male(W-), and female(W-) x male(W-), suggested that the removal of Wolbachia resulted in lower egg production by L. tricolor . The mean embryonic mortality of offspring produced by L. tricolor without Wolbachia was significantly higher than that of control.

Influence of long-term exposure to simulated acid rain on development, reproduction and acaricide susceptibility of the carmine spider mite, Tetranychus cinnabarinus.

Development, reproduction and acaricide susceptibility of Tetranychus cinnabarinus (Boisduvals) (Acari: Tetranychidae) were investigated after long-term (about 40 generations) exposure to various levels of acid rain; pH 2.5, 3.0, 4.0, and 5.6. Deionized water (pH 6.8) served as a control. The mites were reared on eggplant leaves at 28 degrees C, 80%RH and a photoperiod of 14:10 (L:D) in the laboratory. The results showed that the duration of the immature stage was significantly affected by acid rain exposure. The shortest duration (8.90 days) was recorded for populations exposed to pH 5.6 acid rain, while the longest duration (9.37 days) occurred after exposure to pH 2.5 acid rain. Compared with the control population, adult longevity was shortened with an increase in acidity. Similarly, the oviposition duration was also shortened by an increase in acidity. Statistically, female fecundity did not differ significantly between pH 5.6, pH 4.0 and control populations, but did differ significantly between the control population and those exposed to pH 2.5 and pH 3.0 acid rain. This suggested that the mite suffered reproductive defects after long-term exposure to acid rain with higher acidity (pH 2.5 and 3.0). The intrinsic rate of increase among different populations was not significantly affected, but the net reproductive rate of populations exposed to pH 2.5 and 3.0 acid rain was significantly less than pH 4.0, 5.6, and control populations. Bioassay results showed that after long-term exposure to acid rain, susceptibility of the mites to two acaricides, dichlorvos and fenpropathrin, did not change significantly.

[Sublethal effects of fenpropathrin and avermectin on Panonychus citri (Acari: Tereanychidae).] / ç”²æ°°èŠé ¯å’Œé˜¿ç»´èŒç´ å¯¹æŸ‘æ©˜å ¨çˆªèž¨çš„äºšè‡´æ­»æ•ˆåº”.

A leaf disc bioassay was employed to examine the effects of fenpropathrin and avermectin with a sublethal concentration of LC20 on the development and reproduction of F0, F1 and F2 generations by means of life tables. The results showed that after the treatment of fenpropathrin at the sublethal concentration, the number of eggs laid per female significantly increased in F0 generation, the pre-oviposition duration was significantly shortened and the female ratio of offspring significantly increased both in F1 and F2 generations. The intrinsic rate of increase (rm) and finite rate of increase (λ) values all increased, and the generation time (T) and population doubling time (Dt) were shortened in F1 and F2 generations, with significant difference observed between F2 generations and the control. After exposure to avermectin, the number of eggs laid per female significantly decreased in F0 generation, and progeny (F1 and F2) also produced fewer eggs than the control, while the female ratio of offspring increased both in F1 and F2 generations and the pre-oviposition period was significantly shortened. The rm and λ values all increased, and the T and Dt were shortened in F1 and F2 generations. Such effects were more obvious on the F2 generation than the F1 generation. Generally, the effects of fenpropathrin and avermectin with a sublethal concentration of LC20 were not exactly the same on P. citri. Fenpropathrin could promote the development of the contemporary population, while avermectin had certain inhibition on the contemporary population, but both played a certain role in facilitating the development of future populations, which was of significance in developing integrated pest management strategies.

The effect of the insecticide dichlorvos on esterase activity extracted from the psocids, Liposcelis bostrychophila and L. entomophila.

The inhibition kinetics of dichlorvos on carboxylesterase and acetylcholinesterase (AChE) activity extracted from Liposcelis bostrychophila and L. entomophila (Psocoptera: Liposcelididae) were compared. The results showed that L. entomophila had significantly greater specific activity of carboxylesterase than L. bostrychophila (0.045 versus 0.012 micromoles/mg/min). Moreover, the carboxylexterase of L. entomophila showed higher affinity (i.e. lower Km value) to the substrate 1-naphthyl acetate than L. bostrychophila (0.29 versus 0.67 mM). The specific activity and affinity of AChE of the two species were not significantly different. The carboxylesterase of L. bostrychophila was more sensitive to the insecticide dichlorvos than that of L. entomophila. The I50s values of dichlorvos to carboxylesterase for L. bostrychophila and L. entomophila were 1.43 and 3.28 microM, respectively, and to AChE were 324 and 612 nM, respectively. Inhibition kinetics revealed that AChE from L. bostrychophila was 5.8-fold more sensitive to inhibition than AChE from L. entomophila.

[Resistance realized heritability and risk assessment of Panonychus citri to avermectin and fenpropathrin].

On the basis of resistance breeding and selection in laboratory, and by using the threshold trait analysis in quantitative genetics, this paper studied the realized resistance heritability of Panonychus citri (McGregor) collected from Beibei of Chongqing to avermectin and fenpropathrin, and predicted the resistance risk of P. citri to these two acaricides. After 11- and 16-generations of selection with avermectin and fenpropathrin, the resistance of P. citri to the two acaricides increased by 3.8- and 29.9-fold, and the realized resistance heritability was 0.0475 and 0.1544, respectively. Under laboratory condition, to develop a 10-fold increase of resistance required 12-26 generations of selection for avermectin, and 7-16 generations of selection for fenpropathrin under the selection pressure of 50%-90% mortality for each generation. Under field condition, it would require more generations to develop the same resistance level. Comparing with bioacaricide avermectin, pyrethroid fenpropathrin had obviously higher resistance risk to P. citri. The results provided references for the resistance management of P. citri to acaricides.

Population forecasting model of Nilaparvata lugens and Sogatella furcifera (Homoptera: Delphacidae) based on Markov chain theory.

Nilaparvata lugens (Stål) and Sogatella furcifera (Horváth) are the two most important long-distance migratory insect pests that cause great yield losses to rice in China. Accurate long-term population forecast is needed to implement effective management strategies for these two rice pests. In this paper, a transition probability matrix of 5-yr steps of Markov chain theory was constructed based on 31-yr light-trapping data of the two pests from 1977 to 2007 in Jiangkou County, Guizhou, China. The weight of each step for the transition probability matrix was calculated according to its prediction accuracy. Insect occurrence levels in the sixth year were predicted based on the occurrences of the previous 5 yr. Nonparametric Wilcoxon paired sample tests showed that there were no significant differences between the actual and predicted occurrences for both N. lugens and S. furcifera. In addition, the models accurately forecasted field occurrence in 2008 in Jinangkou County for both species. The results showed that the Markov models developed in this study offer an effective method for long-term population forecasting of N. lugens and S. furcifera and thus provide plant protection agencies and organizations with valuable information in implementing appropriate management strategies for these two devastating rice pests in Jiangkou and neighboring areas.

[Relative fitness of Tetranychus cinnabarinus resistant strains at different temperatures].

Based on resistance selection, the life tables of abameetin-resistant (AbR), fenpropathrin-resistant (FeR), and susceptible (S) strains of Tetranychus cinnabarinus at 15 degrees C, 20 degrees C, 25 C, 28 degrees C, 31 degrees C, 34 degrees C, and 36 degrees C were constructed, and the development duration, fertility, and intrinsic rate of increase (r(m)) of the strains were compared, aimed to understand the relative fitness of T. cinnabarinus resistant strains at different temperatures. The results indicated that compared with S strain, AbR and FeR strains had longer development duration at 15 degrees C but lower fertility at 20 degrees C-28 degrees C, and their relative fitness (represented by r(m)) was smaller at 15 degrees C but similar at 20 degrees C - 31 degrees C. For AbR and FeR strains, the fitness cost was moderate at 15 degrees C but lower at 20 degrees C - 31 degrees C. However, at high temperatures ( > or =34 degrees C), FeR strain possessed remarkable fitness cost while AbR strain showed better fitness.