Biological and physiological responses of two Bradysia pests, Bradysia odoriphaga and Bradysia difformis, to Dinotefuran and Lufenuron.

Bradysia odoriphaga and Bradysia difformis are destructive root maggots that cause severe losses to vegetables, flowers and edible fungi. Due to the long-term dependence on single pesticides, Bradysia resistance to insecticides has increased, and field control efficacy has decreased obviously. To screen alternative insecticides, and compare the insecticide susceptibility of these two species, we tested the toxicity of eight insecticides to B. odoriphaga and B. difformis, and measured the sublethal effects of Dinotefuran and Lufenuron on life-history parameters and detoxification enzyme activities. Bioassay results indicated that Dinotefuran and Lufenuron had relatively higher toxicity to B. odoriphaga and B. difformis compared to other neonicotinoid and insect growth regulator insecticides, respectively. Significant adverse impacts caused by sublethal concentrations (LC20) of Dinotefuran and Lufenuron on the life-history parameters of F0 and F1 generations of B. odoriphaga and B. difformis were observed. These included reduced survival, prolonged larval development and reduced adult longevity and fecundity. B. odoriphaga had greater resistance and adaptation to insecticides than B. difformis, and an LC20 concentration of Dinotefuran stimulated the reproduction of B. odoriphaga F1 generation and increased the life table parameters. Detoxifying enzymes (CarE and GSTs) and P450 activities fluctuated after a sublethal concentration (Dinotefuran and Lufenuron) treatment, and at the peak value of enzyme activities, the enhancement of detoxifying enzymes of B. odoriphaga was significantly higher than that of B. difformis. These results indicated that Dinotefuran and Lufenuron should be considered as alternatives to other insecticides for control of root maggots. B. odoriphaga exhibited stronger adaptation to insecticides than B. difformis. These data provide guidance for control of root maggots, and the basic information presented here can help reveal the differences in adaptive mechanisms between B. odoriphaga and B. difformis.

Female Mating Frequency and Reproductive Fitness in the Willow Leaf Beetle (Coleoptera: Chrysomelidae).

Multiple mating in females is common in nature but may involve fitness costs. Adult females and males of the beetle Plagiodera versicolora Laicharting can mate multiple times. We studied the effect of mating frequency and mating pattern (time interval between matings) on female reproductive fitness by measuring fecundity, hatching probability, and female longevity. Fecundity and longevity were similar in single- and double-mated (two matings separated by a 7 d interval) females. However, two and three successive matings and three matings separated by two 7 d interval had a significant negative effect on the lifetime fecundity and longevity of females. Multiple mating had a positive effect on egg hatching, and two matings sufficed to fertilize the full egg load. These results indicate that the two matings separated by a 7 d interval are optimum for reproductive fitness in female P. versicolora. Suboptimal mating frequency (successive mating or an excessive number of matings) exacts a physiological cost that shortens the female life span and reduces fecundity.

Effects of Delayed Mating on Mating Performance and Reproductive Fitness of the Willow Leaf Beetle (Coleoptera: Chrysomelidae) under Laboratory Conditions.

Age at mating is one of the most important factors that affect mating selection, sexual performance, and fecundity. We studied the effects of mating age on the mating performance and reproductive fitness of Plagiodera versicolora Laicharting, a serious pest of poplar and willow, by measuring the time from pairing to successful mating, mating duration, fecundity, hatching probability, and female lifespan. Delayed mating of females and males significantly prolonged the time from pairing to successful mating and the mating duration, but had no effect on the duration of the egg-laying period. Delayed mating of females did not significantly affect fecundity or egg hatching, but significantly prolonged the female lifespan. Although delayed mating of males had a significant negative impact on egg hatching, it had no effect on the lifespan or fecundity of females. These results indicate that delayed mating affects the mating performance of P. versicolora, although it has a limited effect on reproductive fitness. This suggests that delayed mating is unlikely to contribute to the success of mating disruption, when applied to control P. versicolora.

Pathogenicity and in vivo Development of Metarhizium rileyi Against Spodoptera litura (Lepidoptera: Noctuidae) Larvae.

Metarhizium rileyi, a well-known entomopathogenic fungus, could open up new vistas in biological control of insect pests; however, due to its intrinsic shortcomings, such as long pathogenic process, its application is largely limited. To explore which process, the invasion or the following in vivo development, is the main factor responsible for the long pathogenic process, the lethal effect of M. rileyi against Spodoptera litura (Fabricius) was determined by conidial topical application and hyphae body injection, and the host immune response was also monitored. Results showed when larvae were inoculated by conidial topical application, the pathogenicity of M. rileyi varied greatly depending on the larval instar and conidia concentration, and LC50 values ranged from 6.24 × 106 to 6.06 × 109 conidia/ml while LT50 values fluctuated from 4.35 to 9.43 d. However, in vivo study showed when hyphal bodies (Hbs) of M. rileyi were injected into host hemocoel, they would not be recognized by the host's immune system as invaders. There were no significant differences in the hemocytes and phenoloxidase activity between the infected and control larvae at the initial 44 h, indicated that the fungus was able to successfully avoid the attack from the cellular and humoral immune systems, therefore, it could multiply freely in the hemocoel. The in vivo development time of M. rileyi tended to remain constant for 2-3 d regardless of the initial inoculated numbers. Considering no detectable defense response was observed during in vivo development, it can be concluded that host nonself-recognition system does not respond to the hemolymph borne-Hbs.

Does phenoloxidase contributed to the resistance? Selection with butane-fipronil enhanced its activities from diamondback moths.

Using microtitration method, the relationship between Phenoloxidase activity and the resistance of the diamondback moth Plutella xylostella (Linnaeus) to the novel insecticide butane-fipronil was determined in vitro. After selection of the tenth-generation by butane-fipronil, the resistance of the fourth instar larvae was increased 83.80-fold as compared to the susceptible strain. Phenoloxidase activity of the resistant strain (PO(r)) was 1.29-fold higher than the susceptible one (PO(s)). However, the Km and optimum pH values were similar in resistant and susceptible strains, which were 1.11 mM and 6.5, respectively. Both PO(r) and PO(s) have maximum stability at pH values less than 7.0, although PO(s) was less stable at lower pH values than PO(r). In addition, the thermal stabilities of the two phenoloxidase were very similar. It is suggested that PO may play an important role in the increasing resistance of pests to pesticides.

Quantitative structure-activity relationship studies of mushroom tyrosinase inhibitors.

Here, we report our results from quantitative structure-activity relationship studies on tyrosinase inhibitors. Interactions between benzoic acid derivatives and tyrosinase active sites were also studied using a molecular docking method. These studies indicated that one possible mechanism for the interaction between benzoic acid derivatives and the tyrosinase active site is the formation of a hydrogen-bond between the hydroxyl (aOH) and carbonyl oxygen atoms of Tyr98, which stabilized the position of Tyr98 and prevented Tyr98 from participating in the interaction between tyrosinase and ORF378. Tyrosinase, also known as phenoloxidase, is a key enzyme in animals, plants and insects that is responsible for catalyzing the hydroxylation of tyrosine into o-diphenols and the oxidation of o-diphenols into o-quinones. In the present study, the bioactivities of 48 derivatives of benzaldehyde, benzoic acid, and cinnamic acid compounds were used to construct three-dimensional quantitative structure-activity relationship (3D-QSAR) models using comparative molecular field (CoMFA) and comparative molecular similarity indices (CoMSIA) analyses. After superimposition using common substructure-based alignments, robust and predictive 3D-QSAR models were obtained from CoMFA (q2 = 0.855, r2 = 0.978) and CoMSIA (q2 = 0.841, r2 = 0.946), with 6 optimum components. Chemical descriptors, including electronic (Hammett sigma), hydrophobic (pi), and steric (MR) parameters, hydrogen bond acceptor (H-acc), and indicator variable (I), were used to construct a 2D-QSAR model. The results of this QSAR indicated that pi, MR, and H-acc account for 34.9, 31.6, and 26.7% of the calculated biological variance, respectively. The molecular interactions between ligand and target were studied using a flexible docking method (FlexX). The best scored candidates were docked flexibly, and the interaction between the benzoic acid derivatives and the tyrosinase active site was elucidated in detail. We believe that the QSAR models built here provide important information necessary for the design of novel tyrosinase inhibitors.