Youjun Zhang

Further Spread of and Domination by Bemisia tabaci (Hemiptera: Aleyrodidae) Biotype Q on Field Crops in China

ABSTRACT The sweetpotato whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), causes severe crop losses to many crops. The worst of these losses are often associated with the invasion and establishment of biotypes B and Q of this pest. Previous research in 2007 showed that biotype Q occurred with other biotypes in most field populations in China. To determine the current status of the biotype composition in the field, an extensive survey covering mainly eastern parts of China was conducted in 2009. Using polymerase chain reaction primers specific for the mitochondrial cytochrome oxidase I of biotypes B and Q and gene sequencing, we determined the biotypes composition in 61 whitefly populations and their distribution across 19 provinces in China. Our research revealed that only biotypes B and Q have been found in the field in 2009 in China. Among them, biotype Q was dominant in 44 locations (100.0%) and biotype B was dominant in 17 locations (100.0%). The current survey indicates that biotype Q has rapidly displaced biotype B in most locations in China.

Effects of Temperature on the Age-Stage, Two-Sex Life Table of Bradysia odoriphaga (Diptera: Sciaridae)

ABSTRACT The demographics of Bradysia odoriphaga were examined with an age-stage, two-sex life table that was developed at 15, 20, 25, and 30°C under controlled conditions. The intrinsic rate of increase and mean generation time were 0.0574 and 48.08 d at 15°C, 0.1175 and 30.09 d at 20°C, 0.1369 and 26.31 d at 25°C, and 0.1247 and 26.55 d at 30°C, respectively. The gross reproductive rate (GRR), the net reproductive rate (R0), and the pre-adult survivorship (la) were consistent with the relationship R0<la×GRR<GRR. Development was slower at 15°C than at the other temperatures. The mean duration of the total pre-adult stages was 38.01, 27.62, 23.74, and 24.10 d at 15, 20, 25, and 30°C, respectively. The highest values for the intrinsic rate of increase, finite rate of increase, and fecundity (0.1369 d-1, 1.147 d-1, and 50.53 eggs, respectively) and the shortest mean generation time were at 25°C. Still, B. odoriphaga was able to develop, survive, and reproduce across the entire temperature range (15–30°C). This study provides insight into the temperature-dependent phenology of B. odoriphaga and will contribute to the modeling of its population dynamics and to its management in the field.

Tomato Spotted Wilt Virus Infection Reduces the Fitness of a Nonvector Herbivore on Pepper

ABSTRACT Plant pathogens and insect herbivores often share hosts under natural conditions. Hence, pathogen-induced changes in a host plant can affect the herbivore and vice versa. Even though plant viruses are ubiquitous in the field, little is known about plant-mediated interactions between viruses and nonvector herbivores. Here we tested whether the performance of the sweet potato whitefly, Bemisia tabaci (Gennadius) biotype Q, was altered when raised on pepper infected with Tomato spotted wilt virus (TSWV). TSWV infection reduced B. tabaci fecundity and longevity and increased B. tabaci developmental time but did not affect the insects survival or female body lengths. Our results demonstrate that TSWV infection can decrease the fitness of B. tabaci biotype Q on pepper plants.

Effects of sublethal concentrations of bifenthrin on the two-spotted spider mite, Tetranychus urticae (Acari: Tetranychidae)

Abstract Bifenthrin is a broad-spectrum insecticide and acaricide that is widely used in China. We evaluated the effects of sublethal concentrations (LC10 and LC25) of bifenthrin on the eggs and adult females of the two-spotted spider mite, Tetranychus urticae, in the laboratory at 26±1°C, 80% RH, and a 16 h: 8 h (L: D) photoperiod. The sublethal doses of bifenthrin decreased the intrinsic and finite rate of increase, net reproductive rate, survival rate, and reproductive value. The sublethal doses also increased the mean generation time, total pre-ovipositional period, and duration of the larval and nymphal stages. The intrinsic rate of increase dropped from 0.252/day in the control to 0.222 and 0.208/day in response to LC10 and LC25 treatments, respectively. Following LC10 and LC25 treatments, the net reproductive rate dropped from 60.65 offspring/individual in the control to 45.19 and 40.81, respectively. These laboratory results indicate that sublethal concentrations of bifenthrin may decrease the developmental rate of T. urticae, are unlikely to result in the resurgence of T. urtciae populations, and might therefore be useful in the integrated management of this pest.

Three-Way Interactions Between the Tomato Plant, Tomato Yellow Leaf Curl Virus, and Bemisia tabaci (Hemiptera: Aleyrodidae) Facilitate Virus Spread

ABSTRACT Plant defense responses can greatly affect plant viruses and their herbivore vectors. The current article reports on plant defense responses involving jasmonic acid (JA), salicylic acid (SA), and proteinase inhibitor (PI) in the three-way interaction between tomato plants, tomato yellow leaf curl virus, and the whitefly Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae). The results showed that feeding by viruliferous B. tabaci increases the longevity and fecundity of nonviruliferous B. tabaci that subsequently feed on the same plant. Feeding by nonviruliferous B. tabaci alone suppressed plant defense responses involving JA and PI but induced responses involving SA. Feeding by viruliferous B. tabaci increased the suppression of plant defenses involving JA and PI but did not increase responses involving SA. These results indicate that the interactive effects of tomato yellow leaf curl virus and B. tabaci on plants increase vector fitness and virus transmission by reducing plant defense.

Resistance Monitoring for Eight Insecticides on the Sweetpotato Whitefly (Hemiptera: Aleyrodidae) in China

Abstract The sweetpotato whitefly, Bemisia tabaci (Gennadius), is an important pest of many crops worldwide. Because control of B. tabaci still depends on the application of insecticides in China, monitoring the insecticide resistance of B. tabaci populations is essential for achieving control and for managing resistance. In this study, field populations of B. tabaci on vegetables were collected in three regions of China in 2011, 2012, and 2013. The resistance of these populations (all of which were determined to belong to biotype Q) to eight insecticides (abamectin, spinetoram, imidacloprid, thiamethoxam, acetamiprid, nitenpyram, chlorpyrifos, and bifenthrin) was assessed by the leaf-dip method. No resistance to abamectin and spinetoram was detected. All of the B. tabaci populations exhibited resistance to neonicotinoid insecticides; the resistance was 3.6- to 125.0-fold greater than that of a susceptible reference strain. The traditional insecticides chlorpyrifos and bifenthrin had very low toxicity. Bemisia tabaci specimens in some regions exhibited annual differences in resistance to some of the insecticides. The data presented will be helpful for making decisions on the proper insecticide usage in the field.

Effects of Heat Shock on the Bradysia odoriphaga (Diptera: Sciaridae)

Abstract Bradysia odoriphaga is frequently subjected to heat shock during the summer in China. Although the effects of heat shock on insect ecology and physiology have been widely explored, the effects of heat shock on the life history parameters of Bradysia odoriphaga are largely unknown. In the present study, we investigated the effects of heat shock on B. odoriphaga survival and reproduction as well as on offspring development and sex ratio. We exposed adult B. odoriphaga to 31, 33, 35, or 37 °C for different durations (from 0 to 120 min). The results showed that the survival of both sexes declined with the increase in temperature and exposure time, especially at 33, 35, and 37 °C. Longevity was markedly greater for males than females across all treatments. Fecundity generally declined as temperature and exposure time increased, and no eggs hatched when females were exposed to 37 °C for >75 min. The development of offspring larvae was significantly delayed when the parent female and male had been exposed to ≥31 °C for ≥30 min. In addition, the sex ratio of F1 progeny derived from heat-shocked parental adults was increasingly skewed to female as exposure time and temperature treatment increased. Overall, the results indicate that heat shock negatively influences B. odoriphaga.

Management of diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae) by mating disruption

Abstract  Field trials were conducted in China in 2008 and 2009 to evaluate the efficacy of mating disruption (MD) on diamondback moth, Plutella xylostella, in cabbage, Brassica oleracea var. capitata. Effectiveness was positively correlated with the MD dispenser density in the field. A density of 167 MD dispensers per ha produced an average population decrease of about 50% compared to the conventional‐practice field. Significant fewer males were captured in pheromone‐treated and conventional‐practice fields than in the blank control field, but the difference was not significant between the pheromone‐treated and conventional‐practice fields. In addition, fewer eggs and larvae were observed in pheromone‐treated fields. Our results suggest mating disruption coupled with minimal insecticidal supplements is a promising solution for resistance management and control of diamondback moth infestation.

Cloning and characterization of a GABA receptor from Plutella xylostella (Lepidoptera: Plutellidae).

Abstract A full-length cDNA, with an open reading frame (ORF) of 1,449 bp, encoding a subunit of the γ-aminobutyric acid (GABA)-activated chloride channel was isolated from Plutella xylostella (L.) (Lepidoptera: Plutellidae) (GenBank accession no. EF156251). The subunit gene encoded a 483-amino acid polypeptide that showed 84% sequence identity with DmRdl subunit (U02042) (Drosophila melanogaster resistant to dieldrin). When expressed in Xenopus laevis oocytes, the subunit assembled as a functional homomeric complex activated by GABA and abamectin in a dose-dependent manner. The EC50 value of GABA was 0.49 mM (0.41–0.58) (n = 5). However, the responses to abamectin were very robust, with an EC50 of 4.85 μM (4.02–5.89) (n = 6), indicating that abamectin was >100-fold more potent in activating chloride currents than GABA. The results suggest that this subunit is vital to the formation of a functional channel and contains the binding site of abamectin.

A bioassay for evaluation of the resistance of Tetranychus urticae(Acari: Tetranychidae) to selected acaricides

Abstract Chemical control of the two-spotted spider mite, Tetranychus urticae Koch, depends on early monitoring of acaricide resistance. Because few bioassay methods currently used to monitor acaricide resistance in T. urticaeare easy to use or are able to detect multiple kinds of toxicity, a new bioassay is needed. A vial-leaf dipping (VLD) bioassay was developed using a 2-ml microcentrifuge tube coated with acaricide and a 1-cm-diameter leaf disc coated with acaricide. When T. truncatus females were exposed to five acaricides, LC50 values indicated that the VLD bioassay was substantially more sensitive than the conventional slide-dip (SD) bioassay. The VLD bioassay was used to obtain baseline sensitivity to 10 acaricides for adult females of T. urticae. The VLD bioassay was also used to assess the resistance of six field populations of T. urticae to 10 acaricides; the results showed that the adult females of T. urticae populations had different resistance to each acaricide. All the six populations were highly resistant to abamectin and exhibited sensitivity to medium resistance for the other acaricides. It is concluded that the VLD bioassay method is sensitive and easy to use; field chemical trials for control of T. urticae in China could be conducted by the acaricides rotation except abamectin.