Yurong He

Differential fluctuation in virulence and VOC profiles among different cultures of entomopathogenic fungi

Insect-passaged cultures of entomopathogenic fungi grown on potato dextrose agar media have been shown to have altered virulence and profiles of volatile compounds. The present study demonstrated the pathogenic status of FS(0) (in vitro) and FS(1) and FS(2) (insect-passaged cultures grown on PDA) cultures of Metarhizium anisopliae (strains 406 and 02049) and Beauveria bassiana by a non-choice assay, in which filter paper was inoculated with fungal spores at a concentration of 1 x 10(7) spores/ml. The FS(1) and FS(2) cultures of M. anisopliae strain 02049 and B. bassiana produced conidia with high virulence, and the volatile profiles of these conidia comprised relatively lower percentages of branched-alkanes than conidia from the FS(0) cultures. In contrast, the conidia from an FS(0) culture of M. anisopliae strain 406 had somewhat elevated virulence levels, but their volatile profile had <2% branched-alkanes. The FS(1) and FS(2) cultures of M. anisopliae strain 406 did not gain virulence, and these cultures showed a decline in virulence along with major alteration of their volatile profiles. Their volatile profiles mainly comprised branched-alkanes. The volatile profiles of the FS(1) and FS(2) cultures lacked n-tetradecane, which was an important component of all the virulent cultures. Four compounds, 2-phenylpropenal, 2,5,5-trimethyl-1-hexene, n-tetradecane and 2,6-dimethylheptadecane, were detected only from the virulent cultures, suggesting that low LT(50) values were probably due to the production of these compounds. This is the first report to characterize volatiles from FS(0), FS(1) and FS(2) cultures of entomopathogenic fungi; its utility in different aspects opens an interesting area for further investigations.

Fungus Exposed Solenopsis invicta Ants Benefit from Grooming

We investigated aspects of resistance to entomopathogenic fungi in the social insect Solenopsis invicta, the red imported fire ant (RIFA). RIFA reared individually were significantly more susceptible to the entomopathogenic fungi Metarhizium anisopliae var. anisopliae M09 than reared in groups. Fungus exposed ants performed more self-grooming behavior when isolated as individuals and received more allo-grooming when accompanied with four healthy nestmates. Using fluorescence microscopy, we counted the number of fluorescein isothiocyanate (FITC)-labeled conidia on the cuticle of fungus exposed ants reared individually or as groups. The number of conidia on the surface of grouped ants decreased more rapidly than on isolated individuals. Allo-grooming behavior appears to be important in removing the conidia on the surface of RIFA. Individuals help fungus exposed ants by performing intensive grooming behaviors, which either risk infecting themselves or get them immunized as social immunity. We show evidence that contacting with fungus exposed ants would decrease susceptibility of nestmates to the fungus. All these results indicate that RIFA benefit from grooming behavior to fight against the fungal pathogens. Future advances in biological control of RIFA with entomopathogenic fungi are also discussed.

Effects of insecticides on sex pheromone communication and mating behavior in Trichogramma chilonis

Trichogramma chilonis Ishii is an important natural enemy of several lepidopterous pests on crops. The effects of two common insecticides on sex pheromone communication and mating behavior in T. chilonis were evaluated in the laboratory. When only males were exposed to insecticide, beta-cypermethrin LC20 exposure induced significant decrease in sex pheromone perception by males and significant increase in males’ courtship and copulation frequency; beta-cypermethrin LC1 exposure caused significant decrease in males’ courtship and copulation frequency. Males exposed to spinosad LC20 exhibited significantly slower initiated courtship and significantly shorter total copulation duration, and the males exposed to spinosad LC1 exhibited significantly increased sex pheromone perception, compared with control. When both males and females were exposed to insecticide, significantly more courtship and copulation were conducted by treated pairs that survived insecticide (beta-cypermethrin or spinosad) LC20 than control pairs. Our study suggests that even the LC1 and LC20 of tested insecticides could affect the sex pheromone communication and mating behavior in T. chilonis.

Effects of Two Conventional Insecticides on Male-Specific Sex Pheromone Discrimination and Mate Choice in Trichogramma chilonis (Hymenoptera: Trichogrammatidae)

Abstract Trichogramma chilonis Ishii is an important natural enemy of many lepidopterous pests on vegetables and field crops. The effects of two conventional insecticides on male-specific sex pheromone discrimination and mate choice in T. chilonis was evaluated in the laboratory. Beta-cypermethrin LC20 exposure induced decreases in male conspecific sex pheromone discrimination and mating rate in T. chilonis, and these decreases were not due to the lower locomotor activity of the surviving T. chilonis males. Spinosad LC20 exposure caused a significant decrease in male locomotor activity of T. chilonis, but did not affect male-specific sex pheromone discrimination (conspecific sex pheromone discrimination or virgin sex pheromone discrimination) or mating rate. However, there was no significant difference in specific sex pheromone discrimination, mate choice, and locomotor activity between control males and males exposed to the low concentration (LC1) of insecticide (beta-cypermethrin or spinosad). In conclusion, beta-cypermethrin LC20 exposure was harmful to male-specific sex pheromone discrimination and mate choice in T. chilonis.

Effects of three different cultivars of cruciferous plants on the age-stage, two-sex life table traits of Plutella xylostella (L.) (Lepidoptera: Plutellidae): Two-sex life table of P. xylostella

Plutella xylostella is an important pest of cruciferous crops worldwide. However, information regarding the age‐stage, two‐sex life parameters of P. xylostella, which is vital for designing more effective control methods, is currently lacking. The present study reports age‐stage, two‐sex life table parameters for P. xylostella on napa cabbage (Brassica oleracea var. napa), white cabbage (B. oleracea var. capitata), and cauliflower (B. oleracea var. botrytis) under laboratory conditions at 25 ± 2°C, 50–60% relative humidity, and a 16‐h light : 8‐h dark photoperiod. The time for development from an egg to a male or female adult P. xylostella on white cabbage (mean [± SE] 41.15 ± 0.54 and 39.50 ± 0.54 days, respectively) was significantly longer than that on cauliflower and napa cabbage. Furthermore, P. xylostella fecundity on cauliflower (261.90 ± 4.53 eggs female) was significantly highest than on napa cabbage and white cabbage. Intrinsic rate of increase (r) and finite rate of increase (λ) were highest on cauliflower 0.182 day−1 and 1.199 day−1 respectively as comparison to napa cabbage and white cabbage. The highest gross reproductive rate (GRR) and net reproductive rates (R0) of P. xylostella 65.87 and 52.58 respectively on cauliflower then those of other hosts. The findings of the present study indicate that cauliflower is the most suitable cultivar (host) for the development of P. xylostella. Based on these findings, crops like cauliflower can be used as trap crops when napa cabbage and white cabbage are the main crops.

Metarhizium anisopliae infection alters feeding and trophallactic behavior in the ant Solenopsis invicta

In social insects, social behavior may be changed in a way that preventing the spread of pathogens. We infected workers of the ant Solenopsis invicta with an entomopathogenic fungus Metarhizium anisopliae and then videotaped and/or measured worker feeding and trophallactic behavior. Results showed that fungal infected S. invicta enhanced their preference for bitter alkaloid chemical quinine on 3days after inoculation, which might be self-medication of S. invicta by ingesting more alkaloid substances in response to pathogenic infection. Furthermore, infected ants devoted more time to trophallactic behavior with their nestmates on 3days post inoculation, in return receiving more food. Increased interactions between exposed ants and their naive nestmates suggest the existence of social immunity in S. invicta. Overall, our study indicates that S. invicta may use behavioral defenses such as self-medication and social immunity in response to a M. anisopliae infection.

Effects of Insecticides on Oviposition and Host Discrimination Behavior in Trichogramma chilonis (Hymenoptera: Trichogrammatidae)

Abstract Trichogramma chilonis Ishii is an important natural enemy of many lepidopterous pests on various crops. Effects of two conventional insecticides on oviposition and host discrimination behavior in T. chilonis were evaluated in the laboratory through video tracking. During the oviposition period, when the number of host eggs was limited (only one host egg), females exposed to beta-cypermethrin LC1 or LC20 exhibited significantly higher feeding and re-drilling rate and significantly longer post-oviposition duration than control females. Spinosad LC20 treatment not only decreased the wasp oviposition rate but also significantly extended the oviposition duration. When the number of host eggs was six, similarly, females exposed to spinosad LC20 exhibited a significantly lower oviposition rate (79.2%) than control ones (100%). In the host discrimination experiment, females exposed to LC20 of both tested insecticides (beta-cypermethrin and spinosad) spent significantly more time on the extra-patch area. The females that survived spinosad LC20 could not discriminate between unparasitized and parasitized host eggs. Our study suggests that even the LC1 and LC20 of the tested insecticides had negative effects on the oviposition and host discrimination behavior of T. chilonis. Thus, the use of these two insecticides should be carefully evaluated.

Biology, taxonomy, and IPM strategies of Bactrocera tau Walker and complex species (Diptera; Tephritidae) in Asia: a comprehensive review

Bactrocera flies are the serious pests of fruit, vegetables, and nuts over the world. Bactrocera tau Walker is an economically important pest of agricultural crops. In Asia, approximately 30–40% losses of agricultural products are caused by B. tau infestation every year. In Asia, the B. tau contains a complex of sibling species that called the tau complex. However, the basic studies of B. tau and complex species are very important for integrated management. A comprehensive review of the B. tau and complex species has not been provided elsewhere. So, considering the importance of B. tau and complex species, this study provides the published information on ecology, nomenclature, identification tools, geographical distribution, potential invasion, and IPM tactics of B. tau and complex species, which would be more informative for publication facilitating related to integrated pest management (IPM) strategies of B. tau and complex species. In IPM of B. tau and complex species, the phytochemical and biological controls have not been applied successfully in Asia; there is an urgent need to study and applications of these two mentioned control techniques against the B. tau and complex species in Asia.

Pathogenicity of individual isolates of entomopathogenic fungi affects feeding preference of red imported fire ants Solenopsis invicta

Seven isolates of entomopathogenic fungi, Isaria fumosorosea (IFCF-H and IFCF-L), Beauveria bassiana s.l. (Bb02 and Bb04) and Metarhizium anisopliae s.l. (Ma01, SM076 and M09), were selected for their pathogenicity against Solenopsis invicta as well as feeding preference of S. invicta. When ants were treated with a conidial suspension at a concentration of 1 × 108 conidia/ml, the median lethal times (LT50) of IFCF-H, IFCF-L, Bb02, Bb04, Ma01, SM076 and M09 were 3.4, 162.6, 7.3, 2.8, 3.8, 7.3 and 2.7 days, respectively, after 10 days. The median lethal concentrations (LC50) on the 10th day after inoculation were 1.20 × 107, 1.56 × 1010, 4.23 × 107, 3.04 × 106, 6.13 × 106, 2.90 × 107 and 9.90 × 105 conidia/ml, respectively. Furthermore, S. invicta consumed significantly less solution flavoured with Bb04 conidia than the control, which was demonstrated by the lowest preference index (PREF = 0.09). S. invicta did not have a significant feeding preference for other fungal isolates. The pathogenicity (LC50) of fungal isolates was not significantly correlated (R2 = 0.013) with the PREF of S. invicta. However, in the paired-choice experiments between different virulent isolates belonging to the same genera, S. invicta tended to select the solution flavoured with conidia of relatively lower pathogenic isolates such as IFCF-L, Bb02 and SM076. We conclude that the pathogenicity of congeneric fungi may affect the feeding preference of S. invicta. Red imported fire ants might adjust their feeding response to entomopathogenic fungi based on the profile of microbial volatile organic compounds.

Using Two-Sex Life Table Traits to Assess the Fruit Preference and Fitness of Bactrocera dorsalis (Diptera: Tephritidae)

Bactrocera flies are economic pests of agricultural crops all over the world. Among Bactrocera flies, oriental fruit fly is an economically important pest of fruit crops in the world. Basic studies of Bactrocera flies are very important and helpful to the development of integrated management strategies. However, basic studies regarding behavior and age-stage, two-sex life table traits for this pest, which are vital for designing effective control methods, are currently lacking. Considering the importance of B. dorsalis, this study aimed to evaluate the fruit preference and age-stage, two-sex life table traits of B. dorsalis on guava (Psidium guajava), papaya (Carica papaya), and banana (Musa acuminata) fruits in the laboratory. In choice and no-choice tests, the number of visits and oviposition punctures made by female B. dorsalis flies were significantly higher on guava than those on papaya and banana. The life cycle from eggs to male (146.95 ± 3.43 d) and female (164.94 ± 3.85 d) adults was significantly longer on papaya than those on banana and guava. Bactrocera dorsalis females produced significantly more eggs when fed on guava (623.30 eggs female-1) than on papaya (527.80 eggs female-1) or banana (399.60 eggs female-1). Guava was the more suitable fruit for B. dorsalis, and could be used as a bait fruit to manage the B. dorsalis during the fruiting season of papaya and banana.