Fen Zhu

Insecticidal activities of garlic substances against adults of grain moth, Sitotroga cerealella (Lepidoptera: Gelechiidae)

Abstract  The angoumois grain moth, Sitotroga cerealella (Olivier), is one of the most serious stored grain pests around the world. In attempts to reduce the losses caused by the moth and to suppress its populations, the fumigant activities, behavioral influence and ovipositional inhibition of garlic (Allium sativum) essential oil and its two major components, diallyl disulfide and diallyl trisulfide, were investigated against the adult grain moth. Their effects on reduction in survival of first instar larvae to adult emergence were also evaluated. Results showed that these three materials (garlic essential oil, diallyl disulfide and diallyl trisulfide) had significant fumigant activity with 50% lethal concentration values at 1.33, 0.99, and 1.02 μL/L air space, respectively; meanwhile, the three materials possessed high behavioral deterrent activities against adults in the Y‐tube olfactometer. When applied to rice grains, these materials reduced adult longevity and inhibited oviposition, with ovipositional inhibition above 70% at a concentration of 1.5 μL/25 g in either no‐choice or two‐choice tests. In short, the study showed that both diallyl disulfide and diallyl trisulfide, like garlic essential oil, acted as fumigants, produced behavioral deterrence and inhibited oviposition against angoumois grain moth. Our work here indicates that diallyl disulfide and diallyl trisulfide may serve as potential alternatives for grain protectants since both of them can be prepared easily from readily available chemicals.

Effects of UV‐A exposures on longevity and reproduction in Helicoverpa armigera, and on the development of its F1 generation

Abstract  Helicoverpa armigera adults display a conspicuous positive phototactic behavior to light stimuli, and are especially sensitive to ultraviolet (UV) light. The effects of UV‐A (longwave) exposures on adult longevity and reproduction in H. armigera were investigated, as well as the development of the F1 generation. Paired adults were exposed to UV‐A for various time periods (0, 1, 5 and 9 h/day), until the end of adult life. The results showed that adult longevity decreased with increasing exposure time for both sexes, and a significant decrease was observed after exposure for 5 and 9 h/day. Fecundity increased when adults were exposed for 1 and 5 h/day, and a significant difference was observed in the 5 h/day group. Oviposition rates of females in all treatments were significantly higher than in the control. Exposure to UV‐A for longer periods (5 and 9 h/day) caused a decline in cumulative survival of F1 immature stages, but no significant differences were found in egg hatch, pupation and eclosion. The developmental periods of F1 larvae were significantly prolonged after exposure to UV‐A for 5 and 9 h/day. UV‐A radiation had no significant effects on F1 pupal period.

Juvenile hormone facilitates the antagonism between adult reproduction and diapause through the methoprene-tolerant gene in the female Colaphellus bowringi.

In insects, the process whereby juvenile hormone (JH) regulates short-day (SD)-induced reproductive diapause has been previously investigated. However, we still do not understand the mechanism by which JH regulates long-day (LD)-induced reproductive diapause. In this study, we use a cabbage beetle, Colaphellus bowringi, which is a serious pest of cruciferous vegetables in Asia capable of entering reproductive diapause under LD conditions, as a model to test whether JH regulates female reproductive diapause similar to the mechanism of SD-induced diapause. Our results showed that the JH analog (JHA) methoprene significantly induced ovarian development but inhibited lipid accumulation of diapause-destined adults. Meanwhile, the transcripts of the vitellogenin (Vg) genes were upregulated, whereas the expression of the fat synthesis and stress tolerance genes were downregulated. RNA interference of the JH candidate receptor gene methoprene-tolerant (Met) blocked JH-induced ovarian development and Vg transcription, suggesting a positive regulatory function for JH-Met signaling in reproduction. Furthermore, under reproduction-inducing conditions, Met depletion promoted a diapause-like phenotype, including arrested ovarian development and increased lipid storage, and stimulated the expression of diapause-related genes involved in lipid synthesis and stress tolerance, suggesting JH-Met signaling plays an important role in the inhibition of diapause. Accordingly, our data indicate that JH acts through Met to facilitate development of the reproductive system by upregulating Vg expression while inhibiting diapause by suppressing lipid synthesis and stress tolerance in the cabbage beetle. Combined with previous studies in SD-induced reproductive diapause, we conclude that JH may regulate female reproductive diapause using a conserved Met-dependent pathway, regardless of the length of the photoperiod inducing diapause in insects.

Eicosanoids mediate nodulation reactions to a mollicute bacterium in larvae of the blowfly, Chrysomya megacephala.

Nodulation is the temporally and quantitatively most important cellular defense response to bacterial, fungal and some viral infections in insects. We tested the hypothesis that prostaglandins and other eicosanoids are responsible for mediating nodulation reactions to bacterial infection in larvae of the blowfly Chrysomya megacephala. Third-instar larvae treated with Ureaplasma urealyticum formed nodules in a challenge dose-dependent manner. Nodulation was evoked shortly after injection and reached a maximum of approximately 25 nodules/larva within 8h. Larvae treated with the glucocorticoid, dexamethasone and the cyclooxygenase inhibitors, indomethacin and piroxicam were impaired in their ability to form nodules following U. urealyticum infection. The number of nodules decreased with increasing doses of piroxicam. Contrarily, treating larvae with the lipooxygenase inhibitor, esculetin, and the dual cyclooxygenase/lipooxygenase inhibitor, phenidone did not influence nodulation reactions to infection. Supplying dexamethasone-treated larvae with the eicosanoid precursor, arachidonic acid, reversed the inhibitory effect of dexamethasone on nodulation. We infer from these results that eicosanoids mediate nodulation reactions to infection of a bacterial species that lacks cell walls in larvae of the blowfly, C. megacephala.

Sensory genes identification with head transcriptome of the migratory armyworm, Mythimna separata

Sensory system plays important roles in a wide array of insect’s behavior and physiological events, including the host landing and locating, feeding, flying, sex responding, mating and oviposition which happen independently and in sequence. The armyworm Mythimna separata (Lepidoptera: Noctuidae) of migratory insect is destructive for alimentarn crop and economic crop throughout the world. Here we present the high throughput sequencing of the head transcriptome and identify members of the major sensory genes which are crucial for armyworm’s success worldwide, including 8 opsins, 22 chemosensory proteins, 50 odorant binding proteins, 60 odorant receptors, 8 gustatory receptors, 24 ionotropic receptors, and 2 sensory neuron membrane proteins. It is worth noting that a duplication of the LW opsin gene exists in this insect. Several genes were clustered with functionally validated genes, such as Co-receptors of OR and IR, PBPs, PRs, CO2 GRs, bitter GRs and sweet GRs, were also identified. The transcriptome gene library provided the basis for further studies that elucidate the fundamental molecular mechanism of biology and control in M. separata. Our research exhibits the first comprehensive catalogue of the sensory genes fundamental for success and distribution in M. separata, which are potential novel targets for pest control strategies.

Influences of chromium and cadmium on the development of black soldier fly larvae

The black soldier fly Hermetia illucens is a good candidate for waste management. The harvested insects are rich in protein and have the potential to be used in animal feed. However, people are wary about heavy metals in waste. Therefore, it is necessary to understand how the uptake of heavy metals could affect H. illucens and where and to what extent metals are accumulated by the black soldier fly. Based on these considerations, developmental parameters were investigated in the different life stages of H. illucens fed an increasing concentration gradient of cadmium (Cd) and chromium (Cr); additionally, Cd and Cr distribution in the body parts of H. illucens at the different life stages was monitored. We found that Cd and Cr have no effects on larvae survival and eclosion rate, but they do have effects on larvae duration and pupation rate. Both Cd and Cr were transferred into larvae, prepupae, and pupae. While the concentrations of Cd in larvae and prepupae were much higher than that in their diets, the opposite case was observed with Cr. The concentrations of Cd and Cr in H. illucens decreased in later development stages. In individual larva and prepupa, Cd and Cr were mainly included in the body and not in the integument. In the pupa, the puparium contained higher Cd and Cr concentrations than the pupa body. The distribution of Cd and Cr in the different life stages and body parts may present a potential strategy for how H. illucens tolerate and remove heavy metal stress.

Fatty acid synthase 2 contributes to diapause preparation in a beetle by regulating lipid accumulation and stress tolerance genes expression

Diapause, also known as dormancy, is a state of arrested development that allows insects to survive unfavorable environmental conditions. Diapause-destined insects store large amounts of fat when preparing for diapause. However, the extent to which these accumulated fat reserves influence diapause remains unclear. To address this question, we investigated the function of fatty acid synthase (FAS), which plays a central role in lipid synthesis, in stress tolerance, the duration of diapause preparation, and whether insects enter diapause or not. In diapause-destined adult female cabbage beetles, Colaphellus bowringi, FAS2 was more highly expressed than FAS1 at the peak stage of diapause preparation. FAS2 knockdown suppressed lipid accumulation and subsequently affected stress tolerance genes expression and water content. However, silencing FAS2 had no significant effects on the duration of diapause preparation or the incidence of diapause. FAS2 transcription was suppressed by juvenile hormone (JH) and the JH receptor methoprene-tolerant (Met). These results suggest that the absence of JH-Met induces FAS2 expression, thereby promoting lipid storage in diapause-destined female beetles. These results demonstrate that fat reserves regulate stress tolerance genes expression and water content, but have no significant effect on the duration of diapause preparation or the incidence of diapause.

Speciation of heavy metals and bacteria in cow dung after vermicomposting by the earthworm, Eisenia fetida

This work was conducted to evaluate the total concentration and speciation of heavy metals (Cd, Pb and Cr) in vermicompost product (EFCD) by Eisenia fetida (EF) with cow dung (FCD). Meanwhile, the bacterial community and diversity of the three were compared by high-throughput sequencing. Results showed that heavy metal concentrations were declined significantly in EFCD. Sequential extraction indicated that the exchangeable fraction of Cd and Pb decreased markedly and the residual fractions increased in EFCD. Though the exchangeable fraction of Cr increased, the total concentration reduced greatly. Furthermore, the speciation of Cd, Pb and Cr bioaccumulated in EF were different. Besides, the bacterial diversity was highest in EFCD, and twelve genera with species having heavy metal resistance/tolerance were found from the genus of different abundance of the three. Vermicomposting effectively reduced the total concentration and toxicity for heavy metals, and the bacterial composition and diversity were changed greatly during vermicomposting.

Antiviral and antitumor activities of the protein fractions from the larvae of the housefly, Musca domestica

In this study, we present the extraction and purification of protein fractions from the larvae of the housefly, Musca domestica . The bioactivities of the protein fractions were indicated by pseudorabies virus (PRV) and human lung cancer cell line A 549. The crude protein fractions had no toxicity to chick embryo fibroblast-like (CEF) cells but effective to PRV at the concentration of 100 μg/ml (dilute ratio of 1:100). Furthermore, they exhibited better antiviral effect when added to CEF cells 1 h after PRV infection than 1 h prior to PRV infection and could directly deactivate and hinder the adsorption or penetration of PRV into CEF cells. In addition, two major peaks (A1 and A2) were found by DEAE-52 from the crude protein fractions, but only the purified protein fraction A2 showed antiviral and antitumor activities. The results suggest that the protein fractions extracted and purified from the larvae of the housefly have antiviral and antitumor activities and can be further studied. Key words: Musca domestica , antiviral, antitumor, protein.

Latitudinal pattern in body size in a cockroach, Eupolyphaga sinensis

Body size of insects with flexible life cycles is expected to conform to the saw‐tooth model, a model in which the relationship between size and developmental time depends on length of the growing season. In species with high variability in terms of voltinism, however, more complex patterns can be expected. Few empirical studies have demonstrated the existence of such relationships, or whether climatic factors contribute to these relationships. In this study, we investigated the geographic variation in body size of the Chinese cockroach, Eupolyphaga sinensis Walker (Blattaria: Polyphagidae), which has a variable life cycle length. The sizes of adults – collected from 14 localities ranging from temperate to subtropical zones in China – were measured, using body length, body width, and pronotum width as parameters. The relationship between size, latitude, and climate factors (encompassing 10 variables) was then investigated. We found that the body size of E. sinensis varied considerably with latitude: cockroaches were larger at low and high latitudes, but smaller at intermediate latitudes. Thus, the relationship between climate and body size conformed to a saw‐tooth pattern. Results indicate that two factors were significantly associated with body size clines: season length and variability in life cycle length. Our results also demonstrated that climatic factors contribute to latitudinal clines in body size, which has important ecological and evolutionary implications. It can be expected that global climate change may alter latitudinal clines in body size of E. sinensis.