Meloidogyne graminicola Population Structure in China Suggests a South-to-North Expansion.

The distribution range of root-knot nematode Meloidogyne graminicola is rapidly expanding, posing a severe threat to rice production. In this study, the sequences of cytochrome oxidase subunit I (COI) genes of rice M. graminicola populations from all reported provinces in China were amplified and sequenced by PCR. The distribution pattern and phylogenetic tree showed that all 54 M. graminicola populations in China have distinct geographical distribution characteristics; specifically, cluster 1 (southern China), cluster 2 (central south and southwest China), and cluster 3 (central and eastern China). The high haplotype diversity (Hd = 0.646) and low nucleotide diversity (π = 0.00682), combined with the negative value of Tajima's D (-1.252) and Fu's Fs (-3.06764), suggested that all nematode populations were expanding. The existence of high genetic differentiation (Fst = 0.5933) and low gene flow (Nm = 0.3333) indicated that there was a block of gene exchange between most populations. Mutation accumulation with population expansion might be directly responsible for the high genetic differentiation; therefore, the tested nematode population showed high within-group genetic variation (96.30%). The haplotype Hap8 was located at the bottom of the network topology, with the widest distribution and the highest frequency (59.26%), indicating that it was the ancestral haplotype. The populations in cluster 3 were newly invasive according to the lowest frequency of occurrence of Hap8, the highest number of endemic haplotypes, and the highest total haplotype frequency (60%). In contrast, cluster 1 having the highest genetic diversity (Hd = 0.772, π = 0.01127) indicated that it was the most primitive. Interestingly, the highest gene flow (Nm > 1), lowest genetic differentiation (Fst ≤ 0.33), and closest genetic distance (0.000) only occurred between the Guangdong/Hainan population and others, which suggested that there might be channels for gene exchange between them and that long-distance dispersal occurred. This suggestion is further confirmed by the weak correlation between genetic distance and geographical distance. Based on these data, a hypothesis can be drawn that M. graminicola populations in China were spreading from south to north, specifically from Guangdong and Hainan Provinces to other regions. Natural selection (including anthropogenic) and genetic drift were the main drivers of their evolution. Coincidentally, this hypothesis was consistent with the gradual warming trend and the chronological order of reporting these populations. The main factors influencing current M. graminicola population expansion and distribution patterns might be geography, climate, long-distance seedling transport, interregional operations of agricultural machinery, and rotation mode. It reminds human beings of the necessity to be vigilant about preventing nematode disease according to local conditions all year round.

CYP314A1-dependent 20-hydroxyecdysone biosynthesis is involved in regulating the development of pupal diapause and energy metabolism in the Chinese citrus fruit fly, Bactrocera minax.

BACKGROUND: Diapause is an environmentally preprogrammed period of arrested development, and characterized by metabolic depression that can occur during any development stage of insect. The insect steroid hormone 20-hydroxyecdysone (20E), is converted from ecdysone by the cytochrome P450 enzyme shade (CYP314A1), and it exerts a potent effect on the induction and maintenance of diapause in obligatory diapause insects. However, the regulatory mechanism of 20E in obligatory diapause development remains unclear. In this study, the function of 20E in the pupal diapause of Bactrocera minax was investigated. RESULTS: We determined the expression pattern of Halloween P450 genes from larval to adult B. minax, and found differential expression of CYP314A1 from other P450 genes, with a high level in larvae and a low level in pupae. Dysfunction of CYP314A1 by dsCYP314A1 microinjection in third-instar larvae caused significant larval mortality or abnormal pupae. Compared with dsGFP and DEPC-water, dsCYP314A1-injected larvae had significantly reduced 20E titer and altered energy metabolism, and many individuals failed to pupate. Exogenous 20E microinjected into late third-instar larvae or 20E fed to early third-instar larvae both caused similar energy metabolism changes. The 20E-treated larvae of B. minax had reduced total lipids and increased amounts of trehalose and glycogen. Furthermore, 20E-treated diapause individuals showed rapid pupal development. CONCLUSION: The 20E biosynthesis was regulated by the expression of CYP314A1, and was involved in the induction and termination phase of obligate diapause by regulating energy metabolism in B. minax. © 2022 Society of Chemical Industry.

Comparative transcriptome analysis of different developmental stage of Bactrocera minax (Diptera: Tephritidae): Implication of the molecular basis of its obligatory diapause induction.

The Chinese citrus fruit fly, Bactrocera minax (Enderlein), a devastating pest in citrus, has an obligatory diapause at the pupal stage. Although the physiology of obligatory diapause has been well described, the molecular mechanisms underlying the process remain unknow. Here we investigated the molecular mechanisms of obligatory diapause induction in B. minax using high-throughput RNA-Seq data from second-instar larva (2L), third-instar larva (3L) and pupa (P) stages. A total of 116,402 unigenes were obtained, of which 54,781 unigenes were successfully annotated in public databases, and the differentially expressed genes in the 3L vs 2L, P vs 2L, and P vs 3L comparisons were identified. The cluster co-expression patterns of the differentially expressed genes revealed that significantly differentially-expressed genes in the pupal stage were predicted to be related to diapause induction. All differentially expressed genes were investigated by GO functional and KEGG pathway analysis, and the results showed that genes involved in processes such as 20-hydroxyecdysone (20E) biosynthesis, cell cycle and metabolic pathways are likely related to obligatory diapause induction in B. minax. These results provide important information on the transcriptome of the Chinese citrus fruit fly that can be used for further functional studies as well as contributing to our understanding of the molecular basis of obligatory diapause induction and suggesting potential molecular targets for the control of this pest.

Effect of Sex and Air Temperature on the Flight Capacity of Bradysia odoriphaga (Diptera: Sciaridae).

Bradysia odoriphaga Yang & Zhang (Diptera: Sciaridae) is an important pest of Chinese chives. Information on the effects of biotic and abiotic factors on the flight performance of B. odoriphaga is crucial for understanding the pest's ability to disperse and migrate. In this study, the effects of sex and air temperature on the flight performance of B. odoriphaga imagoes were assessed by tethering individual imagoes to computerized flight mills for a 10-h experiment. The results showed that the percentage of imagoes that flew a particular distance gradually decreased as flight distance increased. The percentage of imagoes was significantly higher for males than females when the flight distance was <300 m. Sex and air temperature significantly affected average flight time (which ranged from 14.6 to 68.3 min) and average flight distance (which ranged from 10.4 to 107.2 m), but did not significantly affect average flight speed (which ranged from 3.8 to 6.4 m/min). For both females and males, the average flight distance and flight time were shortest at 18°C and longest at 22°C; the interaction between air temperature and sex was not significant. The results suggest that B. odoriphaga has a poor potential for long-distance migration. These findings will be helpful for developing forecasting and management systems for B. odoriphaga.

Effect of Dietary Protein and Carbohydrates on Survival and Growth in Larvae of the Henosepilachna vigintioctopunctata (F.) (Coleoptera: Coccinellidae).

The ratio of protein and carbohydrate in an insect's nutritional regime can significantly influence its survival, growth, and fecundity. The effects of 11 different artificial diets containing protein (p): carbohydrate (c) ratios were determined in larvae of the phytophagus ladybug, Henosepilachna vigintioctopunctata (F.) (Coleoptera: Coccinellidae). We recorded the developmental times and survival rates of the larvae and weighed their pupae. When the concentration of carbohydrates was kept constant while the concentration of proteins was increased (p29:c20, p31:c20, p33:c20, and p35:c20), H. vigintioctopunctata could successfully complete the larval and pupal stages. The highest survival rate and greatest pupal mass of H. vigintioctopunctata were 72% and 19.5 mg, respectively, when reared on the p33:c20 diet. H. vigintioctopunctata larvae, however, were unable to develop into adults when the concentration of protein remained constant while the level of carbohydrates was increased (p20:c23, p20:c25, p20:c27, and p20:c29), or when the total amount (p + c) was kept at 48% (p22:c26, p 24:c24, p26:c22). Evidently, changing the availability of quality diet, especially the total protein levels, can significantly affect the performance to H. vigintioctopunctata. Our results indicated that the maximum development and survival of H. vigintioctopunctata larvae occurred within a narrow range-when the p:c ratio was (33:20).

Demographic Comparison of Henosepilachna vigintioctopunctata (F.) (Coleoptera: Coccinellidae) Reared on Three Cultivars of Solanum melongena L. and a Wild Hostplant Solanum nigrum L.

Henosepilachna vigintioctopunctata (F.) is a widespread pest found on many solanaceous vegetables. The development and fecundity of H. vigintioctopunctata were studied on three cultivars ('Zihong', 'Eyou', and 'Baijiao') of eggplant, Solanum melongena L., using the two-sex life table theory. These results were then compared with similar parameters from a wild alternate host, Solanum nigrum. Our results showed that there were no significant differences between the developmental times of the larval stages, pupae, oviposition period, adult longevity, and the fecundity of H. vigintioctopunctata reared on the three eggplant cultivars. The survival rates of H. vigintioctopunctata larvae reared on the three eggplant cultivars were higher than that on S. nigrum. The fecundity of H. vigintioctopunctata adults reared on S. nigrum (724.12 eggs), however, was significantly higher than on each of the three eggplant cultivars. The values for the intrinsic rate of increase (r), finite rate of increase (λ), and net reproductive rate (R0) for H. vigintioctopunctata when reared on S. nigrum were 0.1225 d-1,1.1303 d-1, and 299.6 offspring, respectively. Each of these was significantly higher than comparable values when reared on the cultivar Eyou and Baijiao but were not different from those reared on the Zihong. Our results indicated that H. vigintioctopunctata is well adapted to all tested host plant cultivars and that S. nigrum is an important alternate wild hostplant that may potentially contribute to future outbreaks of H. vigintioctopunctata if not taken into consideration when planning an integrated control strategy against the pest.

Morphology and distribution of antennal sensilla of female Phyllotreta striolata (Fabricius) (Coleoptera: Chrysomelidae).

Phyllotreta striolata (Fabricius) is an important pest of Brassicaceae in Southeast Asia and North America. Using scanning electron microscopy, we observed the external structure, number, and distribution of the antennal sensilla in P. striolata females to discuss the putative function of these sensilla in host location and oviposition behaviors. The antenna of female P. striolata is filiform, composed of a scape, a pedicel, and a flagellum with 9 flagellomeres. Five types of sensilla were identified, including sensilla cheaetica, sensilla trichodea, Böhm bristles, sensilla auricillica, and sensilla basiconica (five subtypes, SB1-SB2). External structure and distribution of antennal sensilla are compared with data from other insect species. In addition, we discuss the possible functions of antennal sensilla based on their characteristics.

Phylogenetic divergences of the true bugs (Insecta: Hemiptera: Heteroptera), with emphasis on the aquatic lineages: the last piece of the aquatic insect jigsaw originated in the Late Permian/Early Triassic.

Heteroptera are among the most diverse hemimetabolous insects. Seven infraorders have been recognized within this suborder of Hemiptera. Apart from the well-established sister-group relationship between Cimicomorpha and Pentatomomorpha (= Terheteroptera), the two terminal lineages, the relationships among the other five infraorders are still controversial, of which three (Gerromorpha, Nepomorpha and Leptopodomorpha) are intimately connected to aquatic environments. However, the various and often conflicting available phylogeny hypotheses do not offer a clear background for a connection between diversification and palaeoenvironments. In this study, a molecular data set representing 79 taxa and 10 149 homologous sites is used to infer the phylogenetic relationships within Heteroptera. Bayesian inference, maximum-likelihood and maximum parsimony analyses were employed. The results of phylogenetic inferences largely confirm the widely accepted phylogenetic context. Estimation of the divergence time based on the phylogenetic results revealed that Gerromorpha, Nepomorpha and Leptopodomorpha originated successively during the period from the Late Permian to Early Triassic (269-246 Ma). This timescale is consistent with the origin and radiation time of various aquatic holometabolans. Our results indicate that the aquatic and semi-aquatic true bugs evolved under environmental conditions of high air temperature and humidity in an evolutionary scenario similar to that of the aquatic holometabolans.

[Effects of plant hedgerow on population dynamics of wheat aphid and its natural enemies].

This paper studied the effects of planting different kinds of plant hedgerow (Amorpha fruticosa, Vetiveria zizanioides, Eulaliopsis binata, and Medicago sativa) on the population dynamics of wheat aphid and its natural enemies in the hillside wheat fields in Ziyang City of Sichuan Province, Southwest China. On the 20 degrees hillside, A. fruticosa hedgerow inhibited the occurrence of wheat aphid in the wheat field significantly, and the parasitoid densities were equal to or significantly lower than those in the wheat field with V. zizanioides hedgerow. On the 12 degrees hillside, M. sativa and E. binata hedgerows delayed the peak time of wheat aphid occurrence, and E. binata hedgerow suppressed the wheat aphid population density significantly. In the wheat field with M. sativa hedgerow, the parasitoid densities were significantly higher than those with no hedgerow. An equal or significantly higher ladybird density was observed in the field with M. sativa hedgerow. The olfactory responses showed that E. binata volatiles had repellent effect on both Sitobion avenae and Rhopalosiphum padi, but attracted a spider species of oxyopidae. M. sativa volatiles attracted S. avenae, whereas neither M. sativa nor E. binata volatiles caused obvious behavior response of ladybird adults. Therefore, planting A. fruticosa and E. binata as the hedgerows in hillside wheat fields could not only prevent the soil erosion from seasonal rainfall, but also benefit the control of pest insects.