Transboundary migration of Loxostege sticticalis (Lepidoptera: Crambidae) among China, Russia and Mongolia.

BACKGROUND: The beet webworm, Loxostege sticticalis, a worldwide pest of many crops, performs a seasonal migration, causing periodic outbreaks in Asia, Europe and North America. Although long-distance migration is well documented in China, patterns of transboundary migration among China, Russia and Mongolia are largely unknown. We performed a phase analysis of L. sticticalis periodic outbreaks among three countries based on 30 years of historical population data, analyzed the wind systems during migration over boundary regions, and traced the migratory routes in a case study of outbreaks in 2008 by trajectory simulation. RESULTS: Highly synchronized outbreak years of L. sticticalis were observed between China and Mongolia, China and eastern Siberia, China and western Siberia, Mongolia and eastern Siberia, eastern Siberia and western Siberia from 1978 to 2008, indicating possible transboundary migration between these regions. Winds at 300-600 m altitude, where adult migration usually occurs, also showed a high probability of northwestern winds in Haila'er (China), Chita (Russia) and Choybalsan (Mongolia), favoring successful adult migration from these areas to northern and northeastern China. Back trajectory analysis further showed that the first-generation adults that caused the severe outbreak of second-generation larvae in 2008 originated from eastern Siberia, eastern Mongolia, and the boundary regions of China-Russia and China-Mongolia. CONCLUSION: Our findings demonstrated that the source of L. sticticalis outbreaks in northern China was closely related to the outbreaks in Siberia and Mongolia via long-distance transboundary windborne migration. This information will help guide international monitoring and management strategies against this notorious pest. © 2024 Society of Chemical Industry.

Isolation functional characterization of allatotropin receptor from the cotton bollworm, Helicoverpa armigera.

Insect allatotropin (AT) plays multi-functions including regulation of juvenile hormone synthesis, growth, development and reproduction. In the present study, the full-length cDNA encoding the AT receptor was cloned from the brain of Helicoverpa armigera (Helar-ATR). The ORF of Helar-ATR exhibited the characteristic seven transmembrane domains of the G protein-coupled receptor (GPCR) and was close to the ATR of Manduca sexta in the phylogenetic tree. The Helar-ATR expressed in vertebrate cell lines can be activated by Helar-AT and each Helar-ATL in a dose-responsive manner, in the following order: Helar-ATLI > Helar-ATLII > Helar-AT > Helar-ATLIII. Helar-ATLI and Helar-ATLII represented the functional ligands to Helar-ATR in vitro, while Helar-AT and Helar-ATLIII behaved as partial agonists. The in vitro functional analysis suggested that the Helar-ATR signal was mainly coupled with elevated levels of Ca2+ and independent of cAMP levels. Helar-ATR mRNA in larvae showed the highest level in the brain, followed by the thorax ganglion, abdomen ganglion, fat body and midgut. Helar-ATR mRNA levels in the complex of the brain-thoracic-abdomen ganglion on the 2nd day of the larval stage and during later pupal stages were observed to be relatively higher than in the wandering and early pupal stages.

Isolation and functional characterization of the pheromone biosynthesis activating neuropeptide receptor of Chinese oak silkworm, Antheraea pernyi.

Insect pheromone biosynthesis activating neuropeptide (PBAN) controls the synthesis and actuating of sex pheromones of female adult. In the current examination, the full-length cDNA encoding the PBAN receptor was cloned from the pheromone gland (PG) of Antheraea pernyi (AntpePBANR). The AntpePBANR displayed the characteristic seven transmembrane areas of the G protein-coupled receptor (GPCR) and was closely related to the PBANR from Bombyx mori and Manduca sexta in the phylogenetic tree. The AntpePBANR expressed in mammalian cell lines were enacted by AntpePBAN in a concentration-dependent manner. AntpePBANR activation resulted in the calcium mobilization but did not activate the cAMP elevation pathway. Cells expressing AntpePBANR were profoundly responsive to Antpe-γ-SGNP (suboesophageal ganglion neuropeptides) and Antpe-DH (diapause hormone), different individuals from FXPRLamide (X = T, S or V) family in A. pernyi. Deletion of residues in the C-terminal hexapeptide (FSPRLamide) proved that P, R and L played the key parts in initiating the AntpePBANR, the amination to the last C terminal residues which can also likewise impact the activation of AntpePBAN receptor altogether. The mRNA of the AntpePBANR gene demonstrated the most noteworthy transcript levels in pheromone gland followed by fat body.

The Complete Mitochondrial Genome of the Longhorn Beetle Dorysthenes paradoxus (Coleoptera: Cerambycidae: Prionini) and the Implication for the Phylogenetic Relationships of the Cerambycidae Species.

The longhorn beetle Dorysthenes paradoxus (Faldermann, 1833) (Coleoptera: Cerambycidae) is not only a serious agricultural pest but also a traditionally edible insect in China. However, no genetic information on this species has been acquired. In the present study, we report the mitochondrial genome (mitogenome) of Do. paradoxus, as the first complete mitogenome of Prioninae. The circular mitogenome of 15,922 bp encodes 13 protein-coding genes (PCGs), 22 transfer RNAs (tRNAs), and two ribosomal RNAs (rRNAs), and it contains an A+T-rich region. This mitogenome exhibits the lowest A+T content (71.13%) but harbors the largest AT skew (0.116) among the completely sequenced Cerambycidae species. Eleven of the 13 PCGs have a typical ATN start codon, whereas COI and ND1 are tentatively designated by AAT and TTG, respectively. Only 4 of the 13 PCGs harbor a complete termination codon, and the remaining 9 possess incomplete termination codons (T or TA). Apart from tRNASer(AGN), the other 21 tRNAs can fold into a typical clover-leaf secondary structures. The Do. paradoxus A+T-rich region contains two poly-T stretches and a tandem repeat that comprises two 47-bp-long copies. Both Bayesian inference and Maximum likelihood analyses confirmed the subfamily ranks of Cerambycidae ([Prioninae + Cerambycinae] + Lamiinae) and the close relationship between Philinae and Prioninae/Cerambycinae. However, the data did not support the monophyly of Prioninae and Cerambycinae. The mitogenome presented here provides basic genetic information for this economically important species.

Prostaglandin-mediated recovery from bacteremia delays larval development in fall armyworm, Spodoptera frugiperda.

Insect immunity includes a surveillance system that detects and signals infections, coupled with hemocytic and humoral immune functions. These functions are signaled and coordinated by several biochemicals, including biogenic amines, insect cytokines, peptides, and prostaglandins (PGs). The actions of these mediators are coordinated within cells by various forms of cross-talk among the signaling systems and they result in effective reactions to infection. While this is well understood, we lack information on how immune-mediated recovery influences subsequent juvenile development in surviving insects. We investigated this point by posing the hypothesis that PG signaling is necessary for larval recovery, although the recovery imposes biological costs, registered in developmental delays and failures in surviving individuals. Here, we report that nodulation responses to infections by the bacterium, Serratia marcescens, increased over time up to 5 h postinfection, with no further nodulation; it increased in a linear manner with increasing bacterial dosages. Larval survivorship decreased with increasing bacterial doses. Treating larvae with the PG-biosynthesis inhibitor, indomethacin, led to sharply decreased nodulation reactions to infection, which were rescued in larvae cotreated with indomethacin and the PG-precursor, arachidonic acid. Although nodulation was fully rescued, all bacterial challenged larvae suffered reduced survivorship compared to controls. Bacterial infection led to reduced developmental rates in larvae, but not pupae. Adult emergence from pupae that developed from experimental larvae was also decreased. Taken together, our data potently bolster our hypothesis.

Characterization of the Adult Head Transcriptome and Identification of Migration and Olfaction Genes in the Oriental Armyworm Mythimna separate.

The oriental armyworm Mythimna separate is an economically important insect with a wide distribution and strong migratory activity. However, knowledge about the molecular mechanisms regulating the physiological and behavioural responses of the oriental armyworm is scarce. In the present study, we took a transcriptomic approach to characterize the gene network in the adult head of M. separate. The sequencing and de novo assembly yielded 63,499 transcripts, which were further assembled into 46,459 unigenes with an N50 of 1,153 bp. In the head transcriptome data, unigenes involved in the 'signal transduction mechanism' are the most abundant. In total, 937 signal transduction unigenes were assigned to 22 signalling pathways. The circadian clock, melanin synthesis, and non-receptor protein of olfactory gene families were then identified, and phylogenetic analyses were performed with these M. separate genes, the model insect Bombyx mori and other insects. Furthermore, 1,372 simple sequence repeats of 2-6 bp in unit length were identified. The transcriptome data represent a comprehensive molecular resource for the adult head of M. separate, and these identified genes can be valid targets for further gene function research to address the molecular mechanisms regulating the migratory and olfaction genes of the oriental armyworm.

Increased long-flight activity triggered in beet armyworm by larval feeding on diet containing Cry1Ac protoxin.

Evaluating ecological safety and conducting pest risk analysis for transgenic crops are vitally important before their commercial planting. The beet armyworm, Spodoptera exigua, a long-distance migratory insect pest, is not a direct target of transgenic Cry1Ac-expressing cotton in China, but nevertheless it has recently become an important pest. Migrants leaving their natal field arrive in other appropriate habitat far away in a short time, often followed by larval outbreaks. S. exigua has low susceptibility to Cry1Ac. However, our results from laboratory experiments identified (i) sublethal effects of Cry1Ac protoxin on larval development rate, larval and pupal weight, and adult lifetime fecundity, and (ii) increased long-flight behavior triggered by Cry1Ac which may contribute to larval outbreaks elsewhere. No significant differences in larval mortality, pupation rate, adult emergence rate, longevity, pre-oviposition period, or oviposition period were observed between controls and larvae fed on artificial diet incorporating a low concentration of Cry1Ac protoxin. The negative sublethal effects on some developmental and reproductive traits and lack of effect on others suggest they do not contribute to the observed severity of S. exigua outbreaks after feeding on Cry1Ac cotton. Interestingly, the percentage of long fliers increased significantly when larvae were reared on diet containing either of two low-dose treatments of Cry1Ac, suggesting a possible increased propensity to disperse long distances triggered by Cry1Ac. We hypothesize that negative effects on development and reproduction caused by Cry1Ac in the diet are offset by increased flight propensity triggered by the poor food conditions, thereby improving the chances of escaping adverse local conditions before oviposition. Increased long-flight propensity in turn may amplify the area damaged by outbreak populations. This phenomenon might be common in other migratory insect pests receiving sublethal doses of Bt toxins and warrants further study.

Methoprene influences reproduction and flight capacity in adults of the rice leaf roller, Cnaphalocrocis medinalis (Guenee) (Lepidoptera: Pyralidae).

Juvenile hormone (JH) influences many aspects of insect biology, including oogenesis-flight syndrome tradeoffs between migration and reproduction. Drawing on studies of many migratory insects, we posed the hypothesis that JH influences migratory capacity and oogenesis in the rice leaf roller, Cnaphalocrocis medinalis. We treated adults moths (days 1, 2 and 3 postemergence) with the JH analog (JHA), methoprene, and then recorded the influences of JHA treatments on reproduction. JHA treatment on day 1 postemergence, but not on the other days, shortened the preoviposition period, although JHA did not influence total fecundity, oviposition period, or longevity. We infer day 1 postemergence is the JH-sensitive stage to influence reproduction. Therefore, we treated moths on day 1 postemergence with JHA and recorded flight capacity, flight muscle mass, and triacylglycerol (TAG) accumulation. JHA treatments did not influence flight speed, but led to reductions in flight durations and flight distances. At day 3 posttreatment (PT), JHA-treated females flew shorter times and less distance than the controls; JHA-treated males, however, only flew shorter times than the controls. JHA treatments led to reductions in flight muscle mass in females at days 2-3 PT and reductions in TAG content in females at day 3 PT, but, these parameters were not influenced by JHA in males. These findings strongly support our hypothesis, from which we infer that JH is a major driver in C. medinalis oogenesis-flight syndrome tradeoffs. Our data also reveal a JH-sensitive stage in adulthood during which JH influences the oocyte-flight syndrome in C. medinalis.

Synchronized oviposition triggered by migratory flight intensifies larval outbreaks of beet webworm.

Identifying the reproductive consequences of insect migration is critical to understanding its ecological and evolutionary significance. However, many empirical studies are seemingly contradictory, making recognition of unifying themes elusive and controversial. The beet webworm, Loxostege sticticalis L. is a long-range migratory pest of many crops in the northern temperate zone from 36 °N to 55 °N, with larval populations often exploding in regions receiving immigrants. In laboratory experiments, we examined (i) the reproductive costs of migratory flight by tethered flight, and (ii) the reproductive traits contributing to larval outbreaks of immigrant populations. Our results suggest that the beet webworm does not initiate migratory flight until the 2nd or 3rd night after emergence. Preoviposition period, lifetime fecundity, mating capacity, and egg hatch rate for adults that experienced prolonged flight after the 2nd night did not differ significantly from unflown moths, suggesting these traits are irrelevant to the severity of beet webworm outbreaks after migration. However, the period of first oviposition, a novel parameter developed in this paper measuring synchrony of first egg-laying by cohorts of post-migratory females, for moths flown on d 3 and 5 of adulthood was shorter than that of unflown moths, indicating a tightened time-window for onset of oviposition after migration. The resulting synchrony of egg-laying will serve to increase egg and subsequent larval densities. A dense population offers potential selective advantages to the individual larvae comprising it, whereas the effect from the human standpoint is intensification of damage by an outbreak population. The strategy of synchronized oviposition may be common in other migratory insect pests, such as locust and armyworm species, and warrants further study.

Relationship of flight and reproduction in beet armyworm, Spodoptera exigua (Lepidoptera: Noctuidae), a migrant lacking the oogenesis-flight syndrome.

The beet armyworm, Spodoptera exigua, undertakes long-distance migration. We used flight mills to investigate the interaction between flight and reproduction in this species given the apparent absence of the oogenesis-flight syndrome. This syndrome, common in many migratory insects, is characterized by a suite of traits including migration during the pre-oviposition period followed by a switch to oogenesis. No negative effects of inter-ovipositional flight on lifetime fecundity were observed. Instead, adult reproductive output suffered when female flight was initiated the first day after eclosion and before oviposition, suggesting that migratory flight overlaps with the oviposition period rather than being confined to the pre-oviposition period. Mating status of both females and males had no negative influence on their flight performance except that flight distance and flight duration of 7-day-old mated females were significantly less than in unmated females. Furthermore, the number of eggs produced and mating frequency of females less than 7 days of age were not significantly correlated with flight performance, suggesting reproductive development paralleled and was independent of migratory behavior. This independent relationship between flight and reproduction of adults is consistent with the very short pre-oviposition period in this species, and suggests that resources are partitioned between these activities during pupal development. Together, our results uncovered neither obvious trade-offs nor mutual suppression between flight and reproduction in S. exigua, which indicates the lack of an oogenesis-flight syndrome for coordination of these two energy-intensive processes. We propose a conceptual model of migration for this species based on the current and previous studies.

Diapause termination, post-diapause development and reproduction in the beet webworm, Loxostege sticticalis (Lepidoptera: Pyralidae).

Effects of photoperiod and cold exposure on diapause termination, post-diapause development and reproduction in Loxostege sticticalis were examined. Larvae were reared at diapause inducing condition (22 degrees C, L:D 12:12) consistently or transferred to long day photoperiod (L:D 16:8) and darkness (L:D 0:24) respectively, after entering into diapause. Diapause was terminated in approximately 40% of the larvae after 36 days, and no significant differences were observed between photoperiods, suggesting larval diapause was terminated spontaneously without being induced by photoperiods. Cold exposure significantly hastened diapause termination. The diapause termination incidence increased significantly with peaks of 98% at both 5 degrees C and 0 degrees C exposure for 30 days, as compared to 42% in controls not exposed to cold, while the mortality and number of days required for diapause termination decreased dramatically. The optimal low temperature exposure periods under 5 degrees C or 0 degrees C were 20 days and 30 days, showing a higher termination incidence and shorter time for diapause termination. This suggests that the low temperatures in winter play an important role in diapause termination under natural conditions. The threshold temperatures for post-diapause development in prepupae and pupae were 9.13 degrees C and 10.60 degrees C respectively, with corresponding accumulations of 125 and 200 degree-days. Adults that experienced larval diapause significantly delayed their first oviposition, oviposition period was prolonged, and the lifetime number of eggs laid was decreased, however both males and females have significantly longer longevity. The field validation of diapause termination, the degree-days model, and the relationship between diapause and migration in L. sticticalis were also discussed.

Beet webworm (Lepidoptera: Pyralidae) migration in China: evidence from genetic markers.

Genetic diversity within and among 11 geographic populations of the beet webworm Loxostege sticticalis across five provinces in the northern part of China were evaluated using amplified fragment length polymorphism (AFLP) analysis. Five AFLP primer combinations were used on 88 L. sticticalis samples from different locations, detecting a total of 384 polymorphic and 27 monomorphic fragments. Although extensive genetic diversity occurs among individuals from different geographic populations (P = 93.4%, h = 0.398, I = 0.572), the majority of the genetic diversity is within populations and not between populations (G(ST) = 0.196), which agrees well with the results of analysis of molecular variance (84% of the total genetic variation is within populations), indicating high gene flow (N(M) = 2.046) among natural populations, which are not genetically differentiated. L. sticticalis in northeastern China, northern China, and northwestern China are part of a single large metapopulation. Cluster analyses based on AFLP data were preformed to graphically show groupings between individuals and between populations. Individuals from the same region were not grouped together very well. Eleven subpopulations were clustered into six broad groups, and there was no significant correlation between geographic distance and genetic dissimilarity (r = 0.1236, P = 0.8512). Principle component analysis also indicated a lack of genetic differentiation between the 11 populations. These results indicated that, although high genetic variability existed among individuals, there was little genetic differentiation among geographic populations, which can be explained by the effects of long distance migration of the beet webworm in China and consequent gene flow.

Determination of sensitive stage for switching migrant oriental armyworms into residents.

The sensitive stage for switching migrant oriental armyworm, Mythimna separata (Walker), into residents was determined under the stresses of starvation and cold (5 degrees C) in a laboratory population. Presumed migrants developing from gregarious larvae oviposited significantly earlier when adults were starved or shocked by cold only during the first 24 h after emergence. In contrast, preoviposition periods for migrants starved or cooled on days 2-6 of adult life were not significantly affected. The preresponse period of male migrants starved on day 1 of adult life was also significantly shortened, whereas those treated on following days were not significantly influenced. Similarly, total lifetime fecundity of migrants, which were starved or cooled on day 1 after emergence, was significantly increased; however, the same effect was not observed in migrants that were stressed later. Although preoviposition periods of presumed residents, developing from solitary larvae, starved or shocked by cold during the first several days of adulthood were significantly prolonged, this delay was not related to migratory strategy, because lifetime fecundity was not significantly reduced. The results suggest that the first day of adult life in this species is a sensitive stage during which migrants can shift into residents, although residents cannot shift to migrants. Thus, starvation and cold experienced in this stage induces migrants to modify their developmental path into reproduction and residency.

Amplified fragment length polymorphism analysis of Mythimna separata (Lepidoptera: Noctuidae) geographic and melanic laboratory populations in China.

Genetic diversity within and among three wild-type natural populations and one melanic laboratory population of Mythimna separata (Walker) (Lepidoptera: Noctuidae) were evaluated using amplified fragment length polymorphism (AFLP) analysis. Although extensive genetic diversity occurs among individuals from different geographic populations (P = 54.5%, h = 0.209, I = 0.305), the majority of the genetic diversity is within populations and not between populations (G(ST) = 0.172), indicating high gene flow (N(M) = 2.403) and suggesting that M. separata in northern China are a part of a single large metapopulation. Genetic diversity in the natural populations was significantly higher than that in the melanic laboratory population (with P = 43.4% versus P = 25.9%, h = 0.173 versus h = 0.086, and I = 0.251 versus I = 0.127), suggesting that the melanic laboratory population is narrowly genetic-based and genetically uniform. Genetic similarities based on AFLP data were calculated, and cluster analysis was preformed to graphically display groupings between individuals and populations. Individuals from the same region were not grouped together in cluster analysis of three natural populations, whereas melanic individuals from laboratory population were grouped together very well. Four subpopulations were clustered into two broad groups. Melanic laboratory population became a single group, which had apparent differentiation from the other group in which three natural subpopulations were included. These results indicated that although high genetic variability existed among the individuals of natural populations, there was little genetic differentiation among three geographic populations that could be explained by the effects of the long distance migration of the oriental armyworm in China enhanced the level of gene flow. Influences of migration on the genetic polymorphism and differentiations that make a significant contribution to evolution in this insect are reviewed.

Relative fitness of near isogenic lines for melanic and typical forms of the oriental armyworm, Mythimna separata (Walker).

Melanism in the oriental armyworm Mythimna separata (Walker) is characterized by a black color in adults instead of the normal body color of off-white. Because inheritance of melanism in this moth follows Mendel's law, with the melanic allele (t) recessive to the normal allele (T) at a single autosomal locus, a backcrossing procedure was used to develop near isogenic lines (NILs) for melanic (NILs-tt) and typical forms (NILs-TT) of this moth. Melanic males (tt) and typical females (TT) were crossed in the laboratory, their progeny (F(1)) were interbred, and F(2) melanic males were backcrossed to typical female offspring of the parallel line. This cycle was repeated five times to create NILs for melanic and typical forms of this moth. The effects of the melanic allele on relative fitness were evaluated in terms of developmental and reproductive characteristics. Life tables of the NILs were constructed to determine net reproductive rate (R(0)). Results indicated that NILs-tt possessed apparent developmental and reproductive advantages, including shorter immature development time, higher larval and pupal survival, a shorter adult preoviposition period, and more eggs laid per female compared with the NILs-TT.