Regulation of Migration in Mythimna separata (Walker) in China: A Review Integrating Environmental, Physiological, Hormonal, Genetic, and Molecular Factors

Each year the Mythimna separate (Walker), undertakes a seasonal, long-distance, multigeneration roundtrip migration between southern and northern China. Despite its regularity, the decision to migrate is facultative, and is controlled by environmental, physiological, hormonal, genetic, and molecular factors. Migrants take off on days 1 or 2 after eclosion, although the preoviposition period lasts ≈7 d. The trade-offs among the competing physiological demands of migration and reproduction are coordinated in M. separata by the “oogenesis-flight syndrome.” Larvae that experience temperatures above or below certain thresholds accompanied by appropriate humidity, short photoperiod, poor nutrition, and moderate density tend to develop into migrants. However, there is a short window of sensitivity within 24 h after adult eclosion when migrants can be induced to switch to reproductive residents if they encounter extreme environmental factors including starvation, low temperature and long photoperiod. Juvenile hormone (JH) titer is low before migration but high titers are associated with termination of migratory behavior and the switch to reproduction. Early release of JH by the corpora allata in environmentally stressed 1-d old adults, otherwise destined by larval conditions to be migrants, switches them to residents. Offspring inherit parental additive genetic effects governing migratory behavior. However, they also retain flexibility in expression of both flight and reproductive life history traits. The insect neuropeptide, allatotropin, which activates corpora allata to synthesize JH, controls adult flight and reproduction. Future research directions to better understand regulation of migration in this species are discussed

Comparison of Reproductive and Flight Capacity of Loxostege sticticalis (Lepidoptera: Pyralidae), Developing From Diapause and Non-Diapause Larvae

The beet webworm, Loxostege sticticalis (L.) (Lepidoptera: Pyralidae), uses both diapause and migration as life history strategies. To determine the role of diapause plays in the population dynamics of L. sticticalis, the reproductive and flight potentials of adults originating from diapause and nondiapause larvae were investigated under controlled laboratory conditions. Preoviposition period, lifetime fecundity, and daily egg production of females originating from diapause larvae were not significantly different from those originating from nondiapause larvae, showing that diapause has no significant effect on reproductive capacity when adults are provided with an adequate carbohydrate source. However, females that developed from diapause larvae lived significantly longer than those from nondiapause larvae. Flight capacity, including flight duration, distance and velocity of 3-d-old adults were all significantly greater in adults originating from diapause larvae than those from nondiapause larvae. L. sticticalisadults developing from diapause larvae tended to have more extreme values of longest flight duration and furthest flight distance than those from nondiapause larvae. Together, these results suggest that long-distance flight potential of L. sticticalis is greater after larval diapause than after direct development to adulthood. However, there were no significant differences between sexes within the two categories of moths in terms of total flight duration, total flight distance, flight velocity, and longest flight duration

Response of Reproductive Traits and Longevity of Beet Webworm to Temperature, and Implications for Migration

Beet webworm, Loxostege sticticalis (L.) is a facultative long-distance migratory insect pest in many regions between 36° and 55° N latitude. The outbreaks of larvae are closely related to temperatures encountered by the immigrant adult. But mechanisms linking population outbreaks and migration are not well understood. We investigated the effect of exposing adults to constant temperatures from 14 to 34°C on mating, oviposition, and longevity. Our results showed that both mating percentage and frequency were highest at 22–26°C and decreased at temperatures outside this optimal range. Time of night when mating began was delayed at higher temperatures, while mating duration progressively decreased with increasing temperature. Both preoviposition period (POP) and oviposition period decreased linearly with increasing temperature. Peak daily and lifetime fecundity were highest at 22–26°C and declined at temperatures outside this range, suggesting that 22–26°C is the optimal thermal range for oviposition. Adult longevity was negatively correlated with temperature. Males lived longer than females at lower temperatures, but females lived longer than males in the 30–34°C treatments. Together, our findings suggest that reproduction occurs when the prevailing temperature is around 22–26°C, and that migratory flight is favored outside this range via increases in POP and proportion of virgins. We predict that larval damage or outbreaks of L. sticticalis will occur only in areas where the prevailing temperature is around 22–26°C, which provides a key basis for the prediction of population outbreaks in areas of immigration

Density-dependent prophylaxis in crowded Beet Webworm, Loxostege sticticalis (Lepidoptera: Pyralidae) larvae to a parasitoid and a fungal pathogen

Transmission of parasites and pathogens is generally positively density-dependent: as an insect population\u27s density increases, the risk of an individual becoming attacked or infected also increases. In some insect species, individuals experiencing crowded conditions are more resistant to natural enemies than those experiencing low density conditions, and they are predicted to divert resources to increase resistance. This phenomenon is called density-dependent prophylaxis. Here, possible expression of prophylaxis in fifth-instar larvae of Beet Webworm, Loxostege sticticalis, to biocontrol agents was investigated under rearing densities of 1, 10, and 30 larvae per jar (650 mL). Larvae reared at the moderate density and those reared in isolation displayed the greatest and lowest resistance, respectively, to an entomopathogenic fungus and a parasitoid. Moreover, larvae from the moderate density treatment exhibited elevated phenoloxidase, total haemocyte count and antibacterial activity in the haemolymph, whereas phenoloxidase levels in the midgut were not affected. The results suggest that larval rearing density significantly affects the immune system, and they provide evidence for density-dependent prophylaxis of larval L. sticticalis against its biocontrol agents. These results have implications for understanding the population dynamics and biocontrol of beet webworm

A cadherin-like protein influences Bacillus thuringiensis Cry1Ab toxicity in the oriental armyworm, Mythimna separata

Cadherins comprise a family of calcium-dependent cell adhesion proteins that act in cell–cell interactions. Cadherin-like proteins (CADs) in midguts of some insects act as receptors that bind some of the toxins produced by the Bacillus thuringiensis (Bt). We cloned a CAD gene associated with larval midguts prepared from Mythimna separata. The full-length cDNA (MsCAD1, GenBank Accession No. JF951432) is 5642 bp, with an open reading frame encoding a 1757 amino acid and characteristics typical of insect CADs. Expression of MsCAD1 is predominantly in midgut tissue, with highest expression in the 3rd- to 6th-instars and lowest in newly hatched larvae. Knocking-downMsCAD1 decreased Cry1Ab susceptibility, indicated by reduced developmental time, increased larval weight and reduced larval mortality. We expressed MsCAD1 in E. coli and recovered the recombinant protein, rMsCAD1, which binds Cry1Ab toxin. Truncation analysis and binding experiments revealed that a contiguous 209-aa, located in CR11 and CR12, is the minimal Cry1Ab binding region. These results demonstrate that MsCAD1 is associated with Cry1Ab toxicity and is one of the Cry1Ab receptors in this insect. The significance of this work lies in identifying MsCAD1 as a Cry1Ab receptor, which helps understand the mechanism of Cry1Ab toxicity and of potential resistance to Bt in M. separata

Accelerated and Synchronized Oviposition Induced by Flight of Young Females May Intensify Larval Outbreaks of the Rice Leaf Roller

Physiological management of migration-reproduction trade-offs in energy allocation often includes a package of adaptions referred to as the oogenesis-flight syndrome. In some species, this trade-off may be overestimated, because factors like flight behavior and environmental conditions may mitigate it. In this study, we examined the reproductive consequences induced by different flight scenarios in an economically-important Asian migrant insect, Cnaphalocrocis medinalis. We found that the influences of flight on reproduction are not absolutely positive or negative, but instead depend on the age at which the moth begins flight, flight duration, and how many consecutive nights they are flown. Adult flight on the 1st or 2nd night after emergence, flight for 6 h or 12 h nightly, and flight on the first two consecutive nights after emergence significantly accelerated onset of oviposition or enhanced synchrony of egg-laying. The latter can contribute to subsequent larval outbreaks. However, flight after the 3rd night, flight for 18 h at any age, or flight on more than 3 consecutive nights after adult emergence did not promote reproductive development, and in some scenarios even constrained adult reproduction. These results indicate that there is a migration/reproduction trade-off in C.medinalis, but that it is mitigated or eliminated by flight under appropriate conditions. The strategy of advanced and synchronized oviposition triggered by migratory flight of young females may be common in other migratory insect pests

Population Projection and Development of the Mythimna loreyi (Lepidoptera: Noctuidae) as Affected by Temperature: Application of an Age-Stage, Two-Sex Life Table

The Mythimna (=Leucania) loreyi (Duponchel) has recently emerged as a major pest of grain crops in China. Little is known about its basic biology and ecology, making it difficult to predict its population dynamics. An age-stage, two-sex life table was constructed for this insect when reared on maize in the laboratory at five constant temperatures (18, 21, 24, 27, and 30 °C). Both the intrinsic rate of increase (r) and finite rate increase (λ) increased as temperature significantly increased and mean generation time (T) decreased significantly with increasing temperature. The highest values for net reproductive rate (R0) and fecundity were observed at 24 °C. However, M. loreyi was able to develop, survive, and lay eggs at all temperatures tested (18–30 °C). Development rates at different temperatures for the egg, larval, pupal, as well as for a total preoviposition period, fit a linear equation. The lower threshold temperatures of egg, larval, pupal, preoviposition, and total preoviposition period were 8.83, 10.95, 11.67, 9.30, and 9.65 °C, respectively. And their effective accumulated temperatures were 87.64, 298.51, 208.33, 66.47, and 729.93 degree-days, respectively. This study provides insight into the temperature-based phenology and population ecology in M. loreyi. The results will benefit population dynamics monitoring, prediction, and management of this insect pest in the field

Starvation on First or Second Day of Adulthood Reverses Larval-Stage Decision to Migrate in Beet Webworm (Lepidoptera: Pyralidae)

A facultative commitment to adult migration in the larval stage can be modified again after adult emergence in some Lepidoptera when influenced by an appropriate environmental cue during a sensitive stage. This phenomenon is termed secondary regulation of migration. The sensitive stage in adult beet webworm, Loxostege sticticalis L. (Lepidoptera: Pyralidae), was determined experimentally by starvation of presumed migrant females reared from gregarious-phase larvae (induced by crowding at 10 larvae per 650-ml jar). When presumed migrant adults were starved for 24 h on either of the first 2 d after emergence, the preoviposition period was shortened. In contrast, preoviposition periods were not significantly shortened for migrants starved on day 3 or when starvation lasted for more than 1 d after emergence. Because the preoviposition period corresponds to the migratory period in beet webworm, the results suggest that the first 2 d of adult life in the beet webworm is the sensitive stage during which presumed migrants can be switched to residents by an appropriate environmental cue. During the sensitive stage or not, starvation did not influence lifetime fecundity, oviposition period, longevity, or hatching rate of eggs laid by the starvation-stressed moths. Starvation on the first day also increased tethered flight performance and accelerated both flight muscle and ovarian development. The results suggest that a pulse of starvation in the sensitive period may inhibit the expected migration by accelerating and compressing the cycle of migratory flight muscle development and degeneration, while accelerating ovarian development, which is normally suppressed until after migration

Elevated Plasma Homocysteine Levels in Anti-N-methyl-D-aspartate Receptor Encephalitis

Objective: Homocysteine (Hcy) levels have been investigated in many diseases, such as neurodegenerative and autoimmune diseases. However, changes in Hcy levels in anti-N-Methyl-D-aspartate receptor (anti-NMDAR) encephalitis have not been investigated thus far.Methods: Case data were collected from 45 patients with anti-NMDAR encephalitis and 179 age- and sex-matched healthy controls (HCs). Clinical characteristics, Hcy levels, C reactive protein (CRP) levels, and cerebrospinal fluid (CSF) parameters were determined. Association of Hcy and clinical parameters were evaluated in these patients. Among these 45 patients, 15 had a follow-up evaluation at 3 months after treatment.Results: Hcy levels (p < 0.001) and CRP levels (p = 0.005) from the patients with anti-NMDAR encephalitis were significantly higher than those from HCs. Hcy levels from male patients were significantly lower than those from male HCs (p < 0.001). Comparing anti-NMDAR encephalitis patients after treatment with before treatment, the former has significantly higher Hcy levels (p = 0.004), CRP levels (p = 0.041) and mRS scores (p = 0.002). Furthermore, a significant negative correlation between the changes in Hcy levels and the changes in mRS scores (r = −0.534, p = 0.040) was observed.Conclusion: Elevated plasma homocysteine occurs in anti-NMDAR encephalitis, and seems associated with male sex