Mitochondrial DNA variation among worldwide populations of gypsy moths, Lymantria dispar

Gypsy moth populations from Japan, mainland Asia, Europe, Tunisia, and North America were analyzed for variation in mitochondrial DNA (mtDNA) sequences from three gene regions. These samples resolve into four groups, representing gypsy moths from (1) Okinawa, Japan, (2) Hokkaido, Japan, (3) Honshu and Kyushu, Japan and mainland Asia, and (4) Europe, Tunisia, and North America. Some patterns of geographic variation observed for mtDNA (for example, the distinctiveness of gypsy moths from Hokkaido, Japan) coincide with those observed by Goldschmidt from analyses of morphology, life history, and intersexuality. Other patterns (relative sequence homogeneity across Asia, Honshu, and Kyushu and reduced levels of variation in mainland Japan) do not.     

Pheromone-mediated upwind flight of male gypsy moths, Lymantria dispar, in a forest

Abstract Lymantria dispar L. males flying upwind in a pheromone plume in a forest were video-recorded at 2.5, 10 and 20 m from the source of pheromone. Males flew slower and steered more across the wind as they approached the source. In concert, their ground speed decreased and track angles increased. In contrast to these changes, their drift angles were fairly constant and the transverse component of image flow, above and/or below the moths eyes, showed almost no change. The inter-turn duration (time between sequential turns), a temporal aspect of the male flight manoeuvres, showed a consistent but relatively small increase as the distance from the source increased. The flight tracks narrowed as the males approached close (2.5 m) to the source. Because of unpredicted correlations between physical variables (i.e. temperature, wind velocity) and the distance from the source, we used principal components analysis to generate a set of completely independent variables. Greater than 90% of the variability in the data could be explained by four principal factors which corresponded well with known relationships in the flight manoeuvres. All four of these factors showed a significant regression against distance to the source. Although uncontrolled factors such as temperature and wind velocity may have contributed to changes in flight behaviour, recent data indicate that, in addition to concentration, certain temporal and spatial characteristics (i.e. burst period, burst return period) of plumes in wind vary systematically with distance from the source. We propose that L.dispar males might adjust their flight manoeuvres in response to these changes.     

Forest edges enhance mate‐finding in the invasive European gypsy moth,Lymantria dispar

Habitat type, fragmentation, and edge effects can play important roles in the mate‐finding abilities of many species. These effects can be particularly pronounced in low‐density populations, which are often found at the margins of species' ranges or at the leading edge of an invasion. The European gypsy moth, Lymantria dispar (L.) (Lepidoptera: Erebidae), is a non‐native insect defoliator in the USA and Canada, where flightless females attract male moths through pheromone production and local extirpation of low‐density populations can be due to mate‐finding failure. To assess the effects of habitat edges on the ability of gypsy moths to find mates, we conducted a release experiment with male gypsy moths using female‐baited trap arrays in fields, at forest edges, and in the forest interior. Reduced mate‐finding was expected in fields and near forest edges based on geographic variation in invasion rates, male flight behavior, and pheromone plume dynamics. However, we found that mate‐finding was highest at forest edges, reduced in fields, and lowest within the forest interior. Within an array, traps closest to the forest edge also had the highest mate‐finding, suggesting that habitat characteristics can influence male flight direction in addition to pheromone cues. These results suggest that a moderate level of forest fragmentation enhances mate‐finding ability in the gypsy moth. Understanding the relationship between habitat heterogeneity and mate‐finding success in invasive species can inform predictions of future spread and assist with management plans that target mating disruption.     

Iridoid glycosides and insect feeding preferences: gypsy moths (Lymantria dispar, Lymantriidae) and buckeyes (Junonia coenia, Nymphalidae)

Abstract. 1. The effect of increasing concentrations of an iridoid glycoside, catalposide, was tested on a generalist and an adapted specialist lepidopteran, using artificial diets.
2. Two strains of the gypsy moth, Lymantria dispar (L.) (Lymantriidae), were tested. Larvae of a wild strain showed a negative dose-dependent response to increasing concentrations of catalposide (up to 7.2% dry weight), while a laboratory strain showed no such pattern. Choice tests using the laboratory strain showed that these larvae often preferred diets relatively low in catalposide over those with higher concentrations.
3. In contrast, larvae of the iridoid glycoside specialist, the buckeye, Junonia coenia Hübner (Nymphalidae), showed a positive dose-dependent response and grew better on diets with higher doses of catalposide.
4. We tested whether the improved growth of J. coenia at higher concentrations of catalposide may have been due to extra glucose yielded by hydrolysis of catalposide. Larvae were fed increasing doses of glucose equivalent to the amount potentially obtained by hydrolysing the quantities of catalposide used in the previous experiment. However, added glucose did not effect growth, suggesting that increased growth at higher catalposide concentrations was due to increased feeding rates.     

亚洲型舞毒蛾在北美的适生性

采用DYMEX V2.0软件和ArcGIS分析工具相结合的方法,提出亚洲型舞毒蛾Lymantria dispar(L.)的DYMEX参数指标体系和适生性评判标准,分析亚洲型舞毒蛾在北美的适生范围与适生程度。研究表明,加拿大的南部、美国的大部分地区以及墨西哥中南部极少部分区域为该虫的适生区。研究结果将为国家植物保护部门提供有关亚洲型舞毒蛾的植物检疫决策支持。     

The interaction of edge-fixation and negative phototaxis in the orientation of walking gypsy moths,Lymantria dispar

Summary The visual orientation towards single black stripes and more complex patterns, comprising smooth gradients of brightness was studied in walking gypsy moths. Depending on the width of a black stripe, up to three walking directions are preferred within one stimulus situation: towards the centre of the stripe and towards a region within the stripe closer to each edge. The observed responses are explained by a compromise between edge-fixation and negative phototaxis. This hypothesis turned out to be also applicable to more complex patterns.     

Diurnal pattern of death and sporulation in Entomophaga maimaiga-infected Lymantria dispar

Entomophaga maimaiga Humber, Shimazu, et Soper (Zygomycotina: Entomophthoraceae) is a naturally occurring obligate fungal pathogen specific to gypsy moth, Lymantria dispar (L.) (Lepidoptera: Lymantriidae) larvae. This fungus is considered the most important natural enemy of this pest insect in North America and Asia. A critically important step for the development of E. maimaiga epizootics is the transmission of propagules to healthy larvae, a process known to require high humidity. Some pathogens are known to manipulate the time of day that hosts die so that propagules are produced to maximize chances of survival and thus enhance transmission. The objective of this study was to assess whether E. maimaiga manipulates L. dispar to die at a certain time of day. Laboratory bioassays were conducted at 15 and 20 °C to record the 24‐h activity pattern of death and sporulation exhibited under an L14:D10 photoperiod and 100% r.h. by four isolates of E. maimaiga in its host L. dispar. Events were recorded every 4 h. Our results clearly demonstrate that E. maimaiga‐infected L. dispar larvae die mainly in the afternoon and that the fungus sporulates during the night. The rhythm was independent of the fungal isolate tested and type of spores produced after larval death. By raising the temperature from 15 to 20 °C, the peak death time narrowed and sporulation was initiated earlier at night.     

Host tree influences on the dispersal of first instar gypsy moths, Lymantria dispar (L.)

Abstract. 1. In laboratory tests, first instar gypsy moths attempted dispersal more frequency when exposed to less acceptable foliage.
2. First instars from small eggs attempted dispersal less frequently than larvae from large eggs when exposed to foliage from highly acceptable or marginally acceptable hosts. Dispersal rates of larvae from medium sized eggs were intermediate.
3. These results (1–2) confirm and expand upon the findings of Capinera & Barbosa (1976).
4. In the field, data on the relative densities of larvae on different host species support the conclusion that the frequency of dispersal attempts is inversely related to host acceptability.
5. The implications of these findings for the population dynamics of the gypsy moth are discussed.     

Relationships between leaf age and the food quality of cottonwood foliage for the gypsy moth,Lymantria dispar

Summary The cottonwood tree, Populus deltoides, continues to produce leaves late into the growing season, exposing midseason herbivores to leaves of a wide range of maturity. Gypsy moth larvae preferred and grew best on the oldest cottonwood leaves and suffered higher mortality and 85% less growth when fed young, expanding leaves. Concentration of phenolics in the youngest leaves was 3 times that in the oldest leaves and was negatively correlated with caterpillar growth rate. The active phenolics were not identified; tannin was present but its concentration changed more with season than leaf age.     

Vertical transmission and overwintering of microsporidia in the gypsy moth, Lymantria dispar

Vertical transmission and the overwintering success of three different microsporidia infecting Lymantria dispar (Lepidoptera: Lymantriidae) larvae were investigated. Endoreticulatus schubergi, a midgut pathogen, was transmitted to offspring via female and male via the egg chorion (transovum transmission). Between 8% and 29% of the emerging larvae became infected. No spores of E. schubergi were found in surface-washed eggs. Nosema lymantriae, a microsporidium that causes systemic infections, was transovarially transmitted. Between 35% and 72% of the progeny were infected. Vairimorpha disparis, a fat body pathogen, was not vertically transmitted. The infectivity of spores that overwintered in cadavers of infected L. dispar varied by species, placement in the environment, and weather conditions. Spores of E. schubergi were still infective after an eight month exposure period of cadavers on the ground. Spores of N. lymantriae and V. disparis remained highly infective only when cadavers overwintered under a more or less continuous snow cover for four months.     

Development of male-incubated ovaries in the gypsy moth,Lymantria dispar

Ovaries from Lymantria dispar females were transplanted into an environment lacking vitellogenin, the male milieu, in order to determine how the presence of vitellogenin in the hemolymph affects the process of protein uptake by gypsy moth oocytes. When undeveloped ovaries from newly ecdysed last instar females were transplanted into males of the same stage, follicles detached from the germarium and increased in size, but the growth of oocytes proceeded more slowly than those from female controls. Although chorion fromation was delayed in male-grown ovaries, scanning electron microscopy of chorionated eggs recovered from adult males showed that a chorion with normal surface architecture was formed by the adult stage. SDS-PAGE analysis of the male-grown ovaries and hemolymph from males receiving ovaries showed that vitellogenin production was not stimulated by the organ transplant and only male hemolymph proteins were internalized by the male-incubated ovaries. Thus, in the absence of vitellogenin, endocytosis of male hemolymph proteins occurred, but the rate of oocyte growth was slowed.     

Ultrastructural studies of male-incubated ovaries of the gypsy moth,Lymantria dispar

Ovaries from Lymantria dispar females were transplanted into an environment lacking the vitellogenin ligand; i.e., the male milieu. Transmission electron micrographs comparing the terminal oocytes of male-grown ovaries and normal ovaries showed that yolk sphere diameters were reduced in the male-grown oocytes. However, there were larger numbers of these small yolk spheres per unit area of cytoplasm, indicating that the coalescence of endosomes into yolk spheres is reduced in the absence of vitellogenin. Although there are larger numbers of yolk spheres in male-grown oocytes, the smaller diameter of yolk spheres resulted in less area being taken up by yolk spheres per unit area of cytoplasm in male-grown oocytes, yielding lowered yolk production. This lowered yolk production is a result at least in part of the lowered number of coated vesicles per unit area of submembrane space and in part of the reduced interfollicular spaces seen in male-grown ovaries.     

Structure-activity studies with pheromone-binding proteins of the gypsy moth,Lymantria dispar

Pheromone olfaction in the gypsy moth, Lymantria dispar, involves accurate distinction of compounds with similar structure and polarity. The identified sex pheromone is (7R,8S)-2-methyl-7,8-epoxyoctadecane, 1a, and a known antagonist is (7Z)-2-methyloctadec-7-ene, 4a. The first step in pheromone olfaction is binding of odorants by small, soluble pheromone-binding proteins (PBPs), found in the pheromone-sensing hairs. We have studied the molecular determinants recognized by the two PBPs found in the gypsy moth, using three pheromone/PBP binding assays. Results indicate that (i) PBPs bind analogs of the pheromone with some discrimination; (ii) PBPs experience enhancement of binding when presented with 1a or its enantiomer and 4a simultaneously; and (iii) the binding enhancement is also seen at high ligand:PBP ratios. We found no evidence of allostery, so the synergistic binding effects and the concentration effect may only be explained by multimerization of PBPs with each other, which leads to more than one population of binding sites. We suggest that the enhanced ligand binding at high ligand:PBP ratios may serve to sequester excess ligand and thereby attenuate very strong signals.     

Influence of the forest caterpillar hunter Calosoma sycophanta on the transmission of microsporidia in larvae of the gypsy moth Lymantria dispar

• 1 The behaviour of predators can be an important factor in the transmission success of an insect pathogen. We studied how Calosoma sycophanta influences the interaction between its prey [Lymantria dispar (L.) (Lepidoptera, Lymantriidae)] and two microsporidian pathogens [Nosema lymantriae (Microsporidia, Nosematidae) and Vairimorpha disparis (Microsporidia, Burellenidae)] infecting the prey.
• 2 Using laboratory experiments, C. sycophanta was allowed to forage on infected and uninfected L. dispar larvae and to disseminate microsporidian spores when preying or afterwards with faeces.
• 3 The beetle disseminated spores of N. lymantriae and V. disparis when preying upon infected larvae, as well as after feeding on such prey. Between 45% and 69% of test larvae became infected when C. sycophanta was allowed to disseminate spores of either microsporidium.
• 4 Laboratory choice experiments showed that C. sycophanta did not discriminate between Nosema‐infected and uninfected gypsy moth larvae. Calosoma sycophanta preferred Vairimorpha‐infected over uninfected gypsy moth larvae and significantly influenced transmission.
• 5 When C. sycophanta was allowed to forage during the latent period on infected and uninfected larvae reared together on caged, potted oak saplings, the percentage of V. disparis infection among test larvae increased by more than 70%. The transmission of N. lymantriae was not affected significantly in these experiments.
• 6 Beetles never became infected with either microsporidian species after feeding on infected prey.
• 7 We conclude that the transmission of N. lymantriae is not affected. Because no V. disparis spores are released from living larvae, feeding on infected larvae might enhance transmission by reducing the time to death and therefore the latent period.

     

Pheromone-modulated optomotor response in male gypsy moths,Lymantria dispar L.: Directionally selective visual interneurons in the ventral nerve cord

In response female pheromone the male gypsy moth flies a zigzagging path upwind to locate the source of odor. He determines wind direction visually. To learn more about the mechanism underlying this behavior, we studied descending interneurons with dye-filled micro-electrodes. We studied the interneuronal responses to combinations of pheromone and visual stimuli.

Modelling the use of NPV for the biological control of Asian gypsy moth Lymantria dispar invading New Zealand

1 The accidental introduction of the Asian strain of gypsy moth (AGM) Lymantria dispar (L.) to New Zealand poses a major threat to New Zealand's forestry industry. To aid eradication and control decisions in the event of its establishment, a model was developed for the effect of nuclear polyhedrosis virus (NPV) as biological control for AGM in New Zealand. 2 The model simulates within‐ and between‐season gypsy moth population dynamics, including temperature‐dependent development, density dependence through predation and resource limitation, and interactions with NPV. 3 Following its introduction to New Zealand, AGM is predicted to increase more quickly and have more severe outbreaks than the European strain. In the absence of predators, the model predicts initial outbreaks then damped oscillations to an equilibrium. 4 In the model, a single application of NPV (2500 GPIB ha^?1) at the time of maximum larval density gave up to 80% suppression of peak larval densities in the following year. The same level of suppression was achieved in the absence of predators. 5 In the long term, the model predicted that spraying when an outbreak was just beginning gave best results (a 50–70% reduction of the following two outbreaks). Simulation of threshold spraying resulted in NPV application, on average, every 7 years and suppression of outbreak densities by 40–70%. Following a single application, NPV was maintained in the population as a classical biological control agent, giving approximately a 20% reduction in outbreak densities. 6 Eradication of AGM using NPV was possible if larval densities were very low.     

Male death resulting from hybridization between subspecies of the gypsy moth,Lymantria dispar

We explored the origin of all-female broods resulting from male death in a Hokkaido population of Lymantria dispar through genetic crosses based on the earlier experiments done by Goldschmidt and by testing for the presence of endosymbionts that are known to cause male killing in some insect species. The mitochondrial DNA haplotypes of the all-female broods in Hokkaido were different from those of normal Hokkaido females and were the same as those widely distributed in Asia, including Tokyo (TK). Goldschmidt obtained all-female broods through backcrossing, that is, F1 females obtained by a cross between TK females (L. dispar japonica) and Hokkaido males (L. dispar praeterea) mated with Hokkaido males. He also obtained all-male broods by mating Hokkaido females with TK males. Goldschmidt inferred that female- and male-determining factors were weakest in the Hokkaido subspecies and stronger in the Honshu (TK) subspecies. According to his theory, the females of all-female broods mated with Honshu males should produce normal sex-ratio broods, whereas weaker Hokkaido sexes would be expected to disappear in F1 or F2 generations after crossing with the Honshu subspecies. We confirmed both of Goldschmidt''s results: in the case of all-female broods mated with Honshu males, normal sex-ratio broods were produced, but we obtained only all-female broods in the Goldschmidt backcross and obtained an all-male brood in the F1 generation of a Hokkaido female crossed with a TK male. We found no endosymbionts in all-female broods by 4,′6-diamidino-2-phenylindole (DAPI) staining. Therefore, the all-female broods observed in L. dispar are caused by some incompatibilities between Honshu and Hokkaido subspecies.     

Photoperiod cues and the modulatory action of octopamine and 5-hydroxytryptamine on locomotor and pheromone response in male gypsy moths,Lymantria dispar

Experiments were conducted to determine whether the biogenic amines octopamine (OA) and 5-hydroxytryptamine (5-HT) exert modulatory effects on pheromone responsiveness and random locomotor activity in male gypsy moths. When injected into males, OA significantly enhanced sensitivity to pheromone, while 5-HT enhanced general locomotor activity, results that were very similar to those previously shown for the cabbage looper. Maximal effect of the amines, however, was observed when injection occurred just prior to the onset of scotophase, rather than photophase, as we had originally hypothesized for this diurnally active insect. Male gypsy moths also displayed a prominent scotophase response, with sensitivity to pheromone greater in the scotphase compared with photophase, but with the level of random locomotor activity lower in scotophase than in photophase. The upwind flight behavior of males to a pheromone source in a wind tunnel, as well as the time spent at the source, were also significantly different in the two light regimes. Furthermore, when exposed to a 1 h scotophase (instead of the normal 8), or to continuous dark conditions, while males exhibited response to pheromone and locomotor activity during the same scotophase and photophase periods as observed in a 16:8 light : dark cycle, the levels of response, as well as qualitative aspects of the upwind flight behaviors in both periods were a function of the light intensity. Our combined results suggest that male gypsy moths display a bimodal rhythm of locomotor and pheromone response over the diel cycle, with light intensity and scotophase onset providing critical cues for the expression of behaviors, as well as the modulatory action of the amines. © 1992 Wiley-Liss, Inc.     

提高生态位模型转移能力来模拟入侵物种 的潜在分布

生态位模型利用物种分布点所关联的环境变量去推算物种的生态需求, 模拟物种的分布。在模拟入侵物种分布时, 经典生态位模型包括模型构建于物种本土分布地, 然后将其转移并投射至另一地理区域, 来模拟入侵物种的潜在分布。然而在模型运用时, 出现了模型的转移能力较低、模拟的结果与物种的实际分布不相符的情况, 由此得出了生态位漂移等不恰当的结论。提高生态位模型的转移能力, 可以准确地模拟入侵物种的潜在分布, 为入侵种的风险评估提供参考。作者以入侵种茶翅蝽(Halyomorpha halys)和互花米草(Spartina alterniflora)为例, 从模型的构建材料(即物种分布点和环境变量)入手, 全面阐述提高模型转移能力的策略。在构建模型之前, 需要充分了解入侵物种的生物学特性、种群平衡状态、本土地理分布范围及物种的生物历史地理等方面的知识。在模型构建环节上, 物种分布点不仅要充分覆盖物种的地理分布和生态空间的范围, 同时要降低物种采样点偏差; 环境变量的选择要充分考虑其对物种分布的限制作用、各环境变量之间的空间相关性, 以及不同地理种群间生态空间是否一致, 同时要降低环境变量的空间维度; 模型构建区域要真实地反映物种的地理分布范围, 并考虑种群的平衡状态。作者认为, 在生态位保守的前提下, 如果模型是构建在一个合理方案的基础上, 生态位模型的转移能力是可以保证的, 在以模型转移能力较低的现象来阐述生态位分化时需要引起注意。     

Pheromone‐binding proteins in the Asian gypsy moth females,Lymantria dispar,recognizing the sex pheromone and plant volatiles

Lepidopterans are known to have different pheromone‐binding proteins with differential expression patterns that facilitate specific signal transduction of semiochemicals. Two PBPs of the Asian gypsy moth, Lymantria dispar, were reported to express in both females and males, but their physiological functions were unknown. Results showed that LdisPBP1 and LdisPBP2 were expressed in the sensilla trichodea of males and the s. trichodea and s. basiconica of females. When LdisPBP1 gene was targeted by RNA interference (RNAi) in males, the expression of LdisPBP1 and LdisPBP2 decreased by 69 and 76%, respectively, and when LdisPBP2 gene was targeted by RNAi, they decreased by 60 and 42%, respectively. In females, after treatment with LdisPBP1 dsRNA, LdisPBP1 and LdisPBP2 levels were reduced by 26 and 69%, respectively, and LdisPBP2 dsRNA reduced the relative expression of them by 4 and 62%, respectively. The expression of LdisPBP1 and LdisPBP2 was interdependent. Electroantennogram (EAG) recordings showed that LdisPBPs participate in the recognition of the sex pheromone in males, and the sex pheromone and plant volatiles in females. The function of LdisPBPs represents the sex‐specific roles.