A new psychodid species from Saban tank bromeliads

A new species of Neotropical Psychodidae, Alepia apexalba sp. nov., is described from dry-forest tank bromeliads in Saba, Netherlands Antilles. Larvae, pupae and adults are described and figured. It is possible to relate larvae and adults because the latter were reared from pupae collected from the bromeliads (Tillandsia utriculata) that also contained larvae. Bromeliads are adapted to intercept canopy litter and throughfall water, and decaying litter is washed into and retained by the leaf bases. It is from this aquatic habitat that the larvae and pupae were collected.     

Influence of thermal conditions on habitat use by a rare spring‐emerging butterfly Euphydryas editha taylori

We may expect butterflies as ectotherms to have particularly active life‐history stages that occur in the warmest and lightest times of the year; however, there are temperate species that are active when climatic conditions seem unfavourable and photoperiod short, such as the Taylor's checkerspot (Euphydryas editha taylori). For such species, studies suggest that even subtle changes to microclimate can potentially impact populations. Thus, understanding how in situ variations in microclimate influence the Taylor's checkerspot butterfly could provide much needed insights into more effective management. We conducted a series of surveys that explored (i) adult habitat use, (ii) final instar larval distribution and (iii) adult movement up to and across site boundaries at two sites in Oregon, USA, in 2010 and 2011. We found that in situ habitat use by the Taylor's checkerspot butterfly was strongly influenced by microclimate. Both adult activities and final instar larvae distribution were clustered within the warmest areas of the sites. Moreover, adults did not use up to 59% and larva up to 90% of their sites, despite vegetation structure and composition being uniform. More specifically, butterfly habitat use increased with increasing ground temperatures, and we found that areas with the highest ground temperatures were more exposed to direct sunlight. Similarly, we found that butterflies tended to only move through sunlit site boundaries. We conclude that the Taylor's checkerspot is sensitive to changes in its thermal environment at fine spatial scales. Our results highlight the importance of microclimate as an indicator of habitat quality, and establishing the thermal criteria in which species of concern exists may provide valuable insights into the implications of climate change.     

Water and carbohydrate levels at different developmental stages and dynamics in hibernating pupae of Pieris melete (Lepidoptera: Pieridae)

For insight into the physiological indicators of diapause in Pieris melete, water and carbohydrate (glycogen and trehalose) levels were measured under both natural and laboratory conditions. The highest water content (3.71–3.79 mg/mg dry weight) was found in larvae and developing pupae, which was substantially higher than in diapausing pupae (2.59 mg/mg dry weight). Water content was almost stable during diapause, except for individuals approaching diapause termination (3.43–3.58 mg/mg dry weight). The total carbohydrate level was significantly higher in pre‐pupae (47.41 μg/mg) compared to larvae (22.80 μg/mg) and developing pupae (21.48 μg/mg). The highest level of trehalose was detected in winter diapausing pupae, and no trehalose was found in larvae or developing pupae. Levels of glycogen were highest in pre‐pupae and lowest in diapausing pupae. Levels of total carbohydrate decreased as diapause proceeded, and no significant changes were found in trehalose levels for diapausing pupae under natural conditions or treated for 60–90 days at 5°C. Pupae treated at 20°C for 60–90 days had significantly lower levels of trehalose than those treated for 30 days. Glycogen content was relatively stable at 5°C, but increased after treatment under natural conditions and 20°C for more than 60 days. These results suggest that the dynamics of water and carbohydrate levels are potential physiological diapause indicators, which show metabolic differences between trehalose and glycogen during diapause development.     

Coevolution of the checkerspot butterfly Euphydryas chalcedona and its larval food plant Diplacus aurantiacus: larval response to protein and leaf resin

Summary Prediapause larvae of the checkerspot butterfly Euphydryas chalcedona were raised from hatch until entrance into diapause on artificial diets. The proportions of protein and host plant leaf resin differed among the diets. Larval size growth rates and mortality were monitored and overall rates and efficiencies of food use were computed.Larval survivorship, growth rate and size of larvae at idapause were significantly enhanced by increasing dietary protein content, particularly over the range found in leaves of the host plant. In contrast, an increasing dietary content of Diplacus aurantiacus leaf resin significantly depressed larval surviviorship, growth rates and size of larvae at diapause. A simple dosedependent interaction was observed between the effects of dietary leaf resin and protein on larval success. Dietary content of leaf resin and protein significantly influenced some measures of food utilization efficiency (ECI and ECD), but not others (AD and NUE).The negative interaction between the effects of dietary leaf resin and protein content suggests the leaf resin phenolic compounds reduce the availability of protein to the larvae. The results for efficiency indices of larval food use are potentially in conflict with this interpretation.The influence of host plant leaf resin and protein on larval success, coupled with the relation between photosynthesis and leaf nitrogen content, are consistent with the hypothesis that productivity can be enhanced by herbivore deterrence resulting from leaf resin production.     

Ontogenetic changes in the shelter site of a leaf-folding caterpillar, Vanessa indica

Factors responsible for ontogenetic habitat shifts were examined using larvae of the Indian red admiral butterfly, Vanessa indica (Herbst) (Lepidoptera: Nymphalidae). The larvae of V. indica fold leaves of China ramie, Boehmeria nipononivea Koidz. (Urticaceae), to form shelters that also serve as food. When constructing shelters, old larvae (usually third instar or older) frequently cut trenches at the bases of the leaves, whereas younger larvae do not. This trenching behaviour reduces the force required to fold large ramie leaves. Young larvae used small apical leaves as shelter sites. Once larvae were capable of cutting trenches, they moved proximally on the host plant and used middle leaves that either had completed or were about to complete expansion. Results of bioassays revealed that, for young larvae, apical and middle leaves did not differ in food quality. In contrast, for older larvae, the quality of middle leaves was higher than that of apical leaves. These observations suggest that young larvae decrease the risk of predation during shelter construction by using apical leaves that are relatively easy to fold, and that old larvae employ trenching to decrease the duration of leaf folding and improve growth rate by using middle leaves that are of high quality. Thus, the facilitation of leaf-folding by trenching is considered to reduce the necessity of using apical leaves, and the acquisition of the trenching ability triggers an ontogenetic shift in the selection of larval shelter sites.     

Diapause and development in the tobacco budworm,Heliothis virescens: A comparison of haemolymph ecdysteroid titres

The signal to induce diapause in H. virescens comes early in development (prior to the third instar in most insects), but the signal to break diapause can come shortly after entrance into diapause at pupation. Haemolymph ecdysteroid titres in both diapause-bound and non-diapause-bound Heliothis virescens larvae were similar in the first two thirds of the last-larval instar, when similar changes in morphology and behaviour occurred. However, the number of stepwise increases in titre and the timing of the steps was different in the two groups of larvae. Haemolymph ecdysteroid titres in the last third of the instar were approx, five times higher in non-diapause than in diapause-bound larvae. In diapausing pupae, haemolymph ecdysteroid titres dropped to levels found in larvae which had completed two thirds of the last instar. When diapausing pupae were warmed to break diapause, haemolymph ecdysteroid titres rose again. However, 2 of the 4 high ecdysteroid levels detected in pupae developing after diapause break were considerably lower than those detected for non-diapause pupae.     

Effects of putrescine on diapause induction and intensity,and post‐diapause development of Helicoverpa armigera

Effects of putrescine on diapause induction and intensity, and post‐diapause development in Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) from Wuhan, Hubei, China were studied in the laboratory at different temperatures and photoperiod conditions. The results showed a generally higher incidence of diapause in putrescine‐feeding groups. Putrescine feeding distinctly restricted the development of non‐diapause‐destined and diapause‐destined larvae, except at 0.01% putrescine concentration, which accelerated the development of larvae at 21 °C. Putrescine had no significant effect on the duration of diapause, although it inhibited the post‐diapause development of pupae. Photoperiod played a different role in diapause induction and post‐diapause development between 21 and 23 °C. Putrescine played a definite role in diapause induction and intensity, and post‐diapause development in H. armigera, and a significant interaction between putrescine, photophase, and temperature is to be expected.     

Oviposition behavior and offspring performance in herbivorous insects: consequences of climatic and habitat heterogeneity

The preference–performance hypothesis predicts that when female herbivorous insects determine where to position offspring of low mobility, they will select sites that maximize development and survival of those offspring. How this critical relationship responds to variation in climatic and habitat conditions remains untested, however, despite its important consequences for population and evolutionary dynamics. Here we report on 13 years of data totaling 1348 egg clusters of the montane Gillette's checkerspot butterfly Euphydryas gillettii (Lepidoptera: Nymphalidae). We used these data to test the hypothesis that, in environments with climatic and habitat heterogeneity, the oviposition behavior–offspring performance relationship should vary in both space and time. Orientation of egg clusters for maximum morning sun exposure is known to affect developmental rate. We therefore predicted female preference for morning sun orientation to be variable and a function of climatic and habitat conditions. We found that preference for egg cluster orientation on the leaf tracked the phenology of the start of the female flight season but that seasonal temperatures drove most of the variation in egg cluster development time. The relationship between behavior and performance was also dependent upon the climatic effects on survival; sun‐oriented egg clusters had higher survivorship in the coldest year of the four years for which measurements were made. We also examined how conifer cover affected larval survival and female oviposition behavior in one year. Females selected oviposition sites in more open habitat. However, when egg clusters were oriented to intercept morning sun, conifer cover increased survivorship to diapause. Finally, we found that predator activity was lower for morning sun‐oriented egg clusters suggesting that predation patterns may further influence habitat selection for oviposition. This study exemplifies how the relationship between oviposition behavior and offspring performance is context‐dependent: habitat and climate interact to determine preference–performance outcomes.     

Effect of temperature and photoperiod on diapause development in a Douglas fir seed chalcid, Megastigmus spermotrophus

Douglas fir seeds infested by diapausing larvae of a chalcid, Megastigmus spermotrophus, were transferred under different temperature and photoperiod regimes at various dates during autumn and winter. Both winter diapause and prolonged diapause were compared to the diapause patterns observed in control lots kept under natural conditions. The results showed that exposure to low temperatures in autumn and winter is required for the completion of diapause development. Median adult emergence dates and the date of transfer of larvae to 20°C were negatively correlated. The frequency of prolonged diapause of larvae transferred to 20°C decreased significantly after November. When larvae were submitted to different constant temperatures, the longer the daylength, the higher and faster the reactivation. These results suggest that chalcid larvae can perceive daylength through the seed coat. This phenomenon is probably related to the fact that most of the infested seeds falling in autumn are usually covered by a layer of leaf litter during the winter. Received: 14 June 1996 / Accepted: 24 February 1997     

麦红吸浆虫滞育发生和解除过程中总脂和甘油三酯含量变化

【目的】脂类与昆虫滞育密切相关。本研究旨在明确麦红吸浆虫Sitodiplosis mosellana (Géhin)滞育过程中脂类物质含量的变化规律,探讨麦红吸浆虫滞育与脂类物质变化的关系。【方法】采用香兰素硫酸显色法测定了2008年5月－2010年1月不同时间陕西杨凌养虫圃内麦红吸浆虫滞育前、滞育期及滞育解除后幼虫和蛹体内总脂和甘油三酯含量。【结果】 滞育前幼虫总脂和甘油三酯含量分别为378.12和291.67 μg/mg,显著高于整个滞育期（P<0.05）。滞育年周期中,冬季总脂和甘油三酯含量最高,翌年1月结茧幼虫二者含量分别为335.29 和275.72 μg/mg,显著高于其他季节（P<0.05）;整个滞育期间,裸露幼虫和结茧幼虫总脂和甘油三酯随季节变化趋势相同,但同期结茧幼虫含量高于裸露幼虫;滞育当年与第2年同期幼虫总脂和甘油三酯含量差异不显著（P>0.05）。滞育解除后,总脂和甘油三酯含量随着幼虫的发育和变态逐渐降低,其中中蛹和后蛹显著低于活动幼虫（P<0.05）。【结论】麦红吸浆虫滞育不同时期幼虫及蛹总脂和甘油三酯含量存在明显差异,其滞育与脂类物质的含量密切相关。     

Ontogenetic patterns of cold-hardiness and glycerol production in Sarcophaga crassipalpis

Developmental patterns of low-temperature tolerance and glycerol production were determined for larval, pupal and adult stages of the flesh fly Sarcophaga crassipalpis Macquart (Diptera: Sarcophagidae). Both diapause and non-diapause-destined flies were reared at relatively high temperatures, 20° or 25°C, prior to testing. Cold tolerance was greatest for diapause pupae aged 12–35 days after pupariation. Among non-diapause-destined flies, pupae exhibited a greater level of low temperature tolerance than larvae or adults. Although diapause pupae were more tolerant than non-diapause pupae maximal cold tolerance was not attained in either group until 10 days after pupariation. Non-diapause-destined feeding and wandering larvae had higher glycerol levels than larvae destined for diapause. During the first 6 weeks after pupariation glycerol titres increased steadily in diapause pupae. Rapid loss of glycerol is associated with the termination of pupal diapause.     

Regulatory mechanisms in phenotypic plasticity of diapause and nondiapause pupal colouration of the swallowtail butterfly Papilio machaon

Nondiapause pupae of Papilio machaon L. exhibit pupal colour diphenism comprising green–yellow and brown–white types. To understand the regulatory mechanism underlying the control of pupal colouration in P. machaon, the effect of environmental cues on diapause and nondiapause pupal colouration is investigated. When larvae reared under short‐day and long‐day conditions are allowed to pupate in sites with a smooth surface and a yellow background colour, all diapause pupae exhibit a brown–white type and 89.5% of nondiapause pupae exhibit a green–yellow type, respectively. With rough‐surface pupation sites, all diapause pupae exhibit brown–white and intermediate types, whereas a large proportion of nondiapause pupae exhibit brown–white and intermediate types, although some exhibit a green–yellow type. When extracts prepared from the head‐thoracic and thoracic‐abdominal regions of larval central nervous systems are injected into the ligated abdomens of P. machaon short‐day pharate pupae, all recipients exhibit a brown–white colouration. Furthermore, when each extract is injected into the ligated abdomen of Papilio xuthus L. short‐day pharate pupae with orange‐pupa‐inducing factor activity, recipients injected with the head‐thoracic extract exhibit the brown type, whereas those injected with the thoracic‐abdominal extract exhibit an orange colour. The results indicate that the response to the environmental cues of pupation site in P. machaon changes according to the photoperiodic conditions experienced during larval stages, and that at least two hormonal factors producing brown–white pupae are located in the larval central nervous system, with the secretion of these factors being regulated by the recognition of environmental cues in long‐day larvae.     

Ecological consequences of shelter sharing by leaf-tying caterpillars

A wide variety of insect herbivores construct and inhabit leaf shelters (ties, rolls, folds, and webs). Shelter construction can lead to a high rate of secondary occupation by other arthropods, including other species of constructors. The consequences for the inhabitants of secondarily occupying these shelters are currently unknown. In this study, we conducted field experiments to examine the fitness consequences (survival and attack by natural enemies) for caterpillars that (i) occupy a shelter with conspecifics vs. occur singly; and (ii) establish a new shelter vs. colonize a pre‐existing one. In addition, we conducted factorial laboratory experiments to test the hypothesis that caterpillars sharing shelters with conspecifics might have reduced construction costs (a potential benefit of shelter‐sharing or secondary occupation). Larvae of Psilocorsis quercicella Clemens (Lepidoptera: Oecophoridae) placed in white oak [Quercus alba L. (Fagaceae)] leaf ties alone or in groups of three had equal likelihood of survival from natural enemies. This same caterpillar species, however, had a higher disappearance rate when placed in pre‐existing leaf ties than when placed in newly formed ones, suggesting a potential cost of secondary colonization. A similar experiment with a closely related species [Psilocorsis cryptolechiella (Chambers)], however, failed to detect a cost of secondarily occupying shelters made on beech, Fagus grandifolia Ehrh. (Fagaceae). In the laboratory experiment, we found no evidence of shelter‐sharing benefits; rather larvae reared in shelters in groups of three had lower pupal mass (and thus lower potential fecundity) than larvae reared singly, suggesting a cost of shelter sharing. Moreover, groups of larvae forced to repeatedly construct new shelters tended to have reduced survival relative to the other treatment, suggesting that energetic constraints are more likely to reduce fitness when larvae cohabit shelters. Taken together, these results indicate that the common phenomenon of shelter sharing by leaf‐tying caterpillars has either neutral or negative effects for the occupants. The fact that these leaf‐tying caterpillars actually share shelters may simply reflect limited availability of oviposition sites.     

Pupal colour dimorphism in California Battus philenor: pupation sites, environmental control, and diapause linkage

ABSTRACT.

• 1 Natural pupation sites and corresponding pupal colour (green or brown) were determined for samples of Battus philenor (L.) from two Californian populations.
• 2 Larvae pupate off the ground on trees, shrubs and man-made objects.
• 3 The vertical distribution of pupation sites and relative frequencies of pupae formed on narrow twigs and broad substrates show interpopulation variability, and seem to be determined by habitat-specific and possibly behavioural differences among populations.
• 4 The percentage of‘mismatched’pupae in green leafy environments (brown) is greater than that on wide substrates (green). Heterogeneity in samples of the latter suggest strong but sporadic predation pressure on non-cryptic pupae in exposed areas.
• 5 Green and brown substrates generally promoted formation of cryptic green and brown pupae although rearing conditions modified pupal colour response to substrate colour and larval pupation site choice.
• 6 Warm temperatures and long days increased the production of brown pupae. Short photoperiods increased the tendency of larvae to pupate on narrow twig-like substrates and to form green pupae.
• 7 Green pupae show less tendency to diapause than brown pupae. The difference between percentage diapause in the two colour forms increases under conditions favouring progressively more continuous development.

     

Use of learned visual cues during habitat location by Brachymeria intermedia

Like many other parasitoids, Brachymeria intermedia (Hymenoptera: Chalcididae) uses olfactory cues to find its host, but in addition it appears to use learned visual cues to focus its searching efforts at the macrohabitat level. In laboratory experiments, females were held in cages where Lymantria dispar pupae were hidden either in a vertical, tree-like structure or on the floor. After four days females had learned to search for hosts in the structure in which they previously had found pupae. Such training was reversible. During similar tests in a semi-natural situation, in which pupae were hung from a tree trunk or were hidden under leaf litter, females also tailored their subsequent searching to favour the macrohabitat where hosts previously had been found. This parasitoid most likely uses a combination of visual and olfactory cues during host searching.     

Sexual dimorphism in photoperiodic plasticity of body mass in the green dock leaf beetle <Emphasis Type="Italic">Gastrophysa viridula</Emphasis> (Coleoptera,Chrysomelidae)

Sexual dimorphism in body mass was studied in prepupae, pupae and immature adults of the green dock leaf beetle Gastrophysa viridula under a constant temperature of 24°C and two photoperiods (12L:12D and 22L:2D). Females were significantly heavier compared to males at all the three developmental stages; just after emergence from pupae they weighed, on average, 11.4 mg, while males—10.3 mg. Sex differences in photoperiodic body mass plasticity were revealed: under short-day conditions pupal and adult mass in females was significantly higher compared to long day, but not in males. Such a response to short day (the factor inducing reproductive diapause in this species) is likely to promote accumulation of greater amount of nutrients by females which is necessary for earlier oviposition after overwintering.     

Ultrastructure of neurosecretory cells in the frontal ganglion of the tobacco hornworm, Manduca sexta(L)

Ultrastructural evidence is presented to indicate the synthesis, storage, and packaging of neurosecretory material in the frontal ganglion of Mandaca sera. Two morphologically distinct stages in the development of NSG were observed in the NSC. The immature granule contains granular electron dense material and arises from dilations of the rough endoplasmic reticulum. In diapause pupae the immature granules accumulate, whereas in developing larvae and pupae, they fuse with the proximal face of the Golgi apparatus. The mature granule contains opaque electron dense material and is seen in close association with the distal cisternae of the Golgi apparatus in developing pupae and larvae. The mature granules presumably contain the material from the immature granules which has been chemically altered and condensed by the Golgi apparatus and probably represent the mature NSG.The second process in neurosecretory cells of developing larvae is cyclic and the various stages are described. A comparison of neurosecretion in photoperiodically induced diapause and developing (non-diapause) larvae and pupae is presented.     

Effect of habitat type and soil moisture on pupal stage of a Mediterranean forest pest (Thaumetopoea pityocampa)

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Experimental evidence for an alkali ecotype of <Emphasis Type="Italic">Lolium multiflorum</Emphasis>, an exotic invasive annual grass in the Central Valley,CA, USA

One of the characteristics of highly invaded ecosystems is that exotic species are often poor invaders of edaphically severe sites, which become refuges for native flora. To investigate the invasive potential of Lolium multiflorum (Per.) into alkali sites in California, an ex-situ reciprocal transfer experiment was carried out using seeds from populations of L. multiflorum taken from three sites differing in alkalinity (and inundation), including alkali sink soils (pH 8.5) and sink matrix soils (pH 7.4) located within meters of each other, and non-sink soils (pH 5.0) located several km away. Survivorship, plant height, leaf number and seed production were assessed. In addition, a native composite, Hemizonia pungens (Hick.), commonly found on alkali sinks was also sampled at the sink and sink matrix microsites. Lolium multiflorum plants grown from alkali sink and sink matrix seeds produced fewer leaves and seeds but were taller than plants grown from non-alkali seeds, the latter perhaps an adaptation to frequently inundated soils. Non-alkali genotypes fared poorly in sink soils for all traits, both in comparison to their growth on non-sink soils, and in comparison to the sink and sink edge genotypes. This suggests the existence of L. multiflorum ecotypes adapted to inundated alkali sinks, a genotypic difference that occurs on a broad spatial scale (kilometers), but not so obviously on the micro-site scale (meters) between sink and sink matrix populations. These data suggest that the absence of exotic invasives from alkali sites may be temporary if they are evolving tolerance for these severe sites, and this may threaten the future of the native alkali specialists that currently find refuge in these sites.