Low temperature tolerance and starvation ability of the oak processionary moth: implications in a context of increasing epidemics

• 1 We investigated how modifications in winter and spring temperature conditions may affect the survival of a spring‐hatching Lepidoptera, the oak processionary moth Thaumetopoea processionea.
• 2 Supercooling and chilling injury experiments indicate that eggs are especially cold hardy at the start of the winter period, although this ability is reduced later in the season. In the spring, young larvae are sufficiently cold hardy to ensure no direct mortality as a result of late frosts.
• 3 A comparison of phenological models shows that neonate larvae may await the unfolding of new oak leaves for relatively long periods (e.g. 1–30 days). Under both low (4°C after 5 days at 16°C) and high temperature experimental scenarios (constant 16°C), the majority of neonate larvae can survive starvation for more than 2 weeks.
• 4 Larvae may also suffer from food depletion once their development has been initiated (e.g. during cold springs) if the threshold temperature for feeding is not reached for several consecutive days, or in the case of late frosts affecting foliage availability. When temperature is reduced to 4°C, developing larvae become inactive and do not feed anymore; their starvation survival capability is reduced to approximately 2 weeks (cold spring hypothesis). At 16°C, developing larvae that are deprived of food can only survive for 10 days (late frost hypothesis).
• 5 We conclude that, in the oak processionary moth, neonate larvae are relatively well adapted to early hatching relative to budburst, ensuring them the highest foliage quality for development. In some years, however, phenological asynchrony or cold spring conditions may affect the persistence of populations at the limits of the species' range.

     

Minute tubercles in bitterling larvae: Developmental dynamic structures to prevent premature ejection by host mussels

1. Bitterlings are small freshwater fish that use long ovipositors to lay eggs in host mussels, and they have morphological adaptations to increase larval survival. The most well‐known adaptation is the minute tubercles on the skin surface of larvae; they are developed in early‐stage larvae with weak swimming ability and disappear in free‐swimming larvae before they leave the host mussel.
2. In the present study, I comprehensively analyzed the developmental stages of Rhodeus pseudosericeus larvae, their morphological and physiological characteristics, their migration inside mussels, and the development of minute tubercle in order to elucidate the morphological function of the minute tubercles. These tubercles began to develop 1 day after hatching (formation stage), grew for 2–5 days (growth stage), reached the peak height after 6–7 days (peak stage), abruptly reduced in height after 8–10 days (abrupt reduction stage), and gradually reduced in height (reduction stage) until completely disappearing 27 days after hatching (disappearance stage).
3. The larvae remained in the mussels’ interlamellar space of the gill demibranchs until 10 days after hatching and began to migrate to the suprabranchial cavity 11 days after hatching. At this time, the larvae had a heart rate and the caudal fin began to develop. At 24 days after hatching, the minute tubercles had almost disappeared, and some individuals were observed swimming out of the mussels.
4. The results presented herein elucidate that the minute tubercles are the developmental dynamic structures that the bitterling larvae have morphologically adapted to prevent premature ejection from the mussel.

     

Timing and duration of the life cycle of Asian longhorn beetle Anoplophora glabripennis (Coleoptera: Cerambycidae) in southern England

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Implications of early production in an invasive forest pest

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Egg cannibalism by larvae and adults of the milkweed leaf beetle (Labidomera clivicollis, Coleoptera: Chrysomelidae)

Abstract.

• 1 Egg cannibalism is a form of infanticide that has been implicated in the evolution of guarding of eggs and immatures in some species of insects. The milkweed leaf beetle, Labidomera clivicollis (Coleoptera: Chrysomelidae), exhibits three types of egg cannibalism in the field: siblicide, cannibalism of eggs by older larvae from earlier hatching egg clutches, and cannibalism of eggs by adult females. Unlike their close relative, L.suterella (Choe, 1989), female L.clivicollis do not guard their eggs or immatures. They move slowly about a patch of milkweeds laying multiple egg clutches.
• 2 First instar and older larvae cannibalized eggs in two geographically separated study populations (subspecies) in Austin, Texas, and Bridgeport, New York, U.S.A. Although adult females of both populations cannibalized eggs in the laboratory, only the Texas subspecies, L.c.rogersii, exhibited such cannibalism in the field.
• 3 In the field, correlates of siblicide varied both temporally (within subspecies) and spatially (between subspecies) in terms of whether they were statistically significant, but trends were all in the same direction. Group size was positively correlated with hatching success and siblicide, but negatively correlated with other types of predation. Siblicide was also positively correlated with egg density in a laboratory study of the Texas subspecies, L.c.rogersii.
• 4 In the laboratory, an average of 15–17% of L.c.clivicollis eggs never developed embryos. Although these were almost always cannibalized, some viable eggs were also eaten and there is no evidence that females increased the proportion of infertile eggs they laid to increase siblicide.
• 5 Field data and laboratory experiments showed that adult female L. c.rogersii cannibalized eggs while males rarely did. Females preferentially ate the eggs of other females over their own eggs in an experiment that removed spatial cues.
• 6 Although the selective context of cannibalism is not demonstrated here, I suggest that females may increase siblicide by increasing egg density and may cannibalize eggs to protect their own eggs from being eaten by second and third instar larvae produced by other females.

     

Biology of the Eucalyptus leaf beetle Paropsisterna selmani (Chrysomelidae: Paropsini): a new pest of Eucalyptus species (Myrtaceae) in Ireland

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Targeted sugar provision promotes parasitism of the cereal leaf beetle Oulema melanopus

• 1 Parasitoids may often lack access to sugar (e.g. floral nectar) in agricultural settings. Strategically timed spraying of host plants with sugar solution may provide one means of enhancing parasitism at the same time as minimizing nontarget effects (e.g. benefiting the pest itself).
• 2 Sucrose was sprayed in wheat fields of northern Utah (U.S.A.) to assess the effects on parasitism of the cereal leaf beetle Oulema melanopus by the larval parasitoid Tetrastichus julis.
• 3 Early‐season sugar provisioning, when larvae of the pest were first hatching and parasitoid adults were newly emerged, did not affect the numbers of cereal leaf beetle larvae that matured in treated plots but increased parasitism rates of beetle larvae by four‐fold in 2006 and by seven‐fold in 2007.
• 4 No net influx of adult parasitoids into plots was detected after the application of sugar. Locally‐emerging parasitoids may have spent less time searching for their own food needs versus hosts. A laboratory experiment also confirmed that access to sucrose significantly increased parasitoid longevity.
• 5 The field experimental results obtained demonstrate that applications of sugar, implemented to target a key time of the growing season when benefits are maximized for parasitoids and minimized for their hosts, can strongly promote parasitism of the cereal leaf beetle in wheat fields.

     

Bioenergetics of abbreviated larval development in the bromeliad crab,Metopaulias depressus (Decapoda: Grapsidae)

• 1.1. Larvae of the bromeliad crab, Metopaulias depressus Rathbun, were reared in the laboratory, and changes in dry weight (W), ash-free W (AFW), carbon, nitrogen, hydrogen, protein, lipid, carbohydrates and respiration rate were measured during development from hatching to metamorphosis.
• 2.2. Development was successful in rain-water from bromeliads (pH < 5–6), but not in river water from the same region (pH 8). It is abbreviated, with two non-feeding zoeal stages (2.5–3.5 days each) and a feeding megalopa (8.5–10 days). Development to metamorphosis can also be completed in the absence of food (facultative lecithotrophy).
• 3.3. Dry weight and other absolute biomass values per individual vary significantly between different hatches, whereas changes in the relative (% of W or AFW) composition follow quite invariable patterns: ash increases from hatching through the first part of megalopa development, organic biomass decreases concurrently.
• 4.4. Elemental and biochemical data show that lecithotrophy of the zoeal stages as well as continued endotrophic development in the megalopa depend chiefly on degradation of lipid reserves and less on protein. No significant growth was observed in organic constituents when food was available, but without food the megalopa reached metamorphosis with only half the lipid and less than two thirds the protein of fed siblings.
• 5.5. The relationship between C and lipid is similar in M. depressus larvae as in planktotrophic marine crab larvae, whereas that between N and protein differs; it indicates the presence of unusually large quantities of unidentified non-protein N.
• 6.6. Exuvial losses of late premoult biomass or energy are very low in the zoeal stages (2 and 3%), but increase in the megalopa (16% in W, 10% in C, 7–8% in N, H and energy).
• 7.7. Respiration rate per individual increases gradually during larval development (0.6–0.8 μg O₂/hr). Starved megalopa larvae reveal lower individual but higher W-specific metabolism than fed larvae.
• 8.8. Bioenergetic traits of abbreviated larval development are discussed in relation to those known from regular (planktotrophic marine) development of brachyuran crabs. M. depressus is highly adapted to life and development in a physically extreme terrestrial environment.

     

Estimating temperature effects on Drosophila suzukii life cycle parameters

1. Drosophila suzukii is an invasive, polyphagous pest of soft-skinned fruits, having huge impact on fruit production in Asia, North and South America and Europe including Germany.
2. To investigate the effect of temperature on oviposition, egg-to-adult development success and duration, as well as immature heat survival and adult cold survival for a German D. suzukii population several experiments were conducted under different constant temperatures in the laboratory. The resulting life cycle data were described mathematically as functions of temperature and compared with experimental results of other researchers in a summary table.
3. Curve fittings used herein revealed that minimum, optimum and maximum temperatures are: 13.2, 26.7 and 33.6 °C for oviposition, 14.1, 22.6 and 30.0 °C for egg-to-adult development success, and 9.6, 27.3 and 35.7 °C for egg-to-adult development duration. Eggs and larvae of D. suzukii showed a reduced heat survival within the tested temperature range of 29 to 41 °C and exposure durations from 1 to 8 h. A cold survival rate of 50% was measured at e.g. −6 °C for 4 h in summer morph adults and at e.g. −6 °C for 45 h in winter morph adults confirming that the latter are more cold tolerant.
4. Results obtained in this study for a German population of D. suzukii are similar to those obtained for populations of other origins such as Canada, Japan, Spain and USA. Thus, presumably, present data based on a German D. suzukii population can be used for a new or fine-tune of already existing population dynamics models of D. suzukii in order to support an effective pest management strategy.

     

Veligers from the nudibranch <Emphasis Type="Italic">Dendronotus</Emphasis><Emphasis Type="Italic">frondosus</Emphasis> show shell growth and extended planktonic period in laboratory culture

The planktonic period of planktotrophic veliger larvae from the nudibranch Dendronotus frondosus was characterized by laboratory culture methods. Larvae in culture successfully metamorphosed at 73–86 days after hatching. These veligers have Type 2 (Thompson) larval shells that significantly increased in length over the first 7–14 days after hatching. Direct observations of the development of nudibranch larvae with Type 2 protoconchs are limited, and these data help clarify previous attempts to correlate shell type and growth with minimum planktonic periods. Although these are not absolute values for the planktonic period of D. frondosus larvae, these data show the potential for extended larval dispersal and may help explain reports of an extensive geographic range in north-temperate waters for this species.     

Field and laboratory studies on the timing of oviposition and hatching of the western black-legged tick, Ixodes pacificus (Acari: Ixodidae)

The timing of oviposition and hatching of Ixodes pacificus was investigated in the field and at constant temperatures in the laboratory. Replete females held at temperatures between 9 and 29°C began depositing eggs a mean of 9–70 days after drop off. Egg masses held between 12 and 25°C commenced hatching 25–178 days after the onset of oviposition. Eggs held at 9 or 29°C did not hatch. The lower temperature thresholds for development (LTD) for oviposition and hatching were 6.5 and 9°C, respectively. The number of degree days required for oviposition and hatching was 173 and 588, respectively. Replete females placed in the field on 2 December through to 8 March deposited eggs from 2 February through to 24 April; the eggs commenced hatching between 2 July and 21 August. Unfed larvae from two of 20 egg masses survived through the winter and fed readily when exposed to deer mice (Peromyscus maniculatus) on 22 April. Replete larvae were returned to the field and moulted between 9 and 21 August. Larvae exposed to deer mice in August, 4 weeks after hatching, also fed readily. Although further studies are needed to clarify the timing of nymphal development, the present study suggests that I. pacificus requires more than 1 year to complete its life cycle.     

Larval development of two parasitic flies (Conopidae) in the common host Bombus pascuorum

Abstract.

• 1 Whenever parasitism by more than one female occurs, larvae of parasitoids not only have to resist host defence but also face competition with other (unrelated) larvae. Competition is particularly important in solitary parasitoids where only one larva is able to complete its development. Such a situation is found in Conopidae (Diptera) parasitizing adult bumble bees where larvae of two species of conopid flies, Sicus ferrugineus L. and Physocephala rufipes F. often compete within the common host Bombus pascuorum Scopoli. This study analysed the larval development of the two species and asks how competition among larvae may be regulated.
• 2 Parasitized workers of B.pascuorum were caught in the field and kept according to different experimental schedules in the laboratory. This provided stage-structured data for the temporal course of development of the parasitic larvae. For the analysis, a simulation model was constructed that estimated the duration of all parasitic stages (Manly, 1990, first method). In both species the egg stage was found to be approximately 2 days, first instar 3 days, second instar 4 days, and third instar 3 days. The total development time is an estimated 10.8 days from oviposition in S.ferrugineus and 11.4 days in P.rufipes. S.ferrugineus develops faster in the beginning, probably because of its larger egg size, whereas P.rufipes pupates at larger size. First-instar larvae of both species possess strong, pointed mandibles.
• 3 The success of conopid larvae seems only marginally affected by host defence, for a single larva per host almost always completes development. Under competition, however, mortality rate increases substantially, and most larvae die in their first instar. Moreover, they show signs of melanization. The estimates for developmental times and the patterns found in this study suggest that conopid larvae seem capable of physical attacks, particularly during the first instar, when elimination of competitors is most common, and that S.ferrugineus has a time advantage because of its faster early development. Because most studies have previously been carried out with hymenopteran parasitoids, this study provides new information about the other large group of parasitoid insects, the Diptera, and demonstrates convergent patterns.

     

To hatch or not to hatch? Egg hatch response to larval density and to larval contact in a treehole mosquito

Abstract.

• 1 We investigated the effect on egg hatch of exposure to: (1) varying larval density, and (2) larval contact in Aedes triseriatus Say (Diptera: Culicidae). For 2 days in the laboratory we submerged eggs into a treehole water medium containing 0 (control), 4, 12 or 24 larvae that could either contact the eggs directly or were separated from them by a screen. Following treatment, abundance of microorganisms on the egg surfaces, a food source for newly hatched larvae and a proposed hatching stimulus, was assessed by counts made from serial dilutions of samples.
• 2 We discovered a complex hatching response to larval contact and to larval density, and an interaction between these two factors in their effect on microbial growth. Hatching was inhibited in the 0-larva control, even though microorganisms grew abundantly on the eggs. Hatch rate, as well as microbial counts, were high for eggs in direct contact with 4 larvae. As density increased in the larval contact treatment, microorganisms disappeared from the egg surfaces and hatch rate declined.
• 3 When protected from larval grazing, eggs supported numerous microbial colonies irrespective of larval density. In contrast to the contact treatment group, egg hatch increased with increasing larval density. These observations suggest that the combination of microbial growth and a larval factor stimulates hatch. This hatching response may have evolved because both abundant microorganisms and numerous larvae reflect a habitat of good quality.

     

Publications of Anthony Calhoun Clement (1909–1984)

Summary

Two zoeae and the megalopa of the majid crab Macropodia parva were obtained from laboratory material. At 25±1°C and 35% salinity, the first crab appeared 12 days after hatching; survival to the first crab instar was 27%. The larval stages are described in detail and compared with those of the previously described species of the genus Macropodia. Zoeal characteristics of M. parva that differentiate it from other known Macropodia larvae are the naked telson furcae and the absence, in zoea II, of the exopodal setae on the basis of the maxillule.     

Defence and development in a gregarious leaf-mining beetle

Abstract.

• 1 The gregarious larvae of the chrysomelid beetle Microrhopala vittata mine the leaves of goldenrods (Solidago spp.). These mines serve both as food and as shelter for the larvae.
• 2 Life-table data and experiments indicated that mine initiation and moves to secondary mines represented especially vulnerable stages during larval development. Leaf mines effectively protected M.vittata against predators in the field.
• 3 Field experiments indicated that larvae hatching from larger clutches of eggs stood a greater chance of surviving to pupation, primarily because larvae hatching in groups proved more successful at initiating leaf mines. Once inside the leaf mine, however, larvae feeding in large groups attained lower adult masses, and were more likely to abandon the natal mine and did so earlier in development because large groups more rapidly destroyed a leaf.

     

The biology of Microctonus caudatus (Thomson), a braconid parasite of the ground beetle Harpalus rufipes (Degeer)

• 1 Microctonus caudatus parasitizes the adults of Harpalus rufipes. It is bivoltine, and its summer generation occurred in up to 27% of the study population of H.rufipes. The mean level of parasitism throughout both 1973 and 1974 was 8.4%.
• 2 Many larvae of M.caudatus are found in one host; the maximum number was 92, mean 20.8. There was indirect evidence of competition between larvae within the host, so that about sixty larvae, at most, were able to develop fully.
• 3 Larvae of the summer generation of M.caudatus emerged from host beetles between the end of July and mid September, invariably killing their host. The larvae pupated in the soil and adult parasites emerged from the pupal cocoons about 14 days later.
• 4 M.caudatus is parthenogenetic, and individuals oviposited readily in adult beetles in the laboratory. A culture of the parasite was maintained for almost a year at 15°C under artificial light of natural outdoor daylength, when four generations developed in the year. Time taken for development within the host was longest under short day conditions.

     

The effect of temperature on the development and life cycle regulation of the pine weevil Hylobius abietis and the potential impacts of climate change

• 1 The pine weevil Hylobius abietis is widely distributed in the Palaearctic region where it is a major pest. Although predominantly semi‐voltine, with a 2‐year life cycle, the generation time across its range can vary from 1 to 4 years. The duration of the life cycle and the seasonal timing of weevil activity affect the economic impact and management of this pest, all of which are likely to change in a warming climate.
• 2 To determine the effect of temperature and tree species on weevil growth and development, laboratory experiments were performed with eggs, larvae, prepupae, pupae and adults, using, as appropriate, the host species Scots pine Pinus sylvestris L. and Sitka spruce Picea sitchensis (Bong.) Carr. under constant or alternating temperatures.
• 3 The development rate was linearly related to temperature, with developmental thresholds for eggs, larvae and pupae of 8, 4.5 and 7.3 °C, respectively. Day‐degrees were estimated for each life stage. Larval development was affected by tree species, being slower on Sitka spruce than on Scots pine, and was faster under alternating than constant temperatures.
• 4 The development time for prepupae was highly variable, with an apparent facultative prepupal diapause initiated by temperature. The temperature range 20–17.5 °C marked the transition between median prepupal development times of approximately 25 and 90 days. The prepupal stage may serve to minimize the risk of overwintering mortality in the pupal stage and help to synchronize the life cycle.
• 5 Larval and adult mass was positively related to developmental temperature, demonstrating an inverse temperature size rule, and weevils were heavier when developing on Scots pine than Sitka spruce. Development in alternating temperatures reduced weevil mass on Scots pine. The influence of temperature on weevil mass is likely to have a positive effect on fecundity and overwintering survival. The effects of climate change on development, voltinism and weevil mass are discussed.

     

Studies on the population dynamics of a thistle-feeding lady beetle,Henosepilachna pustulosa (Kôno) in a cool temperature climax forest

1. A field study was carried out on the population dynamics of a thistle-feeding lady beetle, Henosepilachna pustulosa (Kôno ) living in a cool temperature climax forest in northern Kyoto Prefecture, central Japan.
2. Intensive marking, release and recapture program was carried out to estimate the adult population parameters by usingJolly-Seber method.
3. Sampling ratio was around 50%. Marking ratio rapidly rised as the census progressed and approached to 100%.
4. Sex ratio (% ♀) was 63–69% in both overwintered and new adults.
5. Daily survival rate was as high as 0.95 or more and constant throughout the season. Adult longevity in the spring was longer than 40 days.
6. Reproductive rate i. e., the ratio of the number of newly emerged adults in a given generation to that of overwintered adults in the preceding generation, is very small, ranging 1–3, whereas winter survival is higher than 50%, consequently the size of populations in the study area remain in a remarkably constant size and it never reached a level where intraspesific competition occurred.
7. The population characteristics of H. pustulosa are compared with those of the two closely related species, H. vigintioctopunctata and H. vigintioctomaculata, which are the pests of Solanaceous crops. Hp is more K-strategic than the two pest species.

     

Selection of plant parts by Depressaria multifidae (Lep., Oecophoridae) on its seasonally-restricted hostplant, Lomatium grayi (Umbelliferae)

ABSTRACT.

• 1 Depressaria multifidae Clarke feeds on a broader variety of Umbelliferae plant parts than other Depressaria species.
• 2 Early instar larvae feed in the sheaths surrounding floral buds and leaves. Later instar larvae feed in the sheaths and floral stems and on flowers and leaves.
• 3 Floral stems bored by larvae had significantly larger basal stem diameters than floral stems that were not bored. Smaller stems usually have umbels with only male flowers, and wither after flowering, too soon for larvae to complete development. In contrast, larger stems often have umbels with some hermaphroditic flowers, which remain green and erect long enough for larvae to complete development. Hence, selection may favour larvae that bore only in relatively large stems.
• 4 In the laboratory, larvae fed sheaths with enclosed floral buds, flowers, or leaves all pupated at the same weight, but larvae fed floral stems pupated at a significantly lower weight. Larval and pupal development time was the same on all plant parts.
• 5 In the field, larvae restricted to a single umbel throughout development pupated at the same weight as those restricted to a single leaf.
• 6 Unlike in other Depressaria species, nitrogen levels only partly correspond to the pattern of use of plant parts in D.multifidae. Nitrogen values varied as follows: floral buds > immature leaves ≥ flowers > floral stalks > sheaths excluding floral buds or leaves.
• 7 The broad variety of plant parts used by D.multifidae may result partly from the problem of feeding on a small, seasonally restricted hostplant; the greater use of sheaths and floral stems than in other Depressaria species may result from selection for safety from parasites or predators.
• 8 The results for D.multifidae indicate that the way in which an insect feeds on a plant species can vary broadly even at a single site.

     

Relationships between larval density, adult size and egg production in the cowpea seed beetle, Callosobruchus maculatus

ABSTRACT.

• 1 The eggs of the cowpea seed bettle Callosobruchus maculatus (Fab.) are attached to cowpeas. On hatching, the larvae penetrate the testa and remain in the seed until development is complete and adult eclosion has occurred. The adults do not need to feed and were not allowed to do so.
• 2 Strains from Brazil and Nigeria can produce more than twelve adults from a seed bearing numerous eggs, whereas a strain from the Yemen Republic rarely produced more than three.
• 3 In all three strains the mean weight of the adults produced from a single cowpea declined with increasing initial larval density in the seed.
• 4 Egg production by females is positively correlated with their weight at the time of mating, shortly after emergence.
• 5 Lifetime egg production by females of the Brazilian and Nigerian strains was lower if they came from cowpeas with higher initial larval densities. No such relationship could be demonstrated in the Yemen strain.
• 6 The fecundity of one generation of these beetles, at least in some geographical strains, is significantly affected by the number of larvae entering the hosts in which the adults of that generation have developed.