Predation potential of the earwig Euborellia annulipes on fruit fly larvae and trophic interactions with the parasitoid Diachasmimorpha longicaudata

The earwig Euborellia annulipes (Lucas) (Dermaptera: Anisolabididae), a generalist predator, has been observed in fruits infested with fruit fly larvae, which are frequently parasitized by parasitoid wasps. Neither the capacity of earwigs to predate on fruit flies nor intraguild interactions between earwigs and fruit fly parasitoids have been investigated. Here, we studied in laboratory conditions the predation on the fruit fly Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) by the earwig E. annulipes, and whether parasitism of fruit fly larvae by the parasitoid wasp Diachasmimorpha longicaudata (Ashmead) (Hymenoptera: Braconidae) influences predation by the earwig. We evaluated the predation capacity, functional response and prey preference of E. annulipes for parasitized and non-parasitized fruit fly larvae in choice and no-choice tests. We found that earwigs prey on second- and third-instar larvae and pupae of C. capitata and consumed larger numbers of second-instar larvae, followed by third-instar larvae and pupae. Females prey on larger numbers of fruit flies than did males, regardless of the prey developmental stage, but both sexes exhibited a type II functional response. Interestingly, males killed but did not consume fruit fly larvae more than did females. In no-choice tests, earwig females consumed equal numbers of parasitized and non-parasitized fruit fly larvae. However, in choice tests, the females avoided feeding on parasitized larvae. Subsequent tests with hexane-washed parasitized and non-parasitized larvae showed that putative chemical markings left on fruit flies by parasitoids did not drive the earwig preference towards non-parasitized larvae. These findings suggest that E. annulipes is a potential biological control agent for C. capitata, and that, because the earwig avoids consuming larvae parasitized by D. longicaudata, a combination of the two natural enemies could have an additive effect on pest mortality.     

Effect of sub-lethal exposure to ultraviolet radiation on the escape performance of Atlantic cod larvae (Gadus morhua)

The amount of ultraviolet (UV) radiation reaching the earth's surface has increased due to depletion of the ozone layer. Several studies have reported that UV radiation reduces survival of fish larvae. However, indirect and sub-lethal impacts of UV radiation on fish behavior have been given little consideration. We observed the escape performance of larval cod (24 dph, SL: 7.6±0.2 mm; 29 dph, SL: 8.2±0.3 mm) that had been exposed to sub-lethal levels of UV radiation vs. unexposed controls. Two predators were used (in separate experiments): two-spotted goby (Gobiusculus flavescens; a suction predator) and lion's mane jellyfish (Cyanea capillata; a "passive" ambush predator). Ten cod larvae were observed in the presence of a predator for 20 minutes using a digital video camera. Trials were replicated 4 times for goby and 5 times for jellyfish. Escape rate (total number of escapes/total number of attacks ×100), escape distance and the number of larvae remaining at the end of the experiment were measured. In the experiment with gobies, in the UV-treated larvae, both escape rate and escape distance (36%, 38±7.5 mm respectively) were significantly lower than those of control larvae (75%, 69±4.7 mm respectively). There was a significant difference in survival as well (UV: 35%, Control: 63%). No apparent escape response was observed, and survival rate was not significantly different, between treatments (UV: 66%, Control: 74%) in the experiment with jellyfish. We conclude that the effect and impact of exposure to sub-lethal levels of UV radiation on the escape performance of cod larvae depends on the type of predator. Our results also suggest that prediction of UV impacts on fish larvae based only on direct effects are underestimations.     

Costs of reproduction and geographic variation in the reproductive tactics of the mosquito Aedes triseriatus

Intraspecific host discrimination is widespread in solitary parasitoids whose adult females forage for and evaluate host suitability, whereas interspecific discrimination is less common. In some parasitoid species, mostly Diptera and Coleoptera, the larva performs the last step of host searching. It has been suggested that host discrimination will rarely occur in such host-seeking larvae because their low mobility results in a low host encounter rate. We determined the extent to which the larvae of Aleochara bilineata Gyllenhal (Coleoptera: Staphylinidae), a solitary parasitoid of aggregated Diptera pupae: (1) discriminated between unparasitized hosts and hosts parasitized by conspecifics; (2) used semiochemical cues to discriminate; (3) were influenced by life expectancy, presence of conspecifics and host availability in their host acceptance decision; and the extent to which (4) A. bilineata and A. bipustulata L., a species exploiting the same hosts and occurring sympatrically, showed interspecific host discrimination. A. bilineata larvae were able to discriminate between unparasitized hosts and hosts parasitized by conspecifics in a choice experiment. Such behavior has never previously been described for a coleopteran parasitoid or for a parasitoid species whose larvae perform host searching. Host discrimination in this species was not based on the presence of visual or tactile cues (e.g., entrance holes) but rather on chemical cues. The life expectancy of A. bilineata larvae was significantly shorter in the presence than in absence of hosts, and older larvae had lower parasitism success than young larvae in a 24-h experiment. However, the host acceptance decision of A. bilineata larvae was not influenced by larval age or the presence of conspecifics when the ratio of hosts per larva was greater than or equal to 1. When hosts were scarce, the degree of superparasitism increased significantly with the number of foraging conspecifics and the age of the larvae. Both species of Aleochara showed intra- and interspecific host discrimination in a choice experiment. In contrast to A. bipustulata, A. bilineata larvae more frequently parasitized hosts parasitized by A. bipustulata than those parasitized by conspecifics. We suggest that host discrimination will be frequent in solitary parasitoids with host-seeking larvae when hosts are aggregated. Received: 4 June 1998 / Accepted: 1 September 1998     

A first insight into the scanning behaviour of the presocial blow fly larvae

Aggregation of necrophagous larvae has several benefits: the sharing of salivary enzymes (exodigestion), temperature regulation, protection from predators and parasites, etc., and is well developed in blow flies (Diptera: Calliphoridae). The present study focuses on the aggregation mechanism used by the necrophagous larvae of Lucilia sericata Meigen, the common green bottle fly. The ability of single larva to detect and follow a signal (trail) created by conspecifics is investigated initially. A circular ring is drawn in a Petri dish where 20 starved larvae have crawled for a period of 30 min. A naïve (test) larva is then placed in the dish and video‐tracked. Naïve larvae are able to detect the boundaries of the larvae‐crawled area and stay preferentially within this conspecific‐marked zone. In a second step, the orientation of larvae by scanning, a dedicated, ground‐signal detection behaviour of dipteran larvae, is analyzed. Four experimental conditions are tested: control, presence of food, conspecifics, and food + conspecifics. When conspecifics have been previously present in a given area, the scanning behaviour by naïve larvae in this area decreases (both in number and frequency of scans). Accordingly, scanning by necrophagous larvae of L. sericata should be considered not only as locomotion behaviour, but also as a potential way to detect signals from conspecifics for the purpose of aggregation. The chemical composition of the attractant(s), the behavioural effects (attraction or retention) and the implication of larval signalling in the aggregation process are new fields to explore.     

Chromosome aberrations induced by gamma radiation in the somatic cells of a radiosensitive mutant line of Drosophila melanogaster

Chromosome aberrations induced by gamma-rays in ganglia cells of Drosophila melanogaster larvae have been studied. Two strains of Drosophila were used: radiosensitive mutant rad (2) 201G1 and normal strain. It has been shown that the frequency of cells with chromosome aberrations in radiosensitive larvae is much more than in normal larvae after gamma-irradiation. The ratio of chromosome and chromatid deletions number to the number of exchange type aberrations is the same for both strains. The kinetics of chromosome aberrations induced in rad-larvae is similar to the normal one. The conclusion has been made that the realization of rad (2) 201G1 mutation takes place on the cell level.     

The role of the prothoracic gland in determining critical weight for metamorphosis in Drosophila melanogaster

BACKGROUND: The timely onset of metamorphosis in holometabolous insects depends on their reaching the appropriate size known as critical weight. Once critical weight is reached, juvenile hormone (JH) titers decline, resulting in the release of prothoracicotropic hormone (PTTH) at the next photoperiod gate and thereby inducing metamorphosis. How individuals determine when they have reached critical weight is unknown. We present evidence that in Drosophila, a component of the ring gland, the prothoracic gland (PG), assesses growth to determine when critical weight has been achieved. RESULTS: We used the GAL4/UAS system to suppress or enhance growth by overexpressing PTEN or Dp110, respectively, in various components of the ring gland. Suppression of the growth of the PG and CA, but not of the CA alone, produced larger-than-normal larvae and adults. Suppression of only PG growth resulted in nonviable larvae, but larvae with enlarged PGs produced significantly smaller larvae and adults. Rearing larvae with enlarged PGs under constant light enhanced these effects, suggesting a role for photoperiod-gated PTTH secretion. These larvae are smaller, in part as a result of their repressed growth rates, a phenotype that could be rescued through nutritional supplementation (yeast paste). Most importantly, larvae with enlarged PGs overestimated size so that they initiated metamorphosis before surpassing the minimal viable weight necessary to survive pupation. CONCLUSIONS: The PG acts as a size-assessing tissue by using insulin-dependent PG cell growth to determine when critical weight has been reached.     

家蝇幼虫开发生态工程系统动力学仿真的研究

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Characteristics of larvae of the southwestern corn borer, Diatraea grandiosella, obtained from populations present in tropical and temperate regions

A comparative study was undertaken of southwestern corn borers (Diatraea grandiosella) collected from south central Mexico (19°N latitude) and southeast Missouri (37°N latitude). All the life stages of the Mexican insects were found to be larger or heavier, or both, than were those of the Missouri insects. Mexican larvae grew at a higher rate and attained a significantly heavier body weight than did Missouri larvae. Although both Mexican and Missouri larvae underwent ecdyses during diapause, Mexican larvae ecdysed more frequently than did the Missouri larvae at 23°C light:dark 12 h:12 h. Larvae that ecdysed most frequently did not necessarily spend longer in diapause. Electrophoresis of the fat body and haemolymph proteins of Mexican and Missouri larvae revealed similar patterns. The fat body of diapausing Mexican larvae contained substantial amounts of a diapause-associated protein which has been characterized previously from the fat body of Missouri Larvae. Double immunodiffusion confirmed that the diapause-associated protein of the Mexican larvae was identical to that present in the Missouri larvae. Smaller amounts of this protein appear to be present in the fat body of diapausing Mexican larvae than are present in that of diapausing Missouri larvae.     

Influence of aphid honeydew on the foraging behaviour of Hippodamia convergens larvae

1. Environmental cues associated with prey are known to increase predator foraging efficiency. Ladybird larvae are major predators of aphids. The sugary excretion of aphids (honeydew) has been proposed to serve as a prey‐associated cue for ladybird larvae. 2. Ladybird larvae are regularly found on the ground moving between plants or after falling off plants. The use of prey‐associated cues would be particularly beneficial for ladybird larvae on the ground in that such cues would help them to decide which plants to climb because aphids are patchily distributed within as well as amongst plants and, as a result, many plants are either not infested with aphids or do not host an aphid species of high nutritional value for ladybird larvae. 3. Laboratory experiments with larvae of Hippodamia convergens Guérin‐Méneville (Coleoptera: Coccinellidae) were carried out to explore whether honeydew accumulated on the ground is used as a foraging cue. The study also investigated whether, if honeydew is a foraging cue, larvae show differential responses to honeydew of high‐quality prey Acyrthosiphon pisum Harris compared with that of low‐quality prey Aphis fabae Scopoli (both: Homoptera: Aphididae). 4. Hippodamia convergens larvae stayed longer in areas containing honeydew but did not engage in longer bouts of searching. Furthermore, larvae did not distinguish between honeydew from high‐ and low‐quality aphid prey.     

Control of larval-pupal-adult molt in the moth Sesamia nonagrioides by juvenile hormone and ecdysteroids

Sesamia nonagrioides (Lepidoptera: Noctuidae) larvae reared under long day (LD; 16L:8D) conditions pupate after 5 or 6 larval instars, whereas under short day (SD; 12L:12D) conditions they undergo up to 12 additional molts before pupating. This extended period of repeated molting is maintained by high levels of juvenile hormone (JH). Previous work demonstrated that both LD and SD larvae decapitated in the 6th instar pupate but further development is halted. By contrast, about one-third of SD larvae from which only the brain has been removed, undergo first a larval molt, then pupate and subsequently developed to the adult stage. Debrained LD larvae molt to larvae exceptionally but regularly pupate and produce adults. Implanted brains may induce several larval molts in debrained recipient larvae irrespectively of the photoperiodic conditions. The results of present work demonstrate that the prothoracic glands (PGs) and the corpora allata (CA) of debrained larvae continue to produce ecdysteroids and JHs, respectively. PGs are active also in the decapitated larvae that lack JH, consistent with the paradigm that CA, which are absent in the decapitated larvae, are the only source of this hormone. Completion of the pupal-adult transformation in both LD and SD debrained insects demonstrates that brain is not crucial for the development of S. nonagrioides but is required for diapause maintenance. Application of JH to headless pupae induces molting, presumably by activating their PGs. It is likely that JH plays this role also in the induction of pupal-adult transformation in debrained insects. Application of the ecdysteroid agonist RH 2485 (methoxyfenozide) to headless pupae also elicits molting: newly secreted cuticle is in some cases thin and indifferent, in other cases it bears distinct pupal or adult features.     

Effect of entomopoxvirus infection of the smaller tea tortrix, Adoxophyes sp. on the development of the endoparasitoid, Ascogaster reticulatus

Infection of Adoxophyes sp. (Lepidoptera: Tortricidae) larvae by an entomopoxvirus (AsEPV) adversely affected the development of the endoparasitoid, Ascogaster reticulatus Watanabe (Hymenoptera: Braconidae). Parasitoid larvae developing in AsEPV-infected hosts grew more slowly and spent more time in their hosts than did parasitoid larvae developing in noninfected hosts. Percentages of emergence of larval parasitoids that developed in AsEPV-infected hosts were significantly lower than those of parasitoids that developed in noninfected hosts. Parasitoid larvae in AsEPV-infected host perished when their hosts died of AsEPV infection. Significant numbers of parasitized and infected larvae exhibited apolysis to the final instar, whereas noninfected-parasitized larvae died in the penultimate instars due to emergence of parasitoids.     

Environmental induction of larval diapause and life-history consequences of post-diapause development in the Large Copper butterfly,Lycaena dispar (Lepidoptera: Lycaenidae)

Many insects in temperate zones withstand the adverse conditions of winter through entering diapause and the two most important environmental stimuli that induce diapause are photoperiod and ambient temperature. The Large Copper butterfly, Lycaena dispar Haworth (Lepidoptera: Lycaenidae), is a Palearctic butterfly that hibernates as larvae. Since this butterfly is a near threatened species in some regions, there has been a growing need for a standardized protocol for mass rearing of this butterfly based on the adequate knowledge of its ecology. In the present study, we first identified that L. dispar larvae were sensitive to the photoperiodic induction of diapause during their first larval instar. We then investigated to what extent the diapause-inducing effects of photoperiod could be modified by ambient temperatures in L. dispar larvae by exposing them to the range of day-lengths (L:D 14:10, 12:12, 10:14 and 8:16) at three different temperatures (15, 20 and 25 °C). All larvae were induced to enter diapause at low ambient temperature (15 °C) regardless of photoperiod, whereas most of them (86 %) exhibited direct development when temperature was high (25 °C). The photoperiodic induction of diapause was evident when day-length was shorter than 14 h at intermediate temperature (20 °C). Pre-diapause development was prolonged at low temperatures. Finally, we found that post-diapause development of L. dispar larvae was determined by both the chilling temperature experienced by diapausing larvae and the duration of larval diapause. Adult emergence was enhanced when larvae were chilled at 8 °C and when they had been under the state of diapause for 20 days before they were treated to terminate diapause.     

Age-related changes in esterase and acetylcholinesterase activities of the infective larvae of Ancylostom a tubaeforme

Nwosu A. B. C. 1978. Age-related changes in esterase and acetylcholinesterase activities of the infective larvae of Ancylostoma tubaeforme. International Journal for Parasitology8: 355–358. Biochemical assays for non-specific esterase and acetylcholinesterase (ACHE) activities, of physiologically aged infective larvae of Ancylostoma tubaeforme, have been carried out. Butyrylthiocholine iodide (BTC) was not hydrolysed by larval hornogenates. Esterase and ACHE activities decreased with increase in the age of the larvae.     

Susceptibility of Meligethes spp. and Dasyneura brassicae to entomopathogenic nematodes during pupation in soil

The susceptibility of pupating larvae of pollen beetles, Meligethes spp. Stephens (Coleoptera: Nitidulidae) and brassica pod midges, Dasyneura brassicae Winnertz (Diptera: Cecidomyidae) to entomopathogenic nematodes (Nematoda: Rhabditida) was studied in the laboratory. The results showed that brassica pod midge larvae were almost unaffected by the tested nematodes (Steinernema bicornutum, S. feltiae and Heterorhabditis bacteriophora) whereas successful pupation of pollen beetle larvae was reduced with increasing number of nematodes (S. bicornutum, S. carpocapsae, S. feltiae and H. bacteriophora). The exposed larvae had been collected in the field and some of the pollen beetle larvae were parasitised by parasitoid wasps. It appeared that parasitised larvae were less affected by nematodes than non-parasitised larvae.     

Feeding behaviour of the ladybeetle,Pseudoscymnus kurohime

A laboratory study was made of the feeding behaviour of the ladybeetlePseudoscymnus kurohime (Miyatake) when attacking the sugar cane woolly aphidCeratovacuna lanigera Zehntner. The 1st-instar ladybeetle larva was smaller than the 1st instar aphid nymph. All larval stages of the ladybeetle sucked out the body fluids of aphids and left their emptied corpses. The 1st, 2nd, and 3rd instar ladybeetle larvae mostly attacked 1st instar aphids, whereas the 4th-instar ladybeetle larvae attacked all stages of aphids. Ladybeetle adults ate mostly 1st-instar aphids. Young larvae attacked aphids in several different ways: (1) They crawled under an aphid, seized it by its underside and lifted it up. (2) They attacked new born nymphs at birth or shortly afterwards. (3) They fed on an aphid that had been captured by an older larva. The larvae preferred to seize with their mandibles the head or thorax of an aphid, while adults seized their prey by the abdomen. When attacked by an adult, 82% of the aphids secreted droplets from their abdominal cornicles, whereas only 7.2–12% secreted droplets when attacked by larvae. The 4th instar larvae more voracious than the younger larvae.     

Support for the microenvironment hypothesis for adaptive value of gall induction in the California gall wasp, Andricus quercuscalifornicus

Three major hypotheses have been advanced for the adaptive nature of plant galls: nutrition, enemy-avoidance, and microenvironment. Of these, the microenvironment hypothesis has been frequently invoked, but rarely tested directly. We tested this hypothesis in a population of Andricus quercuscalifornicus (Bassett) (Hymenoptera: Cynipidae) wasps inducing galls on Quercus lobata Née (Fagaceae) trees in Northern California, USA. Relative humidity and temperature data gathered from both immature and mature galls in the field indicated that A. quercuscalifornicus larvae modify their microenvironments significantly by raising and stabilizing relative humidity levels inside galls to near saturation. In addition, excised larvae maintained under experimental conditions survived significantly longer under levels of high relative humidity. These data support the hypothesis that through gall induction, A. quercuscalifornicus manipulates its environment adaptively.     

Studies on the arrangement patterns of nucleocapsids within the envelopes of nuclear-polyhedrosis virus in the fat-body cells of the brown tail moth, Euproctis similis

Occluded viruses of the Entomopoxvirus (D)/¹:¹/¹:X/X:I/O ( = Vagoiavirus) group have been found in Othnonius batesi (Scarabaeidae: Melolonthinae), Dermolepida albohirtum (Scarabaeidae: Melolonthinae), and Aphodius tasmaniae (Scarabaeidae:Aphodiinae). Diagnostic criteria are given for the virus infections in the respective native host larvae based upon both macroscopic and microscopical observations where possible. The distinguishing characteristics of the virus spheroids and spindles from the three host species are compared with each other and with similar bodies present in other entomopoxvirus infections. Virus-containing spheroids of the O. batesi and D. albohirtum viruses were barely infective at dosages fed to native host larvae in the laboratory, and the disease course of each was prolonged. Cross-infection feeding trials of the D. albohirtum virus in several other melolonthine species larvae were negative.     

Mediated pathogenicity of the baculovirus AcMNPV by the venom from Euplectrus comstockii Howard (Hymenoptera: Eulophidae)

The compatibility of the venom from the parasitic species Euplectrus comstockii Howard (Hymenoptera: Eulophidae) with the pathogenicity of Autographa californica (Speyer) (Lepidoptera: Noctuidae) MNPV baculovirus (AcMNPV) was tested in third and fourth instar larvae of Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae). The presence of AcMNPV did not alter the ability of the venom to arrest ecdysis in T. ni larvae. The presence of the venom delayed the rate of viruses by AcMNPV but increased the total mortality rates from days 9 to 14 in both third and fourth instar T. ni larvae. The delay in viruses was minimized by administering the virus prior to envenomation. In the presence of the venom, the final LD50 values were lower for fourth instar larvae than for third instar larvae. Surface response equations were developed to visualize the effect of the venom on the viruses caused by AcMNPV.     

Rhythmic signalling and entrainment inVespa orientalis larvae: Characterization of the underlying interactions

Rhythmic “circa-second” contrations of larvae of the hornetVespa orientalis, believed to serve as hunger signals, were studied. A considerable degree of coordination among individual larvae, both in frequency and phase of these contractions, has been observed. The oscillations of singly isolated larvae are of short duration, non-constant, with increasing intervals in between and there is a substantial variability in the patterns shown by different larvae. In contrast, the association of two or more larvae leads to enhancement of their periodic behaviour and to (partial) entrainment. Communication among larvae may perhaps be mediated by the sound pulses (“scratching” noises) which are generated by these contractions. We have subjected individual and grouped larvae to external sound pulses and were able to demonstrate: (a) enhancement of rhythmic activity; (b) phase resetting; (c) entrainment to an external oscillator within a range of frequencies; (d) the existence of a subharmonic mode of entrainment. We propose a simple phenomenologic model to account for these larvae responses. Our model assumes the existence of an “energy” variable which declines with time but is upgraded, in a phase-dependent way, by external stimuli. Based in part on work performed by V. Barenholz-Paniry in partial fulfillment of the requirements for the M.Sc. degree from the Sackler Faculty of Medicine, Tel Aviv University, 1986.     

Larvae of four species of the Hyphydrus lyratus species-group (Coleoptera: Dytiscidae: Hydroporinae)

Abstract  The third instars of the Australian species Hyphydrus lyratus Swartz, H. contiguus Wehncke, H. elegans (Montrouzier) and H. decemmaculatus Wehncke (Coleoptera: Adephaga: Dytiscidae) are described, including a chaetotaxic analysis of the cephalic capsule, head appendages, legs, last abdominal segment and urogomphi. Larvae of these species morphologically resemble other species of Hyphydrus Illiger for which the larvae have been described. A key to identify larvae of the Australian species of Hyphydrus is provided. Larvae of H. effeminatus Watts appear identical to those of H. decemmaculatus . A 822 bp fragment of the CO1 gene of larvae and adults of these species showed very slight differences, suggesting the possibility that, in Australia at least, H. decemmaculatus is polymorphic.