Two tachinid species discriminate between parasitized and non-parasitized hosts

The abilities ofMyiopharus doryphorae (Riley) andM. aberrans (Townsend) (Diptera: Tachinidae) to discriminate between parasitized and non-parasitized Colorado potato beetle (host)Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae) larvae, were investigated under laboratory and field conditions. Laboratory experiments showed that bothMyiopharus species have a significantly greater frequency for larvipositing in non-parasitized hosts over parasitized ones. Direct field observations of larvipositional behavior of bothMyiopharus species over three growing seasons showed effective restraint from larviposition into parasitized hosts, while larviposition into nonparasitized ones occurred readily. Avoidance of previously-parasitized hosts occurred after the larvipositing flies briefly landed on host larvae without attempting to insert the larvipositor. The low levels of superparasitism which occurred in the caged experiments and in the field appeared to be due to a breakdown of the larvipositing parasitoids' restraint when they met only parasitized hosts or when many parasitoids competed for reduced numbers of hosts late in the season.     

Larviposition in the ovoviviparous blowfly Calliphora dubia

This study examined larviposition in Calliphora dubia Macquart (Diptera: Calliphoridae), an ovoviviparous blowfly of considerable forensic importance in Australia. Females in the field carried 22–83 live larvae, exhibiting a strong linear relationship between female size and the number of live larvae carried. Females took just over 1 min (mean 67.7 ± 7.7 s, n = 54) to larviposit live larvae on or near fresh liver in the laboratory. Females laid larvae at a mean rate of 1.2 ± 0.1 larvae/s, with the fastest rate being 3.4 larvae/s. Most females (70%) laid live larvae only, but 14% laid larvae and eggs at the same time and 16% laid eggs only (none of the eggs laid were viable). Females laying only live larvae laid a mean of 53.7 ± 2.3 larvae, whereas those laying only eggs laid a mean of 48.6 ± 2.8 eggs on each occasion. None of the eggs laid were viable. Most females (86%) laid all their larvae in a single spot, even if they engaged in several bouts of laying live larvae. Nearly one‐third of females did not lay all the live larvae in their ovisacs, but retained half of their complement of developed larvae. Females may be opting to spread their larvae across several carcasses in order to increase their survival and not to overcrowd small, ephemeral carcasses. The fact that a blowfly can lay either eggs or live larvae has enormous implications for the accurate determination of the post‐mortem interval (PMI) as the presence of larvae derived from eggs laid on the body add 6–18 h to the PMI. This paper represents the first report of the ability of female calliphorids to resorb some of their own live larvae.     

Risk‐spreading larviposition behaviour of female nose bot flies (Cephenemyia) attacking black‐tailed deer

While baited deer models were under observation nine Cephenemyia jellisoni Townsend (Diptera: Oestridae) females and seven C. apicata Bennett & Sabrosky engaged in a risk‐spreading larviposition behaviour by larvipositing on models only once and then flying away. Additionally, analysis of 225 unobserved larvipostions in which larvae were trapped in adhesive on the muzzles of deer models showed that 94% of C. apicata and 95% of C. jellisoni larviposited on a model only once. The number of single larvipositions was highly significant for both species. The principal adaptive significance of such risk‐spreading larviposition behaviour is that it spreads the reproductive output of a female among many hosts, and in years when adult eclosion and survival rates are low, it ensures that the larvae of the few surviving females will be distributed among a maximum number of hosts. Several other benefits of such behaviour also are discussed.     

Behavioral ecology ofMyiopharus doryphorae (riley) andM. aberrans (townsend), tachinid parasitoids of the colorado potato beetle

The behavior ofMyiopharus doryphorae andM. aberrans, North American tachinid parasitoids of the Colorado potato beetle, was recorded under field and laboratory conditions throughout three growing seasons in western Massachusetts. Eight common behaviors associated with resting, searching, feeding, and larviposition were distinguished, which together accounted for nearly all daytime activity of the females of both tachinids. Several of these behaviors, and in particular larviposition, were closely related to temperature but differed between species. A sequence of five defensive behaviors by the different larval stages of the Colorado potato beetle prevented larviposition in 49% of resisted attempts and perhaps one-fourth of total larviposition attempts byMyiopharus species, yet both parasitoids were highly successful in allocating their progeny during most of the summer. Second- and third-instar beetle larvae were least effective in resisting larviposition. Females of bothMyiopharus species actively guarded recently parasitized hosts from otherMyiopharus females for a period of several minutes after larviposition during the last month of the growing season when second- and third-instar Colorado potato beetle larvae were most scarce. Laboratory studies based on the field observation that femaleM. aberrans doggedly pursued circum-diapausing adult beetles led to the first recorded account ofM. aberrans larvipositing in adult hosts. Flies gained access to a beetle’s vulnerable abdominal dorsum at the instant it lifted its elytra to initiate flight. The late-season switch ofM. aberrans to adult Colorado potato beetles contributed to a seasonal sequence of larviposition-related behaviors concordant with prevailing host densities, which should lend complementarity toM. doryphorae andM. aberrans as biological controls of pest populations.     

Reproductive Biology of Celatoria compressa (Diptera: Tachinidae), a Parasitoid of Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae)

The tachinid Celatoria compressa, a parasitoid of adult Diabrotica species in North America has been studied as a candidate classical biological control agent for the western corn rootworm, Diabrotica virgifera virgifera, in Europe. Prior to its potential importation, a thorough understanding of the parasitoid's reproductive biology is essential, and is an important component in the evaluation of a species as a biological control agent. In this study it has been clarified that C. compressa belongs to a group of a few tachinid species characterised by having eggs that contain fully developed larvae which are laid directly into the host. After mating, the egg load of females increased steadily from day 1 to a maximum egg load on day 4. Thereafter eggs containing fully developed first instar larvae reached a maximum of 31 in 69 eggs. At the first day of larviposition, females laid on average only five eggs into multiple hosts, which is in contrast to the availability of 18 eggs containing fully developed first instars in the uterus per female at that time. During a mean female's larviposition period of 23 days, a total of 33 first instars were larviposited into the hosts, which is only half of the female's egg load. Lifetime fecundity of C. compressa was significantly correlated with longevity. However no relationship was found between body size and either lifetime fecundity or longevity. In this study, an inverse host density-dependent pattern of percent parasitism was shown for C. compressa under 24-h fixed-time laboratory conditions, reflecting a Holling type II response. The number of host parasitized per C. compressa female reached an upper limit of 10 hosts with an increasing host density, which can be explained by the long host handling time of C. compressa.     

Adhesion of bacteria (Serratia spp.) to the foregut of grass grub (Costelytra zealandica (white)) larvae and its relationship to the development of amber disease

Adhesion of pathogenic strains of Serratia spp. to the foregut tissue of the New Zealand grass grub (Costelytra zealandica) was shown to be associated with the development of amber disease. Bacteria were always found adhering to the crop in the region of the cardiac valve in larvae showing disease symptoms after in vivo treatment with pathogenic bacteria while no significant colonization was observed in larvae treated with wild‐type, non‐pathogenic strains. The in vitro inoculation of excised crops with pathogenic and non‐pathogenic strains resulted in a similar pattern of adhesion. It is suggested that adhesion is an early step in pathogenesis and that farther bacterial mediated factors could be required for fall expression of amber disease.     

First finding of larviposition in Calliphora loewi from an island relict forest

Larviposition is widespread in blowflies, but among Calliphora species this behavior has seldom been described. The evidence of larviposition in C. loewi is here reported for the first time and discussed in relation with other blowfly species exhibiting the same behavior. The blowfly C. loewi is considered oviparous but surprisingly, female specimens from Madeira Island (Portugal) were found to carry few large larvae (one to three larvae up to 5.1 mm in size) in the ovipositor and abdomen. The finding of larviposition behavior in C. loewi from Madeira Island is at present enigmatic and further studies are needed to clarify the reproductive biology of this species.     

Overwintering strategy of endoparasitoids in Chilo suppressalis: a perspective from the cold hardiness of a host

Although parasitoids ultimately kill their host, koinobiont parasitoids must protect not only themselves but also their hosts against extreme environments. In this study, the parasitism rate of Chilo suppressalis Walker (Lepidoptera: Pyralidae) was investigated, and the average body weights, supercooling points, and concentrations of glycerol (acting as a cryoprotectant) in the hemolymph were compared between parasitized and non‐parasitized larvae. Five species of koinobiont endoparasitoids parasitized the overwintering C. suppressalis larvae and the total parasitism rate was 47.6% (n = 1 537). Average body weight of parasitized larvae was significantly lower than that of non‐parasitized larvae, and the parasitism rate of the lighter group (20–30 mg) was highest. The supercooling point of parasitized C. suppressalis larvae (?15.7 ± 0.3 °C) was significantly lower than that of the non‐parasitized larvae (?14.3 ± 0.2 °C). In addition, supercooling points were not correlated with body weights between parasitized and non‐parasitized larvae, indicating that cold hardiness of parasitized larvae was enhanced by endoparasitoids. Furthermore, the concentration of glycerol in the hemolymph was significantly higher in parasitized larvae (205.0 ± 7.1 μmol ml^?1) than in non‐parasitized larvae (169.8 ± 14.4 μmol ml^?1), which suggests that the mechanism that decreases the supercooling point of parasitized larvae was associated with glycerol. All these results indicated that the cold hardiness of parasitized C. suppressalis larvae was enhanced by their endoparasitoids, which benefitted overwintering endoparasitoids.     

Observations of parasitoid behaviour in both no‐choice and choice tests are consistent with proposed ecological host range

The solitary larval endoparasitoid Eadya daenerys Ridenbaugh (Hymenoptera: Braconidae) is a proposed biocontrol agent of Paropsis charybdis Stål (Coleoptera: Chrysomelidae, Chrysomelinae), a pest of eucalypts in New Zealand. Eadya daenerys oviposition behaviour was examined in two assay types during host range testing, with the aim of improving ecological host range prediction. No‐choice sequential and two‐choice behavioural observations were undertaken against nine closely related species of New Zealand non‐target beetle larvae, including a native beetle, introduced weed biocontrol agents, and invasive paropsine beetles. No behavioural measure was significantly different between no‐choice and two‐choice tests. In sequential no‐choice assays the order of first presentation (target–non‐target) had no significant effect on the median number of attacks or the attack rate while on the plant. Beetle species was the most important factor. Parasitoids expressed significantly lower on‐plant attack rates against non‐targets compared to target P. charybdis larvae. The median number of attacks was always higher towards target larvae than towards non‐target larvae, except for the phylogenetically closest related non‐target Trachymela sloanei (Blackburn) (Coleoptera: Chrysomelidae, Chrysomelinae). Most non‐target larvae were disregarded upon contact, which suggests that the infrequent attack behaviour observed by two individual E. daenerys against Allocharis nr. tarsalis larvae in two‐choice tests and the frass of Chrysolina abchasica (Weise) was probably abnormal host selection behaviour. Results indicate that E. daenerys is unlikely to attack non‐target species apart from Eucalyptus‐feeding invasive paropsines (Chrysomelinae). Non‐lethal negative impacts upon less preferred non‐target larvae are possible if E. daenerys does attack them in the field; however, this is likely to be rare.     

Soldiers of a European gall aphid,Pemphigus spyrotecae (Homoptera: Aphidoidea): Why do they molt?

A non-migratory aphid,Pemphigus spyrothecae, produces 1 st-instar larvae of 2 types in the gall: thick-legged ones and normal-legged ones. It was found that the thick-legged larvae play a defensive role, hence they may be called soldiers. Unlike the soldiers of other species hitherto reported, at least some soldiers of this species molt and become adults. Their incomplete sterility is explained historically: 1) The migratory ancestor ofP. spyrothecae once produced monomorphic 1st-instar larvae attacking predators in the gall. 2) It acquired a non-migratory life cycle by the larviposition of emigrants in the gall. 3) As a result, 1 st-instar larvae of another morph, which had lived on the secondary host without attacking predators, joined the gall inhabitants. This hypothesis is supported strongly by the fact that the normal-legged 1 st-instar larvae very much resemble the 1 st-instar larvae of migratoryPemphigus species produced on the secondary hosts.     

Life histories of closely related amphidromous and non‐migratory fish species: a trade‐off between egg size and fecundity

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Major radiation of cheilostome bryozoans: Triggered by the evolution of a new larval type?

A macroevolutionary model is developed to account for the “adaptive radiation”; of cheilostome bryozoans that commenced in the Cenomanian after a long phase of low diversity. Living cheilostome species possess one of two types of larvae; planktotrophic (cyphonautes) larvae of relatively long duration, and brooded non‐planktotrophic (coronate) larvae of short duration. Planktotrophic larvae characterize the paraphyletic “malacostegans”; from which “advanced”; cheilostomes with non‐planktotrophic larvae are thought to have evolved monophyletically. Research on other marine invertebrates suggests that gene flow within and between populations is likely to be poorer in species having non‐planktotrophic larvae, and hence the frequency of allopatric and quasi‐sympatric speciation may be greater. Skeletal evidence of larval brooding in the cheilostomes first appears in the late Albian, immediately before their adaptive radiation, and the evolution of non‐planktotrophy with associated increase in speciation rate is proposed to have triggered this radiation.     

Absence of cuticular alkenes allows lycaenid larvae to avoid predation by Formica japonica ants

Chemical mimicry and camouflage based on cuticular hydrocarbons (CHCs) are adaptive strategies that are frequently observed in myrmecophilous insects. The larvae of several lycaenid butterfly species that exhibit obligate associations with specific ant species have been reported to use chemical mimicry. However, little is known about the strategies used by the larvae of species that have facultative associations with multiple ant species. We attempted to reveal the effects of larval CHC profiles on interactions with Formica japonica workers, using three lycaenid species, two facultative ant‐associated (Lycaeides argyrognomon and Zizeeria maha) and one non‐ant‐associated (Lycaena phlaeas), which commonly possess n‐alkanes as the major CHCs. In field bioassays, the lycaenid larvae were attacked by ant workers less often than larvae of Papilio polytes (Papilionidae), the CHCs of which were rich in 7‐alkenes. Treating the lycaenid larvae with 7‐heptacosene and 9‐heptacosene significantly activated ant aggression (biting), whereas treating them with n‐heptacosane, n‐octacosane and 13‐methylheptacosane had little effect. Furthermore, larvae of Pieris rapae (Pieridae), possessing n‐alkanes as the dominant CHCs, suffered an intermediate level of ant biting between the lycaenid and Pa. polytes larvae. However, treatments of the P. rapae larvae with 7‐heptacosene and 9‐heptacosene significantly affected the frequency of ant biting. These findings suggest that the absence of alkenes in larval CHC profiles is an effective means of circumventing predation by ants and allows lycaenid larvae to inhabit the foraging territory of predaceous ants, at least to some extent.     

Fine structure of the genital system in the females of Pergamasus mites (Acari: Gamasida: Pergamasidae)

The female reproductive system in Pergamasus mites consists of an unpaired vagina, vaginal duct, uterus, and ovary. Additionally, there are paired vaginal glands, as well as unpaired ventral and paired lateromedial glandular complexes. The vagina and vaginal duct are cuticle‐lined. In the dorsal wall of the vagina, this lining forms the endogynium which possesses a “sac” and two conspicuous “spherules” and is armed with “stipula” and other cuticular protrusions. The endogynium functions as a spermatheca, being a storing site for the spermatophore. The spherule procuticle is perforated by microvilli of underlying cells that are structurally very unusual. The lining of the vaginal duct forms numerous cuticular fibers directed toward the vagina. There is an external layer of muscles, supposedly functioning as a sphincter. The uterus is an organ in which the fertilized egg is stored for some time and starts embryonic development. Its wall is composed of glandular epithelial cells. The ovary consists of inner and outer parts. The former part is formed by a nutritive syncytium, whereas the latter contains growing oocytes. Two groups of glands connect with the genital tract. Paired vaginal glands are composed of glandular and secretion‐storing parts and open into the vagina. Paired lateromedial and unpaired ventral glandular complexes empty into the genital tract between the vaginal duct and uterus. The structure of the female genital system is discussed in terms of its function and phylogeny. J. Morphol. 240:195–223, 1999. © 1999 Wiley‐Liss, Inc.     

Enemy‐free space and the host range of a lichenivorous moth: a field experiment

According to the enemy‐free space hypothesis (EFS), parasites and predators create a selective force for a specialization on a host that assures better protection against natural enemies than other potential hosts. Few studies have found support for EFS and none of them have covered the whole larval period in natural conditions. I studied the growth and survival of lichen‐feeding moth larvae on five lichen species with and without their natural enemies in natural conditions covering the whole larval period. All the three following EFS predictions gained support. First, natural enemies caused significant mortality of larvae. Second, when natural enemies were present, larval survival was highest on preferred Ramalina lichens. Third, larvae attained higher mass on non‐preferred Parmelia sulcata than on Ramalina species, indicating fecundity cost to feed on Ramalina species instead of P. sulcata. EFS for C. lichenaria larvae on Ramalina species is likely a consequence of shrubby appearance of Ramalina species which provide better larval protection from predation than other hosts.     

Feeding of fall armyworm,Spodoptera frugiperda,on Bt transgenic cotton and its isoline

Studies on insect food intake and utilization are important for determining the degree of insect/plant association and host species’ resistance, and also for helping design pest management programs by providing estimates of potential economic losses, techniques for mass breeding of insects, and identifying physiological differences between species. We studied the feeding and development of fall armyworm, Spodoptera frugiperda (JE Smith) (Lepidoptera: Noctuidae), on transgenic (Bt) and non‐transgenic (non‐Bt) cotton. The larvae of S. frugiperda fed on Bt cotton had a longer development period (23.0 days) than those fed on non‐Bt cotton (20.2 days). Survivorship of S. frugiperda larvae fed on Bt cotton (74.1%) was lower than that of larvae fed on non‐Bt cotton (96.7%). Pupal weight of larvae fed on Bt cotton (0.042 g) was lower than that of larvae fed on non‐Bt cotton (0.061 g). The cotton cultivar significantly affected food intake, feces production, metabolization, and food assimilation by S. frugiperda larvae. However, it did not affect their weight gain. Intake of Bt‐cotton leaf (0.53 g dry weight) per S. frugiperda larva was lower than the intake of non‐Bt‐cotton leaf (0.61 g dry weight). Larvae fed on Bt‐cotton leaves produced less feces (0.25 g dry weight) than those fed on non‐Bt‐cotton leaves (0.37 g dry weight). Weight gain per S. frugiperda larva fed on Bt‐cotton leaves (0.058 g dry weight) was similar to the weight gain for larvae fed on non‐Bt‐cotton leaves (0.056 g dry weight). The cotton cultivar significantly affected the relative growth, consumption, and metabolic rates, as well as other nutritional indices: the figures were lower for larvae fed on Bt‐cotton leaves than for larvae fed on non‐transgenic cotton leaves.     

Influence of temperature changes on larviposition rhythm in the tsetse fly, Glossina morsitans

ABSTRACT. The hourly and quarter-hourly distribution of larval deposition by female Glossina morsitans Westw. was studied at various temperatures. At constant temperature and humidity, peak larviposition occurred 8–9 h after lights on. The effect of confining the flies to daily (LD 12:12 h) regimes of at least twenty-five consecutive cycles that included a sudden increase in temperature of c. 6°C for 2 h was a significant reduction in depositions during each period of increased temperature, and a significant increase before the heat impulse. When the temperature was allowed to fall rapidly, larviposition rate doubled in the following 15 min.     

Morphological and ultrastructural characterization of the alimentary canal in larvae of Streltzoviella insularis (Staudinger) (Lepidoptera: Cossidae)

Streltzoviella insularis (Staudinger) is an important tree‐boring pest, that primarily damages Sophora japonica (Linnaeus) and Ginkgo biloba (Linnaeus), as well as other common species, at great economic cost to the urban landscape construction industry in China. In the present study, the alimentary canal morphology of S. insularis was observed using light microscopy, and its ultrastructure was investigated by scanning and transmission electron microscopy. The foregut of S. insularis can be divided into the pharynx, esophagus, crop, proventriculus, and cardiac valve. The well‐developed crop forms the longest section of the foregut. It is able to store large amounts of food and is lined with a monolayer of epithelial cells. Many sclerotized microspines occur on the surface of the anterior intima and there are dense spines on the posterior intima of the proventriculus. Epithelial cells of the midgut include columnar cells, goblet cells, and regenerative cells, but endocrine cells are absent. The hindgut consists of the pyloric valve, ileum, and rectum. There is no clear distinction between the ileum and colon. The intima surface of the pyloric valve carries many microspines, whereas the intestinal wall of the rectum is thin with well‐developed rectal pads. The rectal epithelial cells form a squamous monolayer. A cryptonephric excretory system is located in the hindgut. There are six spiral Malpighian tubules, in which a cellular layer on a basement membrane encloses a lumen. These results will provide the basis for further studies of the structure and function in S. insularis larvae.     

Predators and invasive plants affect performance of amphibian larvae

Exotic ecosystem engineers induce structural and qualitative habitat changes in invaded landscapes, yet studies rarely examine the effects of both of these changes on native taxa. We used a factorial experiment in natural, predator‐containing environments to determine whether performance of amphibian larvae was affected by predators and/or changes in habitat structure or chemistry associated with the invasive shrub Lonicera maackii. Invertebrate predators significantly reduced survival of American toad Anaxyrus americanus larvae, whereas tadpole development was accelerated in pools inoculated with the chemical signature of L. maackii. The significant effect of L. maackii chemistry on A. americanus larvae suggests that invasive species may have non‐intuitive effects even on native taxa with which they share no trophic connection, and may represent cryptic components of the multiple, interactive drivers of biodiversity change.