Nestedness patterns of container-dwelling mosquitoes: effects of larval habitat within variable terrestrial matrices

Distributions of mosquito larvae likely are a consequence of multiple factors, although two commonly studied factors (quality of the larval environment and the terrestrial matrix in which these habitats reside) have rarely and simultaneously been varied in the field to understand distributions of larvae. We monitored aquatic containers of two leaf detritus levels within a forest, prairie, and industrial habitat across five months to understand the temporal and spatial colonization of aquatic invertebrates in Northcentral Illinois, USA. Data were collected monthly on mosquito populations and the composition of other invertebrates colonizing containers. Overall, six species of mosquitoes colonized containers, with Culex restuans and Aedes triseriatus having the highest relative abundances. There were strong seasonal abundance patterns for these two mosquito species, with the dominant species changing over time in the forest habitat. The responses of other mosquito taxa were more variable, with abundances reflective of either the terrestrial matrix or larval habitat quality. High detritus containers supported the highest abundances of most species encountered, regardless of habitat. Non-mosquito taxa were less common numerically, but analyses suggested that some taxa, such as syrphid larvae, often co-occurred with mosquitoes. Nested subset analysis indicated communities were strongly nested, and that both habitat type and detritus level were important in explaining nested patterns of aquatic invertebrates. Our data show that both the larval habitat and the surrounding terrestrial matrix shape patterns of container mosquitoes, and that other container invertebrates vary in similar ways as mosquitoes. Handling editor: K. Martens     

Zombie fire ant workers: behavior controlled by decapitating fly parasitoids

Laboratory observations were conducted on four separate red imported fire ant, Solenopsis invicta, colonies that contained workers parasitized by the decapitating fly, Pseudacteon tricuspis. Parasitized S. invicta workers remained inside the nest during parasitoid larval development and left the nest approximately 8 – 10 hours before decapitation by the parasitoid. When parasitized ants left the nest, they were highly mobile, were responsive to tactile stimuli, and showed minimal defensive behavior. Ants ultimately entered into a grass thatch layer, where they were decapitated and the fly maggots pupariated. This study reveals that parasitized ants exhibit behaviors that are consistent with host manipulation to benefit survival of the parasitoid. Received 9 November 2006; revised 26 January 2007; accepted 7 February.     

<Emphasis Type="Italic">Toxoneuron nigriceps</Emphasis> parasitization delays midgut replacement in fifth-instar <Emphasis Type="Italic">Heliothis virescens</Emphasis> larvae

We have analyzed the effects of Toxoneuron nigriceps parasitization on the midgut development of its host Heliothis virescens. In parasitized H. virescens larvae, the midgut epithelium undergoes a complete replacement, which is qualitatively not different to that observed in synchronous unparasitized larvae, with similar temporal profiles of cell death and metabolic activity. However, the whole gut replacement process is significantly delayed in parasitized larvae, with complete differentiation of the new gut epithelium being observed 4 days later than in unparasitized controls. The administration of juvenile hormone before commitment and of 20-hydroxyecdysone (20E) after commitment delays and fosters, respectively, the replacement process of the midgut epithelium; moreover, the injection of 20E into developmentally arrested and 20E-deficient host last-instar larvae parasitized by T. nigriceps immediately triggers regular gut development. These hormone-based experiments suggest that endocrine alterations in the larval host, induced by T. nigriceps parasitism, are responsible for the temporal alterations in the gut replacement process. The role of this parasitoid-induced developmental change in the host regulation process is discussed. This work was partially supported by FAR 2006–2007 (University of Insubria) to G.T., by MIUR-FIRB-COFIN (grant no. RBNE01YXA8/2004077251), and by the Centro Grandi Attrezzature (University of Insubria).     

Clonal damselflies (Ischnura hastata) are not significantly affected by mite parasitism

We studied parasitism rate by the terrestrial mite Leptus killingtoni Turk (Acari: Erythraeidae) on asexual parthenogenetic damselflies, Ischnura hastata (Say), and sexual Ischnura pumilio (Charpentier) (Odonata: Coenagrionidae) on Pico island (Azores, Portugal). We sampled 52 water bodies on the island and recorded whether Ischnura specimens were parasitized. Half of the water bodies had either dried up or were almost dry or did not have Ischnura populations. In the remaining 23 ponds, mite parasitism was extremely low, with only 3.6% of I. hastata females bearing one or more mites. Ischnura pumilio was rare on the island (61 specimens examined) and had also very few parasites (9.8% parasitism). We examined the biology of the mite and its effects on the host, by studying mite attachment behavior and seasonal abundance, in an intensive study of one pond (Lagoa do Landroal). At this pond, mite prevalence peaked at the start of the sampling period, with 32% of females of I. hastata parasitized and decreased continuously until the end of the study, when only 2% were parasitized. The analysis of mark–recapture histories of 1 748 females of I. hastata indicates that mites did not affect female survival or recapture rate. Our results suggest that L. killingtoni is unlikely to represent a significant selective factor for odonates on the island of Pico, if its density is as low as during the period of our study, although it could be relevant when it is locally abundant or during periods of outbreak.     

Invasive mosquitoes, larval competition, and indirect effects on the vector competence of native mosquito species (Diptera: Culicidae)

Invasive arthropods that vector pathogens have the potential to influence pathogen transmission both directly, by becoming a novel pathogen vector, or indirectly, by interacting with native vectors. Adult mosquito size is influenced by food availability in the larval stage, and smaller, nutrient-deprived mosquitoes are, in some studies, more efficient viral vectors in the laboratory. This is the first study to examine the indirect impacts that larval competition between Aedes albopictus, an introduced mosquito species, and Ochlerotatus triseriatus, a native mosquito species and the primary vector for La Crosse virus (LACV) in the US, has on native mosquito larval survival, adult size, and vector competence. A. albopictus presence decreased Oc. triseriatus larval survival, but surviving Oc. triseriatus females were larger, potentially owing to a release from intraspecific competition. These larger, native females were more likely to develop both midgut and disseminated LACV infections than females emerging from monospecific treatments. Collectively, these results suggest a need to better understand the ecology of both native and invasive vector species, their interactions, and the potential for those interactions to alter vector-borne disease transmission.     

Parasitism by Pteromalus cerealellae (Hymenoptera: Pteromalidae) on the Cowpea weevil, Callosbruchus maculatus (Coleoptera: Bruchidae): Host density, temperature effects, and host finding ability

Studies on interactions between a larval parasitoid, Pteromalus cerealellae (Boucek) and one of its hosts, Callosobruchus maculatus (F.) were carried out in the laboratory. The number of host larvae parasitized by P. cerealellae increased with host larvae at low densities and tended to a plateau at a density of 25 larvae per female parasitoid. Each parasitoid was able to parasitize more hosts and produced more offspring at 20 and 25 °C than at 30 °C. The number of non-infested seeds mixed with seeds infested with the last instar of C. maculatus did not preclude P. cerealellae from identifying infested seeds and attacking larvae inside them. When infested seeds were tightly packed, several host larvae escaped parasitism. P. cerealellae may be a useful biological control agent in newly harvested cowpea with low C. maculatus infestation, and lowering the temperature of the storage system may enhance the effectiveness of this parasitoid.     

Survey of brown soft scale Coccus hesperidum L. parasitoids in southern California citrus

The parasitoid complex of brown soft scale, Coccus hesperidum L., a multivoltine soft scale, was determined in southern California citrus over the period February 2004–March 2006. The survey was conducted by placing brown soft scale-infested yucca leaves in the canopy of citrus trees and subsequently rearing individually isolated parasitized scales in the laboratory. A total of 14 species parasitized brown soft scale in the field, the most abundant ones belonging to the genus Metaphycus Mercet (75%). The most abundant parasitoid species was Metaphycus angustifrons Compere (38% parasitism), and this is a new record of establishment for this species in California. Coccophagus species accounted for only 11% parasitism. There were important spatio-temporal differences across the parasitoid complex survey locations. We also found that the five most abundant encyrtid parasitoid species showed preferences for scales of different sizes. Our results have implications for biological control of citricola scale, Coccus pseudomagnoliarum (Kuwana), an important pest of citrus in the San Joaquin Valley of central California. Notably, this species is nearly absent in southern California. Brown soft scale is considered to be an alternate host for parasitoids of citricola scale, a univoltine soft scale, at times when the latter species is unavailable for parasitism.     

Intra- and interspecific competition by Fopius arisanus and Diachasmimorpha tryoni (Hymenoptera: Braconidae), parasitoids of tephritid fruit flies

Fopius arisanus (Sonan) and Diachasmimorpha tryoni (Cameron) are two important solitary endoparasitoids of tephritid fruit flies. The former species attacks host eggs while the latter attacks host larvae, and both species emerge as adults from the host puparium. This study investigated intrinsic competition between these two parasitoids, as well as aspects of intraspecific competition within each species in the Mediterranean fruit fly, Ceratitis capitata (Wiedemann). Parasitization by F. arisanus resulted in direct mortality of host eggs and prolonged development of host eggs and larvae. Superparasitism by F. arisanus was uncommon when mean parasitism per host patch was <50%, but increased with rising rates of parasitism. Superparasitism by D. tryoni was more common. In superparasitized hosts, supernumerary individuals of F. arisanus were killed through physiological suppression, while supernumerary larvae of D. tryoni were killed mainly through physical attack. In multiparasitized hosts, dissections showed that 81.6% of D. tryoni eggs in the presence of F. arisanus larvae died within 3 days, indicating physiological inhibition of egg hatch. Rearing results further showed that F. arisanus won almost all competitions against D. tryoni. The ratio of D. tryoni stings to ovipositions was lower in hosts not previously parasitized by F. arisanus than in parasitized hosts, suggesting that D. tryoni can discriminate against parasitized hosts. The mechanism that F. arisanus employs to eliminate D. tryoni is similar to that it uses against all other larval fruit fly parasitoids so far reported. The results are discussed in relation to the competitive superiority of early acting species in fruit fly parasitoids, and to a possible competitive-mediated mechanism underlying host shift by D. tryoni to attack non-target flies following the successful introduction of F. arisanus in Hawaii.     

Effect of parasitism on flight behavior of the soybean aphid, Aphis glycines

Many aphid species possess wingless (apterous) and winged (alate) stages, both of which can harbor parasitoids at various developmental stages. Alates can either be parasitized directly or can bear parasitoids eggs or larvae resulting from prior parasitism of alatoid nymphs. Winged aphids bearing parasitoid eggs or young larvae eventually still engage in long-distance flights, thereby facilitating parasitoid dispersal. This may have a number of important implications for biological control of aphids by parasitoids. In this study, we determined the effect of parasitism by Aphelinus varipes (Hymenoptera: Aphelinidae) on wing development and flight of the soybean aphid, Aphis glycines (Hemiptera: Aphididae). We also quantified the influence of aphid flight distance on subsequent A. varipes development. Parasitism by A. varipes was allowed at different A. glycines developmental stages (i.e., alatoid 3rd and 4th-instar nymphs, alates) and subsequent aphid flight was measured using a computer-monitored flight mill. Only 35% of aphids parasitized as L3 alatoid nymphs produced normal winged adults compared to 100% of L4 alatoids. Flight performance of aphids parasitized as 4th-instar alatoid nymphs 24 or 48 h prior to testing was similar to that of un-parasitized alates of identical age, but declined sharply for alates that had been parasitized as 4th-instar alatoid nymphs 72 and 96 h prior to testing. Flight performance of aphids parasitized as alate adults for 24 h was not significantly different from un-parasitized alates of comparable ages. Flight distance did not affect parasitoid larval or pupal development times, or the percent mummification of parasitized aphids. Our results have implications for natural biological control of A. glycines in Asia and classical biological control of the soybean aphid in North America.     

Differential Parasitism of Native and Introduced Snails: Replacement of a Parasite Fauna

The role of parasites in a marine invasion was assessed by first examining regional patterns of trematode parasitism in the introduced Japanese mud snail, Batillaria cumingi (= B. attramentaria), in nearly all of its introduced range along the Pacific Coast of North America. Only one parasite species, which was itself a non-native species, Cercaria batillariae was recovered. Its prevalence ranged from 3 to 86%. Trematode diversity and prevalence in B. cumingi and a native sympatric mud snail, Cerithidea californica, were also compared in Bolinas Lagoon, California. Prevalence of larval trematodes infecting snails as first intermediate hosts was not significantly different (14% in B. cumingi vs 15% in C. californica). However, while the non-native snail was parasitized only by one introduced trematode species, the native snail was parasitized by 10 native trematode species. Furthermore, only the native, C. californica, was infected as a second intermediate host, by Acanthoparyphium spinulosum(78% prevalence). Given the high host specificity of trematodes for first intermediate hosts, in marshes where B. cumingi is competitively excluding C. californica, 10 or more native trematodes will also become locally extinct.     

Fecundity and Longevity of Green Vegetable Bug,Nezara viridula, Following Parasitism byTrichopoda giacomellii

The effects of parasitism by the ArgentinianTrichopoda giacomellii(Blanchard) on reproduction and longevity of its host,Nezara viridula(L.) are reported. Parasitoid larvae suppress egg maturation, reducing by 70% the fecundity of mature female hosts during the period of larval development. Egg viability was not affected, but mating frequency was reduced by approximately 50%. When parasitized as newly eclosed adults, 84% of females fail to reproduce. In male hosts, fertility and mating frequency were not affected during the period of larval parasitoid development. In male and reproductively immature female hosts, death was coincident with, or occurred shortly after parasitoid emergence (2–4 days); in mature females, death occurred on average 2 weeks after larval parasitoid emergence. Host mortality occurred as a consequence of tissue damage incurred as the parasitoid larvae emerged from the host. Some individuals survived parasitism though no further reproductive activity (mating or oviposition) occurred. The effectiveness ofT. giacomelliias a biological control agent is discussed in relation to its impact on reproduction and survival of its host and contrasted with the action of otherTrichopodaspecies.     

Effect of a turnip rape <Emphasis Type="Italic">(Brassica rapa)</Emphasis> trap crop on stem-mining pests and their parasitoids in winter oilseed rape <Emphasis Type="Italic">(Brassica napus)</Emphasis>

Concerns about the negative effects of chemical control of oilseed rape (Brassica napus L.) pests on non-target species, human safety, and development of insecticide resistance, require alternative control strategies such as the use of trap crops and biocontrol to be developed. Psylliodes chrysocephala(L.) (Coleoptera: Chrysomelidae) (cabbage stem flea beetle) and Ceutorhynchus pallidactylus (Marsh.) (Coleoptera: Curculionidae) (cabbage stem weevil) are two major stem-mining pests of oilseed rape. This study investigated the phenology of these pests and their main parasitoids in the UK, the potential use of turnip rape (Brassica rapa L.) as a trap crop to reduce oilseed rape infestation, and the effects of insecticide treatment on pest incidence and larval parasitism. Water trap samples, plant dissections and pest larval dissections were done to determine: the incidence of adult pests and their parasitoids, the level of plant infestation by the pests and percentage larval parasitism, respectively. The turnip rape trap crop borders reduced P. chrysocephalabut not C. pallidactylus infestation of oilseed rape plots. Treatment of the trap crop with insecticide had little effect on either pest or parasitoid incidence in the oilseed rape. TersilochusmicrogasterSzép. andT. obscurator Aub. (Hymenoptera: Ichneumonidae) were the main larval parasitoids of P. chrysocephalaand C. pallidactylus, respectively. Tersilochus microgasteris reported for the first time in the UK. The implications for integrated pest management are discussed.     

Host range of the parasite Strelkovimermis spiculatus (Nematoda: Mermithidae) in Argentina mosquitoes

Strelkovimermis spiculatus ( Poinar and Camino 1986 ) is a nematode parasite of mosquitoes isolated from the Neotropical region. We investigated the host range of this parasite in mosquito populations for a better understanding of the dynamics of temporary breeding sites. Five grassy‐pool habitats filled by rainwater were sampled from the summer 2007 through the fall 2008. Eight mosquito species were collected: Anopheles albitarsis, Culex chidesteri, Culex dolosus, Culex maxi, Aedes albifasciatus, Psorophora ciliata, Psorophora cyanescens, and Psorophora albigenu. Six of these species were parasitized: Cx. chidesteri, Cx. dolosus, Cx. maxi, Ae. albifasciatus, Ps. ciliata, and Ps. cyanescens. The occurrence of this mermithid in natural mosquito populations was increased from the end of winter to the end of the spring. Prevalence ranged from 11% to 100%. High levels of infections were registered only in Ae. albifasciatus larvae, the most abundant mosquito species (95%), followed by Cx. dolosus (2.7%). Strelkovimermis spiculatus completed its development in all infected mosquito larvae. The presence of S. spiculatus in six natural mosquito populations increases the number of susceptible species to 24.     

Condition and fecundity of the damselfly,Enallagma ebrium (Hagen): the importance of ectoparasites

Summary The extent, magnitude, and cause of natural covariation between degree of parasitism and other variables known or suspected of influencing host fitness (such as host age or body size) has been understudied. We demonstrate that degree of parasitism by larval water mites (Arrenurus spp.) was associated with reduced condition of males and with lowered fecundity of young females of the damselfly, Enallagma ebrium (Hagen) (Odonata: Coenagrionidae). We also demonstrate that degree of parasitism can covary with both age and size of host damselflies. We explain the putative causes of such natural covariation, and we suggest that degree of parasitism, host age, and host size can all interact to determine damselfly fitness. We expect that natural covariation between the host's phenotype and degree of parasitism will be frequently observed. Studies of such natural covariation will help researchers to assess better the importance of several variables on host reproductive success and to understand better the dynamics of host-parasite interactions.     

Potential role of parasitism in the evolution of mutualism in astigmatid mites: Hemisarcoptes cooremani as a model

Phoresy is a symbiotic interaction that results in dispersal, benefiting the relocated organism without negatively impacting the phoretic host. It has long been considered that phoresy among astigmatid mites is somehow an intermediate precursor to the evolution of parasitism within the group. In astigmatid mites, only the heteromorphic deutonymph (hypopode) participates in phoretic dispersal, and the plesiomorphic hypopode may be the key to understanding the dynamics of the evolution of that parasitism. Hypopodes of Hemisarcoptes cooremani (Acari: Acariformes) and their phoretic beetle host Chilocorus cacti (Coleoptera: Coccinellidae) have become the experimental focus for studies concerned with the potential forces that influence the transition of a free-living life style into various coevolved relationships. Previous radiolabeling studies applied to H. cooremani and C. cacti determined that hypopodes of H. cooremani acquired resources from adults of C. cacti while in transit, negating the paradigm that the heteromorphy was purely phoretic. To further probe this relationship, we tested whether materials could be passed from the mites to their hosts. We report here a study using a tritium radiolabel, which indicated that beetles also acquire resources from the hypopodes. These results have implications for understanding the complex relationship between H. cooremani and C. cacti. We propose that this relationship should now correctly be defined as mutualistic (not phoretic) and develop a general model for the potential role of parasitism in the evolution of mutualism among the Astigmata.     

Studies on the characteristics of parasitism ofPlutella xylostella (Lep.: Plutellidae) by a larval parasiteDiadegma semiclausum (Hym.: Ichneumonidae)

Laboratory experiments were conducted to study the characteristics of parasitism of diamondback moth,Plutella xylostella (L.), a worldwide pest of crucifers, by a larval parasite,Diadegma semiclausum Hellén. Results showed that the greater the host larval density, the lesser was the percentage of larvae parasitized. The area of discovery decreased with increasing parasite density, but k-value remained practically unchanged. Parasitism reduced food consumption in parasitised larvae. No difference was observed in duration of larval instars between the parasitized and healthy larvae. As the frequency of superparasitism increased, the proportion of production of female progeny also increased. Presence of parasite larva within the host larva deterred superparasitism greater than the presence of parasite egg. Presence of larva of eitherD. semiclausum or another larval parasite,Cotesia plutellae Kurdjumov, within host larva deterred multiparasitism by either species greater than the presence of egg of either parasite species.Diadegma semiclausum was much more aggressive thanC. plutellae in parasitisingP. xylostella larvae.     

A comparative study of predation of three aquatic heteropteran bugs on Culex quinquefasciatus larvae

The aquatic bugs Anisops bouvieri Kirkaldy 1704 (Heteroptera: Notonectidae), Diplonychus (=Sphaerodema) rusticus Fabricius 1781, and Diplonychus annulatus Fabricius 1781 (Heteroptera: Belostomatidae) are common members of the freshwater insect communities of the East Calcutta Wetlands along the eastern fringe of Kolkata, India. These insects are established predators of dipteran larvae and other organisms. A comparative account of their predatory efficiency was made using larvae of Culex quinquefasciatus Say 1823 in the laboratory. It was revealed that a single adult of A. bouvieri could consume 28–34 fourth-instar mosquito larvae per day, D. rusticus 11–87 fourth-instar mosquito larvae per day, and D. annulatus 33–122 fourth-instar mosquito larvae per day, depending upon the prey and predator densities. The mean predation rate of A. bouvieri and D. annulatus remained stable over a 6-day feeding period but varied for D. rusticus. The predatory impact (PI) values were 14.77–17.31, 46.9–55.73, and 61.74–72.72 larvae/day for A. bouvieri, D. rusticus, and D. annulatus, respectively. Compared to these, the clearance rate (CR) value range was 9.06–13.25 for A. bouvieri, 13.64–15.99 for D. rusticus, and 13.50–16.52 larvae l/day/predator for D. annulatus. The values of mutual interference, “m,” remained 0.06–0.78 for A. bouvieri, 0.003–0.25 for D. rusticus, and 0.09–0.27 for D. annulatus, and did not vary between the days. The difference in predatory efficiency, CR, and PI values varied significantly among the three predators, indicating the possible difference in the function as predators occupying the same guild. It can be assumed that these predators play an important role in larval population regulation of mosquitoes and thereby impart an effect on species composition and interactions in the aquatic insect communities of the wetlands and other similar habitats where they occur.     

Proteomic analysis of parasitized Plutella xylostella larvae plasma

Insects use their innate immunity to defend themselves against foreign invaders, such as microorganisms, nematodes and parasites. Cotesia plutellae, an endoparasitoid wasp that parasitizes the diamondback moth Plutella xylostella, uses several strategies to attack the host immune system, such as injection of viruses, venom, and serosal membrane-derived cells denoted teratocytes. However, the proteome profiles related to these immune deficiency systems have yet to be clearly defined. In this study, we investigate differences in protein expression patterns in parasitized P. xylostella larvae, with a view to identifying parasitism-specific factors. Using 2D polyacrylamide gel electrophoresis, proteins in the host plasma were assessed every 48 h after parasitism by C. plutellae. A large number of protein spots (350 in total) were detected, and approximately 50 spots were differentially expressed in the parasitized P. xylostella larvae every 48 h. In total, 26 potential candidates, including P. xylostella Serpin 2 (pxSerpin 2), translationally controlled tumor protein, signal transduction histidine kinase, apolipophorin-III, and fatty-acid binding protein were identified through quadrupole time-of-flight tandem mass spectrometry and sequence homology analysis. These proteins were classified into the following functional groups: immunity, signaling, lipid metabolism, energy metabolism, amino acid/nucleotide metabolism, and others. The pxSerpin 2 gene was cloned, and its expression profile investigated during the course of parasitism. Real-time PCR analysis of pxSerpin 2 revealed a poor correlation between the mRNA level and protein abundance. Our results clearly suggest that parasitism-specific proteins participate in suppression of the host immune response.