Effects of temperature and photoperiod on development and oviposition of the legume flower thrips, Megalurothrips sjostedti

Chrysomya albiceps, the larvae of which are facultative predators of larvae of other dipteran species, has been introduced to the Americas over recent years along with other Old World species of blowflies, including Chrysomya megacephala, Chrysomya putoria and Chrysomya rufifacies. An apparent correlate of this biological invasion has been a sudden decline in the population numbers of Cochliomyia macellaria, a native species of the Americas. In this study, we investigated predation rates on third instar larvae of C. macellaria, C. putoria and C. megacephala by third instar larvae of C. albiceps in no-choice, two-choice and three-choice situations. Most attacks by C. albiceps larvae occurred within the first hour of observation and the highest predation rate occurred on C. macellaria larvae, suggesting that C. albiceps was more dangerous to C. macellaria than to C. megacephala and C. putoria under these experimental conditions. The rates of larvae killed as a result of the predation, as well as its implications to population dynamics of introduced and native species are discussed.     

The dynamics of intraguild predation in Chrysomya albiceps Wied. (Diptera: Calliphoridae): interactions between instars and species under different abundances of food

The pattern of larval interaction in blowflies confined with Chrysomya albiceps Wied. and C. rufifacies Maquart can be changed in response to the predatory behaviour of the two species to a contest-type process instead of the scramble competition that usually occurs in blowflies. Facultative predation is a frequent behaviour in C. albiceps and C. rufifacies that occurs as an alternative food source during the larval stage. In this study, we investigated the dynamics of intraguild predation by C. albiceps on other fly species in order to analyse interspecific and intraspecific survival in C. albiceps, C. megacephala and C. macellaria Fabricius. The experimental design of the study allowed us to evaluate how factors such as species, density and abundance of food influenced the survival of the calliphorid species. When C. albiceps was confined with C. megacephala or C. macellaria, only adults of C. albiceps survived at different larval densities and abundance of food. In addition, the survival of C. albiceps was higher in two-species experiments when compared to single species experiments. The implications of these results for the dynamics of C. albiceps were discussed.     

Prey choice by facultative predator larvae of Chrysomya albiceps (Diptera: Calliphoridae)

In this study we investigated predation rates on third instar larvae of Chrysomya putoria and C. megacephala by third instar larvae of C. albiceps in a two-choice situation. The highest predation rate occurred on C. putoria larvae and this result is compared to previous experiments, in which C. macellaria larvae were present. Our results suggest that, when C. macellaria is absent C. albiceps larvae attack more C. putoria than C. megacephala larvae. Prey choice decisions and its implications for introduced and native blowflies are discussed.     

Dispersal and Predation Behavior in Larvae of <Emphasis Type="Italic">Chrysomya albiceps</Emphasis> and <Emphasis Type="Italic">Chrysomya megacephala</Emphasis> (Diptera: Calliphoridae)

Chrysomya albiceps and Chrysomya megacephala are exotic blowfly species known by producing myiasis in humans and other animals and by transmitting pathogens mechanically. C. albiceps stand out by being a facultative predator of other dipteran larvae. In this paper we investigated the influence of larval predation on the dispersal of larvae of C. albiceps and C. megacephala single and double species for three photophases. An experimental acrylic channel graduated and covered with wood shavings was used to observe the larval dispersal. The results showed that C. albiceps attacks C. megacephala larvae during dispersal and keeps an aggregated pattern close to the release point, in single and double species, independently of the different photophases. Chrysomya megacephala single species exhibited the same pattern, but in double species this was changed to a random distribution.     

Larval aggregation and competition for food in experimental populations of Chrysomya putoria (Wied.) and Cochliomyia macellaria (F.) (Dipt., Calliphoridae)

In blowflies, larval aggregation in patches of food can be both intra- and interspecific, depending upon the degree to which competitors are clumped among the patches. In the present study, the implications of spatial aggregation for larval competition was investigated in experimental populations of the introduced blowfly Chrysomya putoria and the native Cochliomyia macellaria , using data from survival to adulthood in a range of single- and double-species larval cultures. The reduction in C. macellaria survival rate in the presence of C. putoria suggests that the former species is the inferior competitor. The results on survival to adulthood for both species in single- and double-species cultures can be explained in the light of the relationship between the level of intra- and interspecific aggregation and the efficiency of the larval feeding process. The possible implications of these results for the population biology of both species in natural environments are discussed.     

Dynamics of handling time and functional response by larvae of Chrysomya albiceps (Dipt., Calliphoridae) on different prey species

Abstract:  One way to understand the behavioural patterns exhibited by a predator in response to prey density is to evaluate its functional response. Such evaluation yields information about basic mechanisms of prey–predator dynamics, and is an essential component of prey–predator models. In this paper we analysed experimentally the functional response and the handling time spent by Chrysomya albiceps on different prey species and larval instars of blowflies. The type II functional response was observed when second instar larvae of Chrysomya megacephala and Chrysomya macellaria were consumed. The handling time spent by the predator was significantly different between instars and species. The implications of the functional response and handling time for the interaction dynamics of Brazilian Chrysomyinae species are discussed.     

Spatio-temporal dynamics and transition from asymptotic equilibrium to bounded oscillations in Chrysomya albiceps (Diptera, Calliphoridae)

The sensitivity of parameters that govern the stability of population size in Chrysomya albiceps and describe its spatial dynamics was evaluated in this study. The dynamics was modeled using a density-dependent model of population growth. Our simulations show that variation in fecundity and mainly in survival has marked effect on the dynamics and indicates the possibility of transitions from one-point equilibrium to bounded oscillations. C. albiceps exhibits a two-point limit cycle, but the introduction of diffusive dispersal induces an evident qualitative shift from two-point limit cycle to a one fixed-point dynamics. Population dynamics of C. albiceps is here compared to dynamics of Cochliomyia macellaria, C. megacephala and C. putoria.     

The influence of density-dependent factors on larval development in native and invasive populations of <Emphasis Type="Italic">Harmonia axyridis</Emphasis> (Pall.) (Coleoptera,Coccinellidae)

Effects of the number of larvae per Petri dish (1, 5, and 10) on the preimaginal development of individuals of the native (Irkutsk, southern Siberia) and invasive (Sochi, the Northern Caucasus) populations of the multicolored Asian ladybird Harmonia axyridis were investigated in the laboratory. The experiments were conducted under short (12 h) and long (18 h) day conditions; the larvae were fed on the green peach aphid Myzus persicae or on the eggs of the grain moth Sitotroga cerealella. An increase in the number of larvae developed in one Petri dish resulted in a significant decrease in the rate of development in individuals from both populations which fed on aphids. Survival decreased with an increase in the number of larvae developed in one Petri dish fed on both prey species, but only in larvae from the invasive population of H. axyridis. The weight of emerging adults decreased with the number of larvae per dish in individuals from both study populations, but only when fed on aphids. These data suggest that the influence of density-dependent factors on the development of H. axyridis depends significantly on larval prey species. In addition, larvae from the invasive population have somewhat more aggressive interactions with competitors, this possibly having been one of the prerequisites for invasion.     

Competition and co-existence of Zoophthora radicans and Pandora blunckii, two co-occurring fungal pathogens of the diamondback moth, Plutella xylostella

The entomopathogenic fungi Zoophthora radicans and Pandora blunckii co-occur in field populations of Plutella xylostella and, therefore, are likely to interact during the infection process. We have investigated the possible outcomes of these interactions in the laboratory. Using four isolates, two of each fungal species, inter-specific interaction experiments were done in Petri dishes and on intact plants. In Petri dish experiments, larvae were inoculated directly using sporulating mats of mycelium, both species had the same opportunity to infect and only the relative concentration of conidia of each pathogen species applied was manipulated. In the intact plant experiments, larvae were placed onto fungus-contaminated plants, inoculation was passive and the probability of infection by either or both species of fungi depended on larval activity and proximity to inoculum. In the Petri dish experiment, the species with the largest concentration of conidia out-competed the other regardless of virulence, and results were similar in the intact plant experiment. The ecological implications for competition or co-existence of these two pathogens in the field are discussed.     

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.     

The larvae of some blowflies of medical and veterinary importance

Diagnostic features are described as a series of couplets that enable separation of the third instar larvae of the following pairs of closely related forms of blowflies of medical and veterinary importance: Chrysomya chloropyga (Wiedemann) and Ch.putoria (Wiedemann), Chrysomya albiceps (Wiedemann) and Ch.rufifacies (Macquart), Cochliomyia hominivorax (Coquerel) and Co.macellaria (Fabricius), Lucilia sericata (Mergen) and L. cuprina (Wiedemann), Calliphora augur (Fabricius) and C. stygia (Fabricius).     

Long-term movements of self-marked caddisfly larvae (Trichoptera: Sericostomatidae) in a California coastal mountain stream

1. Over 140 000 larvae of the case-building caddisfly Gumaga nigricula were self-marked as they incorporated glitter into small portions of their cases while reared in streamside troughs. These marked individuals were released into stream pools and their movements monitored in the dry season, when base flow was low and no spates occurred, and in the wet season when base flow was high and several spates occurred. 2. Of the 9,000–10 000 larvae released in each of two stream pools in the dry season, 4–20% (i.e. 377–1817 marked individuals) were observed on three sampling dates (4, 11 and 24 d after release). Most larvae (87–93%) remained within 4 m up- or downstream of the release line after 24 d. No larvae were found outside of the release pools, even after 37 d. 3. Of the > 120 000 larvae released in one stream pool near the beginning of the wet season, 408 larvae were recaptured 130–167 d later, a period that included 30 days of high flow associated with six spates. Estimated survivorship over this period was 0.7–6.2%; there was no relationship between survival and larval size at release. Most (75%) recaptured larvae were found in the pool where they were originally released. The remaining larvae were found downstream of the release pool. Larvae had generally dispersed only a short distance downstream of the release pool (median = 18 m, maximum = 222 m). In addition, four marked pupae were later found 436 m downstream of the release pool. 4. These results illustrate the sedentary nature of larval G. nigricula as well as the important role that high flow events play in larval mortality and dispersal. These case-building larvae move very little during low flow periods, even when food resources appear limiting. In contrast, the frequency and distance of larval dispersal are much greater during periods with high flow. 5. Our observations for G. nigricula support previously published inferences that larval dispersal within a stream can be limited for some aquatic insects. However, our observations also suggest that, even for a relatively sedentary species like G. nigricula, larval dispersal during periods with high flow may contribute significantly to gene flow within a stream reach.     

Behavioral Response to Larval Tracks and the Influence of Tracks on Intraguild Scavenging by Coccinellid Larvae

A paired design was used to determine that Harmonia axyridis 4th instars were not influenced by the presence of conspecific larval tracks, but well-fed H. axyridis 4th instars spent less time on plants that contained tracks left by Coleomegilla maculata 4th instars. To determine if the presence of larval tracks influences intraguild scavenging by H. axyridis 4th instars, dead 4th instars were placed in Petri dishes that contained or did not contain larval tracks. The presence of larval tracks did not influence the feeding frequency or the amount of time before feeding. However, larvae dragged their pygopod on dish surfaces more frequently if the dish contained larval tracks. In addition, starved H. axyridis larvae were more likely to feed on the prey and dragged their pygopod less frequently than well-fed larvae.     

Neighborhood Interactions and Larval Dispersal Behavior in Blowflies

We performed a computational analysis employing a cellular automata model to investigate the larval dispersal behavior of blowflies. The spatially discrete model developed here, incorporates simple behavioral rules in local interactions to produce the large-scale patterns observed in the larval dispersal process. We were able to find parameter ranges that could simulate the required experimental dispersal patterns in the study. In particular, oscillations, initially explained as a response to larval aggregation, could be explained by the combination of different mechanisms acting during the dispersal process. Peaks have characterized the interaction between dispersing larvae, but as a function of time. Then, the number of larvae decreased as a result of the pupation process, and neighborhood interaction became stingy.     

The Effects of Anthropogenic Structures on Habitat Connectivity and the Potential Spread of Non-Native Invertebrate Species in the Offshore Environment

Offshore structures provide habitat that could facilitate species range expansions and the introduction of non-native species into new geographic areas. Surveys of assemblages of seven offshore oil and gas platforms in the Santa Barbara Channel revealed a change in distribution of the non-native sessile invertebrate Watersipora subtorquata, a bryozoan with a planktonic larval duration (PLD) of 24 hours or less, from one platform in 2001 to four platforms in 2013. We use a three-dimensional biophysical model to assess whether larval dispersal via currents from harbors to platforms and among platforms is a plausible mechanism to explain the change in distribution of Watersipora and to predict potential spread to other platforms in the future. Hull fouling is another possible mechanism to explain the change in distribution of Watersipora. We find that larval dispersal via currents could account for the increase in distribution of Watersipora from one to four platforms and that Watersipora is unlikely to spread from these four platforms to additional platforms through larval dispersal. Our results also suggest that larvae with PLDs of 24 hours or less released from offshore platforms can attain much greater dispersal distances than larvae with PLDs of 24 hours or less released from nearshore habitat. We hypothesize that the enhanced dispersal distance of larvae released from offshore platforms is driven by a combination of the offshore hydrodynamic environment, larval behavior, and larval release above the seafloor.     

Larval dispersal of the invasive fall armyworm,Spodoptera frugiperda,the exotic stemborer Chilo partellus,and indigenous maize stemborers in Africa

Larval dispersal either through ballooning or crawling results in a redistribution of the insect population and infestations within and between plants. In addition, invasive species, such as the fall armyworm (FAW), Spodoptera frugiperda (JE Smith) (Lepidoptera: Noctuidae), and the exotic stemborer Chilo partellus (Swinhoe) (Lepidoptera: Crambidae), may displace indigenous stemborers on maize in Africa. To test whether larval dispersal activity may play a role in the displacement of indigenous stemborers, larval dispersal was compared between FAW, C. partellus, and the indigenous species Busseola fusca (Fuller) and Sesamia calamistis (Hampson) (both Lepidoptera: Noctuidae). Twenty potted maize plants were infested with one batch of eggs either from stemborers (B. fusca, S. calamistis, or C. partellus) or from FAW and monitored in the greenhouse for ballooning activities. After egg hatching, both ballooning and non-ballooning larvae were identified according to species and counted. FAW neonate larvae had greater potential for ballooning off than stemborers, irrespective of species. For each species, more females dispersed than males, and their survival rate was higher than that of non-ballooning larvae. In addition, plant-to-plant larval movements were studied using 6.25-m² plots of caged maize in a completely randomized design with five replicates. FAW was found to have wider dispersal and plant damage potential than any of the stemborer species. In conclusion, in contrast to C. partellus, the invasive characteristic of FAW can be explained, in part, by its higher larval dispersal activity compared to stemborers. This difference in larval dispersal might also be considered in sampling plans for monitoring pest density in the field.     

Unexpected collective larval dispersal but little support for sweepstakes reproductive success in the highly dispersive brooding mollusc Crepidula fornicata

In many marine invertebrates, long‐distance dispersal is achieved during an extended pelagic larval phase. Although such dispersal should result in high gene flow over broad spatial scales, fine‐scale genetic structure has often been reported, a pattern attributed to interfamilial variance in reproductive success and limited homogenization during dispersal. To examine this hypothesis, the genetic diversity of dispersing larvae must be compared with the postdispersal stages, that is benthic recruits and adults. Such data remain, however, scarce due to the difficulty to sample and analyse larvae of minute size. Here, we carried out such an investigation using the marine gastropod Crepidula fornicata. Field sampling of three to four larval pools was conducted over the reproductive season and repeated over 3 years. The genetic composition of larval pools, obtained with 16 microsatellite loci, was compared with that of recruits and adults sampled from the same site and years. In contrast to samples of juveniles and adults, large genetic temporal variations between larval pools produced at different times of the same reproductive season were observed. In addition, full‐ and half‐sibs were detected in early larvae and postdispersal juveniles, pointing to correlated dispersal paths between several pairs of individuals. Inbred larvae were also identified. Such collective larval dispersal was unexpected given the long larval duration of the study species. Our results suggest that each larval pool is produced by a small effective number of reproducers but that, over a reproductive season, the whole larval pool is produced by large numbers of reproducers across space and time.     

To eat or get heat: Behavioral trade‐offs between thermoregulation and feeding in gregarious necrophagous larvae

The thermoregulation behavior of Lucilia sericata larvae (Diptera: Calliphoridae), a necrophagous species that feeds on vertebrate cadavers, was investigated. These larvae require high heat incomes to develop, and can elevate temperatures by forming large aggregates. We hypothesized that L. sericata larvae should continue to feed at temperatures up to 38 °C, which can be reached inside larval masses. Thermal regulation behavior such as movement between a hot food spot and colder areas was also postulated. The hypotheses were tested by tracking for 1 h the activity of single, starved third instar larvae in a Petri dish containing 1 food spot (FS) that was heated to a constant temperature of 25 °C, 34 °C or 38 °C with an ambient temperature of 25 °C. The influence of previous conspecific activity in the food on larval behavior was also tested. The crops of larvae were dissected to monitor food content in the digestive systems. Based on relative crop measurements, larvae fed at all food temperatures, but temperature strongly affected larval behavior and kinematics. The total time spent by larvae in FS and the duration of each stay decreased at high FS temperature. Previous activity of conspecifics in the food slightly increased the time spent by larvae in FS and also decreased the average distance to FS. Therefore, necrophagous L. sericata larvae likely thermoregulate during normal feeding activities by adjusting to local fluctuations in temperature, particularly inside maggot masses. By maintaining a steady internal body temperature, larvae likely reduce their development time.     

Relative larval loss among females during dispersal of Lake Sturgeon (<Emphasis Type="Italic">Acipenser fulvescens</Emphasis>)

Mortality that occurs during larval dispersal as a consequence of environmental, maternal, and genetic effects and their interactions can affect annual recruitment in fish populations. We studied larval lake sturgeon (Acipenser fulvescens) drift for two consecutive nights to examine whether larvae from different females exposed to the same environmental conditions during dispersal differed in relative levels of mortality. We estimated proportional contributions of females to larval collections and relative larval loss among females as larvae dispersed downstream between two sampling sites based on genetically determined parentage. Larval collections were composed of unequal proportions of offspring from different females that spawned at upstream and downstream locations (~0.8 km apart). Hourly dispersal patterns of larvae produced from females spawning at both locations were similar, with the largest number of larvae observed during 22:00–23:00 h. Estimated relative larval loss did not differ significantly among females as larvae were sampled at two sites approximately 0.15 and 1.5 km from the last section downstream of spawning locations. High inter- and intra-female variation in larval contributions and relative larval loss between nights may be a common feature of lake sturgeon and other migratory fish species, and likely is a source of inter-annual and intra-annual variation in fish recruitment.     

Intraguild predation among ladybeetles and a green lacewing: do the larval spines of Curinus coeruleus(Coleoptera: Coccinellidae) serve a defensive function?

Laboratory experiments examined interspecific interactions between larvae of three coccinellid species, Curinus coeruleus Mulsant (Chilocorinae), Harmonia axyridis Pallas and Olla v-nigrum (Mulsant) (Coccinellinae), and between these and larvae of the green lacewing, Chrysoperla rufilabris (Burmeister). Larvae of C. coeruleus, although defended on their dorsal surface with long spines, had the smallest mandibles, were the slowest-moving, and the least successful in interspecific larval combat. The long spines of third instar C. coeruleusappeared to reduce their palatability as food to H. axyridis and O. v-nigrum larvae in choice tests with dead larvae, but were not an effective defence against these species in Petri dish arenas. Larvae of O. v-nigrum had a smooth dorsal surface, were intermediate in terms of mandible size, but were the fastest moving, a trait that benefited their survival in intraguild combat. Larvae of H. axyridis were intermediate with respect to dorsal spines and speed of movement, but had the largest mandibles. This species was the most effective intraguild combatant among the coccinellids and the only one to successfully compete against C. rufilabris larvae of similar age. The speed, manoeuverability and long mandibles of C. rufilabris enabled them to impale coccinellid larvae at a relatively safe distance. The spines of C. coeruleus larvae impeded laterally oriented attacks by C. rufilabris, but did not provide sustained protection from repeated attacks. Success in these interactions appeared largely a function of offensive weaponry (mandible size and morphology) and speed of movement, although the role of dorsal spines as defensive structures was not ruled out. Rates of larval cannibalism were highest for C. rufilabris and largely mirrored the level of aggression observed in interspecific combat for each species.