Host-seeking behavior in larvae of the robber fly Mallophora ruficauda (Diptera: Asilidae)

The robber fly Mallophora ruficauda is the most important pest of apiculture in the Pampas region of Argentina. Adults prey on honeybees and other insects, while larvae parasitize larvae of scarab beetles, which live underground. Females of M. ruficauda do not search for hosts but instead lay eggs in tall pastures. Once hatched, larvae drop to the ground and burrow underground to search for their hosts. We tested in the laboratory whether larvae of M. ruficauda actively search for their hosts using host and/or host-related chemical cues. We report that M. ruficauda detects its host using chemical cues that originate in the posterior half of the host's body, most likely from an abdominal exocrine structure. This particular host-searching strategy is described for the first time in Asilidae.     

Description of antennal structures of the parasitoid Mallophora ruficauda (Diptera: Asilidae) and its relationship with resources searching behaviour

The robber fly Mallophora ruficauda is a parasitoid of white grubs (Coleoptera: Scarabaeidae) inhabiting in Pampas region of Argentina. Females locate host’s habitat and lay eggs away from the host in tall grasses. After hatching, larvae fall to the ground and actively seek hosts. Previous works suggested that female would detect the presence of host’s chemical cues, but sensory organs involved in olfaction are still unknown. However, few studies have looked at dipteran parasitoids sensilla, and no study has been undertaken in Asilidae species. The aim of this work was to determine the presence, density, distribution and morphology of chemosensilla in M. ruficauda antennae using optic and scanning microscope techniques. We found that antennae have 4 segments: scape, pedicel, postpedicel and style. We identified basiconic and trichoid sensilla, small and long bristles, and sensory pits. Basiconic sensilla are multiporous and are widely spread between the small bristles through the postpedicel. Trichoid sensilla are grouped in 6–8 units on latero-ventral margin of postpedicel, have mobile base, striated wall and an apical porous. Small bristles are present in the pedicel and postpedicel, and long bristles are found in groups on scape and pedicel. Three different types of sensory pits were observed, with basiconic sensilla, distributed along external and internal lateral side of the postpedicel. Considering the morphological characteristics of the antennae, and based on the olfaction biomechanics, the structure and distribution of these cuticular structures of the parasitoid antennae would contribute to the odour detection mechanism in adults of M. ruficauda.     

Ecological comparisons of robber fly species (Diptera: Asilidae) coexisting in a neotropical forest

Summary Data regarding seasonal abundance, microhabitat preference, and diet were collected over 3 field seasons for adults of 15 robber fly species on Barro Colorado Island, Panama. The species comprised 2 distinct thermal guilds; light-seeking (hereafter LS) species foraged in sunlit areas, while shade-seeking (SS) species foraged only in deep shade. All species were rare during the dry season. During the rainy months, most SS species had flight periods of 2–3 months, and no temporal segregation was apparent. In contrast, most LS species had flight periods of only 4–6 weeks, and a distinct sequence of occurrence was evident during 2 years of censusing. Most SS and LS species displayed a pronounced specificity for perches of a particular substrate type. However, the ranges of perching heights utilized varied considerably among species. Dietary comparisons revealed that mean and maximum prey sizes increased with increasing robber fly size, while minimum prey sizes were constant. Robber fly species <20 mg fed primarily upon nematocerous Diptera, whereas larger species generally fed upon a wide variety of prey types. For each thermal guild, the actual mean overlap for a particular niche dimension was compared to mean overlaps generated by randomly assigning species to thermal guilds. No significant differences from the random null hypothesis were found for the SS guild. However, niche complementarity between dietary and spatial overlaps and dietary overlap was apparent among the 5 large LS species.     

Body temperature regulation in desert robber flies (Diptera: Asilidae)

ABSTRACT.

• 1 We investigated effective thermal environments and behavioural and physiological mechanisms for thermoregulation in two sympatric desert robber flies, Promachus giganteus (Hine) and Efferia texana (Banks). Although similar in body shape and colour, P. giganteus are 4–8 times heavier than E. texana.
• 2 During midday, operative temperatures near the ground were substantially higher for P. giganteus (56–73°C) than for E. texana (54–63°C). Correspondingly, P. giganteus generally perched at greater heights above the ground than did E. texana.
• 3 Both species maintained thoracic temperatures between 40 and 45°C during most of the day. However, differences between thoracic and abdominal temperatures for individual flies were significantly lower in P. giganteus than in E. texana.
• 4 In the laboratory, P. giganteus regulated thoracic temperature by pumping haemolymph into the abdomen. This ability may have accounted for the smaller differences observed between thoracic and abdominal temperatures in P. giganteus and may have allowed this species to search for food and mates during midday when E. texana sought shade.

     

Male perch selection and the mating system of the robber fly,Promachus albifacies (Diptera: Asilidae)

We studied the activity and spatial distribution of the robber fly,Promachus albifacies, in a desert grassland habitat in central New Mexico. Late in the season males spent most of the daytime on or near cholla and yucca plants that had dead stems or dead flower stalks at least 1 m high. Of the three hypotheses (thermoregulation, foraging, mate encounter site) considered as explanations for this distribution, the mate-encounter-site hypothesis was best supported. Plants used by females as oviposition sites were the focus of male activity. Males perched within or near these plants and attempted copulations with females detected nearby. Most matings were initiated at these locations. Seasonal changes in male and female activity also supported the mate-encounter-site hypothesis. Early in the season, females spent little time ovipositing, and predictably, males spent little time on or near these plants. Such a mating system may be described as resource defense polygyny, since males acted aggressively toward one another at oviposition sites even when females were not present. However, the short tenure of males at these sites is suggestive of scramble competition polygyny. We discuss possible reasons why this particular mating system has evolved.     

Impact of predation by the robber fly Proctacanthus milbertii (Diptera: Asilidae) on grasshopper (Orthoptera: Acrididae) populations

The impact of predation by the robber fly Proctacanthus milbertii Macquart on populations of adult grasshoppers from grasslands of the Nebraska sandhills was estimated. Densities of P. milbertii were estimated at 437 individuals per hectare (2 se=122). Overall densities of 23 species of grasshoppers were estimated to be 64,000 individuals per hectare with the most abundant species (Ageneotettix deorum) having a population size of approximately 15,000 individuals per hectare. Based on three estimates of predation level (ranging from 0.5 to 2 prey per day per robber fly), P. milbertii may take from 0.5% to 2% of the adult grasshoppers per day. Species of grasshoppers were taken by P. milbertii in about the same proportion in which they occurred at the study site and no size-selective component of predation was detectable.     

Leinendera achaeta sp. n., a new species of robber fly from Brazil (Diptera,Asilidae, Asilinae)

The third species of the Neotropical genus Leinendera Carrera, 1945, Leinendera achaeta sp. n., is described from Rio Grande do Sul state, Brazil. The habitus, wing and male terminalia are described and illustrated, and a key to the three Brazilian species is provided.     

Differences in egg parasitism of Chrysophtharta agricola (Chapuis) (Coleoptera: Chrysomelidae) by Enoggera nassaui Girault (Hymenoptera: Pteromalidae) in relation to host and parasitoid origin

Abstract The first instances of egg parasitism of Chrysophtharta agricola , a pest of eucalypt plantations, are recorded. Enoggera nassaui was found parasitising C. agricola egg batches in Tasmania, the Australian Capital Territory (ACT), New South Wales and Victoria: this is the first record of this parasitoid species from Victoria. One instance of Neopolycystus sp. parasitising C. agricola eggs in Victoria was also recorded. Parasitism of egg batches by E. nassaui ranged from 0 to 55% between five geographical populations collected in mainland Australia ( n  = 45), and from 0 to 2% between two populations collected in Tasmania ( n  = 300). For mainland sites at which parasitism was recorded, parasitism rates within sites differed significantly from either population in Tasmania. Reciprocal exposure experiments using one Tasmanian (Florentine Valley) and one parasitised mainland (Picadilly Circus, ACT) population were conducted in the laboratory to examine whether these different parasitism rates were attributable to egg or parasitoid origin. Parasitoids from the ACT parasitised C. agricola eggs of both origins more successfully than parasitoids from Tasmania, with up to 65% wasp emergence compared with 33% from Tasmania. Parasitoid origin significantly affected the number of wasps that emerged from exposed batches, but not the total loss from parasitism.     

Landscape and stational distribution of the robber flies (Diptera, Asilidae) in the Lower Volga area

The distribution of 108 species of robber flies over different landscapes and plant associations in the Lower Volga area was studied.     

Reproductive biology of the microtype tachinid fly Zenillia dolosa (Meigen) (Diptera: Tachinidae)

Reproductive biology including mating, adult longevity, fecundity and development of the tachinid fly Zenillia dolosa was investigated for optimizing rearing procedures using Mythimna separata as a host in the laboratory. Females lay microtype eggs containing a first instar larva on food plants of the host and then the eggs must be ingested by the host for parasitization. Mating success was 58.5% with mating duration of 80.7 min. Mating was most successful when day 0–1 females were kept with day 2–4 male flies. Female body size was positively correlated with its fecundity but not with longevity. However, females that survived longer produced more eggs during their lifetime. Parasitoids successfully developed in 4th to 6th instar host larvae. Host instars at the time of parasitoid egg ingestion significantly influenced development time of the immature parasitoid, but did not affect body size of the emerging parasitoid. We suggest that pairing newly emerged females with day 2–4 males should result in higher mating success and using the last instar hosts for parasitization should minimize development time of the parasitoid for rearing.     

Brevibacterium frigoritolerans a novel entomopathogen of Anomala dimidiata and Holotrichia longipennis (Scarabaeidae: Coleoptera)

We describe the isolation, biochemical characterization, phylogenetic analysis, and pathogenecity of a novel entomopathogenic bacterium Brevibacterium frigoritolerans to first instar larvae of Anomala dimidiata and Holotrichia longipennis. The almost full length 16S rRNA sequence of the bacterium has 99% identity with the type strain of B. frigoritolerans, while phylogenetic analysis revealed that the isolate formed a tightly linked branch with the type strain of B. frigoritolerans. Under in vitro bioassay conditions, the isolate infected and caused 89±5.4 and 74±7.7% mortality, in first instar larvae of A. dimidiata and H. longipennis, respectively. The infected larvae exhibited bacteremia like symptoms and mortality occurred between the second and fifth weeks after inoculation. This is an early report on the entomopathogenic potential of the hitherto lesser-known bacterium Brevibacterium frigoritolerans.     

Phonotactic behaviour and vertical sound source localisation of the parasitoid fly Emblemasoma auditrix (Diptera: Sarcophagidae)

1. Acoustically guided movement in a three‐dimensional space is a complex behavioural task performed notably by birds, bats, and some insect species. The precision of acoustic orientation depends on the directionality of the hearing system as well as on auditory behaviour. 2. The fly Emblemasoma auditrix Diptera (Sarcophagidae) is a parasitoid of the cicada Okanagana rimosa Auchenorrhyncha (Cicadidae) and locates its host in the complex habitat of a forest. The phonotactic behaviour of the fly was analysed experimentally with emphasis on the vertical domain in the field. Different experimental setups allowed discriminating subsequent steps in the phonotactic behaviour of E. auditrix. 3. During the phonotactic flight, flies first landed on landmarks, which were used to re‐adjust to the elevation of the sound source. Acoustic targets were located from these resting positions. The sound source elevation was detected at the start of the flight as the longitudinal body axis was adjusted to the inclination of the target sound source. 4. Flies usually did not land directly upon the sound source, but landed nearby, and most often above the target. Within the target area, types of movement for the final approach differed in respect to target position; flies walked predominantly if the final target was located above or below, but for horizontally located targets much of the distance was covered by flight. 5. In conclusion, E. auditrix can locate the acoustic target in complex habitats and uses a flexible multi‐step approach for short‐range phonotaxis.     

Spatial and temporal abundance,substrate partitioning and species co-occurrence in a guild of Neotropical blackflies (Diptera: Simuliidae)

Blackfly larvae were sampled monthly from two smallNeotropical mountain streams 500 m apart from each other in northernVenezuela during a 15-month period, and ten habitat variables weremeasured at two altitudes (800 and 900 m) to determine local spatialand temporal variations in abundance, stream variables, speciesco-occurrence, and substrate preference within the blackflyguild. The blackfly species composition of each stream was the same,with five species (in order of abundance): Simulium ochraceumWalker s.l., S. paynei Vargas, S. metallicum Bellardicytospecies E, Simulium sp., and S. horacioi Okazawa &Onishi. There were clear differences in community structurebetween streams (not among altitudes), although S. ochraceums.l. was the most abundant species in both habitats. Principal component andcorrelation analyses revealed that structural (great depth, width,flow, and discharge) and chemical (low conductivity) factors werethe stream variables best associated to the spatial distribution ofmost blackfly species. Blackfly abundance was greater in the largerstream. Larvae were most abundant on submerged rocks and fallenleaves, although the patterns of substrate use within the guildrevealed substrate partitioning among most blackfly species.There was one general annual peak of abundance at the end of therainy season. We suggest that blackfly community structure in theseNeotropical headwaters streams, over the small spatial scaleexamined here, is largely influenced by interactions among streamsize and velocity-related factors (width, streamflow, discharge andsubstrate availability-stability) and the rainfall regime.     

Dynamics of parasitism in the organ-pipe wasp, Trypoxylon politurn: effects of spatial scale on parasitoid functional response

Abstract.

• 1 Life tables and rates of parasitism were tabulated from mud nests built by Trypoxylon politum (Hymenoptera: Sphecidae) at nine different nesting sites from Missouri and Mississippi.
• 2 Most developmental mortality occurred either during the first two instars of development, or during the inactive prepupal phase. The majority (76%) of deaths were caused by insect parasitoids and cleptoparasites. Levels of parasitism and survivorship varied among nesting sites, and among locations within the two sites surveyed at a fine spatial scale.
• 3 Total developmental mortality, K, was positively associated with the number of hosts (immature T.politum) per site. Within one of two sites sampled at a fine spatial scale, K was negatively associated with the local density of hosts. Levels of total parasitism were positively associated with host population size, and negatively associated with local host density within one of the two sites sampled at a fine spatial scale.
• 4 Levels of parasitism by Melittobia (Hymenoptera: Eulophidae) were positively associated with the number of hosts per site, but negatively associated with the local density of hosts within sites. Melittobia parasitism was also negatively associated with the local density of old nesting material within sites.
• 5 Parasitism by Melittobia was a function of both the numbers of nests per quadrat and the mean nest size per quadrat at one of the two sites surveyed at a fine scale. At the other site, parasitism by Melittobia was a function of mean nest size per quadrat.
• 6 The life cycle and nesting behaviour of T.politum, in relation to the regulation of its numbers, is discussed.

     

Desolation comes from the sky: Invasive Hymenoptera species as prey of Chilean giant robber flies (Diptera: Asilidae) through field observations and citizen science

Robber flies (Asilidae) are the main predatory fly family feeding on beetles, butterflies, other flies for true flies, and even spiders; however, Hymenoptera is the most common prey. Invasive Hymenoptera species are common in central and southern Chile; however, few predators of these are known. The hunting behavior and prey of Chilean robber fly species are also poorly known. The aim of this study is to provide the first hunting behavior records of five Chilean giant robber fly species on invasive Hymenoptera. In addition, an updated distribution of these species is provided. Records of hunting behavior were based on fieldwork collections and citizen science observations. The historical distribution was compared with citizen science observations using chi-square analyzes. Twelve predation events were recorded. Obelophorus terebratus was the most common predator. Bombus terrestris was the invasive Hymenoptera most preyed upon. Both the extension of occurrence of Lycomya germainii as Obelophorus species showed changes in his distribution. Only O. landbecki shown changes in area of occupancy. Citizen science is playing a key role in the knowledge of biological interactions and distribution of endemic and native Chilean robber fly species.     

Temperature‐dependent development of the parasitoid Tachinaephagus zealandicus on five forensically important carrion fly species

The influences of temperature and host species on the development of the forensically important parasitoid Tachinaephagus zealandicus Ashmead (Hymenoptera: Encyrtidae) were studied at six constant temperatures in the range of 15–30°C. T. zealandicus completed development successfully between 15°C and 27°C on five species of Calliphoridae, Calliphora albifrontalis Malloch, Calliphora dubia Macquart, Lucilia sericata Meigen, Chrysomya rufifacies Macquart and Chrysomya megacephala Fabricius. No adult parasitoids emerged from any of the host species reared at 30°C. Temperature and host species significantly influenced development time, emergence success and progeny size. Development was significantly longer on Ch. megacephala and Ch. rufifacies at 18–24°C and significantly longer on Ch. rufifacies and C. albifrontalis at 15°C and 27°C. Parasitoid emergence success was greatest at 21°C, declined at the temperature extremes (15°C and 27°C) and was significantly lower on Ch. megacephala and Ch. rufifacies than on the three other host species. Progeny numbers per host pupa were highest at 21–24°C, declined on either side of this temperature range and were significantly lower on L. sericata, Ch. rufifacies and Ch. megacephala than on either C. dubia or C. albifrontalis. An effect of host species on sex ratio was only observed at 27°C, at which a higher proportion of T. zealandicus females emerged from Ch. megacephala and Ch. rufifacies than from the other host species. The thermal requirements for development (developmental thresholds, thermal constant, optimum temperature) of T. zealandicus in each host species were estimated using linear and non‐linear models. Upper and lower developmental thresholds ranged between 29.90°C and 31.73°C, and 9.73°C and 10.08°C, respectively. The optimum temperature for development was estimated at between 25.81°C and 27.05°C. Given the significant effect of host species on development time, the use of parasitoid–host‐specific developmental data in forensic application is recommended.     

Life history strategy and adult and larval behavior of Macrodiplosis selenis (Diptera: Cecidomyiidae), a species that induces leaf‐margin fold galls on deciduous Quercus (Fagaceae)

Life historical, behavioral and ecological traits of Macrodiplosis selenis, which induces leaf‐margin fold galls on Quercus serrata, Q. mongolica and Q. dentata (Fagaceae) in Japan and South Korea, were studied. Daily activity and larval development indicate that M. selenis is a diurnal and univoltine gall midge. In April, females lay their eggs both on upper and under surfaces of fresh leaves. The duration of the egg stage varies from 5 to 9 days, depending on daily temperatures. Hatched larvae crawl to the upper surface of the leaf margin, where they start to induce galls. Larvae become full‐grown in October, drop to the ground in November and overwinter in cocoons on the ground, while larvae of congeners mature in May and drop to the ground in June. A relatively long period of the second larval stadium from July to October on the host trees seems to be effective for M. selenis in avoiding summer mortalities caused by predation and aridity on the ground and by ectoparasitoids that attack mature larvae or pupae on the host leaves. The spatial distribution pattern of M. selenis leaf galls is contagious and the mean gall density per leaf is significantly correlated with the mean crowding. This study adds new insights of life history strategy and adult and larval behavioral pattern to the ecological knowledge of gall midges, and these kinds of information are essential for further studies of M. selenis population dynamics and interactions with other Quercus‐associated herbivores.     

The causes of seasonal changes in numbers of the yellow dung fly, Scathophaga stercoraria (Diptera: Scathophagidae)

ABSTRACT. 1. Counts of adult Scathophaga stercoraria (L.) on cow pats were made in Houghall, County Durham, in 1964 and 1965.
2. A spring peak of numbers was due to adults (overwintered mainly as pupae or larvae) maturing and going to dung to breed. Numbers then dropped, rising to one or more peaks in late June—early July. In 1964 there was then a summer drop in numbers until late September. In 1965 high numbers persisted in summer associated with cooler, wetter weather. Autumn peaks in both years persisted until severe frosts or snow.
3. Mature adults, developed from eggs laid during the spring peak, form the first generation when breeding in mid-late June. No clear generations can be identified after this, due to eggs being laid daily (females have successive gonotrophic cycles). Changes in adult numbers breeding reflects survival of eggs and newly-hatched larvae 5–6 weeks earlier, and lower survival rates of adults in mid-summer compared with spring and autumn.
4. Adult Scathophaga numbers in vegetation rose as numbers on dung dropped. Females dissected to count ovariole tunica dilatations showed that most flies in vegetation were immature, with some parous flies hunting insects to develop the next batch of eggs.
5. Females on dung were dissected and found to range from immature to seven-parous. Those gravid for the first time were grossly under-represented, possibly due to wider dispersal.
6. It is suggested that seasonal changes in this r-strategist cannot be explained simply in terms of generations nor by the occurrence of adult diapause.