Aggression and risk assessment during predatory interactions between first-instarSinea diadema (Fabricius) (Hemiptera: Reduviidae)

The behaviors exhibited by first-instarSinea diadema (F.) (Hemiptera: Reduviidae) during intraspecific interactions are described. Five distinct behaviors were characterized: posturing, striking, stalking, stridulating, and beaking. Distinct bouts of grappling were also noted. Interactions between unfed 2-day-old nymphs, unfed 3-day-old nymphs, and unfed 5-day-old nymphs were recorded and analyzed. The behavior of the nymphs changed with the duration of food deprivation. As the period of food deprivation increased from 2 to 5 days, the frequency of posturing decreased as the frequency of beaking increased. During noncannibalistic interactions, posturing or striking by one nymph was most frequently followed by posturing by the other nymph. In contrast, during cannibalistic interactions, posturing or striking was usually followed by beaking. The incidence of grappling increased with the duration of food deprivation. Moreover, grappling always preceded cannibalism. Although first instars were capable of capturing and killing conspecifics of the same age, cannibalism occurred only after 4 days of food deprivation. These results suggest that a decision-making process is involved. During interactions the nymphs can assess the vulnerability of the opponent. Whereas recently emerged nymphs usually forego the risk of attacking conspecifics, the attacks made by nymphs deprived of food are more persistent despite the danger of predation by their opponent.     

Respiratory metabolism of the soft tick,Ornithodoros turicata (Dugès)

The rate of oxygen consumption was investigated in fed larval, nymphal and adult Ornithodoros turicata ticks and in starved nymphal and adult ticks. Oxygen consumption rate of fed adult ticks increased with increasing temperature. The metabolic rate of adult ticks was affected by starvation whereby starved adult ticks showed a significantly lower oxygen consumption than their fed counterparts. The oxygen consumption rate of fed female ticks was significantly higher than that of fed males but, there was no significant difference between the oxygen consumption rates of starved female versus starved male ticks. Oxygen consumption of fed larvae was significantly greater than those of fed first through third instar nymphs. Fed and starved nymphal ticks as well as fed adult ticks ventilated continuously. In contrast, starved adults ventilated discontinuously. The ability to reduce metabolic rate, plus the capability to ventilate discontinuously allow O. turicata adults to cope with prolonged starvation.     

Susceptibility of <Emphasis Type="Italic">Amblyomma variegatum</Emphasis> ticks to acaricides in Ghana

The susceptibility of unfed and fed stages of larvae, nymphs and adult females of Amblyomma variegatum ticks were tested using Shaws filter paper dip method against four acaricides; chlorfenvinphos and dioxathion, chlorfenvinphos, gamma benzene hexachloride and amitraz at four different concentrations including the recommended dose rates. Based on their lethal concentrations (LC₅₀ & LC₉₀) chlorfenvinphos and dioxathion combined and chlorfenvinphos alone placed first and second, respectively, in all stages except at the unfed nymphal stage where gamma benzene hexachloride topped with a LC₅₀ of 0.001629, while chlorfenvinphos and dioxathion combined and chlorfenvinphos alone had LC₅₀ of 0.001794 and 0.002258, respectively. Amitraz appeared to have a quick knock-down effect on larvae and nymphs but at the recommended dose rate, showed no mortality of the ticks at that stage. However, at a concentration of 0.040%, amitraz showed a 100% inhibition of oviposition and hatching of laid eggs. Gamma benzene hexachloride produced only 66% inhibition of oviposition while chlorfenvinphos and dioxathion combined and chlorfenvinphos alone produced 100% inhibition of oviposition at their recommended dose rates. Fed nymphs were more susceptible than the unfed nymphs. Eggs laid by engorged female ovipositing ticks, applied with gamma benzene hexachloride, hatched.This revised version was published online in May 2005 with a corrected cover date.     

Visual Evaluation and Recognition of Hosts by the Tick Parasitoid, Ixodiphagus hookeri (Hymenoptera: Encyrtidae)

The role of host size, movement, feeding status, color, and species in the visual host evaluation and recognition behavior of the tick parasitoid, Ixodiphagus hookeri Howard was investigated. Freshly emerged female parasitoids were subjected to a choice bioassay, where the test materials were placed in sealed vials and the vials placed in a Petri dish. When presented with A. variegatum live and mummified nymphs, females examined: larger nymphs significantly longer than smaller nymphs, fed nymphs significantly longer than unfed nymphs, dead and live nymphs for similar lengths of time, and grey live nymphs and yellow-brown and dark brown mummified nymphs for similar lengths of time. The total number of visits to vials containing these test materials were also not significantly different, except there were significantly more visits to yellow-brown mummies when compared to the number of visits to dark brown mummies. When presented with A. variegatum (host) and R. appendiculatus (nonhost) nymphs, the females examined A. variegatum nymphs significantly longer than R. appendiculatus nymphs. The total number of visits to vials containing A. variegatum nymphs were significantly more than the visits to the vials containing R. appendicualtus nymphs. Furthermore, females spent significantly more total examination time per visit on larger and fed A. variegatum nymphs when compared to smaller and unfed nymphs, respectively. Direct and indirect detection were significant when females were presented with fed versus unfed A. variegatum nymphs, grey nymphs versus yellow-brown mummies, and R. appendiculatus versus A. variegatum nymphs. Direct and indirect detection for the rest of the bioassays were not significantly different. Finally, The percentages of females contacting large fed A. variegatum nymphs first were significantly different from those of females contacting small unfed R. appendiculatus nymphs first. The firstcontact percentages for the rest of the bioassays were not significantly different.     

Amplification of tick-borne encephalitis virus infection during co-feeding of ticks

Abstract. Following engorgement of Rhipicephalus appendiculatus larvae on guinea-pigs infected with tick-borne encephalitis (TBE) virus, none of the engorged larvae or emergent nymphs contained detectable infectious virus. However, one of twelve pools, each containing three of the unfed nymphs, was positive when screened by polymerase chain reaction (PCR), indicating a low prevalence of TBE virus infection in the unfed nymphs. After engorgement of the nymphs on four uninfected guinea-pigs, 19/24 (79%) fed nymphs from one guinea-pig and 4/25 (16%) fed nymphs from a second guinea-pig were infected; all the ticks examined from the other two guinea-pigs were uninfected. The results suggest that TBE virus was transmitted from a low proportion of infected nymphs (infected as larvae) to uninfected nymphs as they fed together on an uninfected guinea-pig. Such amplification of the initial infection, at the population level, could play an important role in maintaining TBE virus infections in nature, particularly if there is a low level of vertical transmission from one tick generation to the next.     

Comparative swimming abilities of fed and starved larval largemouth bass (Micropterus salmoides)†

Sustained swimming abilities of fed and starved larval largemouth bass (Micropterus salmoides L.) were compared in the first week after swimming initiation. Fed larvae improved to a sustained velocity of 4·0 cm/sec while starved larvae attained a velocity of only 1·5 cm/sec. Swimming behaviour for fed and starved larvae was quantified for number of moves, average distance/move, and total distance for all moves in 1 min intervals. Fed larvae were always more active than starved larvae, although real differences did not appear until the 4th day after swimming initiation.     

Performance of nymphal and adult southern green stink bug on an overwintering host plant and impact of nymph to adult food-switch

Performance of nymphs and adults of the southern green stink bug,Nezara viridula (L.) (Heteroptera: Pentatomidae) feeding on immature fruits of radish,Raphanus raphanistrum L. (Brassicaceae) was poor compared with feeding on immature soybean [Glycine max (L.) Merrill] pods, but a change from radish to soybean from nymph to adult alleviated some of the detrimental effects of this food on adult performance. Over 50% of nymphs died on radish, while only 15% died on soybean. To complete nymph development (stadia 2 through 5), male and female nymphs required 9.5 and 13.3 days longer on radish compared to soybean. Fresh body weight of 1-d-old adult females and males was ≅65% greater for those reared as nymphs on soybean than on radish, with females being significantly heavier than males on both foods. Survivorship and longevity of females, however, was greater for those fed on radish as nymphs and as adults, as compared to those that fed on soybean or radish followed by soybean. Males lived longer when fed exclusively on soybean. In general, reproductive performance and percentage gain in adult body weight was greatest for insects fed on soybean only, and were better for those whose food was switched from nymph to adult, as compared to those insects fed on radish solely.     

Histological examination ofBorrelia burgdorferi infections in unfedIxodes ricinus nymphs

Borrelia burgdorferi, the agent of Lyme borreliosis, is vectored in Europe byIxodes ricinus. In unfed ticks, the spirochaete resides primarily in the midgut, but a low percentage (5.5%; 4/73) of naturally infected ticks may present a systemic infection involving organs such as the salivary glands and central ganglion (Burgdorferet al., 1983). In this study, we examined 79 unfed nymphs collected in two sites in Switzerland (Neuchatel and Aarberg), and 35 unfed nymphs which were fed as uninfected larvae on 3 infectedApodemus sylvaticus mice. Dieterle silver staining was used to visualize the spirochaetes in the ticks. Of the unfed field-collected nymphs, 21/79 (27%) were infected of which 2/21 (10%) had systemic infections. Taking account of the site of collection, we observed that 0/12 ticks from Neuchatel were systemically infected whereas 2/9 (22%) from Aarberg had a disseminated infection. Out of the 35 unfed nymphs examined after an infectious blood meal on rodents, 14 (40%) were infected and 2 (14%) had a disseminated infection. A total of 4/35 (11%) unfed infected nymphs presented a systemic infection which represents a higher percentage than previously described. The presence of spirochaetes in salivary glands of systemically infected ticks before the initiation of feeding may reduce the time delay generally recorded for the tick-borne transmission ofB. burgdorferi.     

Predation on symbiont sea anemones by their host hermit crab Dardanus pedunculatus

Feeding by host hermit crabs Dardanus pedunculatus on their symbiotic sea anemones Calliactis polypus was investigated using animals collected at Shirahama, Wakayama Prefecture, Japan. In the first experiment, changes in the number of sea anemones on hermit crab shells were recorded in single‐and double‐crab trials without food and single‐crab trials with food. The number of sea anemones significantly decreased under starved conditions. The extent of this decrease per single hermit crab was higher in the double‐crab trials than in the single‐crab trials. Direct observations and video recordings showed that hermit crabs occasionally removed sea anemones from their own shells, and also from partners’ shells in the double‐crab trials, and consumed them. In the second experiment, fed and unfed hermit crabs with or without sea anemones were examined for body weight changes. Fed hermit crabs gained weight whereas unfed hermit crabs lost it. The degree of weight loss in unfed hermit crabs was significantly higher in those without sea anemones, which indicates some value of the latter as food. We offer some speculations on the course of development of this symbiosis, with predation on sea anemones having played an important initial role.     

Kinetics of ingested host immunoglobulin G in hemolymph and whole body homogenates during nymphal development of Dermacentor variabilis and Ixodes scapularis ticks (Acari: Ixodidae)

Patterns in the utilization of host immunoglobulin G (IgG) during nymphal development differed between Dermacentor varibilis (Say) and Ixodes scapularis Say ticks. In unfed nymphs of D. variabilis, host IgG was readily detectable in both hemolymph and whole body homogenates. In unfed nymphs of I. scapularis, host IgG was absent in hemolymph and at very low concentrations in whole body homogenates. Host IgG in unfed nymphs was undoubtedly the remnants of IgG acquired during the larval bloodmeal that persisted through metamorphosis to the nymphal stage. In both tick species, host IgG crossed the midgut into the hemocoel during the latter phases of engorgement. Concentrations of host IgG in I. scapularis declined considerably after replete nymphs molted to the adult stage. In contrast, concentrations of host IgG in D. variabilis remained elevated throughout metamorphosis to the adult stage. When larval D. variabilis were fed on a rat, then 2 months later as nymphs on a rabbit, the rat IgG (“old IgG”) present in unfed nymphs was totally replaced by rabbit IgG (“new IgG”) within 2 d of nymphs attaching to the rabbit. Presumably, the old IgG acquired from a previous bloodmeal was secreted via saliva into the new host. This revised version was published online in July 2006 with corrections to the Cover Date.     

Moulting and survival of <Emphasis Type="Italic">Amblyomma variegatum</Emphasis> (Acari: Ixodidae) nymphs in quasi-natural conditions in Burkina Faso; tick predators as an important limiting factor

The survival rate of Amblyomma variegatum engorged nymphs was studied in 9 cohorts released during the first part of the dry season (i.e. the nymph infestation period in the region) and placed on a natural savannah, either in plastic containers or in cages driven into the soil and open at the bottom. All nymphs put in the containers placed in the sun died rapidly, while a high moulting rate (94%) was observed in containers placed in the shade. This rate reached 63% for the ticks released in the cages. The moulting period lasted from less than 4 to more than 6 weeks, depending on the release period: unfed adults are therefore present in the pasture 4–5 months before the onset of the adult infestation period. The survival rate of the unfed adults did not vary according to the release period of the nymphs: at the beginning of the rainy season, 20–25% of the adult ticks were still alive in the cages. Very important variations in survival and disappearance rates were observed according to the place where the cages had been installed: within a few metres, the survival rate could vary from 0 to 90%, presumably because of the activity of predators which removed also dead tick from the plastic containers. Predators may then have a great but highly variable and unpredictable impact on the natural population of A. variegatum adults. Engorged nymphs released on pasture were able to find suitable micro-habitats allowing survival, covered up to 2.8 metres to reach them, and grouped together at the neck or root network of bushes and grass clumps, sometimes burrowing to a depth of 10 cm.     

The effects of azadirachtin-treated diets on the feeding behaviour and fecundity of the peach-potato aphid,Myzus persicae

Adult apterousMyzus persicae, which had fed for 26 h on diet containing azadirachtin at concentrations of 25–100 ppm, produced nymphs at less than half the rate of aphids on control diets. After 50 h on azadirachtin-treated diets nymph production had virtually ceased. After this period, any nymphs produced by adults that had fed on azadirachtin-treated diets were born dead with undeveloped appendages. Honeydew production on azadirachtin-treated diets was unaffected during the first 26 h period but was approximately three times less than on control diets during the subsequent 24 h period.     

The effect of relative humidity on the behaviour and development of Triatoma brasiliensis

Abstract The preference for relative humidity (RH) and suitability of different levels of this environmental parameter were investigated in the haematophagous bug Triatoma brasiliensis Neiva, 1911 (Hemiptera, Reduviidae). The hygropreference of T. brasiliensis was studied using a RH gradient and the effect of different RHs on the egg hatching, nymph mortality and moulting success was also analysed. The results show that egg hatching in first-instar nymphs of T. brasiliensis was lower at extreme RHs and, particularly, it was lowest at 9.3% RH. The survival of starved nymphs was not affected by RH, but the percentage of engorged nymphs and the ecdysis success of these nymphs once fed was diminished strongly by high humidity. Fourth-instar nymphs preferred to stay at the lowest RH during the first 5 days after feeding and during ecdysis. This preference changed markedly during starvation. Fifteen days after ecdysis, the bugs moved towards intermediate humidities, and 30 days after ecdysis they even preferred the most humid sectors of the gradient. Females preferred to lay eggs in dry environments, suggesting that they may not have a particular hygropreference for oviposition, but that they simply lay their eggs at the RHs where they prefer to stay.     

Food intake in Blattella germanica (L.) nymphs affects hydrocarbon synthesis and its allocation in adults between epicuticle and reproduction

The causal relationship between food intake and hydrocarbon synthesis was examined in vivo and in vitro. Fed Blattella germanica (L.) nymphs synthesized hydrocarbons in a stage‐specific manner, with high rates occurring in the first 6 days of a 13‐day last stadium, in relation to feeding. A similar pattern was exhibited in vitro by sternites and tergites from fed nymphs. In contrast, starved nymphs synthesized hydrocarbons at normal rates for the first 2 days, but then synthesis declined and ceased by day 6. Their abdominal sternites and tergites displayed a similar biosynthetic pattern in vitro, showing that starved tissues lost the capacity to synthesize hydrocarbons, even when provided appropriate nutrients. Synthesis resumed within 2 days of being fed on day 6, reaching a maximum rate 6 days later. Some hydrocarbon appeared on the nymphal cuticle, but almost 4‐fold more hydrocarbon was internal in hemolymph lipophorin, fat body, and the developing imaginal cuticle. Because most hydrocarbon synthesized in nymphs provisions the adult, and synthesis is related to food intake, we examined trade‐offs in allocations in food‐limited insects. Nymphs provided with insufficient quantities of food allocated normal amounts of hydrocarbons to the nymphal epicuticle, but molted into smaller adults with significantly less internal hydrocarbons. These cockroaches directed nearly normal amounts of hydrocarbons to their epicuticle, oocytes, and oothecae, at the cost of internal hydrocarbon reserves for repair and subsequent gonotrophic cycles. Hydrocarbons, thus, appear to serve an important cross‐stadial resource and the object of competition among several nymphal and adult tissues. Arch. Insect Biochem. Physiol. 41:214–224, 1999. © 1999 Wiley‐Liss, Inc.     

Role of small mammals in the ecology of Borrelia burgdorferi in a peri-urban park in north coastal California

The role of small mammals other than woodrats in the enzootiology of the Lyme disease spirochete, Borrelia burgorferi, was assessed in a peri-urban park. Mammals were collected monthly from September through to April. Following tick removal, the animals were tested for B. burgdorferi by culture of ear-punch biopsies. Larvae and nymphs that were intermediate in morphology between Ixodes spinipalpis and Ixodes neotomae occurred on several species of rodents (Peromyscus truei, Peromyscus californicus, Microtus californicus, Rattus rattus and Reithrodontomys megalotis) and the brush rabbit (Sylvilagus bachmani). Morphometric analyses of these I. spinipalpis-like ticks and the offspring from two I. neotomae females from this site suggest that I. neotomae may be conspecific with I. spinipalpis. Borrelia burgdorferi was isolated from eight out of 109 (7.3%), three out of 16 (18.8%), two out of 38 (5.3%) and two out of six (33.3%) P. truei, P. maniculatus, M. californicus and R. rattus, respectively. One brush rabbit yielded the first isolate of B. burgdorferi from a lagomorph in western North America. This isolate and three others derived from unfed I. spinipalpis-like nymphs failed to produce infection when inoculated intradermally into 11–12 P. maniculatus each. Likewise, no spirochetes were detected in 420 Ixodes pacificus nymphs derived from larvae fed on animals inoculated with these isolates. An additional isolate, derived from an I. spinipalpis-like nymph, was recovered by ear-punch biopsies from five out of 12 (42%) needle-inoculated P. maniculatus. However, spirochetes were not detected in 20 I. pacificus nymphs fed as larvae on each of five mice (two infected and three uninfected) inoculated with this isolate. We conclude that brush rabbits and several species of rodents besides woodrats may contribute to the maintenance of B. burgdorferi because they harbour the spirochete and are fed upon by competent enzootic and bridge vectors.     

Molecular evidence for trans‐stadial transmission of Anaplasma platys by Rhipicephalus sanguineus sensu lato under field conditions

This study investigated the transmission of Anaplasma platys by Rhipicephalus sanguineus sensu lato (Ixodida: Ixodidae). Engorged nymphs (n = 404) removed from A. platys‐infected dogs were incubated at 28 °C until moulting. Unfed adults were obtained and divided into 48 pools. Unfed ticks collected from the grounds of the dog shelter, comprising 1800 larvae (n = 18 pools), 3100 nymphs (n = 62 pools) and 85 adults (n = 10 pools, including three male and seven female pools) were sorted into 90 pools. All pools were screened by polymerase chain reaction for the 16S rRNA gene of A. platys. Of 48 pools of unfed adults obtained from engorged nymphs, 12 were positive for A. platys; the infection rate maximum likelihood estimate (MLE) was 3.36 [95% confidence interval (CI) 1.84–5.68]. Anaplasma platys was detected in five of 23 male pools (MLE 2.82, 95% CI 1.06–6.20) and seven of 25 female pools (MLE 3.83, 95% CI 1.72–7.57). Of seven pools of unfed adult females collected from the shelter grounds, one was positive for A. platys (MLE 1.74, 95% CI 0.11–8.22). Among 62 unfed nymph pools, eight were infected with A. platys (MLE 0.27, 95% CI 0.13–0.52). No A. platys DNA was detected in the larva pools. The present results reveal molecular evidence for the trans‐stadial transmission of A. platys by R. sanguineus s.l.     

QUANTITATIVE VARIATION OF 20-HYDROXYECDYSONE IN THE NYMPH OF DERMACENTOR NIVEUS NEUMANN*

Abstract The variation of 20-hydroxyecdysone (20 E) levels in the unfed, feeding and engorged nymphs of Dermacentor niveus was studied. The results showed that 20 E existed in all stages of nymphal development. There were two peaks. A small peak (2. 34 ng/nymph) appeared in the feeding period (5 days after attachment) which was connected with the fast feeding before dropping from the host, and a big peak (16.17 ng/nymph) in the moulting period (8 days after engorgement). The latter might be correlated with epicuticle deposition. From the 6th day to the 8th day after engorgement, the level of 20 E rose rapidly. Apolysis occurred in this period.     

Life history characteristics of Orius insidiosus (Say) fed Aphis glycines Matsumura

The soybean aphid, Aphis glycines Matsumura, is a new invasive pest of soybeans throughout most of the soybean production areas of North America. Field studies have demonstrated that the indigenous predator, Orius insidiosus (Say), is an important natural enemy of the soybean aphid early the soybean crop season. Because soybean aphid is newly introduced into North America, the life history characteristics of predators fed this aphid are not known. In laboratory assays, we measured the survival, development, longevity and reproduction of O. insidiosus fed 1, 3, 6 or 12 seconds to third instars of soybean aphid. O. insidiosus nymphal development decreased from 34.0 to 21.4 days as the number of soybean aphid nymphs provided increased from 1 to 6 aphid nymphs daily. Stage-specific mortality was highest at 68% for first instar O. insidiosus nymphs fed 1 soybean aphid nymph per day. Adult longevity (43.9 days) and fecundity (49.7 eggs per female) was highest for O. insidiosus fed 6 soybean aphid nymphs daily, but longevity (23.5 days) and fecundity (10.1 eggs per female) declined for adults fed 1 soybean aphid nymph daily. The intrinsic rate of increase of O. insidiosus ranged from 0.048 to 0.133. Compared to other prey species, soybean aphid is an adequate prey item for O. insidiosus. Our results suggest that O. insidiosus will be most effective in suppressing soybean aphid population growth in the initial phase of the aphid’s colonization of soybeans.     

Life history of the tick parasitoid Ixodiphagus hookeri (Hymenoptera: Encyrtidae) in Kenya

We conducted laboratory and field experiments to elucidate the life history of Ixodiphagus hookeri, a parasitoid of the ixodid tick Amblyomma variegatum in Western Kenya. Ixodiphagus hookeri females oviposited in unfed host nymphs as well as engorged nymphs, but rarely in engorged larvae. While I. hookeri developed to adults in engorged nymphs, the eggs laid in unfed nymphs disappeared within 2 days after oviposition. As temperature increased, development time of I. hookeri from oviposition to adult emergence in engorged nymphs decreased from 46 days at 23 °C to 35 days at 28 °C, and their immature survival in engorged nymphs decreased from 67% at 23 °C to 22% at 28 °C. No parasitoid adult emerged from hosts at 30 °C. Individual hosts parasitized by single females produced 42–53 adult wasps, 73% of which were females. As a typical pro-ovigenic species, I. hookeri females had an average of 84 mature eggs at emergence and lived only for a few days. When laboratory-reared, unfed nymphs of A. variegatum were attached to cattle for 4–9 days in subsistence farmers’ fields in Western Kenya, 25% of the engorged nymphs and 4% of the unfed nymphs on cattle were parasitized by I. hookeri, demonstrating that I. hookeri females search for and oviposit in A. variegatum nymphs on cattle. Unlike other strains of I. hookeri that overwinter as eggs in unfed nymphs, I. hookeri could continuously reproduce throughout the year in Western Kenya.     

Short‐term effect of hypoxia on ammonia excretion and respiration rates in the crab carcinus maenas

The metabolic response of the crab Carcinus maenas to short‐term hypoxia (60% and 35% saturated seawater) was studied at 17.5°C in fed, 3 day‐unfed and 6 day‐unfed crabs.

Ammonia excretion rate decreased under hypoxia: a 40% and 45% decrease in the normoxic rate was observed in fed crabs at 35% saturation and in 3 day‐unfed crabs at both hypoxic levels respectively. In the 6 day‐unfed crabs, the effect of hypoxia was concealed by the effect of starvation.

Oxygen consumption rate was directly related to the external O₂ tension irrespective of the crab's nutritional state. Stressed crabs behaved as a whole, as oxygen‐conformers.

A strong relationship was observed between ammonia excretion and oxygen consumption rates in fed crabs under hypoxia but not in starved crabs.