Efficiency of CO2 -baited CDC miniature light traps under semi-field conditions and characterizing response behaviors of female Aedes aegypti (Diptera: Culicidae).

Aedes aegypti (L.) (Diptera: Culicidae) is an important vector of viruses causing dengue, Zika, chikungunya, and yellow fever and as such is a threat to public health worldwide. Effective trapping methods are essential for surveillance of both mosquito species and disease presence. The Centers for Disease Control Miniature Light Trap (CDC-MLT) is an updated version of the New Jersey light trap, which was developed early in the 20th century. This trap is widely reported as being less successful for Ae. aegypti than for other mosquito species, although the reason for this is unclear. This trap has engendered more Ae. aegypti-tailored designs that still represent the basic design model. The efficiency of the CDC-MLT alone and with CO2 was tested under semi-field conditions and the behavior of responding female Ae. aegypti was characterized. The CDC-MLT alone failed to capture any mosquitoes and with CO2 the capture efficiency was less than 2%. Understanding the behaviors that mosquitoes exhibit while encountering a particular trap design or trapping concept may suggest trap improvements to increase capture efficiency. Moreover, this work contributes to our understanding of mosquito host-seeking behavior.

Activation, orientation and landing of female Culex quinquefasciatus in response to carbon dioxide and odour from human feet: 3-D flight analysis in a wind tunnel.

This study investigated the interaction between carbon dioxide (CO(2) ) and human foot odour on activation, upwind orientation and landing of host-seeking female Culex quinquefasciatus (Say) (Diptera: Culicidae) in a wind tunnel. More mosquitoes landed on warmed glass beads coated with foot odour than on clean beads; adding a plume of 4% CO(2) did not influence the proportion of mosquitoes landing. A second experiment used 3-dimensional video tracking to assess flight performance. Activation was more rapid with CO(2) and with CO(2) + foot odour than with clean air or with foot odour alone. Upwind flights were fastest with CO(2) and with clean air, and slowest with foot odour; the CO(2) + foot odour treatment overlapped the previous three treatments in significance. Flight headings tended more towards due upwind with CO(2) and with clean air than with CO(2) + foot odour or with foot odour alone. In both experiments, many mosquitoes flew upwind in clean air. There was little evidence of females changing course upon entering or exiting the CO(2) plume or reacting to foot odour during flight.

Genetic independence of female signal form and male receiver design in the almond moth, Cadra cautella.

Efficient signalling requires coordination of signal form and receiver design. To maintain signal function, parallel changes in signaller and receiver traits are required. Genetic correlation and co-evolution among signal and response traits have been proposed to preserve signal function (i.e. coordination) during the evolution of mate recognition systems. Empirical studies have provided support for both mechanisms; however, there is debate regarding the interpretation of some of these studies. Tests for a genetic correlation typically hybridize divergent signalling systems and look at hybrid signal form and receiver design, or impose artificial selection on signal form and look for an indirect response to selection in receiver design. Some of the hybridization studies did not achieve reassortment of genes from the parental types, whereas some of the artificial selection studies incorporated random mating in their designs. As a result of these limitations, the hybridization studies cannot discriminate between genetic correlation and co-evolution with primarily additive genetic effects underlying signal and response traits. Similarly, the artificial selection experiments cannot discriminate between genetic correlation because of linkage disequilibrium and co-evolution. This study examined the mating preferences of male almond moths, Cadra cautella, before and after female moths were artificially selected (using a design incorporating assortative mating) for novel pheromone blend ratios. Our results demonstrate the absence of a genetic correlation between signal and response traits in the almond moth.

Orientation of Culex mosquitoes to carbon dioxide-baited traps: flight manoeuvres and trapping efficiency.

Females of Culex quinquefasciatus Say and Culex tarsalis Coquillet (Diptera: Culicidae) in the host-seeking stage were released and video recorded in three dimensions in a large field wind tunnel as they flew to four kinds of CO2-baited mosquito traps. The trapping efficiency (number of mosquitoes approaching compared to the number caught) was determined for each trap type. The Encephalitis Virus Surveillance (EVS), Mosquito Magnet Freedom (MMF) and Mosquito Magnet Liberty (MML) traps captured only 13-16% of approaching Cx. quinquefasciatus females, whereas the Mosquito Magnet-X (MMX) trap captured 58%. Similar results were obtained for Cx. tarsalis. Orientation behaviour and flight parameters of mosquitoes approaching the four traps were compared. Mosquitoes spent the most time orienting to the EVS trap. Flight speed decreased as mosquitoes entered the vicinity of each trap and a large portion of their time was spent within 30 cm downwind of the traps. Flights became highly tortuous downwind of the poorly performing traps and just upwind of the MMX trap. Differences between traps and possible explanations for the superior performance of the MMX trap are considered.

L-lactic acid: a human-signifying host cue for the anthropophilic mosquito Anopheles gambiae.

Using a dual-choice olfactometer, the role of L-lactic acid was investigated in relation to host-seeking and selection by female Anopheles gambiae Giles sensu stricto (Diptera: Culicidae) mosquitoes in a Y-tube bioassay. L-lactic acid alone was not attractive, but it significantly augmented the attractiveness of CO2, skin odour and skin-rubbing extracts from humans and other vertebrates. Comparing the left and right index fingers of the same person, one could be made more attractive than the other by adding L-lactic acid to the air stream over that finger. The difference in L-lactic acid concentration between the two air streams offered to the mosquitoes fell within the natural range of variation emanating from a human hand, suggesting that L-lactic acid modulates intraspecific host selection by An. gambiae. Analysis of skin rubbings from various vertebrates (carnivores, chickens, primates, rodents, ungulates) indicated that humans have uniquely high levels of L-lactic acid on their skin. Tests with extracts of skin rubbings from cows and humans, with and without added L-lactic acid, suggest that naturally lower levels of L-lactic acid contribute to the lesser attractiveness of non-humans to An. gambiae s.s.

Odour plumes and odour-mediated flight in insects.

Flying insects often follow odour plumes to find resources. Some insects may employ an 'aim-and-shoot' strategy using mechanoreceptors before flight to determine wind direction. Once airborne, insects must use optomotor anemotaxis to set a course upwind. This mechanism uses a visual appraisal of how wind modifies the insect's path. A straight upwind course yields a front-to-rear image flow directly below the insect. Details of this process in male moths flying to female pheromone have emerged mainly from wind tunnel studies. Loss of the pheromone triggers 'casting', or wide lateral excursions without upwind progress, whereas contact with a plume usually induces a zigzag path upwind. The temporally regular counterturns in casting and zigzagging seem to be generated by a central programme. Brief contact with a filament of odour induces a heading towards upwind, and an optimal rate of encounter promotes a rapid, straight upwind course. Other insects, such as parasitoid wasps seeking a host and tsetse flies seeking a blood meal, seem not to have a temporally regular pattern of counter-turns and often fly straight upwind. The availability of visual cues from the odour source itself, the aerial distribution of odour set by turbulent diffusion, and light and wind levels all influence the success of these manoeuvres.

Diel periodicity and influence of age and mating on sex pheromone titer in gypsy moth,Lymantria dispar (L.).

The diel periodicity of sex pheromone titer from pheromone glands of femaleLymantria dispar is described. On the day of emergence (day 0), pheromone titer was generally low; means ranged from 1 to 4 ngcis- 7,8-epoxy-2-methyloctadecane during photophase and gradually increased to 8.4 ng over the course of scotophase. For day-1, -2, and -3 females, the diel fluctuations of titer were more pronounced. Lowest titers (5-9 ng) occurred 0-4 hr after lights-on, and peak titers (19-32 ng) were found 0-4 hr before lights-off. Comparison of the average daily titer among the different age groups (data pooled over six time points at 4-hr intervals) indicated that significantly less pheromone was extracted from glands of day-0 (4.5 ng) than day-1 (12.4 ng), day-2 (15.4 ng), or day-3 females (13.5 ng). No significant differences were found among the three older ages. Femalesin copula exhibited a rapid reduction in titer within the first 0.5 hr of mating initiation (7.6 ng vs. 19.5 ng from virgin females of similar age). After the second 0.5 hr, the reduction in titer was not nearly as marked, falling only to 4.5 ng. Twenty-four hours after mating, titer fell below the limits of detection (0.5 ng). All extracts from pheromone glands of virgin or mated females contained < 1.0 ng of the putative pheromone precursor, 2-methyl-cis-7-octadecene.

Identification of sex pheromone of browntail moth,Euproctis chrysorrhoea (L.) (Lepidoptera: Lymantriidae).

A unique sex attractant pheromone was isolated and identified from extracts of ovipositor tips from the female browntail moth (Lepidoptera: Lymantriidae). The pheromone compound, (Z,Z,Z,Z)-7,13,16,19-docosatetraen-1-ol isobutyrate, CH3CH2CH=CHCH2CH=CHCH2CH= CH(CH2)4CH=CH(CH2)6O2CCH(CH3)2, was identified by a combination of gas chromatography, mass spectrometry, and microreactions and was confirmed by synthesis. Traps baited with 5-50 µg of the synthetic pheromone, dispensed from rubber septa treated with an antioxidant and a UV stabilizer, gave male moth captures that were comparable to traps baited with three virgin females. Higher (250 µg) and lower (0.04-2.5 µg quantities of the synthetic pheromone on septa captured somewhat fewer males. Captures were the same for similar quantities of the natural and synthetic pheromone. Minor, inactive components in the tip extract were identified as a mixture of 7- and 8-pentacosanone.

Selection for increased pheromone response in the male pink bollworm, Pectinophora gossypiella (Lepidoptera: Gelechiidae).

The genetic basis of the duration and incidence of male wing fanning to pheromone in the pink bollworm moth, Pectinophora gossypiella (Saunders), was examined by artificial selection. Using a still-air bioassay, males from a laboratory colony were selected for increased duration of wing fanning when exposed to a 65:35 blend of (Z,E)- and (Z,Z)-7,11-hexadecadienyl acetates. The mean (+/- SE) duration of wing fanning in the selected line increased from 5.4 +/- 1.4 to 17.4 +/- 2.7 s after six generations. The increase in wing fanning duration was the result of an increase in response duration among responders and not the percentage of males that responded. Realized heritability of wing-fanning duration was 0.16 +/- 0.02. The amount and ratio of pheromone produced by females in the male-selected line did not change.

Variability in pheromone composition and periodicity of pheromone titer in potato tuberworm moth,Phthorimaea operculella (Lepidoptera: Gelechiidae).

The ratios and quantities of the pheromone components, (E,Z)-4,7-tridecadien-1-yl acetate (diene) and (E,Z,Z)-4,7.10-tridecatrien-1-yl acetate (triene), in the glands of individual female potato tuberworm moths (Phthorimaea operculella) originating from the United States (California) and Japan (Nagoya) were analyzed by gas chromatography. Quantities of glandextracted pheromone components of Nagoya females fluctuated in a periodic fashion during the photoperiod. Maximal titers coincided with the onset of scotophase (and calling), then gradually declined to minimal levels soon after lights-on. The average daily pheromone quantities decreased significantly as females aged. Both populations exhibited considerable variation in the ratio of the two components. The proportions of triene in the blend ranged from 27% to 88% (triene -X = 56 ± 13% SD; CV = 23%) for California females and from 16% to 71% (42 ± 13%; CV = 31%) for Nagoya females. Nagoya females also stored significantly higher amounts of pheromone in their glands (8.6 ± 3.9 ng) than did California females (2.7 ± 1.4). The differences between the populations, while substantial, would probably not be sufficient to impart a barrier to panmixis, given the wide range of component ratios favored by the males.

Beneficial arthropod behavior mediated by airborne semiochemicals : VI. flight responses of femaleMicroplitis croceipes (CRESSON), a braconid endoparasitoid ofHeliothis spp., to varying olfactory stimulus conditions created with a turbulent jet.

Odor-mediated host-searching by femaleMicroplitis croceipes, a braconid endoparasitoid of larvalHeliothis species, was studied in a flight tunnel. Volatiles emitted by third-instarH. zea feeding on cowpea seedling leaves were released and carried with the wind, resulting either in an irregularly shaped plume, or injected with high velocity, resulting in a conically shaped jet plume. Flight maneuvers ofM. croceipes had a higher stereotype in jet plumes compared to irregularly shaped plumes. Variation in odor concentration in jet plumes due to intermittent feeding of the host larvae did not affect the number of flights. At the levels employed, odor concentration did not alter the rate of upwind progress in jet plumes. Because air velocity inside a jet increases in the upwind direction,M. crocepies regulates its ground-speed during its approach to the odor source.

Wing fanning as a measure of pheromone response in the male pink bollworm,Pectinophora gossypiella (Lepidoptera: Gelechiidae).

A still-air, wing fanning bioassay measured male pheromone response in the pink bollworm moth,Pectinophora gossypiella (Saunders). As pheromone concentration was increased, the duration of wing fanning increased while its latency decreased. Response duration was longest for the natural pheromone blend [44∶:56 (Z,E)- and (Z,Z)-7,11-hexadecadienyl acetates], although responses to 38% and 50%Z,E blends were not significantly briefer. Preexposure to pheromone had no effect on wing fanning in males retested after 24 hr. Wing fanning was highly correlated with upwind flight and other responses observed in a wind tunnel. Wing fanning duration provides a continuous measure of pheromone response and allows a large number of males to be tested in a short time; these two characteristics of the wingfanning assay are helpful for genetic analyses of male response.

Heritable variation in pheromone response of the pink bollworm,Pectinophora gossypiella (Lepidoptera: Gelechiidae).

Heritability of variation in male pheromone response by pink bollworm moths,Pectinophora gossypiella (Saunders), was examined using a still-air, wing-fanning bioassay. Heritability (±SE) of overall responsiveness, as measured by the mean duration of wing fanning to the blend of pheromone components produced by females [44∶56 ratio of (Z, E)- to (Z, Z)-7,11-hexadecadienyl acetate], was 0.385 ± 0.095. Heritabilities of wingfanning duration to blends with 25 and 65%Z, E isomer were 0.377 ± 0.113 and -0.145 ± 0.103, respectively. These findings indicate an asymmetry in the genetic component of variation in response to pheromone blends with high and low proportions of theZ, E isomer. An index of response specificity for individual males was developed based on the response to an off-blend (either 25 or 65%Z, E isomer) relative to the response to the 44%Z, E blend. Heritabilities of response specificity were 0.117 ± 0.059 and -0.043 ± 0.067 for the 25 and 65%Z, E blends, respectively.

Temporal patterns of sex pheromone titers and release rates inHolomelina lamae (Lepidoptera: Arctiidae).

Six hydrocarbon components (2-methylhexadecane,n-heptadecane, 2-methylheptadecane, 2-methyloctadecane,n-nonadecane, and 2-methylnonadecane) were identified in sex-pheromone gland extracts and in airborne collections ofHolomelina lamae. Low variability in the ratio of components among individuals indicates tight regulation of blend composition. Minor changes were evident in the quantity and ratio of the blend as a function of time of day. Based on gland extracts, the total quantity of the six components increased from day 1 (X = 6299 ng) to day 4 (X = 7498 ng) and subsequently decreased. No significant correlations were found between total gland contents and wet or dry weights of moths. Emission rates ofH. lamae females were determined from pheromone adsorbed onto Porapak Q. Quantities released peaked shortly after the onset of calling and decreased rapidly as calling continued. Peak release rates ranged from 13 to 350 ng/10 min, and from 37 to 835 ng/60 min. Noncalling females did not emit detectable quantities of pheromone. Based on release rates and the rate of pulsation of the abdominal tip, the average amount released per pulse is not constant. The mean ratio of components released (0.78∶7.45∶ 84.80∶2.84∶2.59∶1.53) was not very different from the ratio of components in gland extracts of 2-day-old females (0.70∶4.19∶90.12∶ 1.65∶1.91∶1.42). We propose that the blend is atomized rather than volatilized from the gland, thus retaining nearly the same ratios in the female's effluvium as in her gland.

Rate of release of spruce budworm pheromone from virgin females and synthetic lures.

The rate of pheromone [(E)- and (Z)-11-tetradecenal] release from calling virginChoristoneura fumiferana females and synthetic lures was determined in both static and aerated atmospheres. In a static system ca. 2 ng/hr was recovered per female. Owing to the > 75% adsorption onto the females' bodies in static atmospheres, the actual release rate has to be corrected to roughly 9-27 ng/hr, depending on the percentage adsorbed. In the air-flow system, females were found to release between 4 and 20 ng/hr. On a 16∶8 light-dark cycle, calling began 1-2 hr before lights-off and continued nonstop until lights-on. Pheromone was emitted throughout calling, while no pheromone was detected during the noncalling periods.

Role of (Z)- and (E)-11-tetradecenyl acetate pheromone components in the sexual behavior of the (Z) strain of the european corn borer,Ostrinia nubilalis (Lepidoptera: Pyralidae).

A glass tube olfactometer bioassay was used to examine pheromone response of males of the (Z)-pheromone strain ofOstrinia nubilalis (Hubner). The presence of (E)-11-tetradecenyl acetate at the natural ratio to (Z)-11-tetradecenyl acetate (97∶3; Z∶E) did not consistently elevate wing-fanning, upwind walking, or clasper extrusion over (Z)-11-tetradecenyl acetate alone. This bioassay did not reveal the behavioral role of (E)-11-tetradecenyl acetate.

Effect of pheromone concentration on organization of preflight behaviors of the male gypsy moth,Lymantria dispar(L.).

Male gypsy moths (Lymantria dispar L.) in a wind tunnel at 24° respond to decreasing dosages (1 µg to 0.1 pg) of (+)-cis-7,8-epoxy-2-methyloctadecane with a decrease in probability of wing-fanning, an increase in wing-fanning latency, and an increase in the number of behaviors (body jerks, antennal twitches, steps, and wing tremors) preceding fanning. Males initiating any behavior prior to wing-fanning had a 70% probability of wing-fanning and 97% of the males that wing-fanned eventually flew. The sequence of behaviors from quiescence to flight is not organized in a hierarchy, as this concept is used in ethology, nor is it dependent upon the concentration of pheromone. The time-average threshold concentration of pheromone for response of ca. 90% or more quiescent males is ca. 1.9 × 10(-17) g/cm(3) over < 0.3 min.

Mate location strategies of gypsy moths in dense populations.

In high-density populations, the male gypsy moth (Lymantria dispar) "appetitive" flight is primarily vertical and within 1-50 cm of tree boles. Preceding location of a female, males land on trees or occasionally tree foliage and walk while wing-fanning. In high-density populations females may mate before calling, often prior to wing expansion or hardening. Additional matings may occur before any or full deposition of egg masses. Virgin females are not coy, whether their wings are unexpanded, or hardened and held rooflike, or whether they are calling or not. They generally mate with the first willing male and do not exercise sexual selection by an acceptance or rejection reaction. The mating structure in dense populations would seem to reduce selective pressure for female emission of and direct male anemotactic flight to attractant pheromone. A low proportion of males "search" appropriate objects, especially tree trunks, in the walking-wing-fanning state. Such males often are successful in locating virgin females before calling commences. This male strategy presumably would not be successful in low population densities.

Apparency of pulsed and continuous pheromone to male gypsy moths.

Quiescent male gypsy moths (Lymantria dispar) exposed in a wind tunnel to either pulsed (0.5-, 2- or 5-sec on, followed by a two-fold time interval off) or continuous streams of synthetic pheromone responded similarly in the proportions and latencies of wing fanning. Similarly, upwind anemotactic flight tracks in pulsed (1-sec on and 1-sec off) and continuous plumes of pheromone were indistinguishable. These data suggest that in the gypsy moth (1) pulsed pheromone stimuli would not lower the threshold, despite the improvement in the signal-to-noise ratio; and (2) temporal modulation of the pheromone plume at 1-sec intervals does not alter the "preprogrammed" upwind flight pattern.

Gypsy moth (Lymantria dispar L.) attraction to disparlure enantiomers and the olefin precursor in the People's Republic of China.

Pheromone traps baited with disparlure,cis-7,8-epoxy-2-methyl-octadecane, captured males ofLymantria dispar, the gypsy moth, at two widely separated locations in the People's Republic of China. The (+) enantiomer of disparlure attracted significantly more males than the racemate; addition of olefin reduced captures. The duration of the flight period was longer (eight weeks) and peaked earlier near Beijing than farther north near Dunhua (five weeks).