Photoperiodic induction of winged females in the black bean aphid. Aphis fabae

Abstract. The Photoperiodic of winged females (alatae) in the black bean aphid, Aphis fabae Scop. (Homopetera: Aphididae), is investigated in detail with emphasis on the interaction of the maternal and embryonic/young larval photoperiodic clocks. Previous work had shown that in uncrowded conditions the induction of gynoparae (winged females that produce sexual females) requires both prenatal and postnatal exposure to long-night (12 h) Photoperidic cycles: present results show that sole postantal exposure to long nights of any lenght does not induce wing formation in early-born aphids.
When aphids were exposed to experimental light-dark cycles postanatally only, their daughters developed as alate in long nights and as apterae in short nights: the critical night lenght (CNL) was 11:1 h. Additional prenatal exposure to experimental regimes resulted in a significantly shorter CNL (10.6 h). This difference could be accounted for by the fact that more experimental light-dark cycles were experienced in the latter case.
Apterous aphids transferred from LD 16:8 h to LD 12:12 h as either third-or fourth-stadium larvae, or young adults, switched for aptera-production to alata-production. The transition form aptera- to alata-production was rather abrupt in third-stadium transfers but more gradual when transfers occurred as fourth-stadium larvae and adults. Moreover, s the number of days required for 50% of the aphids to become alata-producers increased from 7–8 in third-stadium transfers, to 9–10 and 11–12 in the later transfers.     

Aphid flight-track analysis in three dimensions using video techniques

Abstract. A technique is described for the three-dimensional analysis of the flight paths of small insects using two video cameras placed alongside each other with the optical axes coincident at a point some distance beyond the area of interest. The video signals were mixed and a time base introduced before recording the superimposed images from both cameras on a single VCR. With suitable lighting and a black background, flying aphids appeared on the monitor as double, bright images on a dark background. The distance between the two images was inversely proportional to the distance of the aphid from the camera lenses. A calibration grid was used to insert the correct parameters into software designed to provide the x (vertical), y (horizontal) and z (distance from the cameras) Cartesian co-ordinates for a flying insect and to calculate the distances flown, flight speed and turning parameters. The advantages of the system are that it is designed for a single VCR and monitor, provides automatic synchrony between camera signals and can examine a larger visual arena than screen-splitting methods. It operates with insects as small as aphids, and wind-tunnel studies on the black bean aphid, Aphis fabae Scop., showed that some flight parameters (for the final one-second approach to a visually attractive landing platform) differed according to whether wind was present or not. Thus, ground speed and distance moved differed significantly but turning parameters were unchanged. In addition, flight trajectory on the approach to landing depended upon initial direction of flight and the presence of wind.     

Differential photoperiodic responses in genetically identical winged and wingless pea aphids, Acyrthosiphon pisum, and the effect of day length on wing development

Abstract. Winged and wingless individuals of a pink clone of the pea aphid, Acyrthosiphon pisum (Harris), showed differences in the response curves for photoperiodic induction of both males and sexual females (oviparae). The critical night length (CNL) for ovipara induction in winged aphids was 0.75 h shorter than in wingless aphids, whereas the CNL for male induction in winged aphids was 1.0h longer than in wingless aphids. This means that in winged aphids the CNL for male induction in winged aphids was 0.5 h longer than that for ovipara induction, while in wingless aphids the CNL for male induction was 1.0–1.5 h shorter than that for ovipara induction, and also the shapes of the curves differed.
Winged aphids were produced by wingless mothers which were crowded as young adults. However, when young adults were crowded in long nights, winged aphids were not produced, and the CNL for wing inhibition was between 9.5 and 10h. This effect of photoperiod on wing induction was maternal.     

Reproductive, morphological and behavioural affinities between the alate gynopara and virginopara of the aphid, Aphis fabae

ABSTRACT. 'Normal' alate virginoparae reared under long day conditions (LD 16:8) with postnatal crowding, and 'normal' gynoparae reared in un-crowded, short day conditions (LD 12:12) over two generations were compared in respect of the morph of the progeny, the frequency distribution of secondary rhinaria (placoid sensilla) on the third and fourth antennal segments, and preferred larviposition sites. Although in Aphis fabae the two morphs closely resemble one another morphologically, they differed in each of the above characters. Progeny sequences were analysed after transfer to the opposite photoperiodic regime at various times during postnatal development of the alate mothers. Transfer of presumptive gynoparae from short to long days induced the appearance of virginoparous progeny even when the transfer was made just after the final moult. Transfer of presumptive alate virginoparae from long to short days was effective in inducing oviparous offspring, only if the transfer was made during the first instar; oviparae were always first born. Intermediates between oviparae and viviparae were found at the time when the morph of the progeny changed. Transfer from long to short days also induced gynopara production but there appeared to be an intrinsic mechanism which prevented exclusive gynopara production by alates. When first instar, presumptive gynoparae were transferred to long days, the resulting adults would be described both reproductively and behaviourally as alate virginoparae; the opposite switch, of presumptive alate virginoparae to short days, resulted in adult gynoparae on the same criteria. However, the numbers of secondary rhinaria were influenced more by the prenatal than by the postnatal photoperiodic regime. There was an asymmetry of response in that a switch from short to long days had a greater effect on all three characters monitored than did the opposite switch from long to short days.     

Reproduction and probing behaviour of the bird cherry‐oat aphid Rhopalosiphum padi on detached leaves and leaves on intact seedlings of the winter host,bird cherry Prunus padus

Video recording and electrical penetration graph techniques are used simultaneously to investigate host acceptance (in terms of reproduction) and probing activities of autumn migrants (gynoparae) of the bird cherry‐oat aphid Rhopalosiphum padi (L.) on detached leaves and on leaves on intact plants of the winter host, bird cherry Prunus padus. There are no significant differences between the times taken to first parturition or the number of nymphs produced over a 6‐ or 18‐h period on intact plants or detached leaves. Stylet probing activities (i.e. total probe duration, xylem ingestion, the time to first phloem contact and phloem salivation) are also similar in the two situations.     

Expressed sequence tag‐derived microsatellites for the cool‐water marine copepod Calanus finmarchicus

The copepod Calanus finmarchicus is the major contributor to zooplankton biomass in the North Atlantic and Norwegian Sea, but recent studies have shown a 70% decrease in abundance as well as a northward shift in the species’ range. Insights into dispersal capabilities gained from population genetic studies will be crucial in predicting the response of C. finmarchicus communities to climate change and, consequently, we have developed a set of expressed sequence tag‐derived microsatellite markers to allow fine‐scale elucidation of population structuring and dispersal. Ten polymorphic markers displayed between two and 19 alleles, with levels of expected heterozygosity ranging from 0.044 to 0.924.     

Surveying Predicted Rendezvous Sites to Monitor Gray Wolf Populations

ABSTRACT We used rendezvous site locations of wolf (Canis lupus) packs recorded during 1996–2006 to build a predictive model of gray wolf rendezvous site habitat in Idaho, USA. Variables in our best model included green leaf biomass (Normalized Difference Vegetation Index), surface roughness, and profile curvature, indicating that wolves consistently used wet meadow complexes for rendezvous sites. We then used this predictive model to stratify habitat and guide survey efforts designed to document wolf pack distribution and fecundity in 4 study areas in Idaho. We detected all 15 wolf packs (32 wolf pack-yr) and 20 out of 27 (74%) litters of pups by surveying <11% of the total study area. In addition, we were able to obtain detailed observations on wolf packs (e.g., hair and scat samples) once we located their rendezvous sites. Given an expected decrease in the ability of managers to maintain radiocollar contact with all of the wolf packs in the northern Rocky Mountains, rendezvous sites predicted by our model can be the starting point and foundation for targeted sampling and future wolf population monitoring surveys.     

Laboratory-simulated naturally-decreasing day lengths, twilight and aphid photoperiodism

Abstract. Day-length changes, as well as periods of twilight, that occur in the course of each natural day-night cycle, were recreated for two chosen latitudes in a computer-controlled 'natural-day-length simulator'.The photoperiodic responses of two aphid species, Aphis fabae and Megoura viciae , were examined in conditions which mimicked late summer to autumn at two simulated latidudes, 51.5N (e.g.Ascot, Southern Britain) and 60°N (e.g.southern tip of Shetland Islands, Northern Britain), with temperatures between 16°C ('night') and 18°C ('day').The responses under simulated natural photoperiodic conditions were similar to those observed under conventional experimental conditions of squarewave light-dark cycles (with abrupt lights-on and lights-off and constant light intensities during the light phase): both aphid species responded to civil twilight as light, and the critical day lengths (including civil twilight) for the induction of sexual morphs by the two aphid species observed in the simulator were the same as those found in squarewave light-dark cycles.
Autumn field experiments (51.5°N) with the same clones of A. fabae and M.viciae revealed much longer critical day lengths for gynopara and male induction in A. fabae compared with those in the laboratory, but the same critical day length for ovipara induction in M.viciue. Minimal night temperatures in the field were on average 6°C, whereas maximal day temperatures declined from around 30°C in early September to 12°C at the end of October; it seems that the critical day lengths in A.fabae are temperature dependent, whereas the findings for M.viciae confirm that the critical day length is temperature compensated.     

Central Processing of Communication Sounds in the Anuran Auditory System

SYNOPSIS. The social behavior of anurans (frogs and toads) ismediated by a number of acoustic signals, or calls, that showboth inter- and intraspecific differences in temporal patternand spectral content. These differences provide cues usefulfor call recognition. Neural mechanisms responsible for detectingand analyzing the temporal and spectral cues of the speciesvocalizations have been the subject of investigation for almostthree decades. Here, I summarize the results of studies conductedin the northern leopard frog, Rana pipiens. These results demonstratethat (1) sound analysis is performed in the central auditorysystem of anurans by an array of neural niters operating inthe time and frequency domain, (2) behaviorally relevant soundsare represented by stimulus-dependent spatio-temporal patternsof excitation among differentially tuned filter neurons, and(3) the time and frequency selectivity of these neurons is determined,in part, by GABA-mediated inhibitory interactions that shapetheir excitatory input