摘要:

Abstract.In previous studies we used logistic regression analysis to quantify the change in behavioural phase state ofSchistocerca gregaria(Forskål) nymphs subjected to variations in population density. Such work involved restricting insects in small containers either alone or in a crowd. In the present paper we have shown that the fine‐scale distribution of food plants, perches and favourable microclimatic sites influences the spatial distribution of locusts, both in the laboratory and under semi‐field conditions. When multiple resource sites were provided, solitarious locusts tended to disperse and behavioural gregarization was inhibited. However, provision of only a single site promoted congregation, overcoming the tendency of solitarious insects to avoid each other, and led to behavioural gregarization. The time‐course and extent of this response was fully consistent with our earlier experiments using enforced crowding. We suggest that such quantitative, experimental studies of the effects of environmental microstructure on behaviour may yield fundamental insights into the dynamics of plague formation in the desert

ISSN:0307-6962    

DOI:10.1111/j.1365-3032.1996.tb00862.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract.During the annual life cycle of the bumble beeBombus terrestris(L.) colony, there is a stage characterized by worker reproduction in the presence of the queen. It has been proposed that this is a result of a decrease in queen inhibition. This hypothesis was examined by studying the effects of queens taken from colonies at different stages of development on several aspects of worker physiology and behaviour: rates of Juvenile Hormone (JH) releasein vitro, ovary development, and behaviour associated with reproduction. After optimizing and validating the radiochemical assay for JH release for bumble bee workers, we found that queenless workers had significantly more developed ovaries and higher rates of release of JH than did queenright workers, confirming and extending previous findings that suggest that bumblebee ovarian development is under JH control. Mated queens, separated from their colony and brood, can have the same inhibitory effect on the reproductive development of callow workers. In contrast, workers confined with virgin queens or in queenless groups demonstrated a significantly higher rate of release of JH, overt aggression and threatening behaviours. However, there were no differences in rates of release of JH between workers confined in groups in the laboratory with queens taken from colonies either before or after the onset of worker reproduction. Furthermore, overt aggression and threatening behaviours were similar and low in both types of groups. These results gave no support to the hypothesis that a decrease in queen inhibition is associated with the onset of worker reproduction. We also show that young workers reared in colonies either before or after worker reproduction occurs, or in queenless colonies, all demonstrated similar, low rates of release of JH. These results suggest that older workers may inhibit the corpora allata of younger workers in queenless colonies.

ISSN:0307-6962    

DOI:10.1111/j.1365-3032.1996.tb00863.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract.In females ofDiploptera punctatathe corpora allata undergo a gradual increase in volume during most of the second nymphal stadium. In the first half of the stadium, steady growth of the glands results from a progressive increase in the size of constituent cells. Late in the stadium, cell size declines but the volume of the glands continues to rise due to an increase in cell number. Changes in cell size during the stadium displayed a distinct pattern in relation to Juvenile Hormone (JH) synthesis. Both cell size and activity increased during the first two‐thirds of the stadium, peaked early in the last third of the stadium, and decreased before the moult. The rise in cell numbers late in the stadium corresponded to a wave of cellular mitosis and occurred after a steep decline in the rate of JH biosynthesis. Exposure of late second instars to fenoxycarb. a JH analogue, depressed mitosis significantly, suggesting autocrine regulation of cell proliferation in the corpora allata. Possible mechanisms modulating sequential cycles of growth and atrophy of cells and cell proliferation in these glands are discussed in relation to temporal patterns of JH and ecdysteroid titres in nymph

ISSN:0307-6962    

DOI:10.1111/j.1365-3032.1996.tb00864.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract.Olfactory responses from the entire antenna and from single antennal sensilla of the male turnip moth,Agrotis segetum(Lepidoptea: Noctuidae Schiff.), were recorded after stimulation of the antenna with the sex pheromone component, (Z)‐5‐decenyl acetate (Z5‐10:OAc), and three sulphur analogues of this compound. Adaptation of olfactory receptor neurones tuned to Z5‐10:OAc was investigated after pre‐exposure of these receptor neurones to the key stimulus and to the three sulphur analogues. Both electro‐antennographic and single sensillum recordings revealed that the sulphur analogues had a significantly decreased effect compared to the natural stimulus. The pre‐exposure experiments demonstrated that no further inhibition of neural activity was observed than could be expected from receptor neurone adaptation. Earlier reports, describing sulphur analogues as possible hyperagonists acting on moth pheromone receptor neurones, are not supported by the

ISSN:0307-6962    

DOI:10.1111/j.1365-3032.1996.tb00865.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract.Little is known about the nature of injury due to cold shock, or its prevention by rapid cold‐hardening, in insects. To understand these phenomena better at the system level, physiological and behavioural comparisons were made between control, cold shock injured, and rapidly cold‐hardened flesh flies,Sarcophaga crassipalpisMacquart (Diptera, Sarcophagidae). Cold shock impaired the proboscis extension reflex in response to 0.125,0.5 and 1.0 M sucrose solutions. Cold shock‐injured flies were unable to groom effectively and spent only 12.5% of the first 5 min following general dust application producing ineffectual leg movements. In contrast, control and rapidly cold‐hardened flies exhibited normal grooming behaviour spending 92.4% and 94.1% of the first 5 min following generalized dust application grooming. Cold shock also decreased the mean resting membrane potential of tergotrochanteral muscle fibres from ‐65.9 mV in control flies to ‐41.6 m V. Conduction velocities of the three motor neurone populations innervating the tergotrochanteral muscle were all significantly lower in cold‐shocked flies than in control or rapidly cold‐hardened flies. Finally, cold shock impaired neuromuscular transmission as evidenced by a lack of evoked end p

ISSN:0307-6962    

DOI:10.1111/j.1365-3032.1996.tb00866.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract.To study the reproductive potential of workers in the stingless beeTrigona (Tetragonisca) angustulaIlliger (Apidae, Meliponinae), we examined the morphological quality of their eggs. Worker‐eggs were all placed on the inside of the upper wall of brood cells. Normally, such eggs are consumed by the queen and are therefore referred to as trophic. The provisioning and oviposition processes in queenright colonies are characterized by the occurrence of circular aggregations of workers, ‘rosettes’, around the broodcell opening immediately after the release of a worker‐egg. The ovaries of 35% of these rosette workers contained mature, chorionated eggs. In a single worker ovary, always only one mature egg was found. Some of the eggs, dissected from the ovarioles, showed a reticulate chorion pattern. Worker‐eggs which lacked this pattern were significantly bigger than patterned eggs. Scanning electron micrographs revealed that the patterned worker‐eggs are similar in appearance to queen‐eggs.After a worker‐egg had been removed experimentally from a broodcell, the same cell could be oviposited by a worker again. Light microscopic analysis revealed that all these worker‐eggs lacked the reticulate chorion pattern and were very similar in their morphology. In a colony without a laying queen workers laid eggs which had a reticulate pattern on the chorion. Since these eggs developed into males, we assume that the pattern on the chorion is characteristic for reproductive eggs. We also assume that the queen prevents the release of reproductive eggs by the workers. However, she does not inhibit the development of

ISSN:0307-6962    

DOI:10.1111/j.1365-3032.1996.tb00867.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract.The photoperiodic induction of presexual females (gynoparae) and males of the aphidRhopalosiphum padi(L.) was examined in single clones collected from different latitudes (N clone from Blair Atholl, 56.5d̀N 3.1d̀W; C clone from Leeds, 53.5d̀N 1.4d̀W and S clone from Exeter, 50.4d̀N 3.3d̀W). Critical night lengths (CNLs) for gynopara and male production (CNLs: 50% of maximum production) and inter‐clonal differences, defined by the different forms of progeny produced at a single discriminating night length (12 h 30 min), were measured at 16 ± 1d̀C. The aphid clones differed in CNL and in the morphs produced at the discriminating night length. These differences were used to investigate the inheritance of the photoperiodic response. In crosses between clones the photoperiodic response showed considerable overall variation. The variation in CNLs indicated that the photoperiodic response was unlikely to affect the overwintering success after long‐distance movement of clones from one latitude

ISSN:0307-6962    

DOI:10.1111/j.1365-3032.1996.tb00868.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract.The movement ofSitobion fragariae(Wlk.) (Homoptera: Aphididae) males towards odours from conspecific sexual females (oviparae) and the aphid sex pheromone component (4aS,7S,7aR)‐nepetalactone were demonstrated in a linear‐track olfactometer. Males of the closely relatedSitobion avenae(Fab.) were attracted to odours from conspecific oviparae and also oviparae ofS. fragariae.These results were consistent with the recent identification of this nepetalactone isomer as the major component of the sex pheromone in these species. Males ofS.fragariaewere not significantly attracted to oviparae ofS.avenae.indicating some qualitative or quantitative difference in the pheromones of the two species. Males did not respond to the related (1R,4aS,7S,7aR)‐nepetalactol or to host‐plant odours. Gynoparae of these species moved towards the nepetalactone and also to host‐plant odours. A combination of both stimuli was more attractive than plant odour alone. Gynoparae ofS.fragariaealso responded significantly to the combined treatment when this was tested against the nepe

ISSN:0307-6962    

DOI:10.1111/j.1365-3032.1996.tb00869.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract.FemaleGlossina morsitans morsitansWestwood were video‐recorded in a wind‐tunnel as they entered, in cross‐wind flight, a broad plume of CO2(a component of host odour). At a wind speed that corresponds with peak catches in the field (c. 0.6 ms‐1) odour produced both significant upwind turning responses (in‐flight anemotaxis) and kinetic responses (reduced flight speed and increased sinuosity (d̀m‐1). At a wind speed of c. 0.2 ms‐1flies displayed anemotactic, but not kinetic, responses to odour. At very low wind speeds (0.1ms‐1) neither upwind turning responses nor kinetic responses to odour were detected. The results are discussed with regard to current theory of host‐

ISSN:0307-6962    

DOI:10.1111/j.1365-3032.1996.tb00870.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract.Sperm removal inTenebrio molitor L.(Coleoptera: Tenebrionidae) has been proposed as an adaptation to sperm competition and has been documented when the remating interval between successive copulations is short, but not when it is long (Gage, 1992). If sperm removal is adaptive, it follows that there should be different fertilization outcomes from double matings with different remating intervals.Sperm precedence patterns were assessed using reciprocal double matings of normal and γ‐irradiated (sterile) virgin males of controlled size and age with virgin females of controlled size and age.Immediate last male sperm precedence was high whether the remating interval was short (<10 min) (P2,= 0.89) or long (24h) (P2= 0.92).Sperm precedence in eggs laid in a 16‐day period after the last copulation showed no difference in the pattern of change between females with short and long remating intervals.By examining the aedeagus of males we show that sperm are removed at the end of copulation by the first and the second male to mate with a virgin female regardless of whether the remating interval is short or long.We conclude that sperm removal is unlikely to be the primary mechanism by which males gain such high levels of last male sperm preced

ISSN:0307-6962    

DOI:10.1111/j.1365-3032.1996.tb00871.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY