Structure–function studies on hypertrehalosaemic and adipokinetic hormones: activity of naturally occurring analogues and some N- and C-terminal modified analogues

Abstract The relative potencies, with respect to mobilization of lipids in Locusta migratoria L. and in Schistocerca gregaria Forsk. and of carbohydrates in Periplaneta americana L., of eleven naturally-occurring members of the AKH/RPCH-family of peptides and of some analogues that lacked the N-terminal pyroglutamate residue or had a free threonine acid at the C-terminus instead of an amide are assessed. The time courses for carbohydrate and lipid release shown for the peptides suggest that their transport and degradation rates are similar. Therefore, their relative activities reflect most probably the different abilities to bind to the receptors on the fat body cells of the cockroaches and locusts tested. The results show clearly that the N- and C-terminally modified analogues give poor or almost no responses regardless of the bioassay employed. Compared with the structural requirements of the cockroach receptor(s), the receptor(s) of the locusts appear more specific. In the cockroach bioassay, only the two octapeptides Lom-AKH-II and Grb-AKH, both lacking a proline residue at position 6, have high ED₅₀ values, whereas the ED₅₀ values of all other peptides are between 0.4 and 2.7 pmol. The exception is the nonapeptide Mas-AKH, lacking proline and having a serine residue at position 7 (a unique feature compared with the other peptides): no activity is exerted below 100 pmol and only a poor response is elicited with higher dosages. The L. migratoria receptor(s) bind the decapeptides best (exception: Bld-HrTH). Octapeptides, even Scg-AKH-II and Grb-AKH which lack a proline residue, elicit a maximum response, but ED₅₀ values are 7–15-fold higher than with Lom-AKH-I. Lom-AKH-II, however, gives only a truncated response. The nonapeptide Mas-AKH is able to elicit a maximum response, but 50 pmol are needed instead of 2 pmol (Lom-AKH-I). In 5.gregaria a maximum response is achieved with Lom-AKH-I and Grb-AKH, but injections of Scg-AKH-II, Lom-AKH-II and Rom-CC-I result in only truncated responses. The importance of a β-turn in the molecules and the presence of proline is discussed. No evidence is found for an antagonistic effect on binding of those peptides that fail to achieve maximum responses.     

The endocrine control of phase transition: some new aspects

Abstract. The present article summarizes some recent findings relating to the underlying mechanism of phase transition in locusts, from the nonswarming solitarious phase to the swarming gregarious phase. These phases differ in many traits, such as colouration, morphometrics and behaviour. The most comprehensive theory at present to explain the switch from the nonswarming to the swarming form is that the locusts are brought together by the heterogeneity of the environment. They gather at preferential structures and food plants and physical contact then stimulates individuals to gregarize. Phase change can also be transferred across generations by maternal pheromones. The endocrine regulation of phase polymorphism is still not fully understood. The role of ecdysteroids has been studied, so far with no final conclusion. It is remarkable that the prothoracic glands persist longer in isolated-reared adults, which implies that these glands continue to play a role, although they no longer release important amounts of ecdysteroids. Juvenile Hormone, without any doubt, induces certain solitarious characteristics, such as green colouration, but is not the primary causal factor. A real breakthrough was the discovery of [His⁷]-corazonin, made possible by using a novel assay system, the Okinawa albino mutant of Locusta migratoria , which was known to be deficient in this hormone. This peptide, which is produced in the brain and is most likely released via the corpora cardiaca, promotes the gregarious black pigmentation. It also plays a role in morphometrical phase change as well as in behavioural alterations. Corazonin is apparently quite an important peptide not only in locusts, but also in insects in general.     

The dark-colour-inducing neurohormone of locusts in relation to an albino mutant of Schistocerca gregaria

In the albino mutant of an Okinawa strain of Locusta migratoria (L.) (Orthoptera: Acrididae), albinism is caused by the absence of the dark‐colour‐inducing neurohormone (DCIN), which is present in the corpora cardiaca (CC) of normally coloured phenotypes. This study tests whether the absence of DCIN is responsible for albinism in an albino mutant of another locust, Schistocerca gregaria (Forsk.) (Orthoptera: Acrididae). This seemed feasible because a single Mendelian unit controls albinism in both species. However, implantation of CC, or injection of an extract of CC, from albino donors of S. gregaria, induce dark coloration in crowded nymph recipients of the Okinawa albino mutant of L. migratoria, as effectively as do implanted CC, or injections of extract of CC, from normal phenotype donors of S. gregaria. Therefore, DCIN is present in the albino mutant of S. gregaria, and consequently, the albinism in this mutant is not caused by its absence. Implantation of CC, or injection of extracts of CC, from albino donors of S. gregaria to conspecific albino nymphs does not induce darkening. Only extremely high doses of synthetic DCIN injected into albino nymphs of S. gregaria are effective, inducing some darkening. The dose to induce such darkening in albino nymphs of S. gregaria is 50 nmol, ≈ 5 × 10⁶ times higher than that (10 femtomol) needed to induce equivalent darkening in nymphs of the Okinawa albinos of L. migratoria. The results are discussed and some possible explanations of the observed effects outlined.     

Susceptibility of immature stages of the locusts Schistocerca gregaria and Locusta migratoria migratorioides to the microsporidium Johenrea locustae and effects of infection on feeding and fertility in the laboratory

Second instar nymphs of African migratory locust, Locusta migratoria migratorioides, and desert locust, Schistocerca gregaria, were tested for their susceptibility to the microsporidium pathogen Johenrea locustae (Lange et al. 1996 Lange, C.E., Becnel, J.J., Razafindratiana, E., Przybyszewski, J. and Razafindrafara, H. 1996. Johenrea locustae n.g., n.sp. (Microspora: Glugeidae): A Pathogen of Migratory Locusts (Ortrhoptera: Acrididae: Oedipodinae) from Madagascar. Journal of Invertebrate Pathology, 68: 28–40.  [Google Scholar], Journal of Invertebrate Pathology, 68, 28) in the laboratory. Spores of J. locustae were produced from live L.m. migratorioides, a conspecific to L. migratoria capito. Locusta m. migratorioides and S. gregaria were exposed to wheat seedlings sprayed with 20 mL of three concentrations (10⁶, 10⁷ and 10⁸ spores mL^?1). Both second-instar nymphs of L.m. migratorioides and S. gregaria were susceptible to J. locustae infection at the three concentrations. There was no effect of concentration of the microsporidium on mortalities of S. gregaria (92–98%) 19 days postinfection. Adjusted mortality in L.m. migratorioides at 19 days post-exposure was 24, 43 and 80% at the corresponding treatment concentrations. The effect of infection on fecundity was tested on both L.m. migratorioides and S. gregaria. Spinach leaf discs were treated with different concentrations (0, 10⁴, 10⁵ and 10⁶ spores mL^?1) of J. locustae and presented to female insects for 24 h. Female L.m. migratorioides surviving infection as nymphs laid significantly fewer egg pods than untreated controls at all levels of exposure. The number of eggs per female was also significantly lower in treated lots than in the controls. Higher spore concentrations also adversely affected egg hatching rate. The effect of J. locustae infection on feeding was tested on S. gregaria. There was a significant decrease in food intake among S. gregaria nymphs treated only at the high concentration (10⁶ spores mL^?1).     

Flight capability and flight motor pattern in a sedentary South African grasshopper, Phymateus morbillosus– a comparison with migratory species

Abstract Among the Acridoidea, not all species are strong fliers. We have examined the possible causes for loss of flight in a species with a reduced flight system, the South African grasshopper, Phymateus morbillosus (L.). This is a sedentary species that, in the field, displays only marginal flight (in males) or no flight (in females). In a wind tunnel, however, this species can be stimulated to perform flight movements for a short time. In the present study, several morphometric parameters and aspects of the flight motor output have been examined. The data are compared with those of the migratory locust species ( Locusta migratoria L. and Schistocerca gregaria Forsk.). Phymateus morbillosus can exhibit the typical flight motor pattern for short periods of up to 1 min. Morphometric data and wing-beat frequency in P. morbillosus are similar to that of other members of this insect group. However, female specimens of P. morbillosus are too heavy to lift themselves for active flight. We assume that females of this species invest in the augmentation of reproduction rather than investing in the flight system.     

The time-course of behavioural phase change in nymphs of the desert locust, Schistocerca gregaria

Abstract. The time-course of behavioural phase change was investigated in nymphs of Schistocerca gregaria , using logistic regression analysis of behaviour recorded in a standard assay. Gregarization occurred very rapidly. Solitary-reared nymphs became markedly gregarious in behaviour within 1-4h of being placed in a crowd. These insects re-solitarized equally quickly if removed from the crowd. Crowd-reared locusts also solitarized within l-4h, but this effect was not complete. Results indicate that, while behavioural gregarization is maximal within a few hours of crowding, solitarization is a two-stage process, changing rapidly at first, then more slowly as a function of the period of previous crowding.     

The effects of simultaneous variation in protein, digestible carbohydrate and tannic acid on the feeding behaviour of larval Locusta migratoria (L.) and Schistocerca gregaria (Forskal). I. Short-term studies

ABSTRACT The influence of simultaneously varying the levels in artificial diets of protein, digestible carbohydrate (14% or 28%) and tannic acid (absent or 10%) on the feeding behaviour of the oligophagous Locusta migratoria (L.) and the polyphagous Schistocerca gregaria (Forskal) (Acrididae) was investigated. Total consumption and detailed feeding behaviour were recorded over a 12 h period in choice and no-choice experiments. In addition, amounts eaten by Schistocerca of the 14% protein, 14% carbohydrate diet with and without tannic acid were measured at regular intervals throughout the fifth stadium, and insect growth over this period was recorded. There were no interactive effects of nutrient levels and tannic acid, despite the fact that both species compensated for dilution of dietary protein by increasing consumption. Only male Locusta compensated for dilution of dietary carbohydrates, and this compensation was much less marked than for protein. Tannic acid did influence feeding as a main effect, however. It caused an increase in amounts eaten by Schistocerca in both choice and no-choice experiments. This increased consumption was due to an increase in the number of meals taken. A shorter latency period before and a longer duration of the first meal by naive insects suggested a phagostimulatory rather than a post-ingestive effect of tannic acid. The stimulatory effect was only apparent for the first 24 h of continuous exposure, but this temporary enhancement none the less resulted in the insects being heavier at adult ecdysis. Stadium duration was also somewhat reduced. In a no-choice situation, no effect of tannic acid on the feeding behaviour of Locusta was observed. When given a choice, however, this species took significantly more meals on the tannic acid-free diet, these being of similar average size to meals taken on the tannic acid diet. Significantly more insects took their first meals on the tannic acid-free diet in the choice test, indicating a deterrent effect of tannic acid in Locusta.     

The influence of environmental microstructure on the behavioural phase state and distribution of the desert locust Schistocerca gregaria

Abstract. In previous studies we used logistic regression analysis to quantify the change in behavioural phase state of Schistocerca 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 locust.     

An analysis of the behavioural effects of crowding and re-isolation on solitary-reared adult desert locusts (Schistocerca gregaria) and their offspring

Abstract. The time-course of behavioural change in response to crowding and re-isolation was investigated in adults of Schistocerca gregaria Forskål (Orthoptera, Acrididae) using logistic regression analysis. Crowding solitary-reared adults for a period of 4 h caused them to behave similarly to crowd-reared insects, with their becoming much more active and moving towards rather than away from a stimulus group of locusts. Responsiveness to crowding was greatest in young adults. The behaviour acquired after 48 h of crowding was lost within 1 day of re-isolation. Although experience by solitary-reared adults of crowding for 48 h had only transitory effects on their own behaviour, there was also a long-term influence on the behaviour of their offspring. The strength of this effect was dependent on the age at which adults experienced crowding, increasing in a graded manner with adult age, and hence the recency of crowding before oviposition. Parents crowded at a late stage in the reproductive cycle yielded hatchlings which behaved indistinguishably from those from crowd-reared adults. Such an effect is consistent with the idea that females, through their previous experience of crowding, are effectively predicting the probability that their offspring will emerge into a high-density population, and predisposing their hatchlings' behaviour accordingly.     

对中国飞蝗种下阶元划分和历史演化过程的几点看法

前人把我国飞蝗划分为东亚飞蝗、亚洲飞蝗和西藏飞蝗三个亚种,并推测我国最原始的飞蝗发生地可能是郑州-开封东北至临清-禹南以南的古黄河冲积扇地带。由于飞蝗的形态、生理、生态等性状受气候与生态条件影响,从而在地区间变化很大,而且过去关于我国飞蝗发生动态和演化的分析均忽视了地史中重大气候事件的影响,因此有关结论的可靠性值得质疑并有待深入验证。根据分子群体遗传学的最新研究结果,我们认为：(1)我国飞蝗应被重新划分为青藏种群、海南种群和北方种群3大类群;(2)我国东部地区(辽宁、黄淮平原、陕西和山西)的飞蝗与海南的飞蝗之间的遗传差别已达亚种水平,因此不是东亚飞蝗,而是亚洲飞蝗经过适应性演化在我国华北地区形成的特异地理宗——华北地理宗;(3)华北地理宗的形成应是末次冰期后种群大规模扩张的结果,推测是由蒙新高原的飞蝗沿黄河流域逐步扩散而来;(4)结合历史上飞蝗发生的情况可以推断,在中国,至少在北至北纬46℃的地区,光周期不会成为飞蝗发育的限制性因素,有效积温可能是惟一限制性气候因子。因此,在气候逐渐变暖的趋势下,飞蝗有逐渐向北扩散的可能,东北地区将会逐步具有飞蝗大发生所需要的必要气候条。     

Effect of Paranosema locustae (Microsporidia) on the behavioural phases of Locusta migratoria (Orthoptera: Acrididae) in the laboratory

The ability of parasites to modify the behaviour of their hosts is a wide spread phenomenon, but the effects of microsporidian parasites on locust behaviour remain unexplored. Here the frequencies of directional changes (ND) and jumping (NJ) per minute of gregarious locusts infected with 2000 spores of the microsporidian parasite Paranosema locustae were significantly different from those of untreated locusts 10 and 16 days after infection, being similar to values for solitary nymphs. In contrast, the behaviour of locusts inoculated with the lower doses of 200 spores/locust was sometimes like that of solitary nymphs. At other times, behaviour was intermediate between solitary and gregarious, i.e. transitional. The rearing density did not affect the turning and jumping behaviour of infected locusts, and their behaviours were similar to those of solitary locusts at 10–16 days after infection. Our study demonstrates that infection with P. locustae may lead gregarious locusts to change some of their behaviour to that typical of solitary locusts.     

东北地区亚洲飞蝗染色体核型分析

采用常规压片法对吉林省亚洲飞蝗Locusta migratoria migratoria(L.)的染色体核型进行分析.研究结果表明:亚洲飞蝗性别决定机制为X0型,染色体数目为2n♂=23,染色体组式4L+4M+3S+X,全部为端部着丝粒染色体,NF=23.染色体中最长(L1)与最短(S11)染色体之比大于4:1,臂比大...