Laboratory assessment of the potential of Paranosema locustae to control immature stages of Schistocerca gregaria and Oedaleus senegalensis and vertical transmission of the pathogen in host populations

We tested the effects of Paranosema locustae spores in wheat bran formulation on the immature stages of Schistocerca gregaria and Oedaleus senegalensis under laboratory conditions. Younger instars were the most sensitive to the pathogen. While 100% infection was recorded in younger instar nymphs, older instars were less sensitive, with 16–27% of the inoculated nymphs remaining uninfected at the end of the experiment. Mortality of each instar increased with increased spore concentration. Immature survival time was significantly reduced by the pathogen and none of the nymphs inoculated as first, second, and third instar nymphs developed to adulthood (6–30% and 55–74% of nymphs inoculated as fourth and fifth instar, respectively). Sublethal effects such as delayed host growth, reduced host size, and abnormal wing and leg development (37% of emerging adults) were noted. Almost half the infected adults showed morphological abnormalities at emergence. Moreover, infection in S. gregaria and O. senegalensis by P. locustae did not affect female oviposition. However, 60% of S. gregaria and 52% of O. senegalensis progeny clearly showed infection by P. locustae with infection intensity of 1.08±0.27×10¹ and 1.19±0.32×10² spores/nymph, respectively. In view of the mortality rates, immature survival, host growth, and abnormal development in the P. locustae treatments, and the high prevalence of the pathogen in offspring from infected parents, it can be expected that the reduction in the impact of the two acridid species in the field will be considerable.     

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 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.     

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.     

Projection areas and branching patterns of the tympanal receptor cells in migratory locusts,Locusta migratoria and Schistocerca gregaria

Summary In Locusta migratoria and Schistocerca gregaria, the projection areas and branching patterns of the tympanal receptor cells in the thoracic ganglia were revealed. Four auditory neuropiles can be distinguished on each side of the ventral cord, always located in the anterior part of the ring tract in each neuromere (two in the meta-, one in the meso-, and one in the prothoracic ganglion). Some of the receptor fibres ascend to the suboesophageal ganglion. There are distinct subdivisions within the auditory, frontal metathoracic and mesothoracic neuropiles. The arrangement of the terminal arborisations of the four types of tympanal receptor cells according to their different frequency-intensity responses is somatotopic and similar in the two ganglia. Here the receptor cells of type-1 form a restricted lateroventral arborisation. Cells of type-4 occupy the caudal part with a dorsorostral extension. Cells of type-2 and -3 arborise in a subdivision between both. Most of the stained low-frequency receptors (type-1, -2, and -3) terminate either in the metathoracic or, predominantly, in the mesothoracic ganglion. In contrast, the high-frequency cells (type-4) ascend to the prothoracic ganglion. The receptor fibres of the different types of receptor cells differ in diameter.Abbreviations aRT anterior part of the ring tract - cf characteristic frequency - MVT median ventral tract - SEG suboesophageal ganglion - SMC supramedian commissure - VMT ventral median tract - VIT ventral intermediate tractSupported by the Deutsche Forschungsgemeinschaft; part of program A7 in Sonderforschungsbereich 305 (Ecophysiology)     

饥饿对东亚飞蝗生长和取食的影响

研究了不同龄期东亚飞蝗Locusta migratoria manilensis(Meyen)的耐饥饿能力和3龄后的东亚飞蝗在不同饥饿程度下的取食量和取食速度。结果表明,东亚飞蝗的耐饥饿能力基本随龄期的增加而增强,平均耐饥饿时间为46～116h;同一龄期的东亚飞蝗,饥饿12h后的取食量和取食速度均大于正常情况,饥饿24h后的取食量和取食速度与正常情况下差异不显著,饥饿36、48h后的取食量和取食速度均明显小于正常情况;饥饿程度越大,取食量就越小,取食速度越慢。     

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.     

不同食料植物对东亚飞蝗肠道细菌状况的影响

目的比较在相同的环境条件下不同食料植物对东亚飞蝗肠道细菌状况的影响。方法以墨西哥玉米、野生马唐为食料植物饲喂东亚飞蝗,在其成虫肠道内和粪沙中分离纯化细菌,获得22株菌株,分别对其培养性状、菌体形态、染色反应和生理生化性状进行系统研究。结果上述22个菌株分别属于稀有杆菌属（Rarobact-er）、短状杆菌属（Brachybacterium）、棒杆菌属（Corynebacterium）、棍状菌属（Clavibacter）、葡萄球菌属（Staphylococ-cus）、丙酸杆菌属（Propionibacterium）、埃希菌属（Eschrichia）、气微杆菌属（Aercmicrobium）、沙雷菌属（Serratia）、克雷伯菌属（Klebsiella）、沙门菌属（Salmonella）、志贺菌属（Shigella）、口腔球菌属（Stomatococcus）、短杆菌属（Brevibacteri-um）、地杆菌属（Terrbacter）、微小杆菌属（Exiguobacterium）、皮杆菌属（Dermabacter）、短小杆菌属（Curtobacterium）、纤维单胞菌属（Cellulomonas）、微杆菌属（Microbacterium）、乳杆菌属（Lactobacillus）和凝结芽胞杆菌属（Bacilluscoag-ulans）。结论不同食料植物对东亚飞蝗肠道细菌种类和数量有很大的影响。     

Control of flight by means of lateral visual stimuli in gregarious desert locusts, Schistocerca gregaria

Abstract. Tethered flying locusts were stimulated either by a periodic grating or by a spotted 'swarm-simulating' pattern moving horizontally, parallel to their longitudinal body axis within their lateral visual fields. The direction of movement of the pattern was changed periodically from progressive to regressive and vice versa.
Both kinds of patterns induced a correlated modulation of yaw-torque and thrust. The two measured flight parameters were modulated independently of each other. Each parameter either increased with progressive and decreased with regressive pattern motion or vice versa. The characteristic curves of thrust and yaw-torque responses - i.e. response amplitude versus contrast frequency resp. angular velocity – measured upon stimulation with the periodic grating between 2 and 70 Hz were at a maximum at 10 Hz and decreased at higher and lower contrast frequencies. The shape of the curves was nearly identical. The characteristic curves measured upon stimulation with the 'swarm-simulating' pattern between 60 and 1500^o s^-1 could be simulated using the spatial wavelength content of the pattern and the characteristic curves for periodic gratings.
Therefore, we suggest that the speed and direction of locusts' flight result from the optomotor effectiveness of the pattern image formed by the neighbouring individuals under free flight. The measured responses would thus contribute to the common orientation of groups of locusts within a migrating swarm and thus to swarm cohesion.     

Changes in the auditory system of locusts (Locusta migratoria and Schistocerca gregaria) after deafferentation

Deafferentation experiments during postembryonic development show morphological and/or physiological changes of receptor fibers and of identified auditory interneurons in the CNS of the locusts Locusta migratoria and Schistocerca gregaria after unilateral ablation of one tympanic organ either in the larva or the adult animal.

The effect of azadirachtin on the midgut histology of the locusts, Schistocerca gregaria and Locusta migratoria

The effects of azadirachtin on midgut cells of adult Schistocerca gregaria and Locusta migratoria were investigated by both light and electron microscopy. Pathological effects were seen in both species which could be related to dose and time after treatment. The midgut cells showed a slow necrosis, a rounding up of the cell and swelling of organelles; the nidi were reduced in size and number, the connective tissue beneath the epidermal layer became enlarged with many invading cells/nuclei and the circular and longitudinal muscles become rounded and swollen. The pathological effects were closely linked to a loss of feeding, with injections of 5, 10 and 15 mug/g azadirachtin causing an increasingly rapid onset of the effects associated with an increasingly reduced food intake. At the highest dose, full histopathological effects were seen at 8 hr and death occurred after 3 days. At 1 mug/g, however, the insects showed midgut disruption and reduced feeding by day 3 post-treatment but both feeding and gut pathology had recovered by day 7. At all times, histopathological effects were different from those in starved insects.     

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.     

Immunological evidence for an allatostatin-like neuropeptide in the central nervous system of Schistocerca gregaria,Locusta migratoria and Neobellieria bullata

Methanolic brain extracts of Locusta migratoria inhibit in vitro juvenile hormone biosynthesis in both the locust L. migratoria and the cockroach Diploptera punctata. A polyclonal antibody against allatostatin-5 (AST-5) (dipstatin-2) of this cockroach was used to immunolocalize allatostatin-5-like peptides in the central nervous system of the locusts Schistocerca gregaria and L. migratoria and of the fleshfly Neobellieria bullata. In both locust species, immunoreactivity was found in many cells and axons of the brain-retrocerebral complex, the thoracic and the abdominal ganglia. Strongly immunoreactive cells were stained in the pars lateralis of the brain with axons (NCC II and NCA I) extending to and arborizing in the corpus cardiacum and the corpora allata. Although many neurosecretory cells of the pars intercerebralis project into the corpus cardiacum, only 12 of them were immunoreactive and the nervi corporis cardiaci I (NCC I) and fibers in the nervi corporis allati II (NCA II) connecting the corpora allata to the suboesophageal ganglion remained unstained. S. gregaria and L. migratoria seem to have an allatostatin-like neuropeptide present in axons of the NCC II and the NCA I leading to the corpus cardiacum and the corpora allata. All these data suggest that in locusts allatostatin-like neuropeptides might be involved in controlling the production of juvenile hormone by the corpora allata and, perhaps, some aspects of the functioning of the corpus cardiacum as well. However, when tested in a L. migratoria in-vitro juvenile hormone-biosynthesis assay, allatostatin-5 did not yield an inhibitory or stimulatory effect. There is abundant AST-5 immunoreactivity in cell bodies of the fleshfly N. bullata, but none in the CA-CC complexes. Apparently, factors that are immunologically related to AST-5 do occur in locusts and fleshflies but, the active protion of the peptide required to inhibit JH biosynthesis in locusts is probably different from that of AST-5.     

Spontaneous and neurally evoked contractions of visceral muscles in the oviduct of Locusta migratoria

The oviducts of Locusta migratoria are innervated by a pair of nerves which arise from, the seventh abdominal ganglion. A distinctive network of striated muscle fibres occurs in the oviducts. The lateral oviducts and common oviduct consist of an inner circular layer of muscle and an outer longitudinal layer of muscle. At the junction of the lateral and common oviduct an additional thin longitudinal layer is found adjacent to the basement epithelium. The oviducts contracted spontaneously when isolated from the central nervous system. These myogenic contractions took the form of peristaltic contractions in the lateral oviduct, and intermittent phasic-like contractions of the posterior regions of the lateral oviduct and the common oviduct. These phasic-like contractions were associated with individual complex potentials recorded extracellularly from the muscle fibres. In locusts that had been interrupted in the process of egg laying, there were large-amplitude action potentials, firing in a bursting pattern, in the oviducal nerves. These large action potentials were absent in locusts that had not been egg-laying. These action potentials were associated with both bioelectric potentials and mechanical events in the posterior region of the lateral oviduct and the common oviduct. Electrical stimulation of the oviducal nerve mimicked the effects of spontaneous action potentials, resulting in the appearance of monophasic potentials and contractions. The contractions were graded and dependent upon both frequency and duration of stimulation. It is concluded that the oviducts of Locusta are both myogenic and neurogenic. The role of these contractions in oviposition is discussed.     

Phase polymorphism in Locusta migratoria: the relative effects of geographical strains and albinism on morphometrics

An albino strain, which had originated from Okinawa, Japan, and a normally coloured strain, which had originated from West Africa, have been used to study density‐dependent morphometric phase characteristics and their changes in adults of the migratory locust, Locusta migratoria (L.). By repeated crossings we also obtained congenic albinos and normal phenotypes and investigated their morphometrics with increasing West African genome, eventually reaching 99.6% West African and 0.4% Okinawa gene pool. The data were analysed by the classical morphometric ratios (F/C and E/F; F = length of the hind femur, C = maximum width of the head, E = length of the fore wings), as well as by canonical discriminant (multivariate) analysis. The latter was based on measurements of F, C and E (as above), as well as of M (minimum width of the pronotum) and H (maximum height of the pronontum). Okinawa albinos showed more solitarious morphometrics and a smaller amplitude of morphometric phase change than West African normal phenotypes. Both the morphometric ratios and the canonical discriminant analysis demonstrated clearly that these differences were caused primarily by the strain (Okinawa vs. West African). However, the pigmentation (albino vs. normal colouration) also affected morphometric phase differences; albinos showed more solitarious morphometrics and somewhat more restricted morphometric phase change than congenic normal phenotypes. The effect of the pigmentation was considerably smaller than that of the strain. The results refute Nolte's claim that albino locusts constitute an extreme solitarious phase, even under crowding. However, Nolte's less extreme claim, that albino locusts have more solitarious morphometrics than normally coloured locusts, is validated by the present results.     

Separating food and water deprivation in locusts: effects on the patterns of consumption, locomotion and growth

Abstract. In a factorial experiment, fifth-instar Locusta migratoria (L.) (Orthoptera: Acrididae) were given either dry food (lyophilized grass) and drinking water, food only, water only, or neither food nor water.Food consumption and insect weight were measured daily, and the behaviour of each locust was recorded for 5 h on each of four consecutive days and for 2.5 h on the fifth.Consumption declined progressively in locusts given food only, and those given water only were not observed to drink after the first day of food deprivation.The decline in food consumption on the first day was accounted for by a decrease in the average duration of feeds, which remained constant thereafter.The further decline in consumption over subsequent days was due to a progressive decline in the number of feeds.Although food availability did not slow weight loss relative to locusts given neither food nor water, the availability of water without food did.The proportion of time locomoting increased in all deprivation treatments, but the pattern of change across the five observation days differed markedly between treatments.Locusts given food but no water increased locomotion from 20% of the time budget (the value for controls) to 30% on the first day of deprivation, and by the second day had reached a plateau of approximately 65%.which was maintained until the experiment was terminated on day 5.In contrast, locusts given water but no food approached the 65% level of locomotion on the first day, which was stutistically greater than the 55% observed in those deprived of both food and water.This increase was due both to an increase in the number of locomotion bouts initiated and an increase in the average duration of locomotion bouts.On the second and third days, all deprivation treatments maintained locomotion at around 65%.By day 4, locomotion had decreased to approximately 15% in locusts deprived of both food and water, but not in those deprived of food only or water only.Unlike those given only food, locusts given only water showed a reduction in locomotion of c. 15% on the fifth day.     

Co-localization of the adipokinetic hormones I and II in the same glandular cells and in the same secretory granules of corpus cardiacum of Locusta migratoria and Schistocerca gregaria

Summary The immunocytochemical reactivity of the glandular cells of the corpus cardiacum (CCG-cells) of Locusta migratoria and Schistocerca gregaria was investigated at the electron-microscopic level, using the protein A-gold method, with three antisera against fragments of the adipokinetic hormones AKH I and AKH II. This combination of antisera permitted discrimination between anti-AKH I and anti-AKH II immunoreactivity. Fixation in a mixture of 2% glutaraldehyde and 2% formaldehyde, in combination with low-temperature embedding in Lowicryl K₄M, produced the highest and most consistent selective immunogold labelling of the secretory and ergastoplasmic granules. All secretory granules in all CCG-cells investigated possessed a distinct anti-AKH I-immunopositive reaction, whereas most secretory granules showed a weaker anti-AKH II immunoreaction. Ergastoplasmic granules reacted similar to the secretory granules. The average immunolabelling of the secretory granules was higher in the processes than in the cell bodies of the CCG-cells. The results in Schistocerca gregaria were essentially similar to those in Locusta migratoria. It is concluded that (i) the individual CCG-cells synthesize AKH I as well as AKH II; (ii) these hormones coexist in the same ergastoplasmic and secretory granules; and (iii) these granules contain a higher content of AKH I than AKH II.