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.     

Social aggregation of adult Schistocerca gregaria and Locusta migratoria migratorioides in relation to the final moult and ageing

Laboratory experiments, were carried out on nymphs and adults of the desert locust, Schistocerca gregaria, and the African migratory locust, Locusta migratoria migratorioides, in view of the field observation that locusts become temporarily less gregarious after the final moult. The experiments showed no reduction in grouping after the final moult but did show a reduction in grouping in mature Schistocerca. There was little change in the numbers of locusts found in small groups but a dramatic reduction in the number found in large groups.     

Occurrence and genetics of black‐eyed migratory locusts,Locusta migratoria (Orthoptera: Acrididae)

Black‐eyed Locusta migratoria appeared in albino locusts as a result of crossing between a short‐winged strain originating from Tsushima Island, Japan, and an albino strain originating from Okinawa Island. The black eye trait was recessive to the white eye trait because the crosses between black‐ and white‐eyed albino locusts produced only individuals with white eyes in the F₁ generation. In the F₂ generation, black‐ and white‐eyed individuals appeared in a ratio of 1:3, indicating that the black eye trait was controlled by a simple Mendelian unit. The black eye trait showed no genetic association with other traits including wing morph, adult body dimensions and classical morphometric ratios such as hind femur length / head width and forewing length / hind femur length.     

The dark-colour-inducing neurohormone of locusts: strain-dependent and phase-independent effects on adults of the migratory locust, Locusta migratoria

Abstract.  An albino strain that had originated from Okinawa, Japan, and a normally coloured strain that had originated from West Africa, were used to study the darkening response to injection of graded doses of dark-colour-inducing neurohormone of locusts (DCIN) ([His⁷]-corazonin) of gregarious and solitarious adults of the migratory locust, Locusta migratoria (L.). By repeated crossings, congenic albinos and normal phenotypes were obtained, both with a 99.6% West African genome, and their darkening response was compared with the original Okinawa and West African strains. Within each of these four strains, no difference was found in DCIN-induced darkening between gregarious and solitarious adults despite previous publications in the literature claiming an absence of 'fire-darkening' in gregarious adults of this species. Okinawa albino adults showed a markedly higher darkening response than the other three strains, including albinos with a 99.6% West African genome. This finding demonstrates that the differential darkening response of the Okinawa albinos is caused not by albinism, but by the geographical origin (Okinawa) of the strain. This is the first report of geographical-strain-dependent differences in the response of an insect to a neurohormone. The darkening response of adults reached a maximum on day 10 after injection; subsequently, the dark colour faded slowly. Adults injected 1 day after their moult showed a greater darkening response than those injected after 14 or 28 days.     

Mass spectrometric evidence for the deficiency in the dark-color-inducing hormone,.

A factor present in the brain and corpus cardiacum responsible for the induction of dark colour in Locusta migratoria was recently isolated and identified from the corpora cardiaca of normally pigmented locusts. The purification of this factor, designated as [His7]-corazonin was monitored using an albino mutant from a laboratory colony of an Okinawa (Japan) strain. In this study, we provide unequivocal mass spectrometric evidence that the brain and the corpora cardiaca of this albino Locusta mutant are deficient in [His7]-corazonin. Previously, [His7]-corazonin was shown to be responsible for the induction of dark body colour patterns as observed in crowded locusts. Using nanoflow-liquid chromatography-mass spectrometry, we demonstrated that this dark colour-inducing hormone is, however, present in the corpora cardiaca of solitary locusts (Schistocerca gregaria). Arch.     

A comparison of phase-related shifts in behavior and morphometrics of an albino strain,deficient in [His(7)]-corazonin,and a normally colored Locusta migratoria strain

The albino Okinawa strain of Locusta migratoria is deficient in the neurohormone [His⁷]-corazonin. This peptide induces darkening of the cuticle, one of the typical features of gregarious locusts. As part of a broader study on the possible role of [His⁷]-corazonin in phase transition, we explored whether corazonin-deficiency might be associated with differences in behavior and morphometrics between albino and normal phenotypes of L. migratoria. Using a modification of the logistic-regression assay of behavioral phase state previously derived for Schistocerca gregaria, we found that there were strain dependent behavioral differences between crowd-reared nymphs of the albino Okinawa and the normally colored African strain, with no evidence of the albino strain being obligatorily solitarious. However, upon isolation, a shift towards more solitarious behavior occurs in both strains, even more profoundly in the Okinawa albinos. A shift could also be recorded in morphometrics. The conclusion is that the albino strain, although showing some solitarious features even when crowd-reared, is not, as has been suggested, obligatory solitarious and, as a consequence, the complete absence of corazonin is not sufficient to bring about the solitarious state.     

Endocrine mechanisms controlling body-color polymorphism in locusts.

The present article reviews recent published and unpublished findings on the hormonal mechanisms for the control of body-color polymorphism in locusts. Emphasis is placed on the dark color-inducing factors and their role in the induction of various types of body coloration observed under different environmental conditions. Implantation of corpora cardiaca (CC) taken from normal nymphs of Locusta migratoria induced dark color in nymphs of an albino strain. Using the albino strain for the bioassay, a neuropeptide, [His7]-corazonin, was identified as a dark color-inducing factor for L. migratoria and Schistocerca gregaria. In the former, depending upon the dose and timing of the injection, this peptide and juvenile hormone developed various body colors looking like those found in nature. The body coloration characteristic of gregarious forms was also induced in isolated albino nymphs and field-collected solitary nymphs. In S. gregaria, on the other hand, the peptide induced black patterns, but the orange or yellow background color observed in gregarious forms was not induced when the peptide was injected into solitary individuals. [His7]-corazonin also induced darkening in other grasshoppers and locusts, but not in katydids. Albino L. migratoria developed dark color when implanted with brains or CC taken from other insects belonging to 10 major insect orders, but not with those from Coleoptera. [His7]-corazonin or a similar compound is widespread among insects and plays a pivotal role in controlling body color in some species and presumably other physiological roles in other species. Arch.     

Identification of

The neuropeptides inducing dark color in albino nymphs of the migratory locust Locusta migratoria were isolated from the larval brain of the silkworm, Bombyx mori and from the adult corpora cardiaca (CC) of the cricket Gryllus bimaculatus, respectively, and their amino acid sequences identified. The two peptides isolated from the two different species are identical to [Arg(7)] corazonin, a neuropeptide known to be present in a cockroach and others. This peptide induces a dark color in albino nymphs of L. migratoria at fmol levels, and a high dose of >/=100 pmol caused albino locusts to turn completely black, but it influenced neither body color nor metamorphosis in B. mori and G. bimaculatus. Therefore, the physiological functions of [Arg(7)] corazonin in the silkworm and the cricket remain unknown. The present study demonstrated the usefulness of the albino strain of L. mirgatoria as a specific bioassay system for this peptide.     

Social determinants of aggregation behaviour in adults of the desert locust

The social aggregation behaviour of adults of the desert locust Schistocerca gregaria, was found to be determined by rearing density, in the same way but not to the same extent as that of nymphs. Adult locusts reared crowded since hatching showed more social grouping than adults reared in isolation. For adults, the least amount of grouping was shown by isolates, F₁ of solitaria caught in the field. Both nymphs and adults were found to be attracted to the edge of the testing arena in inverse proportion to their attraction to each other. This edge effect could be used as one behavioural measure of phase polymorphism complimentary to the measure of social aggregation. Unlike nymphs, adults did not rapidly learn to group when forced into contact with one another. Grouping of isolated adults was not found to change with age.     

地灵组培白化苗的超微结构变化研究

应用超薄切片和电镜观察了唇形科水苏属植物地灵组培白化苗和正常苗叶片的超微结构。结果表明：在超微结构上,白化苗与正常苗叶片细胞具有明显差异。多数白化苗细胞中胞质含量稀少,叶绿体数量较少,叶绿体的形态变化较大,极少数为正常形态,多数呈部分解体状态,还有部：分叶绿体呈现膜融合状态。而细胞壁、细胞核以及细胞形态等结构,白化苗与正常苗细胞并无大的差异。     

The chiasma-inducing pheromone of locusts

To the two quantitative criteria for phase transformation of locusts, viz. nymphal colour and adult morphometric ratios, the change in chiasma frequencies during meiosis in the male can now be added: gregarization or swarming induces an increase in chiasma formation. The atmosphere around crowded locusts contains a pheromone which is absorbed and causes a reactive haemolymph in locust hoppers. This haemolymph may be injected into solitarious hoppers or nymphs to induce increased chiasma formation. Certain solvents like risella oil and dimethyl sulphoxide will extract the pheromone from such an atmosphere, and bio-assays with these extracts have been demonstrated to be chiasma-inducing. Such extracts are, however, not chiasma-inducing in the albino mutant, but the haemolymph from crowded normal-coloured hoppers is reactive in the albino hopper. In addition the albino mutant is solitaria-like in both morphometric ratios and chiasma frequencies. These data indicate a relationship between the melanization cycle and chiasma induction: the previously postulated melanin-inducing pheromone and this chiasma-inducing pheromone are probably identical. On the other hand, this pheromone of nymphs and the sex-maturation pheromone of adults are not identical, although the latter may be a modified form of the other. The effect of the nymphal pheromone on adult morphometric ratios is not clear although some correlation has been shown to exist between raised chiasma frequencies in treated solitaries and advances towards gregaria ratios. It may be that in this pheromone we have, what may be called, a gregarizing principle.     

Allatectomy and flight performance in maleLocusta migratoria

Summary Flight performance in locusts is a function of age, with its peak value at 18 days after emergence. While allatectomy retards the normal development of flight capability, it also has the effect of slowing down the decline in flight performance characteristic of operated control locusts as they age. Periodic topical application of synthetic juvenile hormone remedies the initial effect of allatectomy but its effectiveness wears off with age. The period of optimum flight performance is prolonged in locusts allatectomised when mature.A characteristic features of the flight pattern of immature-allatectomised and matureallatectomised locusts when flown about one week after the operation is a rapid decline in flight speed during the first 20 minutes of flight. Eventually, as the allatectomised locusts age, they assume the flight pattern of normal locusts and subsequent differences in flight performance between operated and normal locusts are confined to differences in flight intensity.Allatectomy has no marked effect on the preflight haemolymph total lipid and carbohydrate levels, the mobilisation of lipid and the amount of carbohydrate depleted. The quantity of lipid mobilised is, however, related to flight performance in both allatectomised and operated control locusts. Locusts which fly faster mobilise more lipid. The lipids mobilised by the adipokinetic hormone are 1618; 1818 and 1616 diglycerides in order of abundance. Allatectomy has no effect on the nature of these diglycerides released during flight.     

Albino corpus cardiacum extracts induce morphometric gregarization in isolated albino locusts, Locusta migratoria, that are deficient in corazonin

Abstract.  The neuropeptide [His⁷]-corazonin, present in the central nervous system and corpus cardiacum, is known to mimic a 'gregarizing' effect on phase-related morphometric ratios (hind femur length/maximum head width and fore wing length/hind femur length) when injected into locusts reared in isolation. However, an albino strain is known to exhibit phase-specific changes in these ratios in response to rearing density, although it is deficient in [His⁷]-corazonin. To examine whether there is a second factor responsible for this phenomenon, perhaps a corazonin-like factor that has lost its dark-colour inducing activity, methanol extracts of corpora cardiaca taken from crowd-reared albino nymphs of Locusta migratoria are injected into isolated-reared second-stadium albino nymphs and reared to adults in isolation. The hind femur length/maximum head width and fore wing length/hind femur length ratios are significantly different from those of control oil-injected counterparts, and shift significantly towards the values typical for crowd-reared gregarized individuals. The results indicate that the corpora cardiaca contain a factor similar to [His⁷]-corazonin, although it has no dark-colour inducing activity.     

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.     

Effects of isolation and crowding on the haemolymph pigment composition of the desert locust, Schistocerca gregaria (Orth., Acrididae)

Abstract:  An experimental study on the effect of isolation and crowding of the desert locust, Schistocerca gregaria (Forskål) on haemolymph pigment composition (as measured by absorbance ratios at 460 and 680 nm) was carried out at the International Centre of Insect Physiology and Ecology, Nairobi. The results showed that haemolymph absorbance ratios of gregarious and solitarious locusts were different (P < 0.05) and that there was no phase-specific sex differentiation with regard to this measure (P < 0.05). The haemolymph pigment composition changes during isolation and grouping showed contrasting trends. It changed rapidly in nymphs, but slowly and erratically in adults both resulting from isolation and grouping at hopper stage. Significant shifts in locust phase status were recorded in both situations in nymphs in F₀ generation, and in the adults by the end of the F₂ and F₃ generations of solitary and gregarious conditions, respectively. Shifting of fledglings did not induce significant changes in their mean absorbance ratios in both situations, i.e. isolation and crowding within F₀ generation. The ratio of length of posterior femur (F) to greatest width of the head capsule (C) changed either at a similar rate or more often slower than the haemolymph pigment ratio and both required more than a generation to transform fully. The study has shown that haemolymph pigment composition could be a suitable measure for monitoring phase changes at nymphal stages of the desert locust.     

The role of the glandular lobes of the corpora cardiaca during flight in Locusta

ABSTRACT. Flight performance in Locusta is reduced following severance of the major afferent nerves to the corpora cardiaca or removal of the glandular lobes of the corpora cardiaca. These operations prevent the release of adipokinetic hormone and the consequent mobilization of stored lipid. However, locusts deprived of about 90% of their glandular lobe tissue, while flying poorly, did mobilize lipid. It is suggested that the remaining glandular parenchyma cells are capable of secreting enough hormone to stimulate lipid mobilization, but that the concentration may be inadequate to encourage lipid utilization. After removal of all the glandular lobe parenchyma, the blood carbohydrate concentration was temporarily depressed. Nevertheless flight performance was equally poor, both when haemolymph carbohydrate levels were low and when they had returned to normal. After the injection of trehalose into operated control locusts and locusts deprived of their glandular lobes, flight was still markedly poorer in the operated insects, even though the injection of trehalose prevented adipokinetic hormone release in the intact locust. It seems that the poor flight performance of locusts deprived of their glandular lobes cannot be fully explained by the simple absence of adipokinetic hormone.     

Effects of flight training on flight speed and substrate utilization in locusts

ABSTRACT. Regular flight exercise of adult male Locusta migratoria migratorioides (R and F) accelerated the development of maximum flight speed and disrupted the development of the typical pattern of change of flight speed exhibited when normal (untrained) adult male laboratory locusts are flown on roundabouts. Thus, while untrained mature locusts fly fast initially and then slow to a steady cruising speed after 20 min, trained locusts flew at a relatively constant speed throughout a 60-min test period. Flight training also led to a marked reduction in the size of the fat body and the flight muscles, but flight muscle ultrastructural development was not affected. Regular flight exercise had no long-term effect on haemolymph carbohydrate concentration but lipid levels were significantly depressed.     

Structure-activity relations of the dark-colour-inducing neurohormone of locusts

The dark-colour-inducing effect of several peptides in comparison to that of the dark-colour-inducing neurohormone (DCIN, [His(7)]-corazonin) of locusts was investigated by a bioassay based on nymphs of a DCIN-deficient albino mutant of Locusta migratoria. The study was aimed at elucidating the active part of the DCIN and to explore the contribution of its amino acids to the activity. Graded doses of all peptides were injected in oil. [Arg(7)]-corazonin and DCIN were equally effective. Certain arthropod neuropeptides having the -SXGW- partial sequence (a part of the DCIN and of [Arg(7)]-corazonin; X=His and X=Arg, respectively) yielded the following findings: Scg-AKH-II (adipokinetic hormone II of Schistocerca gregaria X=Thr), Grb-AKH ( adipokinetic hormone of Gryllus bimaculatus X=Thr) and RPCH (red pigment concentrating hormone of crustaceans X=Pro) evoked a moderate darkening response, but Lom-AKH-II (adipokinetic hormone II of L. migratoria X=Ala) was ineffective. Step by step shortening of the sequence of the DCIN at the N-terminal, from pGlu-3-11DCIN to pGlu-9-11DCIN, resulted in a decreasing activity, but even pGlu-9-11DCIN induced a weak response with high doses. Shortening of the DCIN from the C-terminal revealed a moderate activity of 1-7DCIN-NH(2) and a weak activity of 1-5DCIN-NH(2). An octadecapeptide which induces dark colour in moth larvae, having the pentamer FTPRL-NH(2) at its C-terminal, evoked no darkening in the albino locusts. We conclude that although the -SXGW- partial sequence has some role in induction of darkening, for obtaining maximal effect the whole sequence of the DCIN (or of [Arg(7)]-corazonin) is necessary.     

Flight fuel related differences between solitary and gregarious locusts (Locusta migratoria migratorioides)

Abstract. Flight fuel relations of crowded and isolated Locusta migratoria migratorioides were investigated in younger (12–16 days after fledging) and older (27–30 or 27–32 days after fledging) adult males.No phase polymorphism dependent differences were found in resting haemolymph carbohydrate levels of the younger locusts.In the older age group, resting haemolymph carbohydrate levels were slightly though significantly higher in the isolated than in the crowded locusts.Injection of various doses of synthetic adipokinetic hormones (AKHs) did not induce marked changes in haemolymph carbohydrate levels and no differences were found between crowded and isolated locusts.A 30 min flight led to the same decrease in haemolymph carbohydrate levels of isolated and crowded locusts, 43.3% and 44.6% of the resting levels, respectively.We concluded, therefore, that the results do not seem to indicate that isolated locusts rely more heavily on carbohydrates as flight fuel than crowded locusts.Hyperlipaemic responses to flight were less intense in isolated than in crowded locusts, but phase polymorphism dependent differences in flight-induced increase of haemolymph lipid levels were not parallel in 12–16-day-old and 27–32-day-old males.In the younger age group the difference was mainly in the duration of flight needed to induce full response which appeared already after 20 min of flight in the crowded locusts, but only after 45 or 60 min of flight in the isolated ones.In contrast, the older isolated locusts showed markedly lower haemolymph lipid elevations than the crowded locusts even after 30, 45 or 60 min of flight.The hypothesis is forwarded that isolated locusts have a rather coarse adipokinetic strategy focused on a single long-distance migratory flight, whereas gregarious locusts possess a fine adipokinetic balance for reiterative migratory flights and saving fuel reserves for unpredictable long-distance migrations.     

Effect of phase status on responses to AKHI in the desert locust,Schistocerca gregaria gregaria

Hyperlipaemic response to adipokinetic hormone (AKH I) was demonstrated in both solitary and gregarious phases of the desert locust, Schistocerca gregaria gregaria. Time-course studies showed that the gregarious locusts had a faster response to the hormone than their solitary counterparts. At peak response time (90 min), the gregarious locusts were more sensitive to AKH I doses below 2 pmol while the solitary locusts had a higher response above this dose. Upon injection of the hormone, lipoprotein conversion occurred, resulting in the formation of the low density lipoprotein (LDLp). The LDLp formed in the gregarious locusts was much larger than that of the solitary locusts. The fat body lipid reserve (expressed as % fat body dry weight) was significantly (P < 0.01) higher in the gregarious (79.02 ± 2.77%) than in the solitary locusts (65.23 ± 2.55%). Triacylglycerol was the major lipid class representing 83.9 and 73.9% of the total lipids in gregarious and solitary locusts, respectively. The higher fat body lipid reserves and efficient LDLp formation in response to AKH in gregarious locusts compared to solitary locusts suggests a physiological adaptation for prolonged flights. © 1996 Wiley-Liss, Inc.