Female Locusts Research Articles

The NMDA receptor antagonist MK-801 inhibits vitellogenesis in the flesh fly Neobellieria bullata and in the desert locust Schistocerca gregaria

We found that in the flesh fly Neobellieria bullata, vitellogenesis can be inhibited in a dose-dependent way by two injections of 60μg MK-801/g body mass. In the desert locust Schistocerca gregaria, vitellogenesis can also be fully inhibited but only by repeated injections of 200–400μg/g body mass. In this species, the inhibition can be overruled by coapplication of juvenile hormone. Vitellogenin bands remained visible in electropherograms of hemolymph of MK-801-treated female locusts, but vitellogenin did not accumulate as might be expected when only its uptake by the oocytes, and not its synthesis by the fat body, would be affected. Whether MK-801 acts by inhibiting juvenile hormone synthesis by the corpora allata remains to be investigated.

Disruption of aggregation behaviour of oriental migratory locusts (Locusta migratoria manilensis) infected with Nosema locustae

Abstract: The effect of Nosema locustae infection on the aggregation behaviour of the oriental migratory locust, Locusta migratoria manilensis, was studied using a two‐choice arena olfactometer and electroantennography (EAG). Infected locusts had low antennal sensitivity and aggregation responses to faecal extracts and to locust body volatiles. Infected fifth instar nymphs had significantly lower aggregation index than the uninfected nymphs, although with fourth instars the effect on aggregation behaviour only occurred in infected females. With regard to antennal receptor sensitivity, infected adult locusts had significantly lower EAG amplitudes in response to extracts from faeces of the adult males. The effect was most pronounced in female locusts. In contrast, there was no significant difference in the EAG responses between the fifth instar male and female nymphs. Further analysis revealed that EAG responses of fifth instar nymphs and adults infected with N. locustae to the faecal extract and volatiles from fifth instar solitary‐reared nymphs were not significantly affected. In contrast, infected nymphs and adults had remarkably low EAG amplitudes for the remaining stimuli.

Molecular identification of SGPP-5, a novel pacifastin-like peptide precursor in the desert locust

Recently, a new serine protease inhibitor family has been described in arthropods. Eight members were purified from locusts and 13 peptides have been identified by cDNA cloning. The peptides share a conserved cysteine array ( Cys-Xaa 9–12- Cys-Asn-Xaa- Cys-Xaa- Cys-Xaa 2–3-Gly-Xaa 3–6- Cys-Thr-Xaa 3- Cys) with nine inhibitory domains (PLDs) of the light chain of the crayfish protease inhibitor, pacifastin. A molecular identification of a pacifastin-related precursor (SGPP-5) with three novel PLD-related peptides is presented in this study. This is a first report, identifying the presence of a SGPP-transcript in the brain, fore- and hindgut, including a 100-fold difference in fat body SGPP-transcript level of male as compared with female locust.

Sperm competition

Sperm competition

The influence of diet and feeding state on FMRFamide-related peptides in the gut of Locusta migratoria L.

Gut tissues of 2-week post-ecdysis female Locusta migratoria L. were assayed for FMRFamide-like immunoreactivity (FLI) during various feeding states using both radioimmunoassay and immunohistochemistry. The feeding states investigated were: (a) 48- and 24-h starved; (b) 5-, 30-, or 60-min post-feeding initiation; and (c) a diet of wheat grass, carrots, or apples. We determined: (1) the feeding state of a locust influences FLI in all gut tissues; (2) variations in diet appear to influence FLI in all gut tissues; (3) more than one FMRFamide-related peptide (FaRP) responds to differences in diet and state of starvation in the gut tissues; and (4) the protein poor diets (carrot and apple), in conjunction with the assertion that protein to carbohydrate ratio in the diet is the key component for nutrient balancing, suggests that FaRPs may play a role in maintaining balanced nutrient content in the locust.

Pathways and destination of some male gland secretions in female Locusta migratoria migratorioides (R&F) after insemination.

The white secretions (WS) from the tubules of the male accessory glands (AG) of Locusta migratoria are composed of peptides and proteins. The WS are transferred during mating to the female's spermatheca. They have been followed to their destinations with immunological and radioactive marker techniques. In the spermatheca, peptides are split off from WS-protein complexes, permeate the spermathecal epithelium via glandular cells, enter the hemolymph and attach to other proteins in various target organs such as the dorsal fat body, the preterminal/terminal oocytes, and the follicular cells. In developing eggs, they concentrate at the posterior pole where sperm enters the egg, and in early embryogenesis they are found in the germ band. These results extend the functions of the spermatheca and the role of the male during the reproductive process.

FMRFamide-related peptides in the gut of Locusta migratoria L.: a comprehensive map and developmental profile

The gut tissues and associated nervous system of the African migratory locust, Locusta migratoria, were found to contain FMRFamide-like immunoreactive (FLI) material throughout the five larval instars and 2 weeks into the adult stage in both males and females. FMRFamide-like immunoreactivity associated with the locust gut was described using camera lucida techniques. FMRFamide-like immunoreactivity is observed in the frontal connectives, recurrent nerve, and oesophageal nerves; projections from the ingluvial ganglion onto the anterior midgut, and from the proctodeal nerve onto the hindgut and posterior midgut; in the neuropils of the frontal ganglion, hypocerebral ganglion and ingluvial ganglia; 30 cell bodies in the frontal ganglion; multipolar sensory cells on the foregut; and endocrine-like cells in the gastric caecae and midgut. Radioimmunoassay (RIA) was used to determine the quantities of FLI material in foreguts, gastric caecae, anterior and posterior midguts, and hindgut of first–fifth instar larvae, 1–3- and 14–17-day male and female adult locusts. As expected, as the tissue size (assessed by total protein content) increases, so does the amount of FLI material in each tissue. Normalizing for tissue size reveals significant differences in FLI content among the stages for each tissue tested. Reversed phase-high pressure liquid chromatography (RP-HPLC) followed by RIA has identified four groups of FLI fractions present in the gut, and different members of these groups are present in the various gut tissues.

Isolation and identification of the AKH III precursor-related peptide from Locusta migratoria

We have isolated an 8770 Da peptide from extracts of corpora cardiaca of adult male and female Locusta migratoria. The N-terminal amino-acid sequence as partially established by Edman degradation is Ala–Leu–Gly–Ala–Pro–Ala–Ala–Gly–Asp. These nine amino acids correspond to the first nine N-terminal amino acids of the adipokinetic hormone precursor-related peptide γ-chain (APRP-γ), a peptide that is predicted from the gene encoding the adipokinetic hormone III precursor. The APRP-γ chain has a monoisotopic mass of 4387 Da and contains two cysteine residues. It is known that both AKH I and AKH II precursors occur as dimers. After processing they give rise to the active hormones and three dimeric (two homodimers and one heterodimer) adipokinetic hormone precursor related peptides (APRPs). Based on the mass of 8770 Da and the established N-terminal sequence tag, we conclude that the isolated peptide is a homodimer consisting of two APRP-γ units, covalently linked to each other by two disulphide bounds. In analogy with the previous identified APRPs (APRP-1, APRP-2, and APRP-3), this APRP will be designated as APRP-4.

A locust DNA-binding protein involved in gene regulation by juvenile hormone

Although juvenile hormone (JH) has essential roles in insect development and reproduction, the molecular mechanisms of gene regulation by JH remain an enigma. In Locusta migratoria, the partially palindromic 15-nt sequence, GAGGTTCGAG A/ TCCT T/ C, found upstream of a JH-induced gene, jhp21, was designated as a putative juvenile hormone response element (JHRE). When JH-deprived adult female locusts were treated with the active JH analog, methoprene, a fat body nuclear factor that bound specifically to JHRE appeared after 24 h. Binding exhibited a preference for an inverted repeat with GAGGTTC in the left half-site, a single nucleotide spacer, and a right half-site in which some variation is acceptable. Binding to JHRE was abolished by phosphorylation catalyzed by a C-type protein kinase present in the nuclear extracts. The DNA-binding protein is thus believed to be a transcription factor, which is brought to an active state through the action of JH and then participates in the regulation of certain JH-dependent genes.

Evidence for a compound in Comstock-Kellog glands modulating premating behavior in male desert locust, Schistocerca gregaria.

The Comstock-Kellog glands in adult females of certain acridid species, including the desert locust, Schistocerca gregaria have been implicated as a source of volatiles that play a role in mating behavior. A dichloromethane extract of the glands was analyzed for metabolites by gas chromatography, coupled gas chromatography-electroantennographic detection, and mass spectrometry. Coupled gas chromatography-electroantennographic detector (GC-EAD) analysis revealed a component that elicited an electroantennogram response from the antenna of adult male S. gregaria. The compound was identified by GC-MS as pentanoic acid. The levels of the compound in the gland extract varied with age of female locust; it was present in detectable amounts only in 14- to 16-day-old females. In bioassays, pentanoic acid significantly stimulated pre-mating behavior in male desert locust. These results are discussed in relation to the biology of the locust.

Maturation of muscle properties and its hormonal control in an adult insect.

The oviposition of female locusts requires longitudinal muscles to tolerate remarkable lengthening. Whether this ability together with concomitant properties develops during maturation or is present throughout life was investigated. The properties of the locust abdominal muscles involved in oviposition behaviour were investigated with respect to their maturation, segment- and gender-specificity and regulation by juvenile hormone (JH). Muscles from the sixth abdominal segment (an oviposition segment) of mature females (>18 days old) were able to tolerate large extensions (>8 mm). At this length, muscles were still able to generate considerable neurally evoked twitch tension. In contrast, muscle fibres from females less than 5 days old did not tolerate extension of more than 4 mm. At this length, tension generation was negligible. The maximum tension generated at different stimulus frequencies was significantly higher in muscles of females more than 18 days old than in females less than 5 days old. Furthermore, the cross-sectional area of muscle fibres increased significantly during reproductive development. Current-clamp recordings from denervated muscle fibres of females more than 18 days old revealed their ability to generate overshooting action potentials. The potentials were tetrodotoxin (TTX)-insensitive (0.5 micromol l(-1) TTX), but were blocked by Cd(2+) (50 micromol l(-1)) or nifedipine (50 micromol l(-1)), which suggests the involvement of L-type Ca(2+) channels. Action potentials recorded from females less than 5 days old differed considerably in amplitude and shape from those recorded from females more than 18 days old, suggesting their maturation during the first 2 weeks of adult life. Inactivation of the corpora allata (CA) by precocene inhibited the maturation of these muscle properties, whereas injection of JH into precocene-treated females reversed this effect. Homologous muscles from the third abdominal segment (a non-oviposition segment, M169) and muscles from males (M214) revealed no comparable changes, although some minor changes occurred during reproductive development. The results suggest a gender- and segment-specific maturation of muscle properties that is related to reproductive behaviour and controlled by JH.

Analysis of Release and Role of Benzyl Cyanide in Male Desert Locusts, Schistocerca gregaria

Volatiles emanating from living Schistocerca gregaria at various stages of development were trapped by means of a closed-loop-stripping system. Benzyl cyanide was previously identified with GC-MS methods as a volatile that was exclusively released by adult mature gregarious males. The amount of BC released depended on the number of males per group. Mature female locusts did not stimulate the release of benzyl cyanide in gregarious males. After physical isolation of previously grouped males, a steady reduction in benzyl cyanide release was observed. After regrouping the isolated males, BC emission was restored. In olfactometer bioassays, benzyl cyanide had a strong repellent effect on gregarious mature males but only a weak one on immature males. The possible origin and role of benzyl cyanide in sexual behavior are discussed.

Changing Oviposition Preferences of the Desert Locust, Schistocerca gregaria, Suggest a Strong Species Predisposition for Gregarization

Field surveys at five sites within desert locust breeding habitats around Port Sudan during three successive seasons indicated that early in the rainy season the incoming solitary females oviposited predominantly in the vicinity of Heliotropium spp. (∼66%) and millet (∼32%) seedlings. Solitary nymphs also preferred to feed on these plants. Follow-up cage experiments were conducted in the field in which solitary and gregarious female locusts were presented with choices of selected desert plants and egg pods. When presented with bulrush millet, Heliotropium spp., Zygophyllum simplex, and untreated moistened sand, solitary females oviposited adjacent to the first two plants (40% and 60%, respectively). However, when offered a choice of either or both of these plants together with egg pods derived from gregarious and/or solitary insects, solitary females showed a significantly higher preference for ovipositing near gregaria egg pods than near the plants, with solitaria egg pods eliciting the least response. In contrast with solitary females and in the absence of gregaria egg pods, gregarious females preferred to oviposit in untreated moist (control) sand (74–77%) away from the plants (6–14%) or solitaria egg pods (∼4%). However, when present, gregaria egg pods elicited significantly more oviposition. These and previous results indicate a hierarchy of phase-dependent oviposition preferences in the desert locust and are interpreted in terms of a strong propensity of the species to exploit opportunities under appropriate conditions to facilitate congregation and the gregarization of the progeny.

A behavioural analysis of phase change in the desert locust

ABSTRACTA programme of research into phase change in the desert locust,Schistocerca gregaria, is described. The ability to change phase between solitarious and gregarious forms in response to population density is a key feature of locusts and is central to their occasional yet catastrophic impact on humans. Phase polymorphism is an extreme form of phenotypic plasticity. The most labile phase characteristic is behaviour. It is argued that a fully integrated study of behavioural phase change provides a powerful tool for understanding both the mechanisms of phase change and locust population dynamics, both of which offer possibilities for improved management and control of desert locust plagues. An assay for measuring behavioural phase‐state in individual locusts was derived, based on logistic regression analysis. Experiments are described that used the assay to quantify the time‐course of behavioural change, both within the life of individual locusts and across generations. The locust‐related stimuli that provoke behavioural gregarization were investigated. Complex interactions were found between tactile, visual and olfactory stimuli, with the former exerting the strongest effect. Behavioural analysis also directed a study of the mechanisms whereby adult females exert an epigenetic influence over the phase‐state of their developing offspring. Female locusts use their experience of the extent and recency of being crowded to predict the probability that their offspring will emerge into a high‐density population, and alter the development of their embryos accordingly through a gregarizing agent added to the foam that surrounds the eggs at laying. There is also a less pronounced paternal influence on hatchling phase‐state. An understanding of the time‐course of behavioural phase change led to a study of the effect of the fine‐scale distribution of resources in the environment on interactions between individual locusts, and hence on phase change. This, in turn, stimulated an exploration of the implications of individual behavioural phase change for population dynamics. Cellular automata models were derived that explore the relationships between population density, density of food resources and the distribution of resources in the environment. The results of the simulation showed how the extent of gregarization within a population increases with rising population size relative to food abundance and increasing concentration of food resources. Of particular interest was the emergence of critical zones across particular combinations of resource abundance, resource distribution and population size, where a solitarious population would rapidly gregarize. The model provided the basis for further laboratory and field experiments, which are described.

The role of internal pressure and muscle activation during locust oviposition

The oviposition of female locusts is a complex behaviour that includes a dramatic extension of the abdomen. The role of internal pressure during oviposition was investigated by monitoring the intra-tracheal pressure and the activity of selected longitudinal muscles, while movements of the abdomen were visualised with a video imaging system. Locust oviposition consists of a sequence of four distinct phases: (i) probing the substrate and digging without elongation of the abdomen, (ii) longitudinal extension of the abdomen up to four times its normal length, (iii) laying packages of eggs while (iv) gradually withdrawing the abdomen. During extension, neurograms and myograms of selected longitudinal muscles revealed a decreased level of activity. When the abdomen retracted to its normal length, muscle activity re-appeared. In phases two and three, rising internal pressure prevented the abdomen from slipping back when the valves released their lateral grip from the substrate. Locking the genital segments in the hole by relative bending kept the abdomen in place when producing foam or laying eggs. Intra-abdominal pressure, therefore, is not the main cause of abdominal extension, but rather maintains extension when no mechanical locking in the hole prevents the abdomen from elastic retraction.

Influence of Host Plant Damage on the Host-Finding Behavior ofMamestra brassicae(Lepidoptera: Noctuidae)

The influence of interspecific, intraspecific insect infestation, and mechanical damage of 3 host plant species on the attraction, landing, and oviposition of Mamestra brassicae (L.) was studied in a wind tunnel. The presence of aphids did not affect the attraction, landing, or oviposition of mated females. However, when plants damaged by female locusts were used it was found that M. brassicae females were significantly attracted/landed and oviposited more often on the damaged plants than on undamaged cabbage plants. Mated females oriented significantly more often to cabbage plants damaged by conspecific larvae, compared with undamaged plants. Also, these females oviposited more on damaged plants than on control plants. When the damage was increased (from 20 to 80%), the females laid more on damaged plants, but the difference with respect to undamaged plants was not significant. When chrysanthemum plants damaged by M. brassicae larvae were used, mated females did not show any difference in attraction, landing, and oviposition between damaged or control plants. The females were initially attracted/landed and oviposited significantly more often on mechanically damaged cabbage plants, compared with undamaged plants. However, when mechanically damaged tomato plants were used, the mated females did not show any difference in the 1st attraction to damaged and undamaged tomato plants. But, these same females oviposited significantly more on undamaged plants than on damaged tomato plants.

Cloning of the cDNA encoding Scg-SPRP, an unusual Ser-protease-related protein from vitellogenic female desert locusts ( Schistocerca gregaria)

The cDNA coding for a Ser-protease-related protein ( Scg-SPRP) 1 The cDNA sequence encoding Scg-SPRP was submitted to the EMBL-database and received the accession number Y09607. 1 was cloned from desert locust ( Schistocerca gregaria) midgut. The derived amino acid sequence consists of 260 residues and shows strong sequence similarity to insect trypsin-like molecules. It is, however, likely that Scg-SPRP is not a proteolytically active enzyme and that it plays another physiologically relevant role, since two out of three residues which are indispensable for catalytic activity of Ser-proteases are replaced. Northern analysis revealed that the Scg-SPRP gene is expressed in midgut tissue and that this expression is strongly induced in adult female locusts. Moreover, the occurrence of the transcript (1.2 kb) fluctuates during the molting cycle and during the female reproductive cycle. Juvenile hormone (JH III) dependence of transcription was investigated by chemical allatectomy (precocene I) of adult females. This resulted in inhibition of vitellogenesis and in disappearance of the Scg-SPRP transcript. Expression of Scg-SPRP in precocene-treated locusts could be reinduced by additional treatment with JH III or with 20-OH-ecdysone.

Cuticular Hydrocarbons of the Australian Plague Locust, Chortoicetes terminifera (Walker) (Orthoptera: Acrididae), Collected from Widely Separated Geographical Locations

ABSTRACTCuticular hydrocarbon profiles were obtained for adult Chortoicetes terminifera collected from Bimerah in Queensland, Hillston and Boorowa in New South Wales, and Moora in Western Australia. No significant differences were found between male and female locusts from Bimerah, nor between males from any of the four different geographical locations.

Detection of vitellogenin in the haemolymph of larval female locusts (Locusta migratoria) treated with the neurohormone, Lom OMP

The ovary maturating parsin of Locusta migratoria (Lom OMP) is a gonadotropic neurohormone which is active during vitellogenesis over the same period as juvenile hormone (JH). For this reason, a possible vitellogenic effect of the Lom OMP was tested using fifth instar larvae. At this last larval stadium, locusts do not normally produce vitellogenin but the synthesis of vitellogenin can be induced at this time by high doses of JH analogues. Since vitellogenin is rapidly released into the haemolymph, the synthesis of vitellogenin was investigated by detecting the occurrence of vitellogenin in the haemolymph, using SDS-PAGE. The neurohormone Lom OMP was able to induce vitellogenin synthesis in females but not in males. The maximally efficient dose-range was narrow. The timing of vitellogenin occurrence was delayed as compared to that obtained with JH. The Lom OMP inducibility, evaluated by the number of responsive females, was lower than that obtained with JH provided by the implantation of a single corpus allatum. In allatectomized females, the Lom OMP inducibility was not suppressed but, on the contrary, increased. The gonadotropic activity of the Lom OMP thus acts through a vitellogenic effect similar to the gonadotropic activity of JH but the mode of action of Lom OMP is different to and independent of that of JH.

Accumulation and egestion of dietary copper and cadmium by the grasshopper Locusta migratoria R & F (Orthoptera: Acrididae)

Copper and cadmium budgets were studied for a model insect herbivore/host plant system comprising the oligophagous leaf-chewing grasshopper ( Locusta migratoria) feeding on Zea mays (Gramineae). Fifth instar larvae were fed, for between 5 and 20 days, on maize foliage contaminated with either copper, cadmium or on control foliage containing no excess metal. Male and female locusts fed on copper-treated maize retained 45 and 42% of ingested copper respectively, figures not significantly different from the 41 and 33% retained on untreated maize. Remaining copper was egested with the faeces. Locusts fed on copper-treated maize showed an increase of 27% in body copper burden compared with those on the control diet: the increase was independent of time on the diet. Female locusts retained 33% and males 21% of ingested cadmium. Faecal cadmium levels were elevated, and accumulation in both sexes was proportional to time on the Cd-enriched diet. For both copper and cadmium, some ingested metal probably passed directly through the locust gut, bound to undigested food material. Results suggest that grasshoppers may effectively regulate excess dietary copper, but are unable efficiently to regulate cadmium.