Effect of Paranosema (Nosema) locustae (Microsporidia) on morphological phase transformation of Locusta migratoria manilensis (Orthoptera: Acrididae)

Field and laboratory studies demonstrated that Paranosema (Nosema) locustae had significant effects on the morphological phase transformation of Locusta migratoria manilensis (Meyen 1835). In the field, spraying P. locustae on gregarious locusts caused a substantial population reduction by 16 days after treatment, with most of the surviving locusts being phase solitaria. However, the effects of P. locustae on locust phase transformation began before direct mortality had caused a substantial reduction in locust density: locust numbers were still high at day 10, but locusts had already transformed to phase transiens. Laboratory assays showed that while a low dose of P. locustae had no effect on phase transformation, at a higher dose of 1×10⁵ spores/mL, locusts had F/C ratios that were significantly (P<0.05) more solitaria than untreated locusts, with locusts having ratios that were either phase solitaria or on the solitaria side of phase transiens. In a second laboratory experiment that analysed the effects of locust density on phase transformation by P. locustae, there was no obvious effect of density on female locusts 10 days later as all were solitaria at all locust densities. At day 16, female locusts were transiens at higher densities, but were solitaria at 4/cage. With males there were lesser effects. These results provide new evidence for P. locustae having sub-lethal effects on locust phase transformation at a wide range of locust densities.     

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.     

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).     

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.     

“Dark cheeks,” a lethal disease of locusts provoked by a lepidopterous baculovirus

The virus causing nuclear polyhedrosis in Spodoptera littoralis (SINPV-type B) could be cross-transmitted perorally to and from two species of locusts, namely the African migratory locust (Locusta migratoria migratorioides) and the desert locust (Schistocerca gregaria). The virus provokes a lethal disease in locusts which was named “dark cheeks.” The progeny viral DNA replicating in the infected locust hoppers was submitted to restriction endonuclease analysis and was found to be identical with the inoculated parental DNA deriving from SINPV-infected S. littoralis caterpillars. Hence the conclusion that an NPV of a lepidopteran host has for the first time been shown to cross-infect and propagate in members of the hemimetabolous order Orthoptera.     

The primary structure of an endocuticular protein from two locust species,Locusta migratoria and Schistocerca gregaria,determined by a combination of mass spectrometry and automatic Edman degradation

The complete primary structures of two variants of a protein, Abd-5, isolated from the endocuticles of the migratory locust Locusta migratoria and the desert locust Schistocerca gregaria, have been determined. The proteins from the two species are N-terminally blocked with pyroglutamic acid. Their sequences differed only in two positions. Comparison of the sequences to those of other cuticular proteins shows that moderate homologies exist to 11 other cuticular proteins from insects representing four different orders. Amino acid residues in certain positions appear to be strictly conserved.     

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.     

Surface spreading of synaptonemal complexes in locusts

Details are given of techniques for preparing surface spreads of locust spermatocytes for light and electron microscopy. The pachytene synaptonemal complex (SC) karyotypes of Locusta migratoria and Schistocerca gregaria are analysed and compared. Up to six different SCs can be identified in Locusta migratoria based on lengths, centromere positions, and possession of nucleolar organiser regions, but only two SCs are identifiable in Schistocerca gregaria. The total SC length is significantly greater in Schistocerca gregaria than in Locusta migratoria, and this difference is almost exactly proportional to the difference in the genomic DNA contents of the two species.     

Selection of Antonospora locustae (Protozoa: Microsporidae) with higher virulence against Locusta migratoria manilensis (Orthoptera:Acrididae)

Antonospora locustae is a microsporidian parasite of grasshopper insects that is used as a biological control agent. We report on laboratory selection of isolates from different regions with increased virulence. Bioassays were conducted against third instar nymphs of Locusta migratoria manilensis. AL2008L01 was originally imported from the USA in 1986, AL2008M01 was isolated from Melanoplus differentialis in USA and AL2008F01 was isolated from infected Fruhstorferiola tonkinensi collected in Guangdong, China. The results showed that all three isolates can infect the locust and that pathogenicity increased gradually with increased dose. The LD₅₀ values of the original isolates at the highest dose (5×10⁶ spores/nymph) were 19, 23 and 22 days and LD₅₀ values were 3.2×10⁵, 3.4×10⁶ and 0.7×10⁶ spores/g, respectively. After selecting for three generations, the virulence of all isolates increased significantly. LT_50s were reduced to 17, 20 and 21 days at the highest dose (5×10⁶ spores/nymph) and LD_50s were reduced to 1.4×10⁵, 2.5×10⁵ and 1.7×10⁵ spores/g.     

Egg hatching of two locusts,Schistocerca gregaria and Locusta migratoria,in response to light and temperature cycles

The present study showed that the eggs of the desert locust, Schistocerca gregaria, and the migratory locust, Locusta migratoria, responded to photoperiod by hatching when placed on sand in the laboratory. S. gregaria mainly hatched during the dark phase and L. migratoria during the light phase. The importance of light as a hatching cue depended on the magnitude of the temperature change during the thermoperiod; photoperiod played a more important role in the control of hatching time in both species when the magnitude of the temperature change was small. In addition, the eggs of the two species that were covered with sand did not respond to photoperiod and hatched during both the light and dark phases, indicating that light did not penetrate through the sand. Because locust eggs are normally laid as egg pods and a foam plug is deposited between the egg mass and the ground surface, we tested a possibility that naturally deposited eggs perceived light through the foam plug. The eggs that were deposited and left undisturbed in the sand hatched during the light and dark phases at similar frequencies. These results suggest that the eggs of both locust species responded to light and controlled their hatching timing accordingly but would not use light as a hatching cue in the field. The evolutionary significance of the ability of eggs to respond to light in these locusts was discussed.     

Interactions of two insect pathogens, Paranosema locustae (Protista: Microsporidia) and Metarhizium acridum (Fungi: Hypocreales), during a mixed infection of Locusta migratoria (Insecta: Orthoptera) nymphs

Locusta migratoria nymphs were fed Paranosema locustae spores and/or surface-treated with Metarhizium acridum 3 (assay 1), 6 (assay 2) or 9 days (assay 3) post microsporidia application (p.m.a.). These three dates corresponded to the key phases of P. locustae development: (a) mass proliferation, (b) transition to sporogenesis and (c) onset of spore maturation, respectively. As a result, locust mortality due to mixed treatment increased slower, equally and faster, as compared to mortality expected from the combination of two pathogens in assays 1-3, respectively. However, a statistically significant difference in survival times was observed only in assay 3, indicating that only at the phase of spore maturation microsporidia drastically increase locust susceptibility to fungal infection. Analysis of perished nymphs showed that fungal treatment 3 days p.m.a. impeded development of microsporidia. Fungal sporulation on locust cadavers was not affected by co-occurring microsporidiosis.     

Composition and emission dynamics of migratory locust volatiles in response to changes in developmental stages and population density

Chemical communication plays an important role in density‐dependent phase change in locusts. However, the volatile components and emission patterns of the migratory locust, Locusta migratoria, are largely unknown. In this study, we identified the chemical compositions and emission dynamics of locust volatiles from the body and feces and associated them with developmental stages, sexes and phase changes. The migratory locust shares a number of volatile components with the desert locust (Schistocerca gregaria), but the emission dynamics of the two locust species are significantly different. The body odors of the gregarious nymphs in the migratory locust consisted of phenylacetonitrile (PAN), benzaldehyde, guaiacol, phenol, aliphatic acids and 2,3‐butanediol, and PAN was the dominant volatile. Volatiles from the fecal pellets of the nymphs primarily consist of guaiacol and phenol. Principal component analysis (PCA) showed significant differences in the volatile profiles between gregarious and solitary locusts. PAN and 4‐vinylanisole concentrations were significantly higher in gregarious individuals than in solitary locusts. Gregarious mature males released significantly higher amounts of PAN and 4‐vinylanisole during adulthood than mature females and immature adults of both sexes. Furthermore, PAN and 4‐vinylanisole were completely lost in gregarious nymphs during the solitarization process, but were obtained by solitary nymphs during gregarization. The amounts of benzaldehyde, guaiacol and phenol only unidirectionally decreased from solitary to crowded treatment. Aliphatic aldehydes (C7 to C10), which were previously reported as locust volatiles, are now identified as environmental contaminants. Therefore, our results illustrate the precise odor profiles of migratory locusts during developmental stages, sexes and phase change. However, the function and role of PAN and other aromatic compounds during phase transition need further investigation.     

The possible role of two species of Orthoptera in the dissemination of a plant pathogenic fungus

The ability of the locusts, Locusta migratoria and Schistocerca gregaria, to disseminate Colletotrichum graminicola, the fungal pathogen of maize anthracnose, were studied. The insects were fed with the diseased plants and spores were recovered in viable condition from the faeces. The spores recovered were able to grow on artificial media and were still infectious to the host plant.     

Adaptive difference in daily timing of hatch in two locust species,Schistocerca gregaria and Locusta migratoria: The effects of thermocycles and phase polyphenism

This study examined the effects of temperature and phase polyphenism on egg hatching time in the desert locust, Schistocerca gregaria, and the migratory locust, Locusta migratoria. The two species exhibited differences and similarities in hatching behavior when exposed to different temperature conditions. In 12-h thermocycles of various temperatures, the S. gregaria eggs hatched during the cryoperiod (low temperature period), whereas L. migratoria eggs hatched during the thermoperiod (high temperature period). The eggs of both species hatched during the species-specific period of the thermoperiod in response to a temperature difference as small as 1 °C. Furthermore, the locusts adjusted hatching time to a new thermal environment that occurred shortly before the expected hatching time. In both species, the hatching of the eggs was synchronized to a specific time of the day, and two hatching peaks separated by approximately 1 day were observed at a constant temperature after the eggs were transferred from thermocycles 3 days before hatching. Eggs laid by gregarious females hatched earlier than those laid by solitarious females in S. gregaria but this difference was not observed in L. migratoria.     

Peptidomic survey of the locust neuroendocrine system

Neuropeptides are important controlling agents in animal physiology. In order to understand their role and the ways in which neuropeptides behave and interact with one another, information on their time and sites of expression is required. We here used a combination of MALDI-TOF and ESI-Q-TOF mass spectrometry to make an inventory of the peptidome of different parts (ganglia and nerves) of the central nervous system from the desert locust Schistocerca gregaria and the African migratory locust Locusta migratoria. This way, we analysed the brain, suboesophageal ganglion, retrocerebral complex, stomatogastric nervous system, thoracic ganglia, abdominal ganglia and abdominal neurohemal organs. The result is an overview of the distribution of sixteen neuropeptide families, i.e. pyrokinins, pyrokinin-like peptides, periviscerokinins, tachykinins, allatotropin, accessory gland myotropin, FLRFamide, (short) neuropeptide F, allatostatins, insulin-related peptide co-peptide, ion-transport peptide co-peptide, corazonin, sulfakinin, orcokinin, hypertrehalosaemic hormone and adipokinetic hormones (joining peptides) throughout the locust neuroendocrine system.     

Relationships between food quality and fitness in the desert locust, Schistocerca gregaria, and its distribution over habitats on the Red Sea coastal plain of Sudan

The effect of millet, Pennisetum typhoideum Rich. (Poaceae), leaf nitrogen content on fitness parameters of the desert locust, Schistocerca gregaria Forsk. (Orthoptera: Acrididae), was studied under laboratory conditions. Locusts reared on high‐nitrogen leaves were larger, developed faster, had higher survival, reproduced more and earlier, and showed greater synchronization than those fed on low‐nitrogen leaves. Active and passive cannibalism contributed to mortality when locusts were reared on low‐nitrogen leaves, but not when reared on high‐nitrogen leaves. Elevated leaf nitrogen content of host plants increased net reproduction and intrinsic rate of increase, and lowered generation time. The findings show that nitrogen content of host plants affects the potential for population increase in the desert locust. Leaf samples of common plant species were collected in the Heliotropium arbainense (Fresen.) (Boraginaceae) and Panicum turgidum (Forssk.) (Poaceae) plant communities on the Red Sea coastal plain of Sudan during the winters of 1999 and 2000. The levels of leaf nitrogen in host plants were comparable to those in the laboratory studies and consistently higher in plant samples from the Heliotropium community than in samples from the Panicum community. Both in 1999 and 2000, locust densities were much higher in the Heliotropium than in the Panicum plant community. It should be assessed whether the desert locust would be attracted to sites where host plants have high leaf nitrogen content, as this would not only increase their fitness, but also the likelihood of gregarization and outbreaks.     

Immunocytochemical localization of Bombyx-PTTH-like molecules in neurosecretory cells of the brain of the migratory locust,Locusta migratoria

Summary Using a monoclonal antibody directed against a synthetic pentadecapeptide corresponding to the N-terminus of the prothoracicotropic hormone (PTTH) of Bombyx mori, we report the presence of immunoreactive molecules in a large number of median neurosecretory cells of the pars intercerebralis of the migratory locust, Locusta migratoria. These cells correspond to the A₁ cell type which we show to contain also neuroparsins, a family of predominant neurohormones of the migratory locust. In contrast, PTTH-like molecules are absent from A₂ cells of the pars intercerebralis which contain Locusta insulin-related peptide (LIRP). Developmental studies show the presence of PTTH-related substances in neurosecretory cells of Locusta migratoria from late embryogenesis to adult development, including ageing vitellogenic female adults.     

The creation of a recombinant single-chain antibody against α/β-hydrolase of microsporidium <Emphasis Type="Italic">Paranosema locustae</Emphasis> and immunolocalization of the enzyme in an infected host cell

Microsporidia are a group of widespread fungi-related obligate intracellular parasites. Direct contact of most microsporidia with the cytoplasm of an infected host cell entails possible secretion of various proteins from the parasite that allows control physiological processes of the host. Earlier, by means of polyclonal antibodies against α/β-hydrolase of microsporidium Paranosema locustae, the secretion of large amounts of the enzyme into the cytoplasm of fat body cells of infected migratory locust Locusta migratoria was demonstrated. However, yeast fungi Pichia pastoris did not recognize this enzyme as a secretory one during its heterologous expression. In the present study, a library of recombinant single-chain antibodies (scFv fragments) against proteins of the infected fat body of locust was constructed. The use of the phage display technology enabled choosing a miniantibody that specifically recognized the studied enzyme. Immunoblotting and immunolabeling of frozen sections of locust fat body with the selected scFv fragment confirmed the fact of secretion of P. locustae α/β-hydrolase (as two forms of different size) into the infected host cell. Prospects of using the selected scFv fragment for further studies of the secretion mechanism of the parasite’s protein and its role in host–parasite interactions are discussed.     

Is juvenile hormone involved in the maternal regulation of egg size and progeny characteristics in the desert locust?

The role of juvenile hormone (JH) in the maternal regulation of progeny characteristics was examined in the desert locust, Schistocerca gregaria. Female adults of this species are known to produce smaller but more eggs when reared in isolation than do those reared in a group. Eggs laid by isolated females develop green hatchlings typical of solitarious forms, whereas those laid by the latter produce black hatchlings typical of gregarious forms. Topical application of a juvenile hormone analog (JHA), fenoxycarb, or implantation of corpora allata (CA) taken from the migratory locust, Locusta migratoria, caused crowded S. gregaria females to deposit smaller eggs, but did not have a significant effect on the number of eggs per egg pod except at high doses of JHA. The production of smaller eggs by treated and untreated crowded females was closely associated with earlier deposition of the egg pods and shorter oviposition intervals. However, neither JHA application nor CA implantation influenced the progeny characteristics in actively reproducing aged females under crowded conditions, while untreated control females started producing smaller and more eggs upon transfer to isolated conditions. These results may suggest that JH is not directly involved in the maternal regulation of phase-dependent progeny characteristics.