THE TOXICITY OF SOME INSECTICIDES TO FIFTH-INSTAR NYMPHS OF THE DESERT LOCUST

The toxicities of the insecticides γ-BHC, diazinon, dieldrin, DNC, heptachlor and parathion to fifth-instar hoppers of the desert locust were determined. Parathion and dieldrin were the most toxic, followed in descending order by heptachlor, γ-BHC, diazinon and DNC. The resistance of the hoppers to γ-BHC and DNC changed appreciably with age within the instar.
The effects of some factors which might influence the resistance of the insects were examined and are discussed.     

DETERMINATION OF THE RESISTANCE OF LOCUSTS TO DNC IN RELATION TO THEIR WEIGHT, AGE AND SEX

Experiments have shown that the resistance of adults of the desert locust ( Schistocerca gregaria ) and the African migratory locust ( Locusta migratoria migratorioides ) to DNC applied as a contact poison to the ventral surface of the abdomen is directly related to their body weight, irrespective of age or sex.
Varying the site of application of the insecticide had little effect on the susceptibility of the insects except when the dose was applied to the wings or femur, these being less effective sites of entry for the poison.
Increasing the post-treatment temperature from 25 to 36°C. had no noticeable effect on mortality, but the speed of action of the insecticide was much increased.     

THE CUMULATIVE TOXICITY OF γ-BHC AND DIAZINON APPLIED IN SMALL DOSES TO LOCUSTS

The toxicity of γ-BHC and Diazinon when applied over a period of time to adults of the desert locust, Schistocerca gregaria (Forsk.), has been determined. The insecticides were applied in oil solutions, by means of the micro-drop syringe, to the ventral surface of the abdomen.
When doses were applied in two equal portions with a 72 hr. interval, or in four equal portions at 24 hr. intervals, no significant decrease in toxicity, in comparison with a single dose, could be detected with either insecticide. It is concluded, therefore, that if similar effects occur when locusts are sprayed with these insecticides in the field, successive spraying will be fully cumulative over a period of 72 hr. Previous work using DNC has shown that doses applied over 4 days were only half as effective as equivalent single doses and that continued dosing after 4 days brought about very little increase in kill.
The sexes were similar in resistance to γ-BHC when the doses were measured in μg./g., but females were considerably more resistant to Diazinon than males.     

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.     

Sequence analyses of adipokinetic hormones II from corpora cardiaca of Schistocerca nitans, Schistocerca gregaria, and Locusta migratoria by fast atom bombardment mass spectrometry

Structures of the second adipokinetic hormones (AKH II's) from three locust species have been assigned by fast atom bombardment mass spectrometry. The AKH II hormone is identical in two Schistocerca species, S. nitans and S. gregaria, but is different in Locusta migratoria. Both AKH II's are related to red pigment-concentrating hormone (RPCH) from prawns, Schistocerca AKH II being [Thr6]-RPCH and Locusta AKH II being [Ala6]-RPCH. Schistocerca AKH II is also bioactive in Locusta individuals.     

THE EFFECT OF BODY WEIGHT ON THE RESISTANCE TO INSECTICIDES OF THE LAST-INSTAR LARVA OF DIATARAXIA OLERACEA L., THE TOMATO MOTH

At a constant temperature of 24° C. the final larval instar of Diataraxia oleracea lasts about 10 days, during which its resistance to DDT and γ-BHC as contact insecticides progressively increases up to the 5th or 6th day. It then suddenly decreases, this coinciding with cessation of feeding and the beginning of prepupal formation.
Between the 2nd and the 6th days the gross body weight of the last-instar larva increases from about 0.27 to 0.65g. Under the conditions of the experiments, the LD50 of parathion, as a stomach poison, was linearly related to body weight; on the same basis TEPP was slightly less, and lead arsenate, slightly more, toxic to the larger than to the smaller larvae. However, DDT as a stomach or contact insecticide, and γ-BHC as a stomach poison were notably less toxic to the larger larvae. For example, the increase in LD50 for an increase in larval body weight of × 2 was about × 11 for DDT as a stomach poison and about × 12 as a contact insecticide.
The order of effectiveness of the above insecticides as stomach poisons for the last-instar larva of D. oleracea was parathion > DDT > γ-BHC > TEPP = lead arsenate. Zinc fluoarsenate and rotenone were relatively non-toxic. Larvae of D. oleracea were repelled by food leaf treated with an extract of natural pyrethrins.     

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.     

飞蝗及沙漠蝗信息素概述

飞蝗和沙漠蝗自古以来就是重要的农业害虫,这与其生物学特性是密不可分的.信息素对飞蝗和沙漠蝗生物学特征的调节起到了非常重要的作用.到目前为止,沙漠蝗Schistocerca gregaria和飞蝗Locusta migratoria 的研究较为深入,本文对其主要成果进行了综述,以此作为以后飞蝗和沙漠蝗信息素进一步研究的参...     

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.     

Isolation and characterization of nine polymorphic microsatellite loci from the desert locust,Schistocerca gregaria

Because of the scarcity of polymorphic genetic markers, only a few genetic studies on the population structure of the desert locust, Schistocerca gregaria, have been carried out. We isolated and characterized nine polymorphic dinucleotide microsatellite loci. These markers were evaluated using individuals from Niger and Senegal. Seven of these microsatellite markers are also applicable to the nongregarious subspecies Schistocerca gregaria flaviventris. Cross‐species applicability was limited to one of the loci in the sister species S. americana and in the locust Locusta migratoria.     

THE USE OF SEED DRESSINGS CONTAINING γ-BHC IN THE ESTABLISHMENT OF SUGAR-BEET SEEDLINGS

From 1949 to 1952 field trials were made to determine the effect of seed dressings containing γ-BHC, with and without the addition of organic mercurial compounds, upon the establishment of sugar-beet seedlings. Most of the trials were made in fields where no serious pest problems were anticipated. The 1949 trials established the concentration of γ-BHC non-phytocidal to sugar-beet seedlings. Later trials tested the effect on pre- and post-singling plant populations of dressings applied to natural or rubbed seed sown at standardized rates. Parallel tests of dressed seed were made on farms representing a variety of soil types, It was found that the phytotoxiCity of γ-BHC varied with season and soil type, but that a dressing containing 40 % was usually safe. In these trials, the benefits from seed dressing were, as a rule, slight. Generally the combined mercury-γ-BHC seed dressing gave the best pre-singling stand of plants. Most of the improvement was attributable to the organic mercury rather than to the γ-BHC, but where pest attacks occurred, γ-BHC gave marked improvements in stand. Wireworm appeared to be the chief pest controlled: control of pygmy mangold beetle was only partial.     

PROTECTION OF SORGHUM AGAINST SOIL FUNGI, SOIL PESTS AND COVERED SMUT BY COMBINED INSECTICIDE-FUNGICIDE SEED DRESSINGS

Treatment of sorghum ( Sorghum vulgare ) seed with fungicide dressings controlled covered smut ( Sphacelotheca sorghi ), the major disease of sorghum in the Sudan, and usually resulted in appreciably better stands. In the Sudan Gezira, powder dressings containing 20–40%γ-benzene hexachloride (γ-BHC) applied at the rate of 1g./1b. of seed effectively protected sorghum seedlings from root attack by chafer grubs ( Schixonycha sp.) and significantly increased stands and yields. No certain evidence of this effect was obtained with dolichos bean ( Dolichos lablab ) or groundnut ( Arachis hypogaea ), and the different responses shown by these plants as compared with sorghum are attributed largely to differences in seed germination and root system. An application rate of 0·08 %γ-BHC/seed was sometimes slightly but appreciably phytotoxic to sorghum in the field and more markedly so in greenhouse experiments. A powder containing 25% thiram and 20%γ-BHC applied at the rate of 1g./1b. of seed is recommended as the standard seed dressing for sorghum in the Sudan.     

Differential susceptibility of two locust pests to the microsporidium Paranosema (Antonospora) locustae at suboptimal rearing temperature

Paranosema (Antonospora) locustae (Canning) is a microsporidium with an extensive host range including >100 reported insect hosts from the order Orthoptera. The susceptibility of two species of locusts (Orthoptera: Acrididae) – the migratory locust, Locusta migratoria subsp. migratorioides (Fairmaire & Reiche), and the desert locust, Schistocerca gregaria Forsskål – to P. locustae was compared under laboratory conditions at a decreased temperature of 27 °C to enhance susceptibility to infection. Locusta migratoria was found highly vulnerable as infection percentages exceeded 70% at 10⁴, 10⁵, and 10⁶ spores per insect, and mortality increased with increasing dosage. Conversely, P. locustae spores were not found in S. gregaria throughout the experiment. Only at 10⁷ spores per insect, as many as 20% of S. gregaria were infected. This suggests that the desert locust is resistant to P. locustae infection, as opposed to the migratory locust. The laboratory models of these parasite–host systems may be useful for elucidating mechanisms of insect immunity to microsporidia.     

“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.     

蝗虫的发生与防控

蝗虫暴发引起的灾害是全球重要的生物灾害,可影响到全世界十分之一的人口。自2019年,东部非洲、西亚、南亚多个国家遭遇严重的沙漠蝗虫灾害,这场蝗灾不但对该区域的粮食安全构成严重威胁,而且还有可能引发严重的人道主义危机。为了制定合理的防治方案,实施有效防控,避免大规模蝗灾的发生,需要掌握蝗虫的生物学、生态学、暴发和为害规律、防治策略和技术特点及其进展等。本文介绍了世界各地包括沙漠蝗、飞蝗、澳大利亚疫蝗在内的11种可以引起灾害的重要种类的主要分布、为害和特性,并对国内外蝗虫防治策略、技术进展进行了重点综述。最后,针对目前蝗虫防治存在的问题提出了相应建议。     

Artificial miniaturization causes eggs laid by crowd-reared (gregarious) desert locusts to produce green (solitarious) offspring in the desert locust, Schistocerca gregaria

The mechanism underlying the phase-dependent polyphenism in hatchling body coloration was studied by testing for a possible causal relationship with egg size in the desert locust, Schistocerca gregaria. Crowd-reared (gregarious) females typically produce large, black offspring, whereas females reared in isolation (solitarious) deposit small, green offspring. We first tested for possible genetic differences in the role of egg foam by washing or separating eggs from two strains of locust. No solitarizing effect was found in either of the strains tested, supporting a previous finding, using another laboratory strain, to show that the hatchling body coloration and size are pre-determined in the ovary of the mother and no egg foam factor is involved in the control of the hatchling body coloration. Topical application of fenoxycarb, a juvenile hormone analog (JHA), and implantation of extra corpora allata (CA), taken from Locusta migratoria, caused gregarious female adults of S. gregaria to produce small eggs. Some eggs laid by CA-implanted females produced green hatchlings. All large eggs chosen among those deposited by gregarious females produced black hatchlings. When eggs were either kept on dry filter paper at nearly saturated relative humidity during embryogenesis or pricked with a needle so that some egg yolk was squeezed out, some produced small, green hatchlings. These results suggested that the amount of egg yolk or the availability of yolk material may determine the body coloration of hatchlings.     

Circadian rhythm changes in toxicity of the insecticide dieldrin on larvae of the migratory locust Locusta migratoria migratorioides.

Circadian changes in toxicity of the insecticide dieldrin were documented in the larvae (fifth stage) of the migratory locust, Locusta migratoria migratorioides. Insects were housed under light (L): dark (D) = 12:12, with L from 0800 to 2000 h. Topical applications of dieldrin at fixed clock hours, with doses ranging from 0.1 to 8 micrograms/gm body weight, were carried out in a series of experiments on male and female larvae. Twenty-four h after dosing, mortality was recorded to quantify the median lethal dose (LD50) values with reference to time of treatment. Experiments were performed during February, early and late June, and August. Larvae were more susceptible to dieldrin when dosed during the night rather than during the day [analysis of variance (ANOVA); p less than 0.05]. Moreover, female larvae were less susceptible to dieldrin than were male larvae (ANOVA; p less than 0.05). Cosinor analysis revealed circadian rhythms in susceptibility-resistance to the insecticide in all experiments except no. 2. Toxicity was found to be greatest during the nighttime. Cosinor analysis of pooled data of the four experiments documented circadian rhythmicity to toxicity of dieldrin in female but not in male larvae. Regardless of sex, the timing of least susceptibility (greatest resistance and highest LD50 value) to the insecticide, dieldrin, was around 1500.     

THE EFFECT OF EGG WEIGHT ON THE SUBSEQUENT GROWTH OF NESTLING GREAT TITS PARUS MAJOR

Eggs of known fresh weight were removed from Great Tit nests shortly before hatching and artificially incubated. Four to eight chicks were returned to each nest-box on their hatching day and reared by foster parents. The effect of egg weight on subsequent growth was studied for 81 nestlings (13 broods), 50 of them (8 broods) up to the 17th day.
Hatching success of 275 eggs in the incubator was 67·6% and was not correlated with egg weight.
Egg weight had a significant effect on nestling weight up to the 14th day. Young hatched from lighter eggs grew more slowly at the beginning, but recovered before fledging. Mortality after fledging seemed not to be influenced by egg weight.
Maximum weight (mean 19 g) was attained between the 12th and the 17th day and was positively correlated with egg weight.
The effect of brood-size (small in the experiments) on growth increased significantly with age. The range of egg weight for a nest had a significant effect on growth at the beginning, but a small and not significant effect after the 10th day.
The growth of each brood on any particular day was expressed as a deviation from mean growth. These growth deviations, plotted against date, were similar in all nests and were not correlated with any weather data.
The fledging success of 260 early broods was independent of egg weight, but it was positively correlated with egg weight in 78 late broods (data from 1965–71).
The ecological importance of egg weight at different times of the breeding season is discussed.