The insect neuropeptide prothoracicotropic hormone is released with a daily rhythm: re-evaluation of its role in development.

Prothoracicotropic hormone (PTTH) is the central cerebral neurohormone in insect development. Its release has been believed for decades to be confined to one (or two) critical moments early in each developmental stage at which time it triggers prolonged activation of the prothoracic glands to synthesize and release the steroid molting hormones (ecdysteroids), which elicit developmental responses in target tissues. We used an in vitro assay for PTTH released from excised brains of the bug Rhodnius prolixus and report that release of PTTH does occur at the expected time on day 6, but that this release is merely the first in a daily rhythm of release that continues throughout most of the 21 days of larval-adult development. This finding, together with reports of circadian control of ecdysteroid synthesis and titer throughout this time, raises significant challenges to several features of the current understanding of the hormonal control of insect development. New questions are raised concerning the function(s) of PTTH, its relationship with the prothoracic glands, and the significance of circadian rhythmicity throughout this endocrine axis. The significance of the reported observations derives from the set of entirely new questions they raise concerning the regulation of insect development.

Efficacy of ivermectin against the bloodsucking insect, Rhodnius prolixus (Hemiptera, Triatominae)

Ivermectin (0.2 mg/kg body weight) caused a high mortality in nymphs and adults of Rhodnius prolixus following a single meal in mice sub-cutaneously injected with the drug. This effect was more evident in nymphs of 1st-and 2nd-instar than in older nymphs and adults. Third-instar nymphs presented a high mortality when fed on mice treated with ivermectin 24 and 48 hours previously, while mortality was significantly reduced in nymphs fed on mice treated 72 hours before. Surviving 3rd-instar nymphs did not molt. When adult females were fed once on mice treated for 24 hours with ivermectin there was a considerable reduction in egg production. This inhibition was not reversed by a second feeding on normal mice. We concluded that sub-lethal doses of ivermectin caused toxic effects interfering in the neuro-endocrine control of development and reproduction of this bloodsucking insect.

Cloning and characterization of a V-ATPase subunit C from the American visceral leishmaniasis vector Lutzomyia longipalpis modulated during development and blood ingestion

Visceral leishmaniasis (VL) is a serious tropical disease that affects approximately 500 thousand people worldwide every year. In the Americas, VL is caused by the parasite Leishmania (Leishmania) infantum chagasi mainly transmitted by the bite of the sand fly vector Lutzomyia longipalpis. Despite recent advances in the study of interaction between Leishmania and sand flies, very little is known about sand fly protein expression profiles. Understanding how the expression of proteins may be affected by blood feeding and/or presence of parasite in the vector's midgut might allow us to devise new strategies for controlling the spread of leishmaniasis. In this work, we report the characterization of a vacuolar ATPase subunit C from L. longipalpis by screening of a midgut cDNA library with a 220 bp fragment identified by means of differential display reverse transcriptase-polymerase chain reaction analysis. The expression of the gene varies along insect development and is upregulated in males and bloodfed L. longipalpis, compared to unfed flies.

Temperature and the development rates of thrips: evidence for a constraint on local adaptation?

Typically, the relationship between insect development and temperature is described by two characteristics: the minimum temperature needed for development to occur (T-min) and the number of day degrees required (DDR) for the completion of development. We investigated these characteristics in three English populations of Thrips major and T tabaci [Cawood, Yorkshire (N53degrees49', W1degrees7'); Boxworth, Cambridgeshire (N52degrees15', W0degrees1'); Silwood Park, Berkshire (N51degrees24', W0degrees38')], and two populations of Frankliniella occidentalis (Cawood; Silwood Park). While there were no significant differences among populations in either T-min (mean for T major = 7.0degreesC; T tabaci = 5.9degreesC; F. occidentalis = 6.7degreesC) or DDR (mean for T major = 229.9; T tabaci = 260.8; F occidentalis = 233.4), there were significant differences in the relationship between temperature and body size, suggesting the presence of geographic variation in this trait. Using published data, in addition to those newly collected, we found a negative relationship between T-min. and DDR for F occidentalis and T tabaci, supporting the hypothesis that a trade-off between T-min and DDR may constrain adaptation to local climatic conditions.

The defensive functions of plant inhibitors are not restricted to insect enzyme inhibition

Three plant proteinase inhibitors BbKI (kallikrein inhibitor) and BbCI (cruzipain inhibitor) from Bauhinia bouhinioides, and a BrTI (trypsin inhibitor) from B. rufa, were examined for other effects in Callosobruchus maculatus development; of these only BrTI affected bruchid emergence. BrTI and BbKI share 81% identities in their primary sequences and the major differences between them are the regions comprising the RGD and RGE motifs in BrTI. These sequences were shown to be essential for BrTI insecticidal activity, since a modified BbKI [that is a recombinant form (BbKIm) with some amino acid residues replaced by those found in BrTI sequence] also strongly inhibited insect development. By using synthetic peptides related to the BrTI sequence, YLEAPVARGDGGLA-NH(2) (RGE) and IVYYPDRGETGL-NH(2) (RGE), it was found that the peptide with an RGE sequence was able to block normal development of C. maculatus larvae (ED(50) 0.16% and LD(50) 0.09%), this being even more effective than the native protein. (C) 2009 Elsevier Ltd. All rights reserved.

A preliminary study of insect fauna on pig carcasses located in sugarcane in winter in southeastern Brazil

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Variation of genetic expression during development, revealed by esterase patterns in Aedes aegypti (Diptera, Culicidae)

Polyacrylamide gel electrophoresis was used to analyze esterase patterns during development of Aedes aegypti from the cities of Marília and São José do Rio Preto (SJRP), Brazil. The zymograms showed a total of 23 esterase bands, 22 of which were in the specimens from Marília and 19 in those from SJRP. These esterase bands were considered to be the product of 23 alleles distributed tentatively in eight genetic loci. Most of the alleles were developmentally regulated. The larval stage expressed the greatest number of them (19 alleles, from the eight loci, in Marília; and 17 alleles, from seven loci, in SJRP). The pupal stage expressed 10 alleles from seven loci, in both populations, and the adult stage expressed 8 alleles from five and six loci in SJRP and Marília, respectively. Some alleles that were active in every stage were developmentally controlled at the level of expression (amount of product). A single allele was constitutively and highly expressed, in larvae, pupae, and adults, in both populations. Differences in esterase synthesis among stages are probably due to regulatory mechanisms acting in agreement with the requirements of a variable number of processes in which esterases are involved. The larval stage is the most active in developmental processes and shows very intense intake of food and very high mobility. These features may demand increased esterase production at that stage. Comparison of the two populations examined showed (besides the existence of alleles that they do not share) that they exhibit differences in the control of expression of other alleles. Such findings may reflect genetic differences between founders in each population, but the possibility of involvement of the intensive use of insecticides in SJRP is also discussed.

Sugarwin: A Sugarcane Insect-Induced Gene with Antipathogenic Activity

In sugarcane fields, colonization of the stalk by opportunistic fungi usually occurs after the caterpillar Diatraea saccharalis attacks the sugarcane plant. Plants respond to insect attack by inducing and accumulating a large set of defense proteins. Two homologues of a barley wound-inducible protein (BARWIN), sugarcane wound-inducible proteins SUGARWIN1 and SUGARWIN2, have been identified in sugarcane by an in silico analysis. Antifungal properties have been described for a number of BARWIN homologues. We report that a SUGARWIN:green fluorescent protein fusion protein is located in the endoplasmic reticulum and in the extracellular space of sugarcane plants. The induction of sugarwin transcripts occurs in response to mechanical wounding, D. saccharalis damage, and methyl jasmonate treatment. The accumulation of transcripts is late induced and is restricted to the site of the wound. Although the transcripts of sugarwin genes were strongly increased following insect attack, the protein itself did not show any effect on insect development; rather, it altered fungal morphology, leading to the apoptosis of the germlings. These results suggest that, in the course of evolution, sugarwin-encoding genes were recruited by sugarcane due to their antipathogenic activity. We rationalize that sugarcane is able to induce sugarwin gene expression in response to D. saccharalis feeding as a concerted plant response to the anticipated invasion by the fungi that typically penetrate the plant stalk after insect damage.

Genes involved in thoracic exoskeleton formation during the pupal-to-adult molt in a social insect model, Apis mellifera

Background: The insect exoskeleton provides shape, waterproofing, and locomotion via attached somatic muscles. The exoskeleton is renewed during molting, a process regulated by ecdysteroid hormones. The holometabolous pupa transforms into an adult during the imaginal molt, when the epidermis synthe3sizes the definitive exoskeleton that then differentiates progressively. An important issue in insect development concerns how the exoskeletal regions are constructed to provide their morphological, physiological and mechanical functions. We used whole-genome oligonucleotide microarrays to screen for genes involved in exoskeletal formation in the honeybee thoracic dorsum. Our analysis included three sampling times during the pupal-to-adult molt, i.e., before, during and after the ecdysteroid-induced apolysis that triggers synthesis of the adult exoskeleton. Results: Gene ontology annotation based on orthologous relationships with Drosophila melanogaster genes placed the honeybee differentially expressed genes (DEGs) into distinct categories of Biological Process and Molecular Function, depending on developmental time, revealing the functional elements required for adult exoskeleton formation. Of the 1,253 unique DEGs, 547 were upregulated in the thoracic dorsum after apolysis, suggesting induction by the ecdysteroid pulse. The upregulated gene set included 20 of the 47 cuticular protein (CP) genes that were previously identified in the honeybee genome, and three novel putative CP genes that do not belong to a known CP family. In situ hybridization showed that two of the novel genes were abundantly expressed in the epidermis during adult exoskeleton formation, strongly implicating them as genuine CP genes. Conserved sequence motifs identified the CP genes as members of the CPR, Tweedle, Apidermin, CPF, CPLCP1 and Analogous-to-Peritrophins families. Furthermore, 28 of the 36 muscle-related DEGs were upregulated during the de novo formation of striated fibers attached to the exoskeleton. A search for cis-regulatory motifs in the 5′-untranslated region of the DEGs revealed potential binding sites for known transcription factors. Construction of a regulatory network showed that various upregulated CP- and muscle-related genes (15 and 21 genes, respectively) share common elements, suggesting co-regulation during thoracic exoskeleton formation. Conclusions: These findings help reveal molecular aspects of rigid thoracic exoskeleton formation during the ecdysteroid-coordinated pupal-to-adult molt in the honeybee.

Evaluation of different models to describe egg and pupal development of Xyleborus fornicatus Eichh. (Coleoptera: Scolytidae), the shot-hole borer of tea in Sri Lanka

Abstract Development data of eggs and pupae of Xyleborus fornicatus Eichh. (Coleoptera: Scolytidae), the shot-hole borer of tea in Sri Lanka, at constant temperatures were used to evaluate a linear and seven nonlinear models for insect development. Model evaluation was based on fit to data (residual sum of squares and coefficient of determination or coefficient of nonlinear regression), number of measurable parameters, the biological value of the fitted coefficients and accuracy in the estimation of thresholds. Of the nonlinear models, the Lactin model fitted experimental data well and along with the linear model, can be used to describe the temperature-dependent development of this species.

Some factors affecting white stem borer Scirpophaga innotata (Walker) (Lepidoptera : Pyralidae) injury to rice

The amount of injury to rice caused by white stem borer Sciryophaga innotata depends on cultivar, and stage of plant and insect development, as well as insect abundance. Of the cultivars tested, IR64, IR42, Cisadane and Ketan. IR64 were the most susceptible and Ketan the least susceptible to feeding damage. Third and fourth instars consumed more stem dry matter than other stages, although yield reduction depended on the number of tillers injured. On the wider stemmed Ketan, fewer tillers were injured than the narrower IR64. Larvae are more likely to move among tillers in the third instar stage, which tends to coincide with maximum tillering and may result in more tillers injured and in yield reduction. Later instar larvae burrow downwards to the internode where they pupate. Larvae appear to move less among tillers in 'resistant' cultivars. Management strategies should target this pest at third instar and when its abundance in the field warrants control. Fewer than 10% of the neonates establish successfully on stems, and this mortality needs to be taken into account when deciding on control, as does the ability of rice plants to compensate for injury. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.

Chronic malnutrition favours smaller critical size for metamorphosis initiation in Drosophila melanogaster.

Critical size at which metamorphosis is initiated represents an important checkpoint in insect development. Here, we use experimental evolution in Drosophila melanogaster to test the long-standing hypothesis that larval malnutrition should favour a smaller critical size. We report that six fly populations subject to 112 generations of laboratory natural selection on an extremely poor larval food evolved an 18% smaller critical size (compared to six unselected control populations). Thus, even though critical size is not plastic with respect to nutrition, smaller critical size can evolve as an adaptation to nutritional stress. We also demonstrate that this reduction in critical size (rather than differences in growth rate) mediates a trade-off in body weight that the selected populations experience on standard food, on which they show a 15-17% smaller adult body weight. This illustrates how developmental mechanisms that control life history may shape constraints and trade-offs in life history evolution.

Biology of Plutella xylostella L. (Lepidoptera: Plutellidade) Reared on Cauliflower Genotypes

This work was conducted to evaluate biological parameters of Plutella xylostella L. reared on leaves of several cauliflower genotypes under laboratory conditions. The experiment was set in a randomized block design and arranged in a 6 x 2 factorial (genotypes x generations). Leaf disks of the cultivars Barcelona, Verona, Piracicaba Precoce, Sharon, Silver Streak, and Teresopolis Gigante were placed in Petri dishes with 12 newly-hatched larvae. Leaf disks were initially changed after the fourth day, but daily afterwards until the larvae reached the pupal stage. The same procedure was adopted for the second generation. Twenty adults of each sex were separated from each genotype to evaluate their longevity, and I 0 couples from each treatment were used to assess female fecundity. The lowest larval survival was obtained on the 'Silver Streak' (78.9%) and highest on 'Verona' (97.1%). The 'Silver Streak' and `Teresopolis Gigante' showed the lowest pupal weights (4.83 mg and 5.11 mg, respectively), as well as the lowest fecundity, 119.4 and 123.0 eggs/female, respectively, while 'Piracicaba Precoce' the highest (167.7 eggs/female). Males obtained from larvae reared on `Teresopolis Gigante' and 'Silver Streak' lived shorter (5.1 days), while the short-lived females were obtained from larvae reared on 'Barcelona' and 'Verona' (4.9 and 5.0 days). Insect development was prolonged in the second generation in all tested genotypes.

Biologia de Plutella xylostella L. (Lepidoptera: Plutellidae) em cultivaresde couve-flor

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Aspectos biológicos de Chrysoperla raimundoi Freitas & Penny (Neuroptera, Chrysopidae)

Os crisopídeos são importantes predadores e são encontrados em diversos agroecossistemas. A temperatura é um dos fatores determinantes para o desenvolvimento dos insetos, sendo que existe um gradiente de variação aceitável para cada espécie. Portanto, objetivou-se com este estudo verificar a influência de diferentes temperaturas sobre o desenvolvimento embrionário e pós-embrionário de C. raimundoi assim como verificar as conseqüências nas diferentes gerações. As fases jovens foram criadas em três ambientes com temperaturas constantes de 19,0, 25,0 e 31,0ºC e em um ambiente externo sem controle dos fatores abióticos. Foram observados a duração do período embrionário, do primeiro, segundo e terceiro ínstares, a duração do período larval, pupal e ovo-adulto, assim como, a sobrevivência em cada estágio, estádio e a porcentagem de emergência. O desenvolvimento embrionário e pós-embrionário diferiu entre as gerações F2 e F4. Quanto à influência de diferentes temperaturas para a geração F2, os indivíduos criados a 31,0ºC demonstraram redução na taxa de desenvolvimento com relação aos outros dois ambientes. Para a geração F4, observou-se que as diferentes temperaturas influenciaram no desenvolvimento, sendo que a 19,0ºC houve prolongamento do mesmo.