Muhammad Tufail

Regulation of vitellogenin genes in insects

Vitellogenins (Vg) genes code for the major egg yolk protein precursor in insects and many other oviparous species. In insects, the Vg gene is expressed extra‐ovarially in the fat body in sex‐, tissue‐ and stage‐specific manners. During the reproductive phase, the Vg mRNA is expressed in large quantities, which is then translated, secreted into hemolymph and ultimately taken up by the developing oocytes through receptor‐mediated endocytosis. Once sequestered, the Vgs are stored as vitellin (Vn), the main nutritional reserve for the developing embryo. The regulation of Vg genes is directly under the control of hormones at the transcriptional level. Hormones involved in Vg gene transcription are juvenile hormone (JH), ecdysteroids and some neuropeptides. The overall understanding that has emerged is that the insects can be classified, based on the system of hormonal regulation of Vg gene transcription, into three groups: (i) insects (like most of hemipterans) that use only JH for Vg gene transcription; (ii) insects (like dipterans) that need both JH and ecdysteroids for Vg regulation; and (iii) insects like lepidopterans that require JH, ecdysteroids and additional hormones to regulate their reproductive biology. However, why insect species diverge in using different hormones to govern their reproductive physiology remains unclear. The present contribution focuses on the current status of knowledge regarding the regulation of Vg genes in insects. Besides a brief information on biochemical and molecular features, the role of Vg genes as a target of endocrine disruptors will be addressed. Also, the molecular mechanism of Vg gene regulation will be discussed.

Comparative Efficacy of CO2 and Ozone Gases Against Ephestia cautella (Lepidoptera: Pyralidae) Larvae Under Different Temperature Regimes

Comparative efficacy of three different modified atmospheres: 100% CO2, 75% CO2 + 25% N2, and 22 ppm ozone were examined against larval mortality of the almond moth, Ephestia cautella (Walker) (Lepidoptera: Pyralidae) at temperature regimes of 25°C and 35 ± 2°C and 60 ± 5% relative humidity, and 9:15 dark and light. Wandering young larval instars, which are fast growing, large enough in size and considered as more tolerant to modified atmosphere, were collected directly from the rearing culture, placed inside pitted date fruits of vars.: “Khudri,” “Ruziz,” and “Saqie,” were treated with aforementioned gases for 24, 48, and 72 h. The immediate and delayed larval mortality was recorded after each exposure timing. Ozone possessed the strongest fumigant toxicity causing 100% mortality with all varieties, at 25 and 35°C after 24 h exposure and was more effective than 75% CO2 that caused 83 and 100% immediate mortality with variety ruziz at 25 and 35°C, respectively. Extending the treatments exposure time to 72 h, 100% mortality was recorded by exposing larvae to any of the studied gases at 25 and 35°C. These results suggest that gases and temperature used in this study can be effectively used to control E. cautella in dates and stored grains.

Molecular and functional characterization of the American cockroach, Periplaneta americana, Rab5: the first exopterygotan low molecular weight ovarian GTPase during oogenesis

The small Rab GTPases are key regulators of membrane vesicle trafficking. Ovaries of Periplaneta americana (Linnaeus) (Blattodea: Blattidae) have small molecular weight GTP/ATP‐binding proteins during early and late vitellogenic periods of oogenesis. However, the identification and characterization of the detected proteins have not been yet reported. Herein, we cloned a cDNA encoding Rab5 from the American cockroach, P. americana, ovaries (PamRab5). It comprises 796 bp, encoding a protein of 213 amino acid residues with a predicted molecular weight of 23.5 kDa. PamRab5 exists as a single‐copy gene in the P. americana genome, as revealed by Southern blot analysis. An approximate 2.6 kb ovarian mRNA was transcribed especially at high levels in the previtellogenic ovaries, detected by Northern blot analysis. The muscle and head tissues also showed high levels of PamRab5 transcript. PamRab5 protein was localized, via immunofluorescence labeling, to germline‐derived cells of the oocytes, very early during oocyte differentiation. Immunoblotting detected a ∼25 kDa signal as a membrane‐associated form revealed after application of detergent in the extraction buffer, and 23 kDa as a cytosolic form consistent with the predicted molecular weight from amino acid sequence in different tissues including ovary, muscles and head. The PamRab5 during late vitellogenic periods is required to regulate the endocytotic machinery during oogenesis in this cockroach. This is the first report on Rab5 from a hemimetabolan, and presents an inaugural step in probing the molecular premises of insect oocyte endocytotic trafficking important for oogenesis and embryonic development.

Differential Proteomic Analysis of Date Palm Leaves Infested with the Red Palm Weevil (Coleoptera: Curculionidae)

Abstract The red palm weevil, Rhynchophorus ferrugineus (Oliv.) (Coleoptera: Curculionidae), is a highly damaging pest of palm trees worldwide. The infestation is highly concealed in nature. Hence, a highly sensitive and reliable early detection technique needs to be applied in the field for identification and treatment of the infested date palms to curtail further infestation. We have recently reported the differential proteomic analysis of the date palm stem tissues associated with the red palm weevil infestation. In this study, we examine the response of date palm infested with red palm weevil based on the leaf proteome expression changes detected using two-dimensional differential gel electrophoresis (2D-DIGE) followed by Matrix-Assisted Laser Desorption/Ionization-Time-of-Flight (MALDI-TOF). We observed qualitative and quantitative proteome differences between the control and weevil-infested date palm samples. The red palm weevil infestation induced specific responses attributable to weevil feeding, relative to artificially wounded trees (which were used as a control). Differential proteomics led to the identification of 32 red palm weevil infestation-specific protein spots (P ≤ 0.05 having ≥ 1.5-fold modulation) that were further subjected to mass spectrometer analysis for identification and characterization. Proteins involved in plant stress and plant defense, photosynthesis, carbohydrate utilization, and protein degradation were affected in infested plants. The differentially expressed red palm weevil infestation-specific peptides can be used as biomarkers for the identification of early infestation with this insect in date palm trees. Moreover, our study demonstrates the potential use of proteomic strategies in diagnosing phyto-infestation caused by insect pests, diseases, and perhaps even for variety selection.

Biological Traits of Cadra cautella (Lepidoptera: Pyralidae) Reared on Khodari Date Fruits Under Different Temperature Regimes

Abstract The almond moth, Cadra cautella (Walker) (Lepidoptera: Pyralidae), is a serious worldwide pest of dates and other crops, both in the field and in storage. Infestation by this pest significantly limits the sale and export of dates. Modified atmospheres, the temperature manipulations, are the best eco-friendly alternatives in stored product protection. We examined temperature regulation as an ecologically friendly method of pest management in stored food commodities, in particular, its effects on characteristics of C. cautella biology, including development time, oviposition period, fecundity, fertility, and longevity of adults reared on date cultivar ‘Khodari,’ at temperatures of 15, 25, and 35 ± 1 °C, with 65 ± 5% relative humidity and a photoperiod of 15:9 (L:D) h. Six larval instars were recorded at each temperature. Larval development was sluggish at 15 °C; therefore, daily observations were terminated after 180 d of the larval span for this temperature. Total larval spans of 48.95 ± 0.76 and 32.12 ± 1.08 d were recorded at 25 °C and 35 °C, respectively. A mean ovipositional period of 5.80 ± 0.44 d yielding 213.60 ± 13.41 eggs per female, with hatchability of 85.94 ± 2.97%, was recorded at 25 °C, whereas at 35 °C, a mean ovipositional period of 1.60 ± 0.26 d yielded 19.80 ± 5.11 eggs per female, with no hatchability. These differences were highly significant. Our observations of poor development at 15 °C, lower numbers of eggs and absence of hatchability at 35 °C, together with head capsule measurements and growth ratios, can be of benefit when planning management strategies to reduce C. cautella infestation.

r/K-like trade-off and voltinism discreteness: The implication to allochronic speciation in the fall webworm, Hyphantria cunea complex (Arctiidae)

Abstract North America has distinct types of Hyphantria moths (Arctiidae) characterized by red (RD)‐ and black (BL)‐headed larvae, of which the taxonomic status is unresolved. Genetic divergence of 26 populations, based on 710 bp of the mtCOI sequence, showed two phylogenetic lineages, which could not be connected in the haplotype network with 95% confidence. The two lineages are separated by 3.1% sequence divergence and should be considered for full species status. The estimated split occurred 1.2–1.6 million years ago. The range of the RD type covered most of the continent, whereas that of the BL type was limited to eastern deciduous forests. Several biological characteristics were differentiated in the zone of cohabitation where BL had more annual generations than RD. Spring emergence of BL precedes that of RD in the field by at least 1 month, because the diapause in BL was shallow, whereas it was deep in RD. Voltinism requires discreteness of numbers, which functions as a sink of hybrids between the two parental lines that have distinct but equally adaptive reproductive strategies; BL may be more r‐strategist‐like and RD more K‐strategist‐like, because fast‐developing BL has multivoltine life cycle, investing less silk proteins as the round‐the‐clock feeder, and slow‐developing RD univoltine one investing more silk as the nocturnal feeder. Also, intensity of diapause, deep in RD and weak in BL, was grossly different, which may enforce segregation of spring adults. Allochronic speciation avoiding coincidental occurrence of adult stages is therefore the most likely scenario. Because the adults never meet in nature, large morphological differentiation is not required.

Vitellogenesis and Yolk Proteins in Insects

Vitellogenesis is the process of yolk accumulation by the developing oocytes in all oviparous species. In most insects, the major yolk protein precursor vitellogenin (Vg) is synthesized in the fat body, which is then secreted into the hemolymph and ultimately taken up by the developing oocytes through receptor-mediated endocytosis. Once sequestered, the Vgs are stored as major yolk proteins, the vitellins (Vns), which serve as nutritional source for the developing embryo. This article reviews the current state of knowledge on Vgs in insects and their role in oogenesis.