Mohammad Mehrabadi

The Baculovirus Antiapoptotic p35 Protein Functions as an Inhibitor of the Host RNA Interference Antiviral Response

ABSTRACT RNA interference (RNAi) is considered an ancient antiviral defense in diverse organisms, including insects. Virus infections generate double-strand RNAs (dsRNAs) that trigger the RNAi machinery to process dsRNAs into virus-derived short interfering RNAs (vsiRNAs), which target virus genomes, mRNAs, or replication intermediates. Viruses, in turn, have evolved viral suppressors of RNAi (VSRs) to counter host antiviral RNAi. Following recent discoveries that insects mount an RNAi response against DNA viruses, in this study, we found that Autographa californica multiple nucleopolyhedrovirus (AcMNPV) infection similarly induces an RNAi response in Spodoptera frugiperda cells by generating a large number of vsiRNAs postinfection. Interestingly, we found that AcMNPV expresses a potent VSR to counter RNAi. The viral p35 gene, which is well known as an inhibitor of apoptosis, was found to be responsible for the suppression of RNAi in diverse insect and mammalian cells. The VSR activity of p35 was further confirmed by a p35-null AcMNPV that did not suppress the response. In addition, our results showed that the VSR activity is not due to inhibition of dsRNA cleavage by Dicer-2 but acts downstream in the RNAi pathway. Furthermore, we found that the VSR activity is not linked to the antiapoptotic activity of the protein. Overall, our results provide evidence for the existence of VSR activity in a double-stranded DNA virus and identify the responsible gene, which is involved in the inhibition of RNAi as well as apoptosis. IMPORTANCE Our findings demonstrate the occurrence of an insect RNAi response against a baculovirus (AcMNPV) that is highly utilized in microbial control, biological and biomedical research, and protein expression. Moreover, our investigations led to the identification of a viral suppressor of RNAi activity and the gene responsible for the activity. Notably, this gene is also a potent inhibitor of apoptosis. The outcomes signify the dual role of a virus-encoded protein in nullifying two key antiviral responses, apoptosis and RNAi.

Linking pollen quality and performance of Neoseiulus californicus (Acari: Phytoseiidae) in two‐spotted spider mite management programmes

BACKGROUND It has been shown that pollen as a dietary supplement may increase the establishment of generalist predatory mites, and therefore pest control by these mites can be provided. Life table studies were performed to evaluate the nutritional value of seven different pollens (almond, castor-bean, date-palm, maize, bitter-orange, sunflower and mixed bee pollen) as a supplementary food source for the spider mite predator Neoseiulus californicus McGregor. In addition, the nutritional quality of each pollen species was assessed through morphological and chemical analysis. RESULTS Preadult duration was longer when the predator fed on castor-bean pollen (10.01 days) and bee pollen (9.94 days) compared with the others (5.58-7.27 days). The cohort reared on almond pollen had the highest intrinsic rate of increase (r) (0.231 day-1 ), and those on mixed bee pollen had the lowest r (0.005 day-1 ). The levels of nutritional content (sugar, lipid and protein) were significantly different among tested pollens. CONCLUSIONS Comparison of N. californicus life table parameters on different diets revealed that the almond pollen (and after that the maize pollen) was a more suitable diet than the others. These findings will be useful in developing appropriate strategies for conservation of N. californicus to control spider mites.

Gammaproteobacteria as essential primary symbionts in the striped shield bug, Graphosoma Lineatum (Hemiptera: Pentatomidae).

Many members of suborder Heteroptra harbor heritable symbiotic bacteria. Here we characterize the gut symbiotic bacterium in Graphosoma lineatum (Hemiptera: Pentatomidae) by using molecular phylogeny, real-time PCR analysis as well as light and electron microscopy observations. The microscopy observations revealed the presence of a large number of rod-shaped bacterial cells in the crypts. A very high prevalence (98 to 100%) of the symbiont infection was found in the insect populations that strongly supports an intimate association between these two organisms. Real-time PCR analysis also showed that the Gammaproteobacteria dominated the crypts. The sequences of 16sr RNA and groEL genes of symbiont showed high levels of similarity (93 to 95%) to Pantoea agglomeranse and Erwinia herbicola Gammaproteobacteria. Phylogenetic analyses placed G. lineatum symbiont in a well-defined branch, divergent from other stink bug bacterial symbionts. Co-evolutionary analysis showed lack of host-symbiont phylogenetic congruence. Surface sterilization of eggs resulted in increased pre-adult stage in the offspring (aposymbionts) in comparison to the normal. Also, fecundity, longevity, and adult stage were significantly decreased in the aposymbionts. Therefore, it seems that the symbiont might play a vital function in the host biology, in which host optimal development depends on the symbiont.

Pollen quality and predator viability: life table of Typhlodromus bagdasarjani on seven different plant pollens and two-spotted spider mite

Abstract Integrated Pest Management programs rely heavily on maximum preservation of predatory insects and mites. Considering the fact that the pollen spectrum accepted by Typhlodromus bagdasarjani Wainstein & Arutunjan is not known, this study aimed towards a comparison of the suitability of seven different pollens including almond (Prunus amygdalis Batsch), maize (Zea mays L.), sunflower (Helianthus annuus L.), date palm (Phoenix dactylifera L.), bitter orange (Citrus aurantium L.), bee pollen and castor bean (Ricinus communis L.), as well as one prey mite (Tetranychus urticae), under laboratory condition (25 ± 1 °C, 65 ± 5% RH, 16:8 (L:D) h). Furthermore nutritional value of different pollens was compared by calculating the protein, lipid and sugars content. Typhlodromus bagdasarjani was able to survive and reproduce on all pollens offered except on castor bean pollen which was toxic, causing 100% pre-adult mortality. The shortest and longest developmental time was observed when predators were supplied with almond and bee pollen, respectively. Pollens from almond, with the highest values of protein and sucrose, and the middle level of lipid content, had the highest nutritional value for T. bagdasarjani as evidenced by the highest value of the intrinsic rate of increase (r= 0.1605 day -1), finite rate of increase (λ= 1.1741 day-1) and net reproductive rate (R0=13.45 offspring/ individual); and the shortest mean developmental time. According to the results, almond pollen can be used to amplify the experimental and commercial mass rearing programs of this predator and maize plant can be recommended as banker plants in greenhouses.

Natural diets versus factitious prey: comparative effects on development, fecundity and life table of Amblyseius swirskii (Acari: Phytoseiidae)

Abstract Using the most suitable alternative diets that are easily available and less expensive than the natural diets may give rise to reduce the rearing costs of natural enemies. Alternative or additional food used for this purpose should be in accordance with the food spectrum of the respective mite species. To our knowledge no information is accessible on the comparison between natural diets and factitious prey for Amblyseius swirskii Athias-Henriot. Therefore, the objective of this study was to evaluate the nutritional value of three natural diets including almond pollen, maize pollen and Tetranychus urticae Koch, as well as four factitious prey comprising eggs of Ephestia kuehniella Zeller, Tyrophagus putrescentiae (Schrank), decapsulated and encapsulated cysts of Artemia franciscana Leach for A. swirskii. The data would seem to suggest that developmental time of individuals fed on pollens was shorter than that of those fed on factitious prey. The gross and net reproductive rate, intrinsic and finite rate of increase of the individuals consumed factitious prey were lower than those of mites fed on natural food diets, for the simple reason of shorter developmental time and higher oviposition rate of this predator on the latter. In conclusion, our results showed that natural foods were more favorable than factitious prey and among them almond pollen and maize pollen were the most suitable for A. swirskii, and thus it should be taken into account for application in its mass production, and supporting its population in greenhouse or field conditions when used in an augmentative approach.

Attempt to Develop Cost-Effective Rearing of Amblyseius swirskii (Acari: Phytoseiidae): Assessment of Different Artificial Diets

Commercial production of Amblyseius swirskii Athias-Henriot based on storage mites needs both space and labor to maintain large cultures of these prey, and also may lead to health problems for workers. Therefore, the accessibility of a suitable artificial diet could eliminate the mentioned problems; however, the artificial diets must support the persistent production of high quality progeny. This study endeavored to find a more easily available and cheaper nutrient that may further reduce the cost of diet production for A. swirskii. The predators performance was determined when it was fed on a basic artificial diet (AD1) composed of honey, sucrose, tryptone, yeast extract, and hen egg yolk, and on eight other artificial diets consisting of 80% AD1 enriched with different nutrients including maize pollen (AD2), hemolymph of Plusia gamma L. (AD3), Ephestia eggs (AD4), Artemis cysts (AD5), Ephestia last-instar larvae (AD6), multivitamin syrup (AD7), bovine serum albumin (AD8), and bull sperm (AD9). The lowest development time was on AD2. The highest value of fecundity and oviposition period were observed on AD5, followed by AD2 and AD4. The intrinsic rate of increase (r) and the finite rate of increase (λ) reached the maximal value on AD5. Feeding on AD2 and AD5 resulted in highest value of R0 (net reproductive rate). Our results indicated that Artemia cysts and maize pollen had better potential to be used as nutrient in artificial diet for mass production of A. swirskii. Overall, it seems that AD2 is the most cost effective than others.

Quantitative Analysis of Long-Term Mass Rearing of Neoseiulus californicus (Acari: Phytoseiidae) on Almond Pollen

Abstract Long-term feeding effects of the almond pollen on the life table parameters of Neoseiulus californicus McGregor were assessed after 5, 10, and 20 generations after introduction in the rearing arena. Furthermore, to evaluate behavioral characteristics of the mass-reared predator (strain A) in face with the real prey, functional and numerical responses of the predator to different densities of the twospotted spider mite nymphs were determined, and the obtained data were compared with those reared on twospotted spider mite (strain T). Long-term rearing did not significantly affect total fecundity of N. californicus (ranged from 37.79 to 41.91 eggs). Nevertheless, preadult duration in the 5th generation was significantly longer than the 10th and 20th generations. The intrinsic rate of increase (r) in the 10th (0.2056 d–1) and 20th (0.2201 d–1) generations had not significant difference together. However, the r value slightly dropped in the 5th generation (0.1706 d–1) because of the irregular offering of fresh pollen to the rearing colonies before that. Both strains of N. californicus exhibited a type II functional response; however, the N. californicus reared on the almond pollen (strain A) had a higher attack rate (a) and shorter handling time (Th). The individuals reared on the almond pollen had a greater size than those reared on twospotted spider mite; its higher predation potential is probably due to this characteristic. Consequently, the rearing of N. californicus on the almond pollen positively affected its attributes including high survivorship, body size, and fecundity, and subsequently higher potential to control twospotted spider mite.

Small interfering RNA pathway contributes to antiviral immunity in Spodoptera frugiperda (Sf9) cells following Autographa californica multiple nucleopolyhedrovirus infection

Autographa californica multiple nucleopolyhedrovirus (AcMNPV) is a well-known virus in the Baculoviridae family. Presence of the p35 gene in the AcMNPV genome as a suppressor of the short interfering RNA (siRNA) pathway is a strong reason for the importance of the siRNA pathway in the host cellular defense. Given that, here we explored the roles of Dicer-2 (Dcr2) and Argonaute 2 (Ago2) genes, key factors in the siRNA pathway in response to AcMNPV infection in Spodoptera frugiperda Sf9 cells. The results showed that the transcript levels of Dcr2 and Ago2 increased in response to AcMNPV infection particularly over 16 h post infection suggesting induction of the siRNA pathway. Reductions in the expression levels of Dcr2 and Ago2 by using specific dsRNAs in Sf9 cells modestly enhanced production of viral genomic DNA which indicated their role in the host antiviral defense. Using deep sequencing, our previous study showed a large number of small reads (siRNAs of ∼20 nucleotides) from AcMNPV-infected Sf9 cells that were mapped to some of the viral genes (hot spots). Down-regulation of Dcr2 in Sf9 cells resulted in enhanced expression levels of the selected virus hotspot genes (i.e. ORF-9 and ORF-148), while the transcript levels of virus cold spots (i.e. ORF-18 and ORF-25) with no or few siRNAs mapped to them did not change. Overexpression of AcMNPV p35 as a suppressor of RNAi and anti-apoptosis gene in Sf9 cells increased virus replication. Also, replication of mutant AcMNPV lacking the p35 gene was significantly increased in Sf9 cells with reduced transcript levels of Dcr2 and Ago2, highlighting the antiviral role of the siRNA pathway in Sf9 cells. Together, our results demonstrate that Dcr2 and Ago2 genes contribute in efficient antiviral response of Sf9 cells towards AcMNPV, and in turn, the AcMNPV p35 suppresses the siRNA pathway, besides being an antiapoptotic protein.

How pollen supplementary diet affect life table and predation capacity of Neoseiulus californicus on two-spotted spider mite

Abstract Supply of alternative food is generally thought to enhance the performance of generalist predatory mites. The effects of three different pollens (maize, date palm, and bee-collected pollen) as supplementary diets on the life table and predation capacity of Neoseiulus californicus McGregor (Acari: Phytoseiidae) on two-spotted spider mite (TSSM) were determined. Total fecundity on TSSM in the presence of the pollen was significantly higher than those on the pollen alone. The intrinsic rate of increase (r) on TSSM in the presence of the maize pollen (0.1409 day-1) was significantly higher than those on TSSM (as control) and/or the other diets. In addition, N. californicus consumed fewer prey in the presence of the maize pollen than the other pollen types. However, lower prey consumption in the presence of this pollen was compensated by an increase in reproduction and survive. In conclusion, the effectiveness of N. californicus on TSSM in the presence of the maize pollen was superior to the other pollens. However, although the other pollen types had no obvious positive effect on the performance of N. californicus, they might increase long-term persistence of the predator-prey system.

Interactions among food diets and rearing substrates affect development and population growth rate of Typhlodromus bagdasarjani

Abstract Notwithstanding the advantageous traits of Typhlodromus bagdasarjani Wainstein and Arutunjan to feed on alternative food such as pollen ensuring the long-term control of greenhouses pests, the nutritional ecology and the role of this predator in biological pest control are rarely addressed. In the current study, the predators development and reproduction on three food sources including Tetranychus urticae Koch, almond pollen, as well as T. urticae+ almond pollen; and the no food condition were evaluated. Additionally, all diets were tested on both artificial and leaf-based substrates to assess the potential host plant effects on the predators performance. Although all larvae on both rearing substrates successfully developed into protonymphal stage, they did not succeed to reach the next stage. Development of T. bagdasarjani was shorter, both female and male, on artificial substrate mainly feeding on almond pollen. Females feeding on almond pollen and almond pollen + T. urticae on artificial substrates had the highest intrinsic and finite rate of increase as well as oviposition rate. Consequently, almond pollen could be used as a conservation management tool to support the early buildup of pre-established natural populations of T. bagdasarjani in open field crops.