RNA interference and functional characterization of a tergal gland alpha amylase in the German cockroach, Blattella germanica L

Insect α-Amylases and Their Application in Pest Management

Amylase is an indispensable hydrolase in insect growth and development. Its varied enzymatic parameters cause insects to have strong stress resistance. Amylase gene replication is a very common phenomenon in insects, and different copies of amylase genes enable changes in its location and function. In addition, the classification, structure, and interaction between insect amylase inhibitors and amylases have also invoked the attention of researchers. Some plant-derived amylase inhibitors have inhibitory activities against insect amylases and even mammalian amylases. In recent years, an increasing number of studies have clarified the effects of pesticides on the amylase activity of target and non-target pests, which provides a theoretical basis for exploring safe and efficient pesticides, while the exact lethal mechanisms and safety in field applications remain unclear. Here, we summarize the most recent advances in insect amylase studies, including its sequence and characteristics and the regulation of amylase inhibitors (α-AIs). Importantly, the application of amylases as the nanocide trigger, RNAi, or other kinds of pesticide targets will be discussed. A comprehensive foundation will be provided for applying insect amylases to the development of new-generation insect management tools and improving the specificity, stability, and safety of pesticides.

The prevalence of Wolbachia in multiple cockroach species and its implication for urban insect management

Cockroach management relies heavily on the use of conventional insecticides in urban settings, which no longer provide the anticipated level of control. Knowledge of cockroach endosymbionts, like Wolbachia, might provide novel avenues for control. Therefore, we screened 16 cockroach species belonging to 3 families (Ectobiidae, Blattidae, and Blaberidae) for the presence of Wolbachia. We mapped the evolution of Wolbachia-cockroach relationships based on maximum likelihood phylogeny and phylogenetic species clustering on a multi-loci sequence dataset (i.e., coxA, virD4, hcpA, and gatB) of Wolbachia genes. We confirmed the previous report of Wolbachia in 1 Ectobiid species; Supella longipalpa (Fab.), and detected the presence of Wolbachia in 2 Ectobiid species; Balta notulata (Stål) and Pseudomops septentrionalis Hebard, and 1 Blaberid species; Gromphadorhina portentosa (Schaum). All cockroach-associated Wolbachia herein detected were clustered with the ancestor of F clade Wolbachia of Cimex lectularius L. (bed bugs). Since Wolbachia provision C. lectularius with biotin vitamins that confer reproductive fitness, we screened the cockroach-associated Wolbachia for the presence of biotin genes. In toto, our results reveal 2 important findings: (i) Wolbachia is relatively uncommon among cockroach species infecting about 25% of species investigated, and (ii) cockroach-associated Wolbachia have biotin genes that likely provide nutritional benefits to their hosts. Thus, we discuss the potential of exploring Wolbachia as a tool for urban insect management.

Two Antenna-Enriched Carboxylesterases Mediate Olfactory Responses and Degradation of Ester Volatiles in the German Cockroach Blattella germanica

Insects have evolved an extremely sensitive olfactory system that is essential for a series of physiological and behavioral activities. Some carboxylesterases (CCEs) comprise a major subfamily of odorant-degrading enzymes (ODEs) playing a crucial role in odorant signal inactivation to maintain the odorant receptor sensitivity. In this study, 93 CCEs were annotated in the genome of the German cockroach Blattella germanica, a serious urban pest. Phylogenetic and digital tissue expression pattern analyses identified two antenna-enriched CCEs, BgerCCE021e3 and BgerCCE021d1, as candidate ODEs. RNA interference (RNAi)-mediated knockdown of BgerCCE021e3 and BgerCCE021d1 resulted in partial anosmia with experimental insects exhibiting reduced attraction to ester volatile resources and slower olfactory responses than controls. Furthermore, enzymatic conversion of geranyl acetate by crude male antennal extracts from BgerCCE021e3 and BgerCCE021d1 RNAi insects was also significantly reduced. Our results provide evidence for CCE function in German cockroach olfaction and provide a basis for further exploring behavioral inhibitors that target olfactory-related CCEs.

The Inhibitory Effects of RNA-Interference-Mediated Guanylate Cyclase Knockdown on Larval Metamorphosis and Early Progeny Growth of Razor Clam

Guanylate cyclase (GC, cGMPase) is a key enzyme in organisms, catalyzing the synthesis of cGMP from GTP, thus making cGMP work. cGMP plays a vital role in the regulation of cell and biological growth as a second messenger in signaling pathways. In this study, we screened and identified cGMPase from the razor clam Sinonovacula constricta, which encoded 1257 amino acids and was widely expressed in different tissues, especially the gill and liver. We also screened one double-stranded RNA (dsRNA), cGMPase, which was used to knockdown cGMPase at three larval metamorphosis development stages: trochophores-veliger larve, veliger larve-umbo larve, and umbo larve-creeping larvae. We showed that interference at these stages significantly inhibited larval metamorphosis and survival rates. cGMPase knockdown resulted in an average metamorphosis rate of 60% and an average mortality rate of 50% when compared with control clams. After 50 days, shell length and body weight were inhibited to 53% and 66%, respectively. Thus, cGMPase appeared to regulate metamorphosis development and growth in S. constricta. By examining the role of the key gene in the metamorphosis development of S. constricta larvae and the growth and development period, we can provide some data reference for studying the growth and development mechanism of shellfish, and the results provided basic information for the breeding of S. constricta.

Expression profiles of an inactive aspartic protease (Bla g 2 allergen) in different tissues and developmental stages of the German cockroach (Blattella germanica)

Tergal glands are found in many insect species and contain constituents such as pheromones, sugars, proteins, and so forth. Preliminary studies have revealed that tergal gland secretions in the German cockroach (Blattella germanica L.) contain the human allergen Bla g 2 (B. germanica allergen 2), an inactive aspartic protease. Although Bla g 2 protein expression has been detected previously in various German cockroach body parts, including male tergal glands, studies that link protein expression in various life stages and tissues with mRNA and protein abundance have not been conducted. Therefore, the goal of this study was to measure the relative abundances of Bla g 2 protein and mRNA in different tissues and life stages of B. germanica using immunoblotting, quantitative PCR, and liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based quantitative profiling. We found that Bla g 2 protein was detected in every sampled tissue, including the male tergal glands. Protein abundance was relatively high in adult males and their tergal glands in comparison to nymphs and virgin females. Similarly, Bla g 2 mRNA transcript levels were also comparatively higher in male tergal glands and adult males. In conclusion, this study provides new information on the relative abundance and distribution of Bla g 2 allergen, a medically significant protein, in different tissues and developmental stages of the German cockroach and lays the foundation for future studies that aim to determine the function of this protein in B. germanica development.

A Review of Alternative Management Tactics Employed for the Control of Various Cockroach Species (Order: Blattodea) in the USA

Simple Summary

Some cockroaches that live within and around human environments are considered pests of public health importance because they can carry and transfer human pathogenic microorganisms to food and food handling surfaces; infestations could result in cockroach allergen-induced allergic sensitization and asthma in sensitized individuals. In addition, cockroaches can cause psychological stress and stigma in people living in infested locations. Historically, cockroach control has been based on the use of insecticide sprays. However, in certain situations, sole dependence on insecticides for cockroach control can lead to issues such as pesticide resistance evolution and raises public concern due to the impact on the environment and human health. To overcome these problems, the use of reduced risk insecticide options (e.g., baits) and their combined use with alternative tactics is recommended. This review aims to examine alternative tactics used for cockroach control, with emphasis on those that are proven to be efficacious, and/or have potential for their incorporation in management programs of important domestic and peridomestic cockroaches in the USA. Remarkable examples of successful cockroach control programs are those that educate the public, promote cleanliness and hygiene, use traps to monitor infestation levels and utilize insecticide baits.

Abstract

Effective control of domestic and peridomestic cockroaches requires integrated approaches that emphasize concurrent use of chemicals with alternative control tactics. An integrated pest management (IPM) approach is particularly justified in environments where satisfactory cockroach control cannot be achieved due to multiple factors including development of insecticide aversion and resistance in some cockroach species, and poor sanitation or structural issues that foster infestations. While a flurry of research effort has been devoted to study alternative tactics for cockroach control, only a few of them have been evaluated in the context of IPM programs. This review focuses on examining studies on alternative tactics that are proven efficacious, economical, and logistically feasible for their inclusion in IPM programs for important domestic and peridomestic cockroaches in the USA. Management programs that educate the public on cockroach biology, behavior, and the importance of sanitation; use of traps to monitor infestation levels; apply targeted low impact insecticides such as baits, have demonstrated a greater success for effective and sustainable control of cockroaches when compared to an insecticide-only approach. Incorporation of other alternative control methods to IPM programs will require more applied research that validates their use in real-world scenarios and demonstrates their cost-effectiveness.

Silencing the odorant coreceptor (Orco) disrupts sex pheromonal communication and feeding responses in Blattella germanica: toward an alternative target for controlling insect-transmitted human diseases

BACKGROUND

The German cockroach, Blattella germanica, is one of the most severe pests of urban and rural areas. High-throughput genetic screening approaches indicate that the olfactory system of this pest is extremely powerful because it has an extensive array of olfactory receptor genes compared with many other insect species. Several of these genes have been identified previously, but their functions have not yet been characterized.

RESULTS

This study describes the sequence of five transcriptomes of B. germanica adult male antennae, female antennae, maxillary palps, legs, and fifth-instar nymph antennae to investigate expression patterns of odorant receptors (ORs). Approximately 90% of ORs were found to be the most highly expressed genes in adult or nymph antennae. Additionally, every OR requires an odorant co-receptor (Orco) to become fully functional, and this was selected and successfully inhibited by injection of the corresponding double-stranded (ds)RNA targeting the Orco. A strong RNA interference (RNAi) effect was observed in which > 75% of Orco messenger RNA (mRNA) was clearly suppressed after 72 h of treatment. Olfactory behavioral assays showed that Orco-impaired B. germanica respond more slowly and show less attraction to one volatile sex pheromone and food resources compared with a control group.

CONCLUSION

The results show that Orco plays a pivotal role in both sex pheromone and food-seeking olfactory processes, and provide an alternative genetic technique for controlling this urban pest species by olfactory disruption. © 2020 Society of Chemical Industry.

Venom α-amylase of the endoparasitic wasp Pteromalus puparum influences host metabolism

BACKGROUND

Pteromalus puparum (Hymenoptera: Pteromalidae) is an endoparasitoid wasp that parasitizes many butterfly species, including a Brassicaceae pest, Pieris rapae (Lepidoptera: Pieridae), the small white cabbage butterfly. P. puparum females inject venom along with their eggs into hosts to ensure successful parasitism. The venom regulates host development and behavior, suppresses host immunity, and influences host metabolism. It has been shown that the venom contains α-amylases, a group of hydrolytic enzymes that act in insect sugar metabolism. So far, three α-amylases have been identified in P. puparum (Pteromalus puparum α-amylases, PpAmys) and the function of PpAmy1 has been reported. However, the functions of PpAmy2 and PpAmy3 remain unknown.

RESULTS

We studied the functions of an α-amylase highly expressed in muscle-rich tissues (PpAmy2) and an α-amylase highly expressed in venom apparatus (PpAmy3) using RNAi and GC-TOF-MS techniques. Knockdown of PpAmy3 by RNAi reduced the body length and weight of 1-day old larval offspring while there was no significant effect when PpAmy2 was knocked down. Compared to the control injected with siGFP, many metabolites in P. puparum changed when PpAmy2 was knocked down, while the injection of PpAmy3 recombinant protein into host induced metabolite changes in the P. rapae hemolymph.

CONCLUSION

Our study demonstrated that PpAmy2 acts in metabolism in the muscles of the parasitoid while PpAmy3 could influence the host metabolism and may support the development of parasitic wasp offspring. © 2020 Society of Chemical Industry.

A digestive tract expressing α-amylase influences the adult lifespan of Pteromalus puparum revealed through RNAi and rescue analyses

BACKGROUND

Midgut and salivary gland α-amylases are digestive enzymes required for the development of insects and have been investigated in some insect species. However, α-amylases in the endoparasitioid wasps have not been reported. Pteromalus puparum (Hymenoptera: Pteromalidae) is a dominant endoparasitioid wasp that parasitizes many butterfly species, including the Brassicaceae pest Pieris rapae (Lepidoptera: Pieridae). Here, we studied the characteristics and functions of three α-amylases in P. puparum.

RESULTS

We cloned three genes encoding α-amylases in P. puparum, PpAmy1, PpAmy2 and PpAmy3. The full length of the PpAmy1 cDNA is 1872 bp, encoding 496 amino acids, the PpAmy2 cDNA is 1863 bp long, encoding 518 amino acids, and PpAmy3 cDNA consists of 1802 bp encoding 521 amino acids. PpAmys are highly similar in amino acid sequences, but they have separate tissue distributions. Phylogenetic results show that gene duplications may occur between PpAmy2 and PpAmy3. PpAmy1 and PpAmy3 are most highly expressed in the digestive tract and the venom apparatus, respectively, while PpAmy2 is broadly expressed in all tissues. We report that PpAmy1 acts in the digestive tract, where it influences lifespan as demonstrated using RNAi and α-amylase rescue analyses, and there is no significant difference in longevity when PpAmy2 and PpAmy3 are knocked down.

CONCLUSION

PpAmys probably have roles in carbohydrate metabolism of P. puparum and its host/parasitoid relationships. The characterization and functional study of PpAmys lays the foundation for the protection and utilization of parasitoid resources, and the biological control of agricultural pests. © 2019 Society of Chemical Industry.

2018 Highlights of Urban Entomology

The field of urban entomology is primarily associated with the study of ants, bed bugs, cockroaches, termites, and other occasional invader pests that are found within or near human-made structures. A wide array of peer-reviewed studies were published in 2018. The topics of these articles ranged from genomes and basic biology of urban insects to various applied aspects of pest management. Key findings of these papers are presented and discussed from the perspective of the contributions they make to the discipline of urban entomology. Additionally, potential future research opportunities that are evident from these publications have been outlined.

The Amylases of Insects

Alpha-amylases are major digestive enzymes that act in the first step of maltopolysaccharide digestion. In insects, these enzymes have long been studied for applied as well as purely scientific purposes. In many species, amylases are produced by multiple gene copies. Rare species are devoid of Amy gene. They are predominantly secreted in the midgut but salivary expression is also frequent, with extraoral activity. Enzymological parameters are quite variable among insects, with visible trends according to phylogeny: Coleopteran amylases have acidic optimum activity, whereas dipteran amylases have neutral preference and lepidopteran ones have clear alkaline preference. The enzyme structure shows interesting variations shaped by evolutionary convergences, such as the recurrent loss of a loop involved in substrate handling. Many works have focused on the action of plant amylase inhibitors on pest insect amylases, in the frame of crop protection by transgenesis. It appears that sensitivity or resistance to inhibitors is finely tuned and very specific and that amylases and their inhibitors have coevolved. The multicopy feature of insect amylases appears to allow tissue-specific or stage-specific regulation, but also to broaden enzymological abilities, such as pH range, and to overcome plant inhibitory defenses.