Sex Pheromone of the Cotton Mealybug, Phenacoccus solenopsis, with an Unusual Cyclobutane Structure

Ancient origin and conserved gene function in terpene pheromone and defense evolution of stink bugs and hemipteran insects

Insects use diverse arrays of small molecules such as metabolites of the large class of terpenes for intra- and inter-specific communication and defense. These molecules are synthesized by specialized metabolic pathways; however, the origin of enzymes involved in terpene biosynthesis and their evolution in insect genomes is still poorly understood. We addressed this question by investigating the evolution of isoprenyl diphosphate synthase (IDS)-like genes with terpene synthase (TPS) function in the family of stink bugs (Pentatomidae) within the large order of piercing-sucking Hemipteran insects. Stink bugs include species of global pest status, many of which emit structurally related 15-carbon sesquiterpenes as sex or aggregation pheromones. We provide evidence for the emergence of IDS-type TPS enzymes at the onset of pentatomid evolution over 100 million years ago, coinciding with the evolution of flowering plants. Stink bugs of different geographical origin maintain small IDS-type families with genes of conserved TPS function, which stands in contrast to the diversification of TPS genes in plants. Expanded gene mining and phylogenetic analysis in other hemipteran insects further provides evidence for an ancient emergence of IDS-like genes under presumed selection for terpene-mediated chemical interactions, and this process occurred independently from a similar evolution of IDS-type TPS genes in beetles. Our findings further suggest differences in TPS diversification in insects and plants in conjunction with different modes of gene functionalization in chemical interactions.

Morpho-functional Analysis of the Head Glands in Three Auchenorrhyncha Species and Their Possible Biological Significance

The Cicadomorpha Philaenus spumarius, Neophilaenus campestris, and Cicadella viridis are known transmitters of the bacterium Xylella fastidiosa. Here, we studied the ultrastructural organization of their cephalic glands. Our investigations with scanning, transmission, focused ion beam-scanning electron microscopes and light microscope revealed for the first time in Auchenorrhyncha the presence of two types of cephalic glands. Both belonged to the Class III epidermal glands, according to the Noirot and Quennedey classification. Type A glands were the most common, being mainly located around antennae, lorum, and gena. Moreover, these glands were observed also on the abdomen and thorax, always in association with sensilla trichoidea. The second type of glands (type B) were located exclusively at the apical part of the postclypeus in P. spumarius and N. campestris. The ultrastructural organization was similar in both types, being composed of a secretory cell and a conducting canal. Differences were observed in the width of the cuticular opening, being smaller in the type II glands. In addition, we have recorded the presence of a maxillary sensory pit in all species and described sensilla trichoidea ultrastructural organization. Finally, we discussed the ultrastructural organization of the glands and their potential biological role.

Behavioural and electrophysiological responses of Philaenus spumarius to odours from conspecifics

The meadow spittlebug, Philaenus spumarius L. (Hemiptera: Auchenorrhyncha: Aphrophoridae), is the main vector of Xylella fastidiosa subsp. pauca strain ST53, the causal agent of the Olive Quick Decline Syndrome. Philaenus spumarius and other Auchenorrhyncha are known to communicate via vibrations, whereas the possible occurrence of semiochemical communication has been poorly investigated so far. Through a chemical ecology approach, we provide evidence of intraspecific chemical communication in P. spumarius. In Y-tube olfactometer bioassays, males were attracted to unmated females as well as toward the headspace volatile extracts collected from unmated females. Conversely, females did not respond to unmated male volatiles or their extracts, nor did males and females respond to volatiles from individuals of the same sex. Electroantennography assays of unmated male and female headspace extracts elicited measurable responses in the antennae of both sexes. Male responses to body wash extracts from both sexes were stronger compared to female responses. Thus, suggesting the presence of compounds that are highly detected by the male's olfactory system. The female head seemed to be the source of such compounds. This is the first record of intraspecific chemical communication in P. spumarius and one of the very few records in Auchenorrhyncha. Possible biological roles are under investigation.

Biology, ecology, and management of cotton mealybug Phenacoccus solenopsis Tinsley (Hemiptera: Pseudococcidae)

The cotton mealybug Phenacoccus solenopsis Tinsley (Hemiptera: Pseudococcidae), is a highly invasive and harmful pest. It causes considerable loss of cotton crops in China, India and Pakistan. Little is known about its bionomics since it was first recorded in Pakistan and India in 2005. Rapid spread of this pest worldwide has accelerated research on its biology, ecology and management. The P. solenopsis has a short life cycle, and optimal temperatures lead to an increase in the number of generations per year, which is a serious threat to cotton crop production. Cotton mealybug is native to the USA, although it has now spread to >43 countries. Insecticidal control is the primary and dominant practice for this pest, and its resistance to commonly used insecticides is increasing. Biocontrol agents have strong potential for the management of nymphal instar stages. We read >250 articles related to our review title and finally reviewed recent advances in the understanding of P. solenopsis biology, ecology and control approaches, aiming to highlight integrated and biological management practices of this pest. © 2021 Society of Chemical Industry.

Mating Disruption of Pseudococcus calceolariae (Maskell) (Hemiptera, Pseudococcidae) in Fruit Crops

Simple Summary

The citrophilous mealybug is an economically important pest that is mainly controlled using insecticides, not always successfully, and with unintended negative environmental side effects. In our research, we tested a specific and sustainable control tool using the mealybug sex pheromone. Mating disruption is a technique that aims to reduce mating between males and females by inundating the area with the synthetic sex pheromone of the species, thereby reducing reproduction and consequently populations over time and damage. For this purpose, the mealybug pheromone, incorporated into a polymeric substance for its release, was applied in a tangerine and an apple orchard, in two seasons (2017/2018 and 2019/2020). In all seasons, a reduction in the males catches in traps after deploying pheromone was observed, which would indicate a decrease in the probability of successful mating compared to control plots. The duration of this effect was around one year. Mealybug abundance on trees was extremely low throughout the trials, so it was not possible to observe a reduction of populations or damage. This research shows that the use of this pheromone-based technique has good potential for controlling the citrophilous mealybug, with the advantage of being environmentally friendly and non-toxic.

Abstract

Pseudococcus calceolariae, the citrophilous mealybug, is a species of economic importance. Mating disruption (MD) is a potential control tool. During 2017–2020, trials were conducted to evaluate the potential of P. calceolariae MD in an apple and a tangerine orchard. Two pheromone doses, 6.32 g/ha (2017–2018) and 9.45 g/ha (2019–2020), were tested. The intermediate season (2018–2019) was evaluated without pheromone renewal to study the persistence of the pheromone effect. Male captures in pheromone traps, mealybug population/plant, percentage of infested fruit at harvest and mating disruption index (MDI) were recorded regularly. In both orchards, in the first season, male captures were significantly lower in MD plots compared to control plots, with an MDI > 94% in the first month after pheromone deployment. During the second season, significantly lower male captures in MD plots were still observed, with an average MDI of 80%. At the third season, male captures were again significant lower in MD than control plots shortly after pheromone applications. In both orchards, population by visual inspection and infested fruits were very low, without differences between MD and control plots. These results show the potential use of mating disruption for the control of P. calceolariae.

Synthesis of the Sex Pheromone of the Oleander Scale ( Aspidiotus nerii)

A total synthesis of the oleander scale [ Aspidiotus nerii (Bouche)] sex pheromone, the unique sesquiterpenoid containing a cyclobutane moiety of this class of compounds, has been developed. In order to implement this sex pheromone as a new environmentally friendly tool to manage this pest, a more cost-effective, multigram synthesis was required. This new synthetic route, having a Blaise reaction, iron-catalyzed carbon-carbon coupling, and [2 + 2] photocycloaddition reactions as key steps, provides a general access to 4-alkyl lactones as well as a robust access to the target sex pheromone. Starting from readily available compounds as 3-hydroxypropanenitrile, ethyl bromoacetate, and 2-acetyl butyrolactone, the synthetic sequence afforded the A. nerii sex pheromone with minimum intermediate purification and good overall yield in nine linear steps.

Sex pheromone of a coccoid insect with sexual and asexual lineages: fate of an ancestrally essential sexual signal in parthenogenetic females

Sex pheromones play a central role in intersexual communication for reproduction in many organisms. Particularly in insects, reproductive isolation that leads to speciation is often achieved by shifts of pheromone chemistries. However, the divergence and evolution of pheromones remain largely unknown. This study reveals a unique evolutionary consequence for terpenoid pheromones in coccoid insects. Coccoids, such as mealybugs, show clear sexual dimorphism: males are dwarf and short-lived, whereas females are wingless and almost immobile. Female pheromones are therefore indispensable for males to navigate for sexual reproduction, but some females can reproduce asexually. Interestingly, a derived asexual lineage that reproduces by parthenogenesis coexists with its ancestral lineage that reproduces sexually in a population of the pineapple mealybug, Dysmicoccus brevipes Here, we isolated, characterized and synthesized a novel monoterpene, (-)-(anti-1,2-dimethyl-3-methylenecyclopentyl)acetaldehyde, as a pheromone of the sexual females of Dbrevipes This monoterpene aldehyde, with an irregular linkage of isoprene units, is notable, because all mealybug pheromones previously reported are carboxylic esters of terpenols. This compound was, however, never produced by the asexual females. As a consequence of acquiring parthenogenetic reproduction, the asexual females appear to have abandoned the production of the sex pheromone, which had been essential to attracting males in their ancestors.

(1S,3R)-cis-Chrysanthemyl Tiglate: Sex Pheromone of the Striped Mealybug, Ferrisia virgata

Derivatives of 2,2-dimethyl-3-(2-methylprop-1-enyl)cyclopropanecarboxylic acid (chrysanthemic acid) are classic natural pyrethroids discovered in pyrethrum plants and show insecticidal activity. Chrysanthemic acid, with two asymmetric carbons, has four possible stereoisomers, and most natural pyrethroids have the (1R,3R)-trans configuration. Interestingly, chrysanthemic acid-related structures are also found in insect sex pheromones; carboxylic esters of (1R,3R)-trans-(2,2-dimethyl-3-(2-methylprop-1-enyl)cyclopropyl)methanol (chrysanthemyl alcohol) have been reported from two mealybug species. In the present study, another ester of chrysanthemyl alcohol was discovered from the striped mealybug, Ferrisia virgata (Cockerell), as its pheromone. By means of gas chromatography-mass spectrometry, nuclear magnetic resonance spectrometry, and high-performance liquid chromatography analyses using a chiral stationary phase column and authentic standards, the pheromone was identified as (1S,3R)-(-)-cis-chrysanthemyl tiglate. The (1S,3R)-enantiomer strongly attracted adult males in a greenhouse trapping bioassay, whereas the other enantiomers showed only weak activity. The cis configuration of the chrysanthemic acid-related structure appears to be relatively scarce in nature, and this is the first example reported from arthropods.