Aphagy and vestigial stylets in first-instar nymphs of Aradidae (Hemiptera, Heteroptera)

Aradidae are known for their remarkably long stylets, coiled at rest in the anterior part of the head. However, previous reports indicated that at least some species lacked stylets during the first nymphal instar. A more detailed examination of Aradus betulae 1st-instar nymphs showed that their mandibular and maxillary stylets are abnormally short, not coiled, improperly interlocked, and clearly non-functional. The anteclypeus is relatively small and its internal diverticulum, which accommodates the stylet coil in the older stages, is vestigial. In contrast, the labium, labrum, food canal, and associated structures and muscles, including protractors and retractors of the stylets, are all normally developed. First-instar nymphs of Aradidae are the first known Heteroptera with non-functional mouthparts. To explain this phenomenon, a hypothesis is proposed which links previously unexplained records of non-feeding (but endowed with regular, functional mouthparts) 1st-instar nymphs of various pentatomomorphan families with the special role of that stage in acquiring microbial gut symbionts. A presumed loss of symbionts in the ancestors of Aradidae may have led to reduction of the now useless stylets in the first instar, which retained aphagy, despite a spectacular elongation of stylets in the older, feeding instars.

Insect Mouthpart Transcriptome Unveils Extension of Cuticular Protein Repertoire and Complex Organization

Insects have developed intriguing cuticles with very specific structures and functions, including microstructures governing their interactions with transmitted microbes, such as in aphid mouthparts harboring virus receptors within such microstructures. Here, we provide the first transcriptome analysis of an insect mouthpart cuticle (“retort organs” [ROs], the stylets' precursors). This analysis defined stylets as a complex composite material. The retort transcriptome also allowed us to propose an algorithmic definition of a new cuticular protein (CP) family with low complexity and biased amino acid composition. Finally, we identified a differentially expressed gene encoding a pyrokinin (PK) neuropeptide precursor and characterizing the mandibular glands. Injection of three predicted synthetic peptides PK1/2/3 into aphids prior to ecdysis caused a molt-specific phenotype with altered head formation. Our study provides the most complete description to date of the potential protein composition of aphid stylets, which should improve the understanding of the transmission of stylet-borne viruses.

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First transcriptome of aphid retort glands and stylet cuticular protein composition

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A pyrokinin transcript is mandibular gland specific at the onset of adult moult

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Stylet cuticle is of higher protein complexity than other insect cuticles

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A new class of low-complexity cuticular proteins is predicted

Pronymphs, hatching, and proboscis assembly in leafhoppers and froghoppers (Hemiptera, Cicadellidae and Aphrophoridae)

Pharate 1st instar nymphs enclosed in the embryonic cuticle, referred to as pronymphs, were studied in a froghopper Aphrophora pectoralis Mats. (Aphrophoridae) and the leafhoppers Oncopsis flavicollis (L.), Populicerus populi (L.), Alebra wahlbergi (Boh.), Igutettix oculatus (Lindb.), and Scenergates viridis (Vilb.) (Cicadellidae). The species vary in the relative length of the pronymphal antennae and details of sculpturing of the cephalic region. No egg bursting structures were observed, except small denticles on the crown region of S. viridis pronymphs. Rudimentary mandibular and maxillary stylets of a pronymph are external, short, tubular appendages containing tips of the corresponding nymphal stylets, whose more basal parts develop inside of the head. Casting off of the embryonic cuticle results in the nymphal stylets being passively pulled out and assuming a close-set parallel orientation. Once the sheaths of unsclerotized cuticle secreted by the peripodial epithelium and enveloping each developing stylet have been cast off with the exuviae, the bare stylets become squeezed and interlocked into a functional bundle. The roles of the maxillary plates, clypeus, labrum, and labium in the stylet bundle assembly are discussed. The process repeats after each molt.

Stylet biogenesis in Bactericera cockerelli (Hemiptera: Triozidae)

The discovery of 'Ca. Liberibacter solanacearum', causal agent of certain solanaceous and apiaceous crop diseases, inside the functional (intrastadial) and pharate stylet anatomy of the potato psyllid prompted elucidation of the mechanism of stylet replacement as a novel exit portal in the transmission pathway. In Hemiptera, presumptive (formative) stylets, secreted during consecutive pharate instars, replace functional stylets lost with the exuviae. In potato psyllids, each functional stylet has a hollow core filled with a cytology that extends out of the core to form a hemispherical aggregate of cells, the 'end-cap', somewhat resembling a golf ball on a tee. A tightly folded mass of extremely thin cells, the 'matrix', occurs inside the end-cap. Micrograph interpretations indicate that during the pharate stage, the end-cap apolyses from the core and 'deconstructs' to release and expand the matrix into a long, coiled tube, the 'atrium'. Cells that were in contact with the inner walls of the functional stylet core maintain their position at the apex of the tube, and secrete a new stylet, apex first, the growing length of which descends into the tube until completed. They then despool from the coils into their functional position as the exuviae is shed.

Sex differences in piercing-sucking sites on leaves of Ligustrum lucidum (Oleaceae) infested by the Chinese white wax scale insect, Ericerus pela (Chavannes) (Hemiptera: Coccidae)

The type of host tissues and cells ingested by piercing and sucking insects greatly affects their nutrient intake, which may subsequently affect insect fitness. This study describes the sex differences in feeding site selection between male and female nymphs of the Chinese white wax scale insect (CWWS), Ericerus pela (Chavannes), feeding on leaves of the Chinese privet, Ligustrum lucidum. Our data showed that the stylet tips of female nymphs terminated in the phloem sieve elements of main or lateral veins, while those of male nymphs terminated in the palisade parenchyma. We concluded that female nymphs fed from sieve elements and males fed from parenchyma cells. The potential impact of these feeding patterns was discussed in relation to the selection of a site for attachment, nutrient acquisition, and mouthpart stretching mechanism. Among these factors, selection of a site for attachment and mouthpart stretching mechanism may be the main cause of sex differences in feeding sites between female and male nymphs of CWWS.

[Ultrastructure of Ericerus pela (Chavannes) nymph mouthparts and ecological adaptations]

The ultrastructure of nymph mouthparts of the Chinese white wax scale (CWWS), Ericerus pela, consists internally of the crumena, tentorium, the stylet bundle, comprised of two mandibular stylets and two maxillary stylets, and the external clypeolabral shield, labium and sensilla. The mouthpart morphology and structures of the female nymphs are similar to the male. The mouthparts of CWWS have significantly different features in comparison to aphids and other coccids. First, the mouthparts of CWWS have a crumena and a developed tentorium. Second, the labrum is highly degraded and the labium is short and one-segmented. Third, the maxillary stylets have two 'T' type locks. Lastly, the hairs of the mouthpart are sparse and the sensilla are simple. As the labrum and labium of CWWS displayed a high degree of degradation and the tentorium was found to be highly developed, the stretching of the stylet bundle was considered to be controlled by the tentorium and crumena together. Furthermore, the degraded sensilla may be related to a specialization of feeding behavior. There were no significant differences in the length and diameter of the stylet bundles between the female and male. However, the length and diameter of the stylet bundles were significantly different between the first instar nymphs and the second instar nymphs. The first instar nymphs had stylet fascicles that were shorter and soft and initially lived on the leaves of the host trees, presumably because the leaves were thinner and they were able to pierce the leaves while the stylet bundle was relatively soft. However, the second instar nymphs had stylet bundles that were relatively hard. After the numphs molted, the degree of ossification of the stylet bundles was enhanced (increased) and the nymphs returned to the branches for living, where the strengthened stylet bundles may provide a better adaption for the thicker bark. All told, the first and second stage instar CWWS nymphs switched from leaves to the branches in order to find a safe habitat and stable food source.

Anterior alimentary canal of the pear Psylla, Psylla pyricola foerster (Homoptera, Psyllidae)

Scanning and light microscopy investigations of the anterior alimentary canal of the pear psylla, Psylla pyricola Foerster (Homoptera: Psyllidae), revealed the morphology of the labium and stylets, as well as the presence of sensory structures and a valve in the precibarium. The labium consists of three telescoping segments with an internal labial groove, which surrounds and supports the stylet bundle. Also a part of the labial groove is the internal labial clamp. The stylet bundle is comprised of paired styliform mandibles and maxillae, which interlock to form the food and salivary canals. The stylet bundle proximal to the labium forms a large loop within a membranous crumena. When fully retracted the coiled stylets are under tension. Stylet extension generates increasing tension so that when retracted the stylets readily recoil within the crumena. Penetration of leaf tissues by the stylet bundle is dependent on the interaction between stylet muscles, opening and closing of the labial clamp, the barbed stylet tips, and the ventral position of the labium. Proximal to the crumena the paired stylets separate and diverge at the entrance of the precibarium, which is formed by the interlocking of the epi-and hypopharynges. There are 18 sensory structures in the precibarium, as well as a precibarial valve. These structures appear to be homologous to similar structures observed previously in aphids and leafhoppers. The morphology and the location of the precibarial sensilla suggest that, like the precibarial sensory organs of aphids and leafhoppers, they are gustatory and probably mediate acceptance or rejection of plant fluids, thus playing a major role in locating tissues for feeding.

BIONOMICS OF THE PEAR PSYLLA, PSYLLA PYRICOLA FOERSTER, IN THE OKANAGAN VALLEY OF BRITISH COLUMBIA

In the Okanagan Valley of British Columbia, the pear psylla, Psylla pyricola Foerster, develops only on pear. It overwinters in a variety of protected situations in or near pear trees, e.g., under bark scales, in ground crevices, occasionally under the bark of apple tree interplants in pear orchards, and even in such unlikely quarters as the nests of hornets. Four summer generations and an over-wintering generation occurred in 1961 and 1962. Development of the psyllid from egg to adult required 6 to 7 weeks in the cool weather of spring but only 4 to 5 weeks in midsummer. Heavy rains readily remove nymphs from leaves and twigs but cannot dislodge the firmly attached eggs. Adults have been noted clinging to leaves and twigs in winds of up to 55 miles per hour. Biological control of the pear psylla is affected mainly by two predators, the anthocorid bug, Anthocorus melanocerus Reuter, and the neuropteran, Chrysopa oculatus Say. Dormant oil sprays are detrimental to the anthocorid. There was a major migratory flight of the pear psylla in August and September and two minor migratory flights in late March and mid-June. Aitborne psyllids decreased in numbers with elevation.