Scent gland apparatus in the Western conifer seed bug Leptoglossus occidentalis Heidemann (Heteroptera: Coreidae)

The coreid Leptoglossus occidentalis is a Nearctic bug responsible for severe seed losses to pine orchards. When disturbed, adults and nymphs emit a defensive secretion deemed an allomone. Here we describe the gross morphology of the scent gland apparatus and the related evaporatory structures in nymphs and adults of L. occidentalis, through light microscopy and scanning electron microscopy. Adults of both sexes possess a metathoracic scent gland complex (MTG) including a central orange‐yellow reservoir and a pair of white lateral glands, connected by ducts to the reservoir. The MTG belongs to the diastomian type, with two ostioles located on the metathorax associated with a microsculptured cuticular accumulation area, i.e. evaporatory area, which can prevent the spread of the secretion on to non‐evaporative cuticle and increase scent fluid evaporation. A high number of male‐specific sternal gland pores were observed. These pores and associated glands are likely the source of an attractant pheromone, which could be extremely useful in monitoring and combating this invasive pest. In nymphs, MTG is replaced by two dorsal abdominal scent glands (DAGs) located between the 4th and the 6th urotergites. DAGs are reddish cuticle‐lined sacs with gland cells forming the gland wall; the scent substances are released through two orifices lying on the mid‐dorsal abdominal line between urotergites IV–V and V–VI. Also in nymphs, peculiar cuticular evaporatory areas surround both orifices.     

First records of the western conifer seed bug Leptoglossus occidentalis Heid. (Heteroptera, Coreidae) from Russia and Ukraine, regularities in its distribution and possibilities of its range expansion in the palaearctic region

The paper presents the first records of the western conifer seed bug Leptoglossus occidentalis Heidemann, 1910 for the fauna of Russia (Rostov Province) and Ukraine (Crimea and Zaporizhia Province). The dependence of the spread of this species on positive and negative temperatures and the availability of food plants is considered. The forecast of further expansion of its range in the Palaearctic Region is given.     

Specific biochemical marker-based techniques for the identification of damage to Douglas-fir seed resulting from feeding by the western conifer seed bug, Leptoglossus occidentalis Heidemann (Hemiptera: Coreidae)

Specific biochemical marker-based techniques were tested for their ability to distinguish between seeds of Douglas-fir, Pseudotsuga menziesii (Mirbel) Franco, that were filled or unfilled (aborted) at maturity and those that were damaged or emptied by the western conifer seed bug, Leptoglossus occidentalis Heidemann. A polyclonal antibody raised against salivary gland extracts from L. occidentalis successfully identified residual salivary proteins on Western blots containing proteins from Douglas-fir seeds that had sustained various degrees of seed bug feeding damage. In a single blind experiment, the polyclonal antibody correctly identified 100% of undamaged control, 97% of unfilled control (aborted), and 98% of seed bug damaged seeds. Polyclonal antibodies raised against insoluble alfalfa crystalloid storage protein (11S globulin) detected the depletion of 11S globulin and the subsequent appearance of its hydrolyzed fragments in the soluble protein fraction of Douglas-fir seeds that were fed-upon by the seed bug. Feeding by L. occidentalis nymphs caused ca. 98% depletion of insoluble protein, but only ca. 53% reduction in the amount of soluble protein in seeds that appeared empty on radiographs. By comparison, unfilled (aborted) seeds contained significantly less insoluble and soluble protein than empty seeds that were fed-upon by L. occidentalis; moreover, no crystalloid (11S globulin) breakdown products were generated. The biochemical markers described in this study are reliable tools that can be used to identify conifer seeds that have sustained light to severe damage from L. occidentalis feeding.     

Morphological and biological characteristics of the Korean population of Leptoglossus occidentalis Heidemann (Heteroptera: Coreidae), an invasive insect pest of conifer cones

In this study, we investigated the morphological and biological characteristics of a serious insect pest of conifer cones, the western conifer seed bug (WCSB), Leptoglossus occidentalis Heidemann (Heteroptera: Coreidae), in Korea. WCSB adults shared external morphology with overseas populations, including zig-zag fascia on the coria, dilation of the hind tibiae, and color pattern on the abdominal dorsum. The average body length and width of WCSB adults were 17.20 and 4.85 mm, respectively, in males and 19.05 and 5.55 mm in females. The average body weights were 111.27 and 169.89 mg in adult males and females, respectively. On average, eggs were 2.12 mm long and 1.17 mm wide. The average body lengths of the first- to fifth-instar nymphs were 3.07, 4.76, 8.77, 13.56, and 15.53 mm, respectively. For biological characteristics, developmental durations of the egg and five nymphal instar stages were 8.6, 3.7, 7.6, 5.8, 5.8, and 9.1 days, respectively, in laboratory conditions. Nymphal mortality was 47.5% in total. The average life expectancy of WCSB adults was 58.2 and 63.9 days in males and females, respectively. Oviposition of the adult females started 23.4 days after emergence, and the total number of eggs laid by a single adult female was 68.6 on average. The results of this study offer basic morphological and biological information that can be used to design an effective control strategy to manage the WCSB population in Korea.     

Life table for Leptoglossus occidentalis Heidemann (Heteroptera: Coreidae) and prediction of damage in lodgepole pine seed orchards

Abstract 1 Fecundity, egg hatch and nymphal survivorship of Leptoglossus occidentalis Heidemann were determined and used to develop a damage prediction formula for seed bugs in lodgepole pine seed orchards. 2 A single overwintered L. occidentalis female may lay up to 80 eggs during early and mid‐season cone development. 3 Up to 83.4% of eggs that were attached to branches with tape hatched successfully, compared with 53.5% of eggs attached to needles with wire. Egg parasitism was only observed in egg masses attached with wire. 4 Egg masses attached with wire suffered approximately 30% mortality from parasitism, primarily by Gryon pennsylvanicum (Ashmead). 5 Approximately 15.1 and 2.5% of first instars survived to adulthood in 2000 and 2001, respectively. Survival of caged nymphs that were protected from predators was 14.5 and 17.8%, respectively. 6 A composite survival table indicated that 9.3% of eggs laid by L. occidentalis are expected to survive to adulthood. 7 Based on previously determined damage estimates for each life stage of feeding during three periods of cone development, a hypothetical density of one seed bug per tree early in the season will result in an expected seed loss of approximately 310 seeds.     

Measuring the impact of Leptoglossus occidentalis (Heteroptera: Coreidae) on seed production in lodgepole pine using an antibody-based assay

We measured the impact of Leptoglossus occidentalis on seed production in lodgepole pine, Pinus contorta variety latifolia Engelmann, using an antibody marker developed to detect residual saliva in fed-on seeds. Nymphs, adult females, and adult males were caged on cones during early, mid- and late season cone development. Individual analysis of 12,887 seeds extracted from 365 cones revealed that 37.3% seeds tested positive for seed bug saliva. The antibody assay was 38 times more effective than radiography at detecting seed bug damage. Radiography can detect partially emptied seed but cannot discriminate between aborted seeds and those emptied by seed bugs. The antibody marker was least sensitive in detecting early season damage compared with mid- and late season damage. We hypothesize that residual saliva in seeds fed on early in the season was either absorbed by the damaged seed or degraded over time. Early season feeding resulted in the greatest number of seeds fused to cone scales and the extraction efficiency for cones exposed to feeding during this time was reduced by 64% compared with control cones. Adding fused seeds to antibody-positive seeds raised the proportion of damaged seeds to 48.3%. At all stages of cone development, adult females were the most destructive life stage, damaging up to two seeds per day late in the season. When seed losses were adjusted to damage per degree-day, female damage was greatest early in the season, while males caused the same amount of damage regardless of cone development period. The results of the antibody assay provide baseline data for developing damage prediction formulae, and establish L. occidentalis as a potentially serious pest in lodgepole pine seed orchards.     

Distribution analysis of Leptoglossus occidentalis Heidemann (Heteroptera: Coreidae) in South Korea using climate and host plant ensemble maps

Leptoglossus occidentalis Heidemann (Heteroptera: Coreidae) is a notorious pest that causes irreversible damage to coniferous forests in South Korea. However, an effective control strategy is still under development. In this study, we used CLIMEX to analyze the potential distribution of L. occidentalis in relation to climate and host plants in South Korea for the identification of effective control spots. The climate needs of L. occidentalis under current and future climate conditions were analyzed and projected on a map along with the distribution of coniferous forests. The CLIMEX model projected that the area of L. occidentalis distribution would decrease slightly in 2060 compared with that at present. However, it was projected that occurrence in mountainous regions would be sustained, suggesting continued damage to coniferous forests in South Korea.     

Functional anatomy of vagina muscles in the blood-feeding insect,Rhodnius prolixus

The physiology of the muscles associated with the vagina in the blood-feeding insect, Rhodnius prolixus Stal, was investigated with the use of Methylene Blue staining to visualize the anatomy, and a micro force transducer to record spontaneous and neurally-evoked contractions. The vagina is associated with a dorsal muscle and a set of paired lateral muscles. The dorsal muscle extends from the base of the common oviduct to apodemes located laterally on sternite VIII, the first genital segment. The lateral muscles extend from a medially-located apodeme on the posterior edge of sternite VI around each side of the common oviduct to travel posteriorly along the side of the vagina before inserting laterally on apodemes on sternite VIII. The vagina muscles display spontaneous and neurally-evoked contractions that are prolonged but transient. The response to evoked contractions shows that the muscles are innervated by both excitatory and inhibitory motor axons. The degree of tension generated by evoked contractions is dependent on the frequency of stimulation with maximal tension being generated at 20–30 Hz. This tension, which often exceeds 400 mg, is transient and returns to a baseline within 1 to 2 min during continuous stimulation. These results, which are the first to describe this chamber in this well-studied insect, are discussed with respect to the act of egg laying.     

The first record on Leptoglossus occidentalis (Hemiptera: Coreidae) in Korea,a potential pest of the pinaceous tree species

Based on body appearance and COI gene sequence, we report a leaf-footed bug, Leptoglossus occidentalis (Hemiptera: Coreidae), for the first time from Korea. The bug was first encountered in Changwon-si, Gyeongsangnam-do, Korea in 2010, and then again in 2011. We should be alert against the species, because it is an important pest of Pinaceae in Europe. Explanations on its brief morphology and photographs are provided. The worldwide distribution and life history of the bug, and its damage symptom are introduced briefly herein.     

New occurrence of the invasive alien leaf‐footed bug Leptoglossus gonagra (Hemiptera: Coreidae) in South Korea

The invasive alien leaf‐footed bug Leptoglossus gonagra (Fabricius 1775), native to the Americas, is herein recorded from South Korea for the first time. Forty nymphs and adults were collected on 22 September 2016 from arable lands of two separate sites. These individuals were identified based on the analysis of morphological characters and cytochrome oxidase c subunit 1 sequences. A neighbor‐joining tree indicated the existence of two clades: Group A from Brazil, and Group B from Asia and Oceania. Mean genetic distance between clades was 8.11%, range 7.60–8.57%. Within clades, mean genetic distance was 0.42% (0.17–0.83%) in Group A and, 0.45% (0.00–0.83%) in Group B. Colonies of 2nd‐final instar nymphs and adults were found, on top of leaves, flowers, fruits, and between the stems of pumpkins (Cucurbita moschata). Nymphs and adults damaged host plants by sucking their leaves, stems, fruits, and buds. After the first discovery in 2016, we were unable to find the bugs again (in 2017–2019). Therefore, the invasion of this species seems to have occurred only temporarily, during the warm season. We suggest that the species may have failed to overwinter as it is normally distributed in regions warmer than Korea. Nevertheless, possible appearances of this species must be continuously monitored as it is a potential pest of various plants cultivated in South Korea.     

The directional homing behaviour of the subsocial shield bug,Parastrachia japonensis (Heteroptera: Cydnidae), under different photic conditions

The female subsocial shield bug, Parastrachia japonensis, provisions its nymphs by foraging on the ground in the forest during the Japanese rainy season, and the bug uses homing navigation to drag a drupe back to its burrow by the shortest route during the day. To study whether or not this bug performs this provisioning behaviour under different photic conditions, we observed the homing behaviour and homing direction of bugs in the field around the clock and/or under various weather conditions. The bugs foraged the whole day during the busiest provisioning period, and the number of walking bugs was not affected by the different weather conditions. Such navigational behaviour, regardless of the time of the day and the weather conditions, is rare in insect navigation. To test whether the bug uses visual cues, we covered the compound eyes and ocelli with opaque or clear paint just before homing began. During the day and at night, and in all weather conditions, the homing direction of blind bugs, but not those with clear-painted eyes was disoriented, indicating that this species uses visual cues dominantly under all photic conditions.     

Spatio-temporal variation of natural and sexual selection in breeding populations of the coreid bug,Colpula lativentris (Heteroptera: Coreidae)

Spatio-temporal variations of lifetime reproductive succes (LRS) of both male and female individuals of a coreid bugColpula lativentris were measured and analyzed using the multiple regression method of Arnold and Wade (1984a, b). The standardized variance of LRS was larger in males than that in females as males often to secure mates for a long period whereas females could easily find mates and oviposit simply dependent on ovarial maturation. LRS was partitioned into 4 consecutive fitness components: (1) reproductive lifespan, (2) copulating efficiency, (3) guarding efficiency (for males) or oviposition efficiency (for females), and (4) number of eggs per clutch. In males copulating efficiency was the largest determining factor of LRS, whereas in females reproductive lifespan was the most important factor. Such tendencies were stable on both a yearly and local basis. Patterns of relative contribution of natural selection (reproductive lifespan and number of eggs per clutch) and sexual selection (copulating efficiency and guarding or oviposition efficiency) to LRS were clearly different between males and females. This sexual difference is, at least to some extent, thought to be brought about by sexual selection among males for mating opportunity, though no physical fight was observed among males. Directional selection on body length was found only in relation to the clutch size of females because large females tended to lay larger clutches. No significant directional selection was found in other fitness components.     

Reproduction and egg diapause of the oriental chinch bug,Cavelerius saccharivorus okajima (Heteroptera: Lygaeidae), in the subtropical winter season in relation to its wing polymorphism

Reproduction and egg diapause of the oriental chinch bug, Cavelerius saccharivorus, in the subtropical winter season were investigated in relation to its wing polymorphism. Macropterous females collected from the southern part of Okinawa Is. in the autumn season delayed their oviposition and were less fecund early in the adult life period, but survived much longer than brachypterous females collected from the same locality. The total fecundity was not significantly different between wing morphs. The diapause of eggs laid by brachypters tended to be terminated more easily at a high temperature than that of eggs laid by macropters. This indicated that the eggs laid by macropters were more intense in their diapause than those laid by brachypters. However, irrespective of the parental wing form, diapause showed considerable variation in its intensity within and between clutches.     

Functional anatomy of the hypopharynx and the salivary pump in the feeding apparatus of the assassin bug Rhodnius prolixus (Reduviidae, Heteroptera)

Focussing on the blood-feeding reduviid Rhodnius prolixus, we investigated the structure and function of the hypopharynx in (1) conducting the saliva towards the mouthparts and (2) bringing together the salivary pump and the stylets to ensure the difficult task of supplying the two closed antidromic streams of blood and saliva, while allowing the mouthparts to be moved forth and back during the feeding process. The distal apex of the hypopharynx forms a needle-like structure that is X-shaped in cross section. It arranges the interlocking of the maxillae in a manner resembling the fixed slider of a zip-lock. Further proximal, the hypopharynx extends into the maxillary food channel as a wide tongue. The salivary pump possesses two separate efferent ducts. The dorsal duct originates in the retrograde angle of the cupula (part of the salivarium) and conducts saliva directly into the maxillary salivary channel. The ventral duct originates at the distal opening of the cupula. It extends into a bag, the distal opening of which can be closed by a ventral bolster-like cuticle and opened by muscles. We show for the first time for heteropteran mouthparts that the saliva is not exclusively discharged into the maxillary salivary channel (via the dorsal efferent duct of the salivary pump), but that a large amount of saliva directly flows into the tube of the labium (via the ventral efferent duct of the salivary pump), which encloses the piercing stylets. However, within a short section, saliva may also pass from the ventral salivary duct into the maxillary salivary channel. Similar double salivary efferent ducts are present in the reduviids Triatoma dimidiata, T. infestans, Dipetalogaster maxima, Panstrongylus megistus, in the pyrrhocorid Pyrrhocoris apterus, and in the pentatomid Troilus luridus. It might thus be a more common feature of the Heteroptera.     

Mating experience weakens starvation tolerance in the seed bug Togo hemipterus (Heteroptera: Lygaeidae)

Organisms are exposed to various stresses caused by environmental fluctuations. One of the most common stresses is the shortage of food. Individuals of many species must survive periods of starvation. There appears to be a trade‐off between reproduction and survival. When residual reproductive value declines for an individual, life‐history theory predicts an increase in current reproductive investment. Current reproductive investment differs between virgin and mated individuals. It is likely that mating experience influences starvation tolerance. However, few studies have investigated sex differences in the effect of mating experience on starvation tolerance or clarified the causes of reductions in starvation tolerance in both sexes. In the present study, these questions are investigated using the seed bug Togo hemipterus (Heteroptera: Lygaeidae).The results of the present study demonstrate that mating is costly for both sexes. Mated males show very short survival times and a daily reduction in weight, and daily energy expenditures are significantly greater in mated males than in virgin males. It is possible that starvation increases the mating effort of males, such as behavioural activities and the amount of time spent searching for females. A trade‐off between survival duration and lifetime fecundity is found in virgin females. However, there is no trade‐off in mated females, which have very short survival times. Whether male seminal substances contribute to the short survival times of mated females is considered. This is the first report demonstrating the influence of sex and mating experience on starvation tolerance. Sex‐specific causes for reductions in starvation tolerance are discussed.     

Reproductive properties of the oriental chinch bug,Cavelerius saccharivorus Okajima (Heteroptera: Lygaeidae), in relation to its wing polymorphism

Reproductive properties of the oriental chinch bug, Cavelerius saccharivorus, were investigated for three types of female adults: brachypters produced in both high and low density populations and macropters produced in high density populations. With respect to egg-laying potential in terms of clutch size, clutch number, and total fecundity, macropters were superior to brachypters produced in the same high density population, although inferior to brachypters produced in the low density population. The mean fecundity of female adults in each type was positively correlated with mean body length. Macropterous females markedly prolonged their initiation of both copulation and oviposition and had a much longer life span compared with both types of brachypters. However, there was no fundamental difference in reproductive schedules between the two types of brachypters.     

Studies on the mating system of the winter cherry bug,Acanthocoris sordidus Thunberg (Heteroptera: Coreidae) II. Harem defence polygyny

The mating system of the winter cherry bug, Acanthocoris sordidus, was analyzed precisely. As a result, it was found that male adults of this species establish a small territory for mating on the stem of host plant which harbors females. These males abandoned their territories soon after the disappearance of monopolized females. Thus it was confirned that the cue for the territorial establishment of males is the presence of females per se on the host plant. Moreover, most aggregations of adults observed on the host plant contained only a single male. This one-male unit in the mating was named a harem. Harem holding males were usually big in body-size and had a high chance of copulations. The defence behaviors of harem holding males, the mating disparity among males, and the oviposition habit of females in relation to the mating system, were observed. The results obtained were discussed in relation to the sexual selection theories.