Response to orphaning in two Neotropical termites: shape Armitermes euamignathus and shape Embiratermes festivellus

In this paper we examine the potential of the termites Armitermes euamignathus Silvestri: 1901 and Embiratermes festivellus (Silvestri, 1901) (Isoptera, Termitidae, Nasutitermitinae) to produce neotenics experimentally. Three nests of the mound-building termite A. euamignathus, from the Brazilian cerrado, had their primary queens removed in August 1994. After 12 months, only one mound survived; it had a normal appearance. In this healthy, orphaned colony we found the primary king, six physogastric nymphoid female replacement reproductives, two ergatoid female replacement reproductives, 46 nymphs, several presoldiers, soldiers, workers, larvae and many eggs. These data show that neotenics in A. euamignathus may originate from both workers and nymphs, but nymphoids are produced in larger numbers. The biometric study of nymphs and nymphoids suggests that these brachypterous neotenics were derived from third instar nymphs after a single moult or from four instar nymphs after a reduction of wing bud length. A piece of an E. festivellus nest with some third instar nymphs, soldiers and workers was kept under laboratory conditions. After 12 months, the whole experimental subcolony was examined and appeared to contain two pigmented nymphoid females, two pigmented nymphoid males, only one larva, seven nymphs of the same instar, 148 workers, five soldiers and many eggs. These results also indicate the capacity of the termite E. festivellus to produce nymphoid neotenics. These neotenic females were laying eggs, but they were not physogastric after a year, unlike some nymphoids of the same species collected from natural colonies.     

Quantitative changes and synthesis of cyanoprotein in whole body and tissues during development of the bean bug,Riptortus clavatus

Changes in biliverdin-binding cyanoprotein content in whole body and tissue extracts during development of nymphal and adult (non-diapause) bean bugs, Riptortus clavatus were analyzed by rocket immunoelectrophoresis (RIE). RIE using anti-CPegg serum can be used to determine the content of CP-A (Cp-1, 2 and 3) and CP-B (CP-4) separately. During the nymphal stage CP content of whole body changes cyclically in each instar. In the first nymphal instar, CPegg is the main CP which disappears during the first-second instar ecdysis. In nymphal bugs from the 2nd to 4th instars only CP-B (CP-4) is detected, and at the beginning of each instar the CP content is very low but increases toward the next ecdysis, after which CP decreases and disappears very rapidly. In the 5th nymphal instar, CP-B is the major CP but CP-A (CP-1, 2 and 3) is also detected. These changes in whole body CP content of 5th instar nymphs are observed in both females and males. The content of total CPs in the 5th instar nymph reaches about 1000 μg in the whole insect. During nymphal-adult ecdysis, nymphal CPs decrease and disappear at day 2 after emergence. In female adults CP-A (CP-1 only) increases rapidly after day 4 of adult emergence, while no CP is detected in male adults. In females CPs were detected only in the fat body, hemolymph and ovary. In the mid-5th-instar nymphs, CPs (CP-A and B) are mainly distributed in the hemolymph. CPs in the Hemolymph decrease during nymphal-adult ecdysis, whereas they increase in the fat body. CPs disappear from both the hemolymph and fat body by 2 days after ecdysis. Subsequently in the adult stage only CP-A increases again in the fat body and ovary. By tracer experiments using [³⁵S]-methionine, the fat body was shown to be the site of CP synthesis. CP-A and B synthetic activity was detected in nymphal females whereas, only CP-A synthesis was observed in adult females, while no CP synthesis was seen in adult males.     

Body‐color and behavioral responses by the mid‐instar nymphs of the desert locust,Schistocerca gregaria (Orthoptera: Acrididae) to crowding and visual stimuli

The effects of crowding and isolation on body color and behavior were observed for the mid‐instar nymphs of the desert locust, Schistocerca gregaria. Some of the solitarious (isolation‐reared) nymphs that were crowded for 1 or 4 h during the third instar developed black patterns at the fourth instar, but most individuals remained unaffected. Black patterns appeared in all individuals that were crowded for 1 day or longer, but even after 4 days of crowding the black patterning for some individuals was not as intense as that for the gregarious (crowd‐reared) controls. Isolation of gregarious nymphs caused the black patterns to recede or disappear at the last (fifth) nymphal instar, but it was necessary to isolate the nymphs from the beginning of the first instar to obtain body coloration looking like solitarious nymphs in most individuals. Solitarious nymphs that were allowed to see gregarious nymphs developed different intensities of black patterns depending on the body size and number of nymphs shown. The behavioral phase shift from one phase to another was observed when the nymphs were crowded or isolated for 2 days or longer, as previously reported for the last nymphal instars of the same strain. Behavioral gregarization was induced for isolated nymphs that were allowed to see a group of nymphs through a transparent double wall. These results suggested that body‐color phase shift occurred more rapidly for mid‐instar nymphs than for late instar nymphs but the rate of behavioral phase shift was similar for the two instars.     

Photoperiod and temperature affect the life cycle of a subtropical cockroach, Opisoplatia orientalis: seasonal pattern shaped by winter mortality

Abstract.  Opisoplatia orientalis is an ovoviviparous cockroach living in the subtropical areas in Japan. Both adults and nymphs overwinter on Hachijo Island (33°N). The nymphs sampled before and after overwintering showed a similar pattern in frequency distribution of head widths with a definite peak of fifth instars. The present study was conducted to determine how this pattern was formed by investigating the effects of photoperiod and temperature on development and reproduction. Photoperiod influenced the number of nymphal instars, resulting in a longer duration of nymphal development at LD 12 : 12 h than at LD 16 : 8 h. However, the rate of development at each instar was only affected to a small extent by photoperiod and no sign of diapause was detected. It was suggested that the photoperiodic response controlling the number of nymphal instars might have evolved to adjust the timing of adult emergence and reproduction to the favourable season. The prereproductive period and time intervals between nymph depositions were prolonged as temperature declined, but there was no evidence for diapause in adults. Mortality occurred in eggs and embryos inside of the body of the females during winter. Thus, it was inferred that female adults would reset ovarian development in spring and deposit nymphs in summer simultaneously, and these nymphs would reach the fifth instar before winter comes. This winter mortality hypothesis was supported by experiments in which reproductive activity and mortality were monitored for field-collected adults under either constant or changing temperature conditions simulating those in the field.     

Effect of mating combinations on the host parasitisation and sex allocation in solitary endoparasitoid,Aenasius arizonensis (Hymenoptera: Encyrtidae)

Aenasius arizonensis (Girault) is an important solitary endoparasitoid of Phenacoccus solenopsis Tinsley. To optimise the mass production of high-quality females, it is important to assess the influence of mating regimes on the progeny fitness and sex allocation. We, therefore, hypothesise that mating combinations in A. arizonensis adults emerged from different host instars may influence parasitism and sex allocation in the subsequent generation. Therefore, we compared three nymphal instars (1st, 2nd and 3rd) and adults host stages of P. solenopsis for parasitism and sex allocation by A. arizonensis. Further, F₁ female progeny of the parasitoid emerged from different host instars was henceforth evaluated for its fitness in six mating combinations. A. arizonensis females parasitised all the host stages except the 1st instar nymphs. The parasitised 2nd instar nymphs yielded only males, while the sex ratio in the later host instars was strongly female-biased. The parasitoid females preferred 3rd instar nymphs with respect to higher parasitism (74.0–84.0%) and produced more females in the F₁ progeny as compared to other host stages. F₁ females that emerged from 3rd instar nymphs produced significantly higher parasitism (74.0–79.0%). These mating combinations also yielded more female progeny in the F₂ generation. However, parasitism by F₁ females was significantly lower (9.0–12.0%) when mated with males that emerged from 2nd instar P. solenopsis nymphs. Moreover, latter combinations yielded only male progeny in F₂ generation. These findings can be used in laboratory mass rearing of this parasitoid vis-à-vis biological control of P. solenopsis.     

Changes in salivary nitrophorin profile during the life cycle of the blood-sucking bug Rhodnius prolixus

The insect Rhodnius prolixus is a hematophagous hemipteran that has five nymphal instars. Fifth instar nymphs contain, in their salivary glands, four nitrophorins which have already been described in the literature (NP1, NP2, NP3 and NP4). Two new hemeproteins were isolated and partially characterized from first instar nymphs. NP2, that shows an anticoagulant activity, was also identified, but NP1, NP3 and NP4 were not found. As these new hemeproteins have amino-terminal sequences clearly homologous to already described nitrophorins and were capable of binding nitric oxide, they were named nitrophorins 5 and 6, although they showed an unusual Soret band at 412 nm. In each subsequent nymphal stage, a new nitrophorin emerges. In the second instar, NP4 comes into view, in the third instar NP1 appears, and NP3 is only found in fifth instar nymphs and adults, showing that the nitrophorin profile of R. prolixus saliva is stage-specific.     

Effects of a juvenile hormone analog, pyriproxyfen, on the apterous form of Lipaphis erysimi

Effects of a juvenile hormone analog, pyriproxyfen, on various developmental stadia of the apterous form of the turnip aphid, Lipaphis erysimi (Kaltenbach), were bioassayed at three concentrations (50, 100, and 150 mg [AI]/l) in the laboratory. Supernumerary-molted nymphs with 1-3 extra molts were found when the first three nymphal instars were treated, and all these nymphs died prematurely. In contrast, all treated fourth instar nymphs molted normally to adults. The longevity of all pyriproxyfen-treated L. erysimi nymphs and adults and the fecundity of treated adults were reduced by 50%. Higher concentrations of pyriproxyfen (100 and 150 mg [AI]/l) caused sterility in adults from treated fourth instars; whereas the lowest concentration (50 mg [AI]/l) did not cause any adult sterility. A majority of adults from treated fourth instars and treated adults produced normal nymphs, and some adults produced dead nymphs with normal appendages or dead and deformed nymphs without any appendages. Normal nymphs produced by the adults from treated adults or treated at fourth instars developed more slowly from first instar to adult than the water-treated nymphs, and all adults in the new generation apparently reproduced normally. The potential role of pyriproxyfen in a vegetable aphid IPM program was discussed.     

Caste development systems of the Neotropical termite <Emphasis Type="Italic">Constrictotermes cyphergaster</Emphasis> (Isoptera,Termitidae)

The caste developmental system of the Neotropical termite Constrictotermes cyphergaster was investigated in 12 natural colonies from the semi-arid Caatinga region of northeastern Brazil. Twelve measurements were taken of different body parts of the larvae, workers, presoldiers, soldiers, nymphs, and alates for morphometric analyses, and principal component analyses (PCA) were performed based on these parameters. The nymphal line comprised one larval instar, followed by five nymphal instars, and alates, in agreement with the developmental pattern described for Termitidae species. The apterous line included two larval instars, followed by workers, presoldiers, and soldiers. Both workers and soldiers were found to be monomorphic and composed only of male specimens, with only one instar phase each. C. cyphergaster, like most of the Nasutitermitinae, has only male soldiers. The presence of male workers, with only one instar, suggests a simplified system of differentiation in the apterous line of C. cyphergaster. These patterns, which had not previously been described for ‘full nasute’ Nasutitermitinae, are similar to the differentiation patterns of the ‘mandibulate nasute’ Cornitermes walkeri.     

Comparison of relative growth patterns of nymphal legs in relation to the oviposition habits of three heteropteran species

In most animals, morphological changes are closely correlated to changes in behavior during ontogeny. Females of the winter cherry bug, Acanthocoris sordidus (Thunberg), often oviposit away from host plants. First-instar nymphs of A. sordidus can develop to the second instar only with water. Thus, it is the second-instar nymphs that have to search for host plants when A. sordidus females oviposit off host plants, implying that movement is of greater importance during the second instar than during other instars. We investigated the relative growth pattern of nymphal legs of A. sordidus to determine whether the morphology of this species is adapted to changes in locomotion. For comparison, we examined the relative leg lengths of the nymphs of two species, Hygia opaca (Uhler) and Leptocorisa chinensis Dallas, that do not need to search for their host plants due to the species’ oviposition habits. As predicted, second-instar nymphs of A. sordidus had the longest relative leg length of all instars. On the other hand, the relative growth patterns of the nymphal legs of H. opaca and L. chinensis differed from that of A. sordidus, indicating that relative leg growth is more strongly affected by oviposition habits than by phylesis.     

Inter- and intra-instar food consumption in the German cockroach, Blattella germanica

Food consumption was measured in an insecticide-susceptible (Orlando) and-resistant (Village Green) strain of German cockroach, Blattella germanica (Dictyoptera: Blattellidae), throughout each stadium. All instars exhibited a similar pattern of consumption over the course of the instar; consumption was low to moderate at the beginning of each instar, climbed steadily to a maximum near the middle, declined progressively from the mid-instar maximum, and ceased or was minimal several days before the next molt. Consumption ceased or was minimal during the final two to four days of each instar. Cumulative consumption for the six instars was significantly greater in the Village Green strain as compared with the Orlando strain. Village Green nymphs consumed 79.6±0.7 mg of rat chow while Orlando nymphs consumed 63.7±3.4 mg. Total consumption by instar increased significantly with each successive instar in the Village Green strain. In addition, Village Green sixth instar females consumed significantly more food than sixth instar males. A similar trend was observed for the Orlando strain; consumption tended to increase in each successive instar. Relative consumption rate (food consumed/cockroach/instar divided by the mean weight of the instar) was highest in the first two instars and decreased in subsequent instars.     

Observations on Antricola ticks: small nymphs feed on mammalian hosts and have a salivary gland structure similar to ixodid ticks

Ticks use bloodmeals as a source of nutrients and energy to molt and survive until the next meal and to oviposit, in the case of females. However, only the larvae of some tick species are known to feed upon bats; females are obligatorily autogenous, and nymphal stages are believed to not feed. We investigated the presence of blood in a natural population of nymphal Antricola delacruzi ticks collected from bat guano; their ability to feed upon laboratory hosts; and the microscopic structure of both salivary glands and gut. DNA amplification of gut contents of freshly collected material was positive for a mammal in 4 of 11 first instar nymphs, but we were unsuccessful in the amplification of host bloodmeal DNA from late instar nymphs. All early nymphal stages (n = 10) fed on rabbits, and host DNA was detected and sequenced from gut contents. However, all the large nymphs (n = 10) rejected feeding, and host DNA remained undetected in these ticks. All stages of A. delacruzi have salivary glands similar in morphology to the ixodid agranular Type I salivary gland acini and to granular Type II or Type B acini. All stages of A. delacruzi had a similar gut structure, consisting of digestive cells in the basal portion that contained hematin granules. Neither regenerative nor secretory cell traces were observed in the sections of gut.     

Host suitability of different instars of the whitefly Bemisia tabaci `biotype Q' for Eretmocerus mundus

Eretmocerus mundus Mercet is a parasitoidof Bemisia tabaci (Genn.) indigenous tothe Mediterranean and is used commercially foraugmentative biological control in Spain andelsewhere. A better understanding of thesuitability of different host instars wouldhelp optimize production and field application.Incidence of parasitism, development time,survivorship and sex ratio were evaluated whendifferent nymphal instars of the sweetpotatowhitefly Bemisia tabaci biotype `Q' wereoffered for parasitization. Experiments wereconducted on sweet pepper at 25 °C, 75%RH and 16:8 (L:D) photoperiod. E. mundusoviposited in all nymphal instars of B.tabaci except the mature 4th instar orpharate adult (previously designated, `pupa').Incidence of parasitism was greatest (33.8± 5.1 parasitized nymphs) and developmenttime shortest (14.1 ± 0.1 d) whenoviposition occurred under 2nd and3rd instar nymphs compared to 1st or4th instars. Survivorship (85%) andoffspring sex ratio (39.8% female) did notdiffer statistically for parasitoids developingin whiteflies that were parasitized asdifferent instars. Although 2nd and3rd instars were clearly the mostfavorable host stage for E. mundus, itscapacity to parasitize and develop on a widerange of host stages is a favorablecharacteristic for both rearing and fieldapplication.     

Parasitism,host feeding and immature development of Encarsia formosa reared from Trialeurodes vaporariorum and Bemisia tabaci on Trialeurodes ricini

Encarsia formosa Gahan (Hymenoptera: Aphelinidae), a thelytokous parasitoid, is an important biological control agent of whiteflies because of its outstanding reproduction and host‐feeding ability. In this study, we evaluated the parasitism, host feeding and developmental time of E. formosa populations reared on Trialeurodes vaporariorum (Westwood) (EFT) or on Bemisia tabaci (Gennadius) (EFB) when different nymphal instars of the castor whitefly, Trialeurodes ricini (Misra), were offered as hosts, with an aim to understand the preference of the parasitoid on nymphal instars of T. ricini. Experiments were conducted on castor bean plants at 26 ± 2°C, 50–60% RH and 16 : 8 (L : D) photoperiod. The results showed that E. formosa successfully oviposited and fed on all nymphal instars of T. ricini. However, numbers of the first instars fed on by the E. formosa populations reared on T. vaporariorum (EFT) and B. tabaci (EFB) were significantly greater (45.9 and 31.3, respectively) than those of the second (EFT: 30.4 and EFB: 15.8), the third (EFT: 22.4 and EFB: 13.2) and the fourth nymphal instars (EFT: 6.0 and EFB: 3.8). The number of T. ricini nymphs parasitized by E. formosa varied significantly among different instars, and the parasitism rates on the first instar (EFT: 15.2; EFB: 7.7) and fourth instar (EFT: 19.3; EFB: 4.9) were greater than those on the second and third instars. Encarsia formosa reared on T. vaporariorum had a significantly higher host feeding and ovipositing potential on T. ricini than EFB. When parasitizing the fourth instar nymphs, E. formosa completed development in a significantly shorter time (12.9 day) than when ovipositing in other instars (17.8–19.1 day). These results showed that EFT had a better host adaption than EFB. The information from this study should be useful for us to better understand the performance and nymphal preference of E. formosa from T. vaporariorum and B. tabaci when they parasitized and fed on T. ricini, and the interactions of parasitoids with different host whitefly species.     

Queen replacement in the termiteMicrocerotermes papuanus

In experimentally orphaned field nests ofMicrocerotermes papuanus Holmgren, 1911, large numbers of workers develop into replacement reproductives (ergatoids) in only one moult. The females become functional egg-layers after approximately two months. Nymphs normally reach the last instars in August–September; at that time, in the orphaned nests, some nymphs moult to nymphoid replacement reproductives. Over long time periods, these nymphoids completely replace the ergatoids and the females become physogastric. Although time-efficient, queen replacement seems energetically expensive for the society, suggesting that this process is under weak selective pressure inM. papuanus, compared with sympatric species such asNasutitermes princeps.

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Le remplacement de la reine chez le termiteMicrocerotermes papuanus

Résumé Dans les nids deM. papuanus rendus expérimentalement orphelins, un grand nombre d'ouvriers se transforment, en une seule mue, en sexués de remplacement ergatoïdes. Les femelles se mettent à pondre au bout d'environ deux mois. Les nymphes atteignent normalement leurs derniers stades en août-septembre. A ce moment, dans les nids orphelins, certaines d'entre elles se différencient en sexués nymphoïdes. Dans les expériences de longue durée, ces nymphoïdes remplacent complètement les ergatoïdes et les femelles deviennent physogastres. Bien que rapide, le remplacement de la reine paraît coûteux pour la société du fait du grand nombre d'individus, ouvriers et nymphes, impliqués. Ceci suggère que la pression de sélection sur ce phénomène est faible chezM. papuanus, par comparaison avec des espèces sympatriques telles queN. princeps.

     

Comparative studies on alate wing formation in two related species of rotten-wood termites: <Emphasis Type="Italic">Hodotermopsis sjostedti</Emphasis> and <Emphasis Type="Italic">Zootermopsis nevadensis</Emphasis> (Isoptera,Termopsidae)

Summary Termite colonies are comprised of several types of castes that differentiate throughout postembryonic development. In termopsid termites (family Termopsidae), alates are normally differentiated from apterous instars by two nymphal instar stages and three moulting events. Here, we report that of the rotten-wood termite Hodotermopsis sjostedti. There is only a single nymphal instar between the pseudergate and alate stages. During the annual alate production season in June/July, we observed some nymphs with small wing buds which were dorsally swollen. Those nymphal individuals subsequently moulted into alates through only a single moult. We examined their histology and internal morphology and observed that the folding pattern of the newly formed wings was very different from that seen in second stage nymphs of the closely related species Zootermopsis nevadensis. The newly formed wings of H. sjostedti are formed inside the relatively smaller wing buds and therefore must be folded in a complicated manner. Our observations revealed that the tips of the folded wings were elongated and bent, such that they overlapped in the median plane. We suggest that heterochronic evolutionary change accounts for the compression of nymphal development into a single instar. We also suggest that this probably occurred at either the individual or colony level in this species.Received 18 August 2003; revised 11 December 2003; accepted 8 January 2004.     

Determination and distribution of a female-specific protein in the brown planthopper, Nilaparvata lugens Stal (Homoptera: Delphacidae)

Electrophoretic analyses of hemolymph and body or ovary homogenates from reproducing females, males, and 5th instar nymphs of the brown planthopper, Nilaparvata lugens Stal, revealed a protein band of 175 kDa in females. An immunoblot test using antibody against this protein showed a positive reaction with a 175 kDa protein from female body or ovary homogenates. It is likely that this protein in hemolymph is vitellogenin (Vg). Distribution of Vg was determined by immunofluorescence and immunogold labeling techniques. The results showed that the positive immunofluorescence reactions were present in yolk particles, the intercellular space of follicle cells, hemolymph, and the epithelial plug of ovarioles. In addition, the yeast-like symbiotes (YLS) in mycetocytes of adults and various nymphal instars as well as those free in hemolymph or entering oocytes also exhibited a positive reaction. Electron micrographs showed that immunogold particles were found most in yolk mass and YLS over other tissues. Especially the YLS in various developmental stages all contained immunogold particles, implying that the symbiote is somewhat related with production of the female-specific protein.     

稻虱红单节螯蜂寄生不同虫龄白背飞虱对二者发育表现的影响

【目的】为了解稻虱红单节螯蜂Haplogonatopus apicalis与白背飞虱Sogatella furcifera间的互作关系,开展了稻虱红单节螯蜂在白背飞虱不同龄期寄生时,对寄主及其自身发育表现影响的研究。【方法】在室内25℃条件下,观察了被寄生的白背飞虱各龄若虫及其寄生蜂稻虱红单节螯蜂的发育表现。【结果】白背飞虱2, 3, 4和5龄若虫被寄生后,当龄及其后各龄的历期均显著延长;2和3龄若虫被寄生后,成虫羽化率仅分别为54.29%和60.95%,显著低于在4和5龄若虫被寄生后的成虫羽化率（分别为96.20%和100%）。稻虱红单节螯蜂寄生白背飞虱5龄若虫后的发育历期（23.77 d）显著短于寄生2龄若虫后的发育历期（27.77 d）;寄生3龄若虫的成蜂羽化率最高,为56.19%;而寄生5龄若虫的羽化雄蜂比例最高,为77.12%。【结论】稻虱红单节螯蜂寄生可使白背飞虱若虫发育历期显著延长,白背飞虱2和3龄若虫是稻虱红单节螯蜂发育的适宜寄主。     

Consequences of stress induced by heat on fitness of Delphacodes kuscheli and its yeast‐like endosymbionts

The planthopper Delphacodes kuscheli is the main vector of Mal de Río Cuarto virus in Argentina, disease that severely affects maize production. In this study, we investigated the effects of heat stress on fitness traits and on the number of its obligate yeast‐like symbionts (YLS). The exposition of newly‐hatched nymphs to 35°C for 3 days, a well‐known procedure used to reduce the number of YLS in planthoppers, was applied. To compare different fitness components between control and heat‐treated insects, we estimated nymphal instars development time, nymphal survival, adult body length, longevity, fecundity and fertility. Also, correlates of fitness, as proportion of sexes and wing forms of the emerging adults, were evaluated. In heat‐treated group, the nymphal developmental time increased due to an increase in the fifth instar duration, and the nymphal survival, body length of adults and fecundity were reduced when compared to control. There was a significant association between treatments (control and heat‐treated insects) and wing morphs. The heat treatment successfully reduced the number of YLS in third instar nymphs of D. kuscheli. Our results revealed the negative effect of heat stress on development, survival and reproduction of D. kuscheli and on the load of its YLS endosymbionts suggesting that YLS could play a crucial role in the development and reproduction of these planthoppers.     

Specific developmental window for establishment of an insect-microbe gut symbiosis

The alydid stinkbug Riptortus pedestris is specifically associated with a beneficial Burkholderia symbiont in the midgut crypts. Exceptional among insect-microbe mutualistic associations, the Burkholderia symbiont is not vertically transmitted but orally acquired by nymphal insects from the environment every generation. Here we experimentally investigated the process of symbiont acquisition during the nymphal development of R. pedestris. In a field population, many 2nd instar nymphs were Burkholderia free, while all 3rd, 4th, and 5th instar nymphs were infected. When reared on soil-grown potted soybean plants, Burkholderia acquisition occurred at a drastically higher frequency in the 2nd instar than in the other instars. Oral administration of cultured Burkholderia cells showed that 2nd and 3rd instar nymphs are significantly more susceptible to the symbiont infection than 1st, 4th, and 5th instar nymphs. Histological observations revealed rudimentary midgut crypts in the 1st instar, in contrast to well-developed midgut crypts in the 2nd and later instars. These results indicate that R. pedestris acquires the Burkholderia symbiont from the environment mainly during the 2nd instar period and strongly suggest that the competence for the symbiont infection is developmentally regulated by the host side. Potential mechanisms involved in infection competence and possible reasons why the infection preferentially occurs in the 2nd instar are discussed.