Nymphal Growth Research Articles

The burrower bug Macroscytus japonensis (Hemiptera: Cydnidae) acquires obligate symbiotic bacteria from the environment

Many plant-feeding stinkbugs belonging to the infraorder Pentatomomorpha possess a specialized symbiotic organ at the posterior end of the midgut, in which mutualistic bacterial symbionts are harbored extracellularly. In species of the superfamily Pentatomoidea, these symbionts typically are verticallytransmitted from host mothers to offspring, whereas in species of the superfamilies Coreoidea and Lygaeoidea they are acquired from the environment. In the pentatomoid family Cydnidae, vertical symbiont transmission has been reported in several species. Here, we report the first case of environmental symbiont acquisition in Cydnidae, observed in the burrower bug Macroscytus japonensis. A comprehensive survey of 72 insect samples from 23 sites across the Japanese archipelago revealed that (1) symbionts exhibit remarkably high diversity, forming six distinct phylogenetic groups within the Enterobacteriaceae of the γ-Proteobacteria, (2) most symbionts are cultivable and closely related to free-living Pantoea-allied bacteria, and (3) symbiont phylogenetic groups do not reflect the host phylogeny. Microbial inspection of eggs revealed the absence of bacteria on the egg surface. These results strongly suggest that symbionts are acquired from the environment, not vertical transmission. Rearing experiments confirmed environmental symbiont acquisition. When environmental symbiont sources were experimentally withheld, nymphs became aposymbiotic and died before molting to the second instar, indicating that nymphs environmentally acquire symbionts during the first-instar stage and that symbionts are essential for nymphal growth and survival. This study highlights Cydnidae as the only pentatomoid family that includes species that environmentally acquire symbionts and those that vertically transmit symbionts, providing an ideal platform for comparative studies of the ecological and environmental factors that influence the evolution of symbiont transmission modes.

The effect of transport temperature and duration on survival and growth of house cricket nymphs and eggs

Abstract The transport of live insects is becoming increasingly common within the food and feed industry. However, very little information is available as to its effects on the insects themselves. The aim of this study was to monitor how variation in transport conditions, such as duration of transport and external temperature and humidity, directly and indirectly affect the survival and growth of nymphs of the house cricket, Acheta domesticus. In addition, we investigated the effect of external temperature on the viability of eggs upon completion of a transport event. We investigated how four different temperatures (5 °C, 15 °C, 25 °C, 35 °C) and four possible transport durations (1, 2, 3, 6 days) affected survival and growth of the cricket nymphs. To gain insight into the potential transport of eggs, its effect on egg hatch-rate was studied by storing eggs at three different temperatures (6 °C, 18 °C and 30 °C) before moving the eggs to optimal hatching conditions. We found that humidity remained constant inside the transport boxes and was different from the exterior humidity. Temperature had a significant effect on nymph survival and growth. The extreme temperatures negatively affected nymph survival, and increased temperature was correlated with increased growth. The development of eggs was also sensitive to temperature, and transport of eggs at suboptimal temperatures prolonged incubation time considerably. Finally, based on the results of this study, we discuss temperature optimisation as the most critical factor to consider during transport of live house cricket nymphs and eggs.

Dynamic Energy Budget approach for modeling growth and reproduction of Neotropical stink bugs

Global warming and other climate change drivers have a significant impact on the life cycle of insects which in turn affect their population dynamics and geographic distribution. Among these insects are stink bugs (Hemiptera: Pentatomidae), which are hemimetabolous agricultural pests that cause major damage on crops in many countries. Their life cycle consists of three stages: egg, nymph, and adult. The nymph grows and molts through a small number of instars until reaching emergence, at which point growth ceases. The Dynamic Energy Budget (DEB) theory provides the framework for modeling the life cycle of stink bugs. Nevertheless, determining the most accurate model for nymphal growth and energy allocation during the adult stage remains a challenge, as the best model is not always evident. For two species of the Pentatomidae family, we parameterized and evaluated four DEB models that differ in nymphal growth and the energy allocation rules in adults: isomorphic or V1-morphic nymphal growth combined with the energy allocation scheme in adults that follows the κ-rule or the scheme that the κ-rule is not operational in adults. Overall, all models fit the data, but those with isomorphic nymphal growth reproduce the growth trajectories and instar duration better. However, with the available data we cannot conclude which rule is most likely the energy allocation in adults. Using these models, we further studied the effects of temperature and food availability on individual dynamics and its life cycle. Simulations show that temperature has a higher impact on the duration of life stages and survival, while food availability affects egg production. When simulating a variable environment in terms of temperature for both a summer and a fall generation, the results reveal that the summer generation has higher feeding and egg production rates in comparison to the fall generation. DEB models are valuable tools for simulating individual under various environmental conditions and when combined with appropriate modeling approaches, they can predict population traits and even the potential distribution of a species.

Optimization and establishment of laboratory rearing conditions for Cimex lectularius L. against variable temperature and relative humidity

Emerging infestations of bed bugs are affecting normal human lifestyle globally. This study has been designed to optimize the rearing conditions for Cimex lectularius L. (Hemiptera), to support the scientific research on them. Bed bugs have been projected onto three different temperature (20 °C, 25 °C, and 30 °C) and relative humidity (50%, 70%, and 90%) conditions to check their overall growth and survival rate. Adult mortality, weight loss, egg laying, percentage hatching, hatching initiation and completion, nymph mortality, and molting have been evaluated to optimize the best conditions. The temperature at 25 °C with 90% RH showed minimum mortality for adults (female 13.33 ± 3.33% and male 6.67 ± 3.33%) and nymphs (13.33 ± 3.33%), while maximum egg laying (40.33 ± 1.86), with highest percentage hatching (98.23 ± 0.58%). At 30 °C with 90% RH, hatching initiation and completion (5.19 ± 0.12 days and 7.23 ± 0.16 days) as well as molting initiation and completion (3.73 ± 0.12 days and 7.00 ± 0.24 days) were found to be fastest. Thus, it can be concluded that 25 °C with 90% RH is ideal for rearing of adults and 30 °C with 90% RH is appropriate for rapid growth of nymphs.

Field and laboratory life cycle studies of Malenka depressa (Banks, 1898) (Plecoptera: Nemouridae)

During 1982–1985, laboratory and field studies of 125 eggs, 8055 nymphs and 1426 adults indicated a univoltine slow life cycle for Malenka depressa (Banks, 1898) in a first-order perennial stream in the Mediterranean climate of the San Francisco Bay area. Nymphal growth and adult emergence were continuous throughout the year, further enhanced by a thick, protective tree canopy shading of the canyon that provided an insulated stabilised thermal tube of cool air, ground and stream water temperatures. Leaf senescence of the overhead California bay trees was a perennial source of allochthonous food for the immature stages. Maximum assimilation efficiency for middle to late-nymphal growth stages fed on bay leaves was 42% at 10 °C.

Field Evaluation of Cotton Expressing Mpp51Aa2 as a Management Tool for Cotton Fleahoppers, Pseudatomoscelis seriatus (Reuter).

The cotton fleahopper (Pseudatomoscelis seriatus Reuter) is considered a highly economically damaging pest of cotton (Gossypium hirsutum L.) in Texas and Oklahoma. Current control methods rely heavily on the use of foliar-applied chemical insecticides, but considering the cost of insecticides and the critical timeliness of applications, chemical control methods are often not optimized to reduce potential yield losses from this pest. The Bacillus thuringiensis (Bt) Mpp51Aa2 (formerly Cry51Aa2.834_16) protein has proven effective against thrips and plant bugs with piercing and sucking feeding behaviors, but the impact of this toxin on cotton fleahoppers has not been investigated. To evaluate the Mpp51Aa2 trait effectiveness towards the cotton fleahopper, field trials were conducted in 2019, 2020, and 2021, comparing a cotton cultivar containing the Mpp51Aa2 trait to a non-traited isoline cultivar under insecticide-treated and untreated conditions. Populations of cotton fleahopper nymphs and adults were estimated weekly by visually inspecting cotton terminals. Square retention was also assessed during the first week of bloom to provide some insight on how the Bt trait may influence yield. While cotton fleahopper population differences between the traited and non-traited plants were not consistently noted during the pre-bloom squaring period, there was a consistent increase in square retention in cotton expressing Mpp51Aa2 relative to non-traited cotton. Additionally, cotton expressing Mpp51Aa2 offered similar square protection relative to non-traited cotton treated with insecticides for the cotton fleahopper. These findings indicate that the Mpp51Aa2 protein should provide benefits of delayed nymphal growth, population suppression, and increased square retention.

Biology of Patanga japonica (Orthoptera, Acrididae): Nymphal growth, host plants, reproductive activity, hatching behavior, and adult morphology

The biology of Patanga japonica (Bolívar, 1898), including seasonal nymphal growth, host plants, mating, oviposition, hatching, and adult morphology, was studied under outdoor and indoor conditions in central Japan. A field census showed that this grasshopper had a univoltine life cycle and overwintered in the adult stage. Body size was found to increase with a delay in the time of adult emergence in females but not in males, and protandry was observed. The insects were mainly associated with a few plant species. Feeding tests showed that at least one of the 5 test nymphs molted to the second stadium on 37 plant species, and more than 50% did so on 23 plant species. Mating was frequently observed in April and May under outdoor conditions, and the daily maximum number of copulating pairs was positively correlated with air temperature. Copulatory behavior, including stridulation, is described in detail. Oviposition was frequently observed in May and June under outdoor conditions. Larger females produced more eggs per pod, and a negative relationship was observed between egg lengths and the number of eggs per pod, showing a trade-off. On average, female adults had 124 ovarioles. Egg hatching occurred at different times during the daytime, but the eggs from each pod hatched synchronously. Synchronous hatching was also observed in eggs kept in groups of 2, 4, and 10, but hatching occurred earlier in larger group sizes. Eggs achieved synchronous hatching by either delaying or advancing hatching time. Two eggs separated by several millimeters hatched less synchronously than those kept in contact with one another. However, similarly separated eggs restored hatching synchrony when connected by thin wire, suggesting the involvement of vibrational signals in embryo–embryo communication. Morphometric analysis suggested that P. japonica adults change some morphometric ratios in response to crowding. Variation in pronotum shape was not significantly affected by crowding.

Aphid BCR4 Structure and Activity Uncover a New Defensin Peptide Superfamily.

Aphids (Hemiptera: Aphidoidea) are among the most detrimental insects for agricultural plants, and their management is a great challenge in agronomical research. A new class of proteins, called Bacteriocyte-specific Cysteine-Rich (BCR) peptides, provides an alternative to chemical insecticides for pest control. BCRs were initially identified in the pea aphid Acyrthosiphon pisum. They are small disulfide bond-rich proteins expressed exclusively in aphid bacteriocytes, the insect cells that host intracellular symbiotic bacteria. Here, we show that one of the A. pisum BCRs, BCR4, displays prominent insecticidal activity against the pea aphid, impairing insect survival and nymphal growth, providing evidence for its potential use as a new biopesticide. Our comparative genomics and phylogenetic analyses indicate that BCRs are restricted to the aphid lineage. The 3D structure of BCR4 reveals that this peptide belongs to an as-yet-unknown structural class of peptides and defines a new superfamily of defensins.

The locust plagues in the Yangtze River Delta of China during the Ming and Qing Dynasties

The Little Ice Age was concurrent with frequent natural disasters in China during the Ming and Qing Dynasties (1368–1911 AD). Using historical documents created in the Yangtze River Delta during these dynasties, we reconstructed the severity and frequency of locust plagues. We uncovered their temporal and spatial patterns, the relevant influencing factors, and the applied control measures. These locust plagues occurred in the Yangtze River Delta during summer and autumn and were considered moderate-degree disasters. The locust plagues during the Qing Dynasty were less harmful than those during the Ming Dynasty. The locust plagues occurred north of 31°N and were concentrated around lakes and rivers. Regarding long-term changes, three periods of frequent locust plagues were identified: 1520–1540 AD, 1610–1670 AD, and 1850–1870 AD. The locust plague cycles were dominated by long-term changes of 100 and 350 years, alternating with short-term changes of 10–30 years. Locust growth and development typically occur under suitable climate conditions. However, in the Yangtze River Delta, the relationship between locust outbreaks and temperature changes was insignificant, whereas flood disasters provided suitable humidity conditions for locust nymph growth. Locust plague outbreaks had a series of social impacts, one direct result was rising food prices. When facing locust plagues, the Ming and Qing Dynasties formed effective top-down preventative measures corresponding to local conditions. The locust plagues in the Yangtze River Delta during the Ming and Qing Dynasties occurred with regularity, were responsive to local hydrological conditions, and impacted social economies and technologies.

Temperature effects on Mormon cricket Anabrus simplex embryo development, hatching and nymphal growth: Thermal performance curves change with ontogeny

Thermal performance curves for development are an essential tool for population modeling and pest management. More broadly, they characterize how selection on thermal limits or maximum rates change with life stage. The effects of temperature on development of Mormon cricket embryos, and hatching and development of nymphs were measured on a population from the Bighorn Mountains of Wyoming and modeled with four non-linear equations. Taylor's Gaussian curve characterized embryonic development, which was most rapid at 26.9 °C. However, half-grown embryos aestivated at high temperatures, resulting in a significant shift in the optimum temperature to complete embryonic development to 24.1 °C and a reduction in the breadth of the performance curve (thermal breadth). Fully grown embryos hatched fastest at relatively low temperatures (21.8 °C), whereas nymphal development was maximized at relatively high temperatures (35.7 °C). Thermal breadths for nymphal hatching and development were also significantly broader than that for embryonic development. Differences in optimum temperature and thermal breadth of each life stage should be taken into consideration in population modeling, comparisons among populations, and epigenetic studies of acclimation.

CCHamide-2 Signaling Regulates Food Intake and Metabolism in Gryllus bimaculatus.

Simple SummaryCCHamide-2 is a newly identified neuropeptide associated with the regulation of feeding behavior as a brain-gut peptide in insects. Data revealed CCHamide-2 signaling inhibited feeding along with increasing circulating carbohydrate and lipid levels in the two-spotted crickets, Gryllus bimaculatus. Consequently, we demonstrated that the signaling involving CCHamide-2 and its receptor contributes to the regulation of feeding and metabolism in the neuropeptide-mediated regulatory network of energy homeostasis in insects.Neuropeptides play vital roles in energy homeostasis in insects and other animals. Although the importance of the regulatory network of neuropeptides in feeding and metabolism has been illuminated, a complete understanding of the mechanisms has not been addressed as many factors are involved in the regulation. CCHamide-2 is a newly identified brain-gut neuropeptide that regulates feeding behavior in several insect species including Drosophila melanogaster. However, little is known about the mechanisms controlling the feeding-related behavior and metabolic functions modulated by CCHamide-2 in other insects. In this study, we addressed the functions of CCHamide-2 in the two-spotted cricket, Gryllus bimaculatus, which was used as the experimental material to research the mechanisms of feeding and metabolism in this omnivorous insect species. Knockdown crickets by RNA interference against GbCCHamide-2R increased the amount of food intake, while injection of chemically synthetic GbCCHamide-2 peptide reduced the amount of food intake. Further, knockdown and peptide injection experiments revealed that GbCCHamide-2 signaling increased the concentrations of circulating lipids and carbohydrates, and the carbohydrate-rich diet increased the transcript levels of GbCCHa-2R. Moreover, GbCCHa-2 injection decreased the transcript level of Gbilp. By contrast, GbCCHamide-2 signaling did not affect nymphal growth or the transcript level of GbAKH, as well as feeding preferences. Taken together, CCHamide-2 signaling in G. bimaculatus regulates food intake associated with alterations in lipid and carbohydrate levels in hemolymph.

Serratia symbiotica Enhances Fatty Acid Metabolism of Pea Aphid to Promote Host Development.

Bacterial symbionts associated with insects are often involved in host development and ecological adaptation. Serratia symbiotica, a common facultative endosymbiont harbored in pea aphids, improves host fitness and heat tolerance, but studies concerning the nutritional metabolism and impact on the aphid host associated with carrying Serratia are limited. In the current study, we showed that Serratia-infected aphids had a shorter nymphal developmental time and higher body weight than Serratia-free aphids when fed on detached leaves. Genes connecting to fatty acid biosynthesis and elongation were up-regulated in Serratia-infected aphids. Specifically, elevated expression of fatty acid synthase 1 (FASN1) and diacylglycerol-o-acyltransferase 2 (DGAT2) could result in accumulation of myristic acid, palmitic acid, linoleic acid, and arachidic acid in fat bodies. Impairing fatty acid synthesis in Serratia-infected pea aphids either by a pharmacological inhibitor or through silencing FASN1 and DGAT2 expression prolonged the nymphal growth period and decreased the aphid body weight. Conversely, supplementation of myristic acid (C14:0) to these aphids restored their normal development and weight gain. Our results indicated that Serratia promoted development and growth of its aphid host through enhancing fatty acid biosynthesis. Our discovery has shed more light on nutritional effects underlying the symbiosis between aphids and facultative endosymbionts.

Life history and ecology of the Maghrebian endemic Choroterpes atlas Soldán & Thomas, 1983 (Ephemeroptera: Leptophlebiidae)

Knowledge of the basic life history traits of an aquatic organism such as voltinism and growth patterns is a fundamental step in understanding its potential use as indicator taxon and how it adapts to its complex environment. The distribution and life cycle of the Maghrebian endemic Choroterpes atlas Soldán & Thomas, 1983 was studied over a two year period. Random forest classification indicated that the species occupied both permanent and intermittent streams with high water depth, large river bed width and strong water flow. Density-based clustering of body measurements allowed the identification of last-instar nymphs which exhibited a significant sexual dimorphism: F-0 females were significantly larger than corresponding males. In addition, size-frequency plots and generalized additive models indicated that C. atlas exhibited a multivoltine annual cycle with three overlapping generations. Nymphal growth of the first generation happened in winter and spring with emergence occurring in June/July. The second generation grew from June/July to September whereas the third generation was completed from August/September to November. GAMs also indicated that body size varied significantly between years. The large regional distribution, habitat requirement, and phenology of C. atlas may ideally complement the potential use of Ecdyonurus rothschildi as a useful environmental indicator for North African streams and rivers.

Oxygen doesn't limit mayflies when the temperature soars

As air breathers, we probably don't appreciate how difficult it is for aquatic creatures to breathe. ‘The oxygen concentration in water is only about 3% that in air and the oxygen diffusion rate in water is 3×105 times lower’, says David Funk from the Stroud Water Research Center, USA, explaining that aquatic animals have to work ∼15 times harder than terrestrial creatures to breathe. And the situation for cold-blooded (exothermic) creatures is even more perilous when the temperatures rise and their metabolism begins running faster. ‘The temperature-dependent performance of animals is believed to be shaped by the capacity for oxygen delivery in relation to oxygen demand’, Funk explains, adding that oxygen availability was thought to be the factor that sets the highest temperatures at which fish and aquatic insects can survive. Knowing that adult mayflies that develop in warm conditions tend also to be smaller, possibly as a consequence of running low on oxygen, Funk, Bernard Sweeney and John Jackson, also from Stroud Water Research, decided to find out how oxygen availability affects the development and survival of mayflies over a range of temperatures. But the team didn't stop at investigating one species of mayfly: Neocloeon triangulifer nymphs only thrive in well-oxygenated streams over a narrow temperature window of 8°C, while two robust populations of Cloeon dipterum are capable of surviving in relatively stagnant water in their comfort zone of 14–30°C. Allocating 50 larvae from each species to individual 1.8 l miniaquaria, Funk created environments with high (45%) oxygen, down to normal (∼20% oxygen), while the temperature ranged from 20°C up to 32°C – the temperatures at which the females are unable to produce offspring. ‘We raised over 4400 hatchlings through their entire lives in 90 separate vessels housed in four giant water baths’, Funk says with a smile.Monitoring the hottest youngsters with access to 45% oxygen, it was clear that the souped-up oxygen supply didn't compensate for the challenge of developing in hot water: the youngsters failed to thrive. If oxygen was limiting the nymphs’ ability to survive in hot water, then those with access to unprecedented amounts of oxygen (45%) should have flourished. In short, the availability of oxygen does not limit the mayflies’ ability to survive and grow in sizzling conditions. Some other factor is responsible for their high mortality when the mercury rises.Then Funk monitored how a lack or abundance of oxygen affected the youngster's development, paying close attention to their gills, eyes and leg length. ‘The most technically difficult thing was measuring the gill size’, says Funk, recalling how he had to be on hand as the youngsters transformed into adults, so that he could retrieve the discarded skins to measure the size of all seven pairs of gills. Comparing the nymphs’ growth at high and low temperatures (25 and 20°C), they found the hottest nymphs were always smallest, even in 45% oxygen. Oxygen availability wasn't restricting the nymph's growth either. However, the team was astonished by the impact that low oxygen had on the youngsters’ gills. ‘I noticed that mayflies reared in hypoxic conditions responded by greatly increasing the size of their gills. We had no idea they could do this, but quickly realised that gill size could be a valuable indicator of oxygen stress’, says Funk.So, oxygen availability doesn't seem to be the factor that restricts mayfly nymph growth and survival when the temperature soars, but the aquatic insects do respond to low oxygen by increasing the size of their gills to make the most of the meagre levels.

The Effect of Some Biological Parameters of Brevicoryne brassicae (L.) (Hemiptera: Aphididae) on Different Cauliflower Cultivars

In this article, some biological parameters of Brevicoryne brassicae were studied on four different cauliflower cultivars (Casper RZ, Barcelona F1, Karbeyaz F1 and Mor karnabahar). This study was conducted under controlled conditions: 25±1 0C, 65±5% relative humidity (RH), and 16:8 (L:D) h photoperiods. The maximum and minimum developmental times were observed on Karbeyaz F1 and Barcelona F1 cultivars, respectively. When we examine the total development period, the shortest Barcelona F1 cultivar (6.73 days) and the longest total nymphal growth period were determined on Karbeyaz F1 (7.07 days). When the biological parameters of B. brassicae were examined, it was determined that the varieties with the lowest rm values were on Barcelona F1 cultivar. When the Ro values are compared, it is seen that the lowest value is obtained in Barcelona F1 variety. When the To values were examined, it was determined that the lowest value was obtained on Karbeyaz F1 variety, followed by Barcelona F1, Casper RZ and Mor karnabahar varieties. Keywords: Brevicoryne brassicae, cauliflower cultivars, life table, biological parameters DOI: 10.7176/JSTR/6-13-09

The Effect of Some Biological Parameters of Aphis fabae Scopoli (L.) (Hemiptera: Aphididae) on Different Eggplant Cultivars

In this article, some biological parameters of Aphis fabae were studied on three different eggplant cultivars (Adana topağı, Kemer and Pala). This study was conducted under controlled conditions: 25±1 0C, 65±5% relative humidity (RH), and 16:8 (L:D) h photoperiods. The maximum and minimum developmental times were observed on Pala and Adana topağı cultivars, respectively. When we examine the total development period, the shortest Adana topağı cultivar (6.14 days) and the longest total nymphal growth period were determined on Pala (8.50 days). When the biological parameters of A. fabae were examined, it was determined that the varieties with the lowest rm values were on Kemer cultivar. When the Ro values are compared, it is seen that the lowest value is obtained in Kemer variety. When the To values were examined, it was determined that the lowest value was obtained on Adana topağı variety, followed by Kemer and Pala varieties. Keywords: Aphis fabae, eggplant cultivars, life table, biological parameters DOI: 10.7176/JSTR/6-13-10

Elevational Changes in Mormon Cricket Life Histories: Minimum Temperature for Nymphal Growth Declines With Elevation.

As the mean temperature and the duration of the growing season decline with elevation, growth of immature insects should initiate at a lower temperature, but it should also be faster to complete development prior to season's end. Although flightless, Mormon crickets migrate in large aggregations across broad spatial and elevational distances that might limit adaptations to local environments. In addition, selection to be active at cooler temperatures might limit selection to maximize growth rate. I measured growth rate in controlled environments for nymphs from three populations that vary in altitude (87-2,688 m) but are similar in latitude (43.2-45.7°N). Growth rate increased significantly with mean rearing temperature between 22 and 30°C. The intercept of the regression of growth rate on temperature increased with elevation, whereas the slope did not change significantly. For any given rearing temperature, growth rate increased with elevation, which suggests that selection to initiate growth at cooler temperatures did not compromise growth rate. Body mass did not differ between the two lower elevations, whereas the highest elevation population had smaller hatchlings and adults. Critical thermal minimum (base temperature) declined with elevation (0.7°C per 1,000 m), and the degree days were 509 across all elevations. For pest management, a base temperature from midelevation of 15.3°C (60°F) and growing degree days of 509 (equivalent to 916 Fahrenheit-based degree days) are reasonable estimates for applications from sea level to 2,700 m.

Seasonal Development of Plant Bugs (Heteroptera, Miridae): Subfamily Bryocorinae

Data on seasonal development of plant bugs from subfamily Bryocorinae (Miridae) are reviewed and analyzed. All of the species of bryocorines whose seasonal development has been studied so far belong to the tribe Dicyphini, owing to the latter’s economic importance as agents of biological control in greenhouses. Macrolophus melanotoma, M. pygmaeus, and Nesidiocoris tenuis have homodynamic seasonal development and the lower developmental threshold of about 8–9°C. If food is available, they can remain active all year round and produce annually a varying number of generations, depending on the local climatic conditions. To survive adverse low-temperature winter conditions these species use various natural protected microhabitats and can overwinter at different developmental stages. The other two bryocorines studied (Dicyphus errans and D. hesperus) exhibit heterodynamic seasonal development and overwinter in the state of adult diapause. Induction of this diapause is controlled by a long day-type photoperiodic response. Also, the nymphal growth rate of D. errans is affected by day length and this quantitative photoperiodic response ensures that nymphs of this species reach the diapausing stage (adult) in appropriate time, which is crucial for successful overwintering. The threshold photoperiod for induction of winter adult diapause varies with latitude in D. hesperus, only nymphs being sensitive to day length in this species. Pilot experimental studies should precede any planned introduction of a biocontrol agent, as these may reduce the risk of invasions. During the early stages of settling in a new area, it is seasonal adaptations controlling development of bug populations in their natural environments that are particularly important. In greenhouses, higher efficiency of biocontrol measures can be achieved with southern multivoltine populations of homodynamic species, especially if these grow rapidly as immatures, have high reproduction rates at the adult stage, and easily switch to novel prey. Under field conditions, polyphagous heterodynamic univoltine species and populations with deep obligate diapause are more likely to naturalize successfully.

A remarkable life strategy in the Iberian endemic Acinipe segurensis (Bolívar, 1908) (Orthoptera: Pamphagidae)

SummaryThe first data on the developmental life cycle of Acinipe segurensis (Bolívar, 1908) are provided as well as a morphological description of the nymphal stages. Data provided refer to the number of nymphal stages in the two sexes and their duration. The species hibernate in the egg stage. Males undergo four nymphal stages before reaching the adult stage, while females undergo five, the extra stage being the third one. Morphological features studied concerning the number of antennal segments, the morphology of the wing rudiments on lateral lobes of the meso- and metanotum and the morphology of the external genitalia both in male and female, allowed us to briefly describe and illustrate the different nymphal stages. The life cycle is different from other Pamphagini species as concerns the hibernation period and the rate of nymphal growth. A discussion on the possible causes of such divergences is given.

Effects of RNAi-based silencing of chitin synthase gene on moulting and fecundity in pea aphids (Acyrthosiphon pisum)

The pea aphid, Acyrthosiphon pisum, is an important agricultural pest and an ideal model organism for various studies. Chitin synthase (CHS) catalyses chitin synthesis, a critical structural component of insect exoskeletons. Here, we identified a CHS gene from A. pisum, ApisCHS. The ApisCHS expression profiles showed that ApisCHS was expressed in various developmental stages and in all tested tissues of A. pisum, including the epidermis, embryo, gut and haemolymph. Notably, ApisCHS exhibited peak expression in the middle of each nymphal period and was extremely highly expressed in the epidermis and embryo. RNA interference (RNAi) showed that ~600 ng of dsRNA is an effective dose for gene silencing by injection for dsRNA delivery; moreover, 1200 ng·μL−1 dsRNA induced CHS gene silencing by a plant-mediated feeding approach. A 44.7% mortality rate and a 51.3% moulting rate were observed 72 h after injection of dsApisCHS into fourth-instar nymphs, compared with the levels in the control (injected with dsGFP). Moreover, a longer period was required for nymph development and a 44.2% deformity rate among newborn nymphs was obtained upon ingestion of dsApisCHS. These results suggest that ApisCHS plays a critical role in nymphal growth and embryonic development in pea aphids, and is a potential target for RNAi-based aphid pest control.