Efficiency of food utilization by Dichroplus maculipennis (Orthoptera: Acrididae: Melanoplinae) on four crop plants under controlled conditions

The aim of this study was to analyze the food utilization efficiencies and the relative growth and consumption rates of different developmental stages and sexes of D. maculipennis under controlled conditions on wheat, oat, corn, and soybean plants, important crops in the Pampas region of Argentina. As expected from a polyphagous species, D. maculipennis was observed to consume all four of the plant species offered. Nevertheless, the consumption of both nymphs and adults was differentiated. Oat and wheat were more consumed than corn and soybean. Females presented higher consumption rates (384.6 ± 30.64 mg/individual/day) than males (278.71 ± 24.26 mg/individual/day). Adult females had the highest growth rate, followed by nymphs of the same sex, and then adult males. The highest values of ECI and ECD were obtained in soybean; females had higher values of food efficiencies than males, and nymphs had greater values than adults. In relation to this, soybean was the highest quality food; the amount of nitrogen present in soybean was approximately twice that found in the other species. The nutritional needs of D. maculipennis might have been satisfied by feeding on low quantities of soybean, which is, among the food offered, the most “nutritionally balanced food”.     

Effects of brief exposures to low temperature on the development, longevity and fecundity of the grain aphid Sitobion auenae (Hemiptera: Aphididae)

First instar nymphs and adults of the grain aphid Sirobion auenae that had been reared at 10°C and 20°C over a number of generations, were cooled to -5°C and -10°C for 1 h and 6 h and returned to 20°C to assess the effects of brief exposures to low temperatures (cold-pulses) on their survival. rate of development, longevity and fecundity. A strong acclimation response was observed in first instar nymphs, with significantly less mortality in groups reared to 10°C compared to 20°C. Mean development time from first instar to adult was not significantly affected by low temperature exposure at the first nymphal stage. Longevity in all groups cooled as first instars was reduced by the sub-zero cold-pulses, and was also dependent on temperature and exposure time. Acclimated aphids survived longer than non-acclimated individuals. Reproductive rate, in terms of the number of nymphs born per aphid per day, was unaffected by cold stress applied at the first instar stage. Total fecundity was however reduced, being a function of the number and longevity of the survivors. Adult aphids were less cold hardy than nymphs; mortality was higher at -10°C than -5°C increasing with duration of exposure from 1 h to 6 h. Mean fecundity was reduced significantly in aphids cooled at the adult stage, the number of aphids born per day decreasing as the exposure period of the cold-pulse increased, suggesting that low temperature had affected embryogenesis. All the nymphs born to adults surviving exposure to -5°C for 6 h died within 48 h of birth, indicating that low temperature has a pre-natal effect on mortality.     

Efficacy of multiple biocontrol agents against the sweet potato whitefly Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) on tomato

Abstract: Biological control provides an environmentally harmonious and potentially stable management tactic to combat noxious pests such as Bemisia tabaci, notorious for its resistance to synthetic pesticides. Bioassays conducted under control chamber conditions integrating applications of the parasitoid Encarsia formosa, reared for 20 years on Trialeurodes vaporariorum, and the fungus Verticillium lecanii on the third‐fourth instar nymphs of B. tabaci on tomato, showed a comparable effect between the parasitoid‐fungus combined treatment and the fungus treatment alone (70.7% vs. 70.4%). Analysis of our results indicates antagonism between the two biocontrol agents related to the parasitoids’ ability to discriminate between infected and healthy B. tabaci nymphs. The parasitoid treatment alone produced 36.3% mortality, with no mortality in the distilled water controls. The behavioural performance of the parasitoid could have either genetic or environmental causes. Bioassays studying the feeding habit of the imported mirid predator Macrolophus caliginosus (adults) and the indigenous mirid Camptotylus reuteri (nymphs and adults) on eggs, or early second instar nymphs of B. tabaci, and choice preference tests indicated a significant difference in feeding between M. caliginosus and C. reuteri. There was no significant difference in percentage feeding of M. caliginosus on eggs (2.2%) or second instar nymphs (8.0%). There was a significant difference in feeding of M. caliginosus adults (18.6%) when offered eggs and second instars in the same arena compared with eggs or second instars offered separately. These results could be attributed to the biological behaviour of the predator having a type III functional response. Studies with the local C. reuteri species showed no significant difference in adult and nymphal consumption on second instars of B. tabaci compared with nymphs on eggs. However, C. reuteri adults fed less on eggs compared with nymphs. This local predatory species appears to be more efficient than M. caliginosus in feeding on particular stages of B. tabaci without depending on prey density. This is further supported by the low consumption of both adults and nymphs in the choice test (4% and 2.3%, respectively) compared with M. caliginosus adults (18.6%).     

Multiple host use by a sap-sucking membracid: population consequences of nymphal development on primary and secondary host plant species

Aconophora compressa is a gregarious, sap-sucking insect that uses multiple host plant species. Nymphal host plant species (and variety) significantly affected nymphal survival, nymphal development rate and the subsequent size and fecundity of adults, with fiddlewood (Citharexylum spinosum) being significantly best in all respects. Nymphs that developed on a relatively poor host (Duranta erecta var “geisha girl”) and which were moved to fiddlewood as adults laid significantly fewer eggs (mean ± SE = 836 ± 130) than those that developed solely on fiddlewood (1,329 ± 105). Adults on geisha girl, regardless of having been reared as nymphs on fiddlewood or geisha girl, laid significantly fewer eggs (342 ± 83 and 317 ± 74, respectively) than adults on fiddlewood. A simple model that incorporates host plant related survival, development rate and fecundity suggests that the population dynamics of A. compressa are governed mainly by fiddlewood, the primary host. The results have general implications for understanding the population dynamics of herbivores that use multiple host plant species, and also for the way in which weed biological control host testing methods should be conducted. Handling Editor: Robert Glinwood     

The effects of aggregation on survival and growth rate in the wood‐feeding cockroach Panesthia angustipennis spadica (Blaberidae)

The wood‐feeding cockroach Panesthia angustipennis spadica Shiraki (Blaberidae) is a gregarious species, and its groups containing both nymphs and adults have often been observed in the field. To clarify the effects of aggregation with a parent and siblings on nymphal development in P. angustipennis spadica, we raised nymphs of this species in the laboratory under the following three experimental categories: (a) aggregate with a female adult; (b) aggregate without a female adult; and (c) solitary. Survival rates did not significantly differ among the three categories. Unexpectedly, our results clearly showed that nymphs raised in aggregates with a female adult were smaller, lighter, and reached a lower instar than those raised without a female adult. These results indicate that the presence of a female adult does not positively affect nymphal development; i.e. there may be no direct parental care in this species as indicated by previous studies. Moreover, solitary nymphs grew faster and larger than nymphs in aggregates, showing that the aggregation with siblings also has no positive effect on nymphal development. Thus, it seems likely that external factors, e.g. predation and environmental conditions, may drive aggregating behavior in P. angustipennis spadica.     

Influence of <Emphasis Type="Italic">Lecanicillium attenuatum</Emphasis> on the development and reproduction of the cotton aphid, <Emphasis Type="Italic">Aphis gossypii</Emphasis>

The activity of entomopathogens on insect pests has been investigated for many species but the influence of entomopathogenic fungi on factors other than mortality relating to population increase has not been frequently studied. The influence of Lecanicillium attenuatum CS625 (=Verticillium lecanii CS625) on development and reproduction of cotton aphid (Aphis gossypii) was investigated. A conidia suspension of the isolate was applied onto first instar nymphs. Increased spore concentration did not significantly affect each nymphal stage, total nymphal period, pre-reproductive period and the age of first larviposition. A significant dose effect on reduction of life span, reproductive period and fecundity was observed in 1st and 3rd instars after spore application. When conidia were applied to 1st instars, life span was significantly reduced to 10.8 and 8.4 days at 1 × 10⁴ and 1 × 10⁸ conidia/ml, respectively from 12.2 days in the control. During the life span, total fecundity was 41 ± 7.3, 26 ± 0.8 and 22 ± 5.7 nymphs per female at 1 × 10⁴, 1 × 10⁶ and 1 × 10⁸ conidia/ml, respectively compared with 51 ± 2.0 nymphs per untreated female. Reproduction period was also significantly shortened with increasing spore concentration. Application of spores to 3rd instars showed a similar trend. However, daily fecundity of individual aphids was not affected by spore dose. It was concluded that the isolate of L. attenuatum is able to affect populations of cotton aphid by reducing life span and total fecundity as well as by killing the aphids directly.     

Influence of azadirachtin on development and reproduction of Nezara viridula L. (Het., Pentatomidae)

Abstract:  The potential of azadirachtin as an insect growth regulator was evaluated in Nezara viridula L. by applying different doses to fifth instar nymphs. At doses of 200–500 ng per insect almost all the individuals died during moulting to adults and the survivors showed a great number of nymphal characteristics, and also died very soon after. At lower doses, from 2 to 50 ng per insect, approximately 50% of the adults seemed normal. No effect was observed during the last nymphal instar, even at the highest dose applied. The fertility and fecundity of adults, males and females, developing from nymphs treated with different low doses of azadirachtin were also studied. When azadirachtin was applied at 20 ng per insect on fifth instar nymphs, females developing from these nymphs showed a conspicuous reduction of fecundity. This same effect was evident when untreated females mated with males obtained from treated nymphs. Finally, azadirachtin applied at 1  μ g/cm² to the oviposition surface showed a remarkable oviposition repellency.     

Host-stage preference and functional response of aphid parasitoid Diaeretiella rapae (McIntosh) (Hym.: Braconidae) on greenbug,Schizaphis graminum (Rondani) (Hem: Aphididae)

Searching capacity is of great importance in the efficiency of natural enemies. In this research, the host-stage preference and functional response of Diaeretiella rapae (McIntosh) to different densities of greenbug, Schizaphis graminum (Rondani) were determined on Pishtaz wheat leaves at 25 ± 1°C, 60–70% relative humidity, and a photoperiod of 16:8 h (L:D). The host-stage preference was investigated by exposing 60 number of all nymphal instars and adults of greenbug to individual parasitoid females at eight replicates. Results indicated significant preference of D. rapae to second instar nymphs of S. graminum to perform functional response experiment. Densities of 2, 4, 8, 16, 32, 50, 64, 90 and 130 second instar nymphs of greenbugs were exposed to individual mated female wasps at 10 replicates for 24 h. Type of functional response was determined by logistic regression and its parameters, searching efficiency (a) and handling time (T _h), were estimated by non linear regression. The results indicated that the functional response of D. rapae was type III and values of searching efficiency, handling time and maximum rate of parasitism were calculated by two models as 0.1364 ± 0.084, 0.5761 ± 0.0179, 41.6594; 0.06489 ± 0.00652 (h^?1), 0.5628 ± 0.0173 (h) and 42.6439 (aphids/parasitoid/day), respectively.     

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.     

Laboratory assessment of the potential of Paranosema locustae to control immature stages of Schistocerca gregaria and Oedaleus senegalensis and vertical transmission of the pathogen in host populations

We tested the effects of Paranosema locustae spores in wheat bran formulation on the immature stages of Schistocerca gregaria and Oedaleus senegalensis under laboratory conditions. Younger instars were the most sensitive to the pathogen. While 100% infection was recorded in younger instar nymphs, older instars were less sensitive, with 16–27% of the inoculated nymphs remaining uninfected at the end of the experiment. Mortality of each instar increased with increased spore concentration. Immature survival time was significantly reduced by the pathogen and none of the nymphs inoculated as first, second, and third instar nymphs developed to adulthood (6–30% and 55–74% of nymphs inoculated as fourth and fifth instar, respectively). Sublethal effects such as delayed host growth, reduced host size, and abnormal wing and leg development (37% of emerging adults) were noted. Almost half the infected adults showed morphological abnormalities at emergence. Moreover, infection in S. gregaria and O. senegalensis by P. locustae did not affect female oviposition. However, 60% of S. gregaria and 52% of O. senegalensis progeny clearly showed infection by P. locustae with infection intensity of 1.08±0.27×10¹ and 1.19±0.32×10² spores/nymph, respectively. In view of the mortality rates, immature survival, host growth, and abnormal development in the P. locustae treatments, and the high prevalence of the pathogen in offspring from infected parents, it can be expected that the reduction in the impact of the two acridid species in the field will be considerable.     

Suitability of Aphis craccivora (Hemiptera: Aphididae) and Bemisia tabaci (Hemiptera: Aleyrodidae) biotype-B as prey for Chrysopa pallens (Neuroptera: Chrysopidae)

The suitability of Aphis craccivora Koch (Hemiptera: Aphididae) and Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae) biotype-B eggs and nymphs as prey for pre-imaginal development and survival, adult longevity, and fecundity of the lacewing, Chrysopa pallens (Rambur) (Neuroptera: Chrysopidae) was evaluated under laboratory conditions at 25±1°C, 50±10% RH and a photoperiod of 16 h L:8 h D. Survival of C. pallens from first instar to adult eclosion was significantly different between the larvae that fed on the two prey species. C. pallens fed on A. craccivora completed development from egg to adult emergence, but those fed on eggs and nymphs of B. tabaci could not complete development, resulting in abnormal pupae and no normal adults emerged. The net reproductive rate (R ₀), intrinsic rate of natural population increase (r _m ), finite rate of increase (λ), mean generation time (T), index of population trend (I), doubling time (DT), and gross reproductive of rate (GRR) of C. pallens that fed on A. craccivora were 201.9 eggs per female, 0.13/d, 1.1/d, 40.1 d, 68.5, 5.2 d, 203.1 eggs per female, respectively. These results could be useful for mass-rearing of C. pallens and for understanding its population dynamics in the field in relation to the availability of different prey species.     

Nymphal and adult performance of Apolygus lucorum (Hemiptera: Miridae) on a preferred host plant, mungbean Vigna radiata

Mungbean, Vigna radiata (L.) Wilczek, a preferred host plant of Apolygus lucorum (Meyer-Dür) (Hemiptera: Miridae), is used in China as a trap crop for this pest in cotton fields. Little is known, though, about the relationship between adult oviposition preference and offspring performance of A. lucorum on mungbean. In this study, we compared the oviposition preference of A. lucorum on mungbean versus cotton plants in both open-field plots and field cages. Field-plot experiments demonstrated that the population density of first instar nymphs of A. lucorum and the ratio of first instar nymphs to adults were significantly higher on mungbean than on cotton. Choice and no-choice cage experiments revealed that the number of eggs laid on mungbean was significantly higher than on cotton. We also compared adult longevity and fecundity, as well as offspring survival and development on these two host plants. We found that A. lucorum adult females survived longer and laid more eggs on mungbean than on cotton (P?<?0.05). Mungbean also promoted higher rates of development than did cotton (P?<?0.05), but did not affect nymphal survival (P?>?0.05). In summary, the preference of A. lucorum adults for mungbean is consistent with both adult and nymphal performance. This study furthers the understanding of the relationship between the polyphagous species A. lucorum and its host plants, which will help improve trap-cropping strategies for the control of A. lucorum that are based on the use of mungbean.     

Rearing method and life-table data for the cocoa mirid bug Sahlbergella singularis Haglund (Hemiptera: Miridae)

The mirid bug Sahlbergella singularis feeds on cocoa pods and shoots, causing considerable crop losses. As laboratory experimentation requires numerous insects, this study aimed at improving available rearing method of S. singularis for Cameroon. Fifty second to fifth nymphal stages were collected at a cocoa farm and reared to the adult stage on cocoa pods in an insectary (T = 24.7 ± 0.9°C, RH = 84.5 ± 6.8%, photoperiod: 12 : 12 L : D). Newly emerged females were confined for 5–6 days on cocoa twigs for sexual maturation and each female paired with a male for 24 h. The pairs were returned to the field and enclosed in mousseline sleeves on attached cocoa pods, for egg laying. After 16 days (expected egg lifetime), the sleeve cages were checked daily to detect newly hatched nymphs. Then, the pods were collected and brought to the insectary, where nymphs continued to emerge and develop into adults. Our method allowed the production of 14.6 ± 6.7 nymphs per female per generation, for 15 consecutive generations. Nymphal survival was calculated to be 68.2% and the mean duration of the nymphal development was measured at 22.7 ± 3.1 days. The rearing performance was evaluated using life‐table calculations. The net reproductive rate (R₀) was 6.59; the intrinsic rate of increase (r) was 0.037 per female per day with a population doubling time (T_d) of 18.9 days. On average each female contributed 9.70 individuals to the population given a mean generation time (T_c) of 52.1 days. The percentage of reproductive females and the mean number of nymphs per female were significantly different between generations, with 86.8% and 18.1% in generation G7 as compared to 45.8% and 8.4% for generation G5, respectively. As rainfall showed concordant variations during the period of investigation, we discuss the impact of this factor on mirid fecundity.     

Biometric studies of some stoneflies and a mayfly (Plecoptera and Ephemeroptera)

Aspects of the nymphal/adult developmental change were investigated in biometric studies of several species of Plecoptera: Nemouridae near Schlitz, Hesse, Germany. Preliminary information on the mayfly, Baetis vernus Curtis, is also provided. Nemourid nymphs pass through 3 wing bearing stages before reaching adulthood. Instars can be identified by their characteristic shapes, as expressed by the wing length/head width (WL/HW) ratio. Size does not allow instar discrimination, mainly due to sexual size differences. HW is ca 10% larger in last instar female than in male nemourid nymphs; exuviae shed at the moult to adult represent about 14% of nymphal ash free dry weight (AFDW). Biomass lost with exuviae during the many larval moults should be accounted for in estimates of production. Freshly emerged nemourid females are about 6% larger and 30% heavier than males. The HW/AFDW relationship is the same in both sexes. Through terrestrial feeding during adult life, males double their weight on average. Mature females are up to three times heavier than freshly emerged ones. They invest about 30% of their final AFDW in reproduction.Shape of last instar nymphal Baetis was expressed as the ratio wing length/mesonotum length. It is size-dependent, a characteristic, instar-specific shape may not occur in this mayfly. Nymphal and subimaginal exuviae together represent about 14% of last instar nymphal dry weight. Females of Baetis are about 55% heavier than males. Unlike in Plecoptera, the size/weight (ML/AFDW) relationship differs between sexes.     

Fecundity,nymphal development and longevity of field‐collected tropical bedbugs,Cimex hemipterus

This study examined the fecundity, oviposition, nymphal development and longevity of field‐collected samples of the tropical bedbug, Cimex hemipterus (Fabricius) (Hemiptera: Cimicidae). Under environmental conditions of 26±2°C, 70 ± 5% relative humidity and a 12‐h photoperiod, with bloodmeals provided by a human host, six strains of tropical bedbug had a fecundity of up to 50 eggs per lifetime, over 11–14 oviposition cycles. Increased feeding frequency improved fecundity. After feeding and mating, adult females normally took 2–3 days to produce a first batch of eggs. The oviposition period lasted 2–7 days before cessation of the oviposition cycle. The egg incubation period usually lasted 5–7 days before the emergence of first instars. The nymphs underwent five stadia (the first four of which each took 3–4 days, whereas the last took 4–5 days) before becoming adults at a sex ratio of 1 : 1. More than five bloodmeals were required by the nymphs to ensure a successful moult. Unmated adults lived significantly longer than mated adults (P < 0.05). Unmated females lived up to almost 7 months, but the longevity of mated males and females did not differ significantly (P > 0.05).     

Stage-based mortality of grassland grasshoppers (Acrididae) from wandering spider (Lycosidae) predation

Mortality rates in insects, including grasshoppers (Acrididae), are often stage- or size-specific. We estimated stage-specific mortality rates for three common grasshopper species from a Nebraska (USA) sandhills grassland (Ageneotettix deorum, Melanoplus sanguinipes and Phoetaliotes nebrascensis), and partitioned the impact due to wandering spider predation from remaining sources. Survivorship was estimated for multiple developmental stages (3rd instar through adult) under experimental conditions that either prevented or permitted predation from free-living, wandering spiders (primarily Schizocosa species). Total stage-specific mortality, including spider predation, examined over the period of single stages was greatest for the youngest stages (91% for 3rd instar, 73% for 4th instar, 63.5% for 5th instar and 30.4% for adults). For the developmental stages considered and averaged for all species, the contribution to total mortality from spider predation over the 10-d period (approximately the length of a developmental stage) ranged from 17% for 3rd instar nymphs to 23% for 4th and 5th instars, and an undetectable level for adults. While spiders may depress grasshopper numbers, contributions from spider predation to grasshopper population dynamics are uncertain.     

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.     

Independent and joint action of cis- and trans-permethrin in Triatoma infestans (Hemiptera: Reduviidae)

The toxicity of pure cis- and trans-permethrin or mixtures of the two isomers topically applied to first, third, and fifth instar nymphs of Triatoma infestans (Klug) at 26°C was determined. The cis-isomer was more active than the trans-isomer in the three stages evaluated. When the two isomers were simultaneously applied to first instar nymphs, an additive effect was observed. Similar treatments of third and fifth instar nymphs resulted in an antagonistic effect. In third instar nymphs, the cis-isomer was more active than trans-isomer at all the three temperatures assayed (16°, 26°, and 36°C). The toxicity of the cis-isomer was lower at 36°C than at either 16° or 26°C. Temperature had no significant effect on the toxicity of the trans-isomer within the temperature range assayed. The toxicity of either isomer to third instar nymphs was not affected by pretreatment of nymphs with PBO (an inhibitor of mixed-function oxidases activity) or TPP (an inhibitor of esterase activity), suggesting that these detoxification pathways are not relevant in the metabolism of cis- or trans-isomers. Arch. Insect Biochem. Physiol. 37:225–230, 1998. © 1998 Wiley-Liss, Inc.     

Life history characteristics of Orius insidiosus (Say) fed Aphis glycines Matsumura

The soybean aphid, Aphis glycines Matsumura, is a new invasive pest of soybeans throughout most of the soybean production areas of North America. Field studies have demonstrated that the indigenous predator, Orius insidiosus (Say), is an important natural enemy of the soybean aphid early the soybean crop season. Because soybean aphid is newly introduced into North America, the life history characteristics of predators fed this aphid are not known. In laboratory assays, we measured the survival, development, longevity and reproduction of O. insidiosus fed 1, 3, 6 or 12 seconds to third instars of soybean aphid. O. insidiosus nymphal development decreased from 34.0 to 21.4 days as the number of soybean aphid nymphs provided increased from 1 to 6 aphid nymphs daily. Stage-specific mortality was highest at 68% for first instar O. insidiosus nymphs fed 1 soybean aphid nymph per day. Adult longevity (43.9 days) and fecundity (49.7 eggs per female) was highest for O. insidiosus fed 6 soybean aphid nymphs daily, but longevity (23.5 days) and fecundity (10.1 eggs per female) declined for adults fed 1 soybean aphid nymph daily. The intrinsic rate of increase of O. insidiosus ranged from 0.048 to 0.133. Compared to other prey species, soybean aphid is an adequate prey item for O. insidiosus. Our results suggest that O. insidiosus will be most effective in suppressing soybean aphid population growth in the initial phase of the aphid’s colonization of soybeans.     

灰飞虱长、短翅型品系对高、低温的适应能力差异

【目的】灰飞虱Laodelphax striatellus种群存在长翅和短翅个体,其翅型分化受遗传和环境条件的影响。本研究旨在明确经连续定向选育的灰飞虱长、短翅型品系对高、低温的适应能力差异。【方法】在室内分别长期定向筛选63和65代建立灰飞虱长、短翅型品系,并在南京田间采集灰飞虱自然种群;分别在25℃, 30℃和35℃恒温条件下测定上述灰飞虱长、短翅型品系和自然种群的繁殖力、存活率和发育历期,测定若虫在5℃和-20℃下的存活率以及若虫和成虫的过冷却点,通过品系间存活率、发育历期、生殖力和过冷却点的比较分析,确定灰飞虱长、短翅型品系对高温和低温的耐受能力。【结果】在25℃, 30℃和35℃下,灰飞虱自然种群雌成虫的繁殖力均显著高于室内筛选后的长、短翅型品系,而长、短翅型品系雌成虫之间的繁殖力均无显著差异;长、短翅型品系的繁殖力在25℃和30℃之间均无显著差异,但自然种群在25℃下的繁殖力显著高于30℃条件下的繁殖力;35℃下长、短翅型品系基本无若虫产生。25℃下长翅型品系、短翅型品系和自然种群若虫的存活率无显著差异,但在30℃下,短翅型品系若虫的存活率显著低于自然种群,而与长翅型品系差异不显著;35℃下长、短翅型品系的若虫最长只能存活到3龄,且两品系间无显著差异,而自然种群可存活到5龄。25℃下,短翅型品系若虫的发育历期显著短于自然种群,而与长翅型品系无差异;但是在30℃下,短翅型品系若虫历期显著长于长翅型品系和自然种群。长翅型品系、短翅型品系和自然种群灰飞虱3-4龄若虫在5℃低温下的存活天数无显著差异,并且长翅和短翅型品系在-20℃极端低温下暴露10 min后其死亡率也无显著差异且均显著高于自然种群。3个品系(种群)成虫的过冷却点无显著差异,但5龄若虫的过冷却点表现为短翅型品系显著高于自然种群,而与长翅型品系无显著差异。【结论】经连续定向选育的灰飞虱长、短翅型品系对低温和高温的适应力基本相当,且低于自然种群。在高温条件下灰飞虱短翅型品系的发育速率低于长翅型品系。