Mating system of Bracon hebetor (Hymenoptera: Braconidae)

Abstract.

• 1 We report on the mating system of a field population of the parasitic wasp, Bracon hebetor, on a corn pile infested by the Indian meal moth, Plodia interpunctella. We demonstrate that the mating system is based upon male scramble competition polygyny with male aggregations on high places on the corn.
• 2 The sex ratio among adults was greater than 80% males on the surface of the corn, whereas below the surface the sex ratio was less than 45%. Males actively courted females on the surface, but there were no aggressive interactions among males during courtship or mating.
• 3 Approximately 20% of the females found on the surface of the corn had no sperm in their spermathecae, regardless of age, but the numbers of unmated females decreased later during the day.
• 4 In laboratory studies we showed that females from this population oviposit a female biassed sex ratio, and that only 14% of females were mated before dispersing from their place of emergence.
• 5 Thus sib-mating is unlikely in this gregarious parasitoid. This outcrossing mating system probably arose because of severe inbreeding depression that B.hebetor suffers via a sex locus: diploids that are heterozygous at the sex locus develop into females, but homozygous diploids are male and are generally inviable. The female biassed sex ratio may have evolved in B. hebetor in response to males being the more expensive sex, females dispersing more frequently from the population than males, or a fraction of females remaining unmated in the population.

     

Life History of Bracon hebetor (Hymenoptera: Braconidae) on Plodia interpunctella (Lepidoptera: Pyralidae) on a Dried Vegetable Commodity

Life history of Bracon hebetor Say was studied on Plodia interpunctella Hübner. The life span of female (mean±s.e.) was estimated to be 20.88±0.97 days. The females laid eggs from the first day on after emergence and the oviposition period ranged from 11 to 27 days. But 65% of the total eggs were laid in the first 10 days. The progeny sex ratio (female/total) in the first 15 days was female-bias ranged from 0.51±0.08 to 0.88±0.02, but changed into male-bias ranged from 0.14±0.04 to 0.34±0.12. The overall sex ratio of progeny produced per female was estimated to be 0.66. Total number of progeny per female and net reproduction rate were estimated to be 205.17±13.03 and 136.21, respectively. Other life table statistics were presented.     

Biological, nutritional, and histochemical basis for improving an artificial diet for Bracon hebetor Say (Hymenoptera: Braconidae)

The biology of Bracon hebetor Say (Hymenoptera: Braconidae) reared on fifth instars of Anagasta kuehniella (Zeller) (Lepidoptera: Pyralidae) (natural diet) and in vitro (artificial diet) was evaluated. Data on the number of instars, development time and food intake were collected, and histochemical tests were conducted to detect proteins and lipids in the parasitoid's digestive tract. The data disclosed differences that can help to improve artificial rearing of B. hebetor. B. hebetor had three instars in both diets, but the developmental time on the artificial diets was prolonged due to the increase in larval and pupal development times. Larvae grew faster on the natural host and required a lower food intake (2.7 microl) as compared to that required by the larvae feeding on the artificial diet (3.8 microl). Analysis of diet protein content and host hemolymph and the observations on the parasitoid larvae gut content indicated altogether the artificial diets requires the addition of others sources of proteins and lipids to improve the overall nutrition quality of the in vitro rearing system for this ectoparasitoid.     

Effect of ellagic acid on the larvae of Spodoptera litura (Lepidoptera:Noctuidae) and its parasitoid Bracon hebetor (Hymenoptera:Braconidae)

The present study was aimed at investigating the effect of plant based compound, ellagic acid on parasitoid Bracon hebetor (Say) through its host, the common cutworm, Spodoptera litura (Fabricius). The effect on S. litura was ascertained by feeding six days old larvae on artificial diet incorporated with different concentrations (5 ppm, 25 ppm, 125 ppm, 625 ppm, 3125 ppm) of ellagic acid and water as control. Its effect on B. hebetor was determined by allowing the adult B. hebetor to parasitize the treated host larvae. The mortality of S. litura larvae was increased whereas adult emergence declined with increasing concentration of ellagic acid. The developmental period was delayed significantly and all the nutritional indices were reduced with treatment. Ellagic acid at LC₃₀ (7.70 ppm) had not much influence on the growth of parasitoid B. hebetor but LC₅₀ (43.45 ppm) adversely influenced the development of the parasitoid, B. hebetor when reared on treated larvae of S. litura. This was evident from reduced parasitization, fecundity, egg laying, egg hatching, emergence, increased larval mortality, reduced pupation and prolonged development of the immature stages at LC₅₀. However, parasitization, egg hatching and larval mortality of the parasitoid were not significantly impacted at LC₃₀ indicating the possibility of its use in integrated pest management programmes.     

Single-locus complementary sex determination absent in Heterospilus prosopidis (Hymenoptera: Braconidae)

In the haplodiploid Hymenoptera, haploid males arise from unfertilized eggs, receiving a single set of maternal chromosomes while diploid females arise from fertilized eggs and receive both maternal and paternal chromosomes. Under single-locus complementary sex determination (sl-CSD), sex is determined by multiple alleles at a single locus. Sex locus heterozygotes develop as females, while hemizygous and homozygous eggs develop as haploid and diploid males, respectively. Diploid males, which are inviable or sterile in almost all cases studied, are therefore produced in high frequency under inbreeding or in populations with low sex allele diversity. CSD is considered to be the ancestral form of sex determination within the Hymenoptera because members of the most basal taxa have CSD while some of the more derived groups have other mechanisms of sex determination that produce the haplo-diploid pattern without penalizing inbreeding. In this study, we investigated sex determination in Heterospilus prosopidis Viereck, a parasitoid from a relatively primitive subfamily of the Braconidae, a hymenopteran family having species with and without CSD. By comparing sex ratio and mortality patterns produced by inbred and outbred females, we were able to rule out sl-CSD as a sex determination mechanism in this species. The absence of sl-CSD in H. prosopidis was unexpected given its basal phylogenetic position in the Braconidae. This and other recent studies suggest that sex determination systems in the Hymenoptera may be evolutionary labile.     

Single-locus sex determination in the parasitoid wasp Cotesia glomerata (Hymenoptera: Braconidae)

The parasitoid Cotesia glomerata usually produces female-biased sex ratios in the field, which are presumably caused by inbreeding and local mate competition (LMC); yet, sibling mating increases the production of males, leading to the male-biased sex ratio of broods in the laboratory. Previous studies have suggested that the sex allocation strategy of C. glomerata is based on both partial LMC in males and inbreeding avoidance in females. The current study investigated the presence of single-locus complementary sex determination (sl-CSD) as a sex-determining mechanism in this species through inbreeding experiment, cytological examination and microsatellite analysis. Cytological examination detected diploid males in nine of 17 single pairs of sibling mating, thus in agreement with the proportion of matched matings predicted by the sl-CSD model. Sex ratio shifts in these matched sibling matings were consistent with the sl-CSD model with less viable diploid males. The haploid males have a single set of maternal chromosomes (n = 10), whereas diploid males possess a double set of chromosomes (2n = 20). Microsatellite analyses confirmed that diploid males produced from the matched matings inherited segregating genetic materials from both parents. Thus, this study provides the first solid evidence for the presence of sl-CSD as a sex-determining mechanism in the braconid genus Cotesia.     

Alterations in esterases are associated with malathion resistance in Habrobracon hebetor (Hymenoptera: Braconidae)

Biochemical mechanisms of malathion resistance were investigated in a malathion-resistant strain of the parasitoid Habrobracon hebetor Say collected from a farm storage in Kansas. General esterase activities were significantly lower in the resistant strain compared with those in a susceptible strain. However, no significant differences were found in activities of malathion specific carboxylesterase (MCE), glutathione S-transferase and cytochrome P450 dependent O-demethylase activities, cytochrome P450 contents, and sensitivity of acetylcholinesterase to inhibition by malaoxon between the 2 strains. Because MCE was not elevated in the resistant strain, the weak malathion resistance in H. hebetor may result from a different mechanism compared with that hypothesized for some insect species in which reduced general esterase activity is accompanied by an elevated MCE. Decreased esterase activity in the resistant strain suggested that null alleles of some esterases were associated with the resistance. Indeed, E1 and E2, major esterases in the susceptible strain, were not present in the resistant strain on polyacrylamide gels that were stained for esterase activity using the model substrate 1-naphthyl acetate. In contrast, the activity of esterase E3 on the gels was much higher in the resistant strain as compared with that of the susceptible strain. These findings indicate that malathion resistance in H. hebetor is associated with both an increased activity of the esterase E3 and null alleles of the esterases E1 and E2.     

Potential non-target effects of Sclerodermus harmandi (Hymenoptera:Bethylidae) on Triaspis sp. (Hymenoptera:Braconidae)

Sclerodermus harmandi (Buysson) (Hymenoptera: Bethylidae) is a generalist parasitoid that has been mass-produced and released for biological control of many agricultural and forest pests in China. However, few studies have examined the potential non-target risks of this parasitoid in targeted agriculture or forest ecosystems. In this study, we demonstrate that S. harmandi successfully attacks Triaspis sp. (Hymenoptera: Braconidae), an important native natural enemy of the pine weevil pest Pissodes punctatus Langor et Zhang in Yunnan Province of China. When exposed to older larvae of Triaspis sp. at three different parasitoid-to-host group sizes (1:1, 2:2 and 3:3) with a constant 1:1 parasitoid-to-host ratio, S. harmandi successfully attacked 100%, 75% and 83.3% of the test larvae, respectively. All life stages (egg, larva, pupa and adult) of S. harmandi were observed on Triaspis sp. larvae, indicating that Triaspis sp. are suitable for the completion of S. harmandi development. There were no significant differences in the number of S. harmandi progeny produced among the different parasitoid-to-host exposure treatments. Immature stages of S. harmandi on parasitized Triaspis sp. took 25.4 days to complete their development (the egg stage: 3.6 days, the larval stage: 5.0 days, the pupal stage: 16.5 days). Together, results from our study indicate that mass-releases of S. harmandi for biological control of forest pests in Yunnan Province may adversely affect some valuable non-target insects such as Triaspis sp. We suggest that the potential non-target risk of S. harmandi be considered in future augmentative release biological control programmes against forest pests.     

Cold hardiness of Habrobracon hebetor (Say) (Hymenoptera: Braconidae), a parasitoid of pyralid moths

The ectoparasitoid Habrobracon hebetor (Say) attacks stored-product infesting pyralid moths that are able to overwinter under extremely cold conditions. The extent to which H. hebetor can withstand these conditions is not known, but has important implications for the ability of H. hebetor to provide long-term suppression of these pests in temperate climates. We investigated basic cold hardiness aspects of a mutant eye-color strain of H. hebetor. Feeding larvae and adults of H. hebetor had supercooling points (SCPs) at temperatures higher than those of eggs and pupae. Mean SCPs of females and males were equivalent, as were those of naked and silk-encased pupae. Feeding on honey prior to being subjected to low temperatures significantly increased the SCP of adult females by approximately 8 degrees C. Mortality of pupae and adults increased significantly whenever the temperature dropped below the mean SCP, indicating that H. hebetor does not tolerate freezing. For pupae and adults exposed to -12 and -5 degrees C, the hourly mortality rate increased with time of exposure. Pupae and adults exposed to -12 degrees C for different time intervals showed high mortality after only 1d of exposure. At -5 degrees C, none survived 12d of exposure. A better understanding of how well this parasitoid tolerates low temperatures will be useful in evaluating its potential as a biological control agent of stored-product moths in temperate regions.     

Effects of traditional insecticides on Habrobracon hebetor (Hymenoptera: Braconidae): bioassay and life-table assays

The lethal and sublethal effects of the insecticides chlorpyriphos and fenpropathrine, which are overused in tomato production, were evaluated on the larval, pupal and adult stages of the parasitoid Habrobracon hebetor in the laboratory. Dose-response bioassays were carried out on immature and adult stages by using dipping and contact residue methods, respectively. The LC₅₀ of chlorpyriphos varied from 40 to 2000 times less than the recommended field rate and 10–100 times less for fenpropathrine treatments on the different life-history stages. To assess the sublethal effects, all life-history stages were exposed to LC₂₅ equivalent concentration of each insecticide and the demographic parameters of surviving parasitoids were studied. In LC₂₅ tests on adult stage, mean longevity and fecundity showed significant differences between chlorpyriphos (15.93?±?1.37 d and 128.20?±?20.20 eggs) and fenpropathrine (12.76?±?0.78 d and 124.00?±?12.27 eggs) as compared with the control (20.41?±?0.72 d and 281.00?±?12.95 eggs). In addition, net reproductive rate and intrinsic rate of increase indicated significant differences between chlorpyriphos (22.89?±?6.43 and 0.19?±?0.02) and fenpropathrine (14.44?±?3.58 and 0.17?±?0.02) as compared with the control (55.55?±?12.54 and 0.24?±?0.02). Briefly, we can conclude that both insecticides had negative effects on H. hebetor. However, the negative effect of fenpropathrine on r_m was higher than that of chlorpyriphos. In conclusion, field studies are recommended to determine the total effects of these insecticides on H. hebetor.     

麦蛾柔茧蜂幼虫唾液腺的显微与超微形态观察

本文采用解剖学观察、显微摄影、透射电镜等方法对麦蛾柔茧蜂Habrobracon hebetor幼虫唾液腺的显微形态、超微结构以及发育特性进行了观察和分析。麦蛾柔茧蜂幼虫唾液腺为一对无色透明至乳白色的管状腺体,自口腔沿中肠两侧向后延伸,单侧腺体在中部先分支、后合并成一不规则环状,端部呈单盲管状。唾液腺管道长度随幼虫龄期增加而呈线性增长。对唾液腺切片进行超微结构观察,发现腺管由两类差异明显的单层细胞组成,I型细胞微绒毛层较厚,胞内除有丰富的内质网和线粒体之外,还含有大量囊泡,并观察到囊泡运输分泌颗粒的现象;II型细胞微绒毛短,胞内的内质网和线粒体数量丰富。本文研究为深入探究寄生蜂幼虫的消化生理以及寄生蜂-寄主互作机制奠定了基础。     

<Emphasis Type="Italic">Bracon (Glabrobracon) jenoi</Emphasis> sp. n. (Hymenoptera: Braconidae: Braconinae) from Turkey

Bracon (Glabrobracon) jenoi sp. n. (Braconinae) is described from the Turkish Central Anatolia region. Morphological diagnostic characters are figured and compared with the related species B. (G.) colpophorus (Wesmael, 1838).     

Novel diterpenoids and hydrocarbons in the Dufour gland of the ectoparasitoid Habrobracon hebetor (Say) (Hymenoptera: Braconidae)

Chemical constituents contained in the Dufour gland of the ectoparasitoid Habrobracon hebetor (Say) (Hymenoptera: Braconidae) were characterized. Three terpenes, beta-springene, a homo-beta-springene, and a homo-geranyllinalool constitute approximately 37% of the gland components, with the remaining 63% all being hydrocarbons. The hydrocarbons consist of a homologous series of n-alkanes (n-C21 to n-C31), a trace amount of 3-methyl C23, a homologous series of internally methyl-branched alkanes (11-methyl C23 to 13-methyl C35), one dimethylalkane (13,17-dimethyl C33), a homologous series of monoenes (C(25:1) to C(37:1)) with the double bonds located at Delta9, Delta13 and Delta15 for alkenes of carbon number 25 to 31 and at Delta13 and Delta15 for carbon numbers 33 to 37 and three homologous dienes in very low amounts with carbon numbers of 31, 32, and 33. The terpenoid and hydrocarbon composition of the Dufour gland was similar in virgin and mated females. However, in contrast to the hydrocarbons, the amount of beta-springene and homo-geranyllinalool increased significantly with time after adult emergence from the cocoon. Although many hydrocarbons in the Dufour gland are the same as those on the cuticle of this species [Howard and Baker, Arch. Insect Biochem. Physiol. 53:1-18 (2003)], substantial differences also occur. Of particular note is the chain length of alkenes and location of the double bonds: cuticular alkenes have a chain length of C23 to C29 and double bond locations at Delta5, Delta7, and Delta9, whereas the Dufour gland alkenes contains a greater range of carbon numbers and have no Delta5 or Delta7 alkenes. The Dufour gland contains only one of the long-chain dimethylalkanes found on the cuticle. Also, no terpenoids are found on the cuticle, and the Dufour gland contains none of the secondary wax esters that are major components on the cuticle. GC-MS analysis of lipids carried in the hemolymph of H. hebetor indicated that all hydrocarbons found on both the cuticle and in the Dufour gland are present, as are some of the wax esters. However, none of the terpenoids were detected in the hemolymph. This suggests that the hydrocarbons are synthesized in other tissues or cells, probably by oenocytes, and differentially partitioned between the cuticle and the Dufour gland. The terpenoids are most likely synthesized within the Dufour gland. Analysis of surface lipids from eggs laid within 18 h indicated that no diterpenoids were present. Rather, the lipids present on the eggs were n-alkanes, monomethylalkanes, alkenes, and secondary alcohol wax esters. This composition did not reflect that of the Dufour gland, hence eggs are not being coated with Dufour gland components during oviposition.     

Sublethal toxicity of two insect growth regulators on Habrobracon hebetor (Hymenoptera: Braconidae) under laboratory conditions

The sublethal effects of lufenuron and lufenuron?+?fenoxycarb were tested on the adult stage of the parasitoid wasp Habrobracon hebetor under laboratory conditions. Bioassay tests were carried out in the incubator at a temperature of 26?±?1?°C, relative humidity of 65?±?10% and photoperiod of 16:8 (L:D). Exposure cages were used for the experiments. Tests were conducted in three replications. Young female wasps were exposed to the residues of the pesticides’ sublethal concentrations (LC₂₅) after 1, 24, 48 and 72 h, and then their mortalities were recorded. Results showed that both insecticide treatments had significant differences compared to the control, but not between themselves (df?=?1, F?=?29.21, α?<?.0001). It was also revealed that the time between insecticides application and H. hebetor release would significantly affect the survival of searching parasitoids (df?=?3, F?=?237.01, α?<?.0001). In this regard, the releasing programme should be postponed for at least 24 h after using these insect growth regulators.     

麦蒲螨寄生麦蛾柔茧蜂初报

本文对麦蒲螨Pyemotes tritici(Lagreze-Fossat et Montagne)侵染印度谷螟Plodia interpunctella (Hubner)和麦蛾柔茧蜂Habrobracon hebetor(Say,1836)的症状进行了扼要的记述,同时介绍了该螨的主要寄主及分布情况.这是该螨寄生麦蛾柔茧蜂的首次报道.     

Efficacy of pesticides on the functional response on larval ectoparasitoid,Habrobracon hebetor Say (Hymenoptera: Braconidae)

Exposing to sub-lethal and low lethal doses of pesticides may cause changes in natural enemy behavioural, such as functional, response. In this study, the effects of chlorpyrifos, carbaryl, abamectin and spinosad were evaluated on the functional response of the Habrobracon hebetor to different densities of last instar larvae of Anagasta kuehniella Zeller. Young adult females of the parasitoid were exposed to LC₃₀ of chlorpyrifos, carbaryl, abamectin and spinosad that were 0.32, 4.03, 3.05 and 17.51?mg a.i./l for 24?h, respectively. Host densities of 2, 4, 8, 16, 32 and 64 were offered to treated young females for 2?h in 10-cm Petri dishes and then the parasitism data were recorded. Experiments were conducted in eight replications. Functional response type was determined using logistic regression and the parameters were appraised by non-linear regression using statistical analysis software. Functional response was type Ш in control and insecticide treatments. Searching efficiency in control, chlorpyrifos-, carbaryl-, abamectin- and spinosad-treated wasps were 0.008?±?0.002, 0.002?±?0.0009, 0.0034?±?0.0013, 0.0076?±?0.002 and 0.0073?±?0.002?h^?1and handling times were 1.38?±?0.1, 7.64?±?1.01, 3.3?±?0.315, 1.55?±?0.1 and 1.46?±?0.11?h, respectively. Chlorpyrifos and carbaryl had the highest effect on searching efficiency of H. hebetor. Spinosad and abamectin showed less adverse effect on the functional response parameters. Finally, after conducting the advanced field studies, spinosad and abamectin may be used as a compatible chemical material with biological control agent in integrated pest management programmes.