A comparison of life history traits of sexual and asexual strains of the parasitoid wasp,Lysiphlebus fabarum (Braconidae: Aphidiinae)

1. This study examined biological characteristics of sexual and asexual strains of the parasitoid wasp, Lysiphlebus fabarum (Marshall) (Hymenoptera: Braconidae). 2. Strains were reared in different instar hosts (the black bean aphid, Aphis fabae Scopoli) under identical environmental conditions (21 °C, 65–75% RH, and LD 16:8 h). 3. Results showed that the second instar of the aphid is the most suitable growth stage for both strains, as the wasps that emerged from the second instar hosts were larger, more fecund, and had larger egg size. Trade‐offs between the fitness components of the parasitoid were clearer when the parasitoids were reared in suboptimal instars. 4. According to the results, sexual females emerged around 1 day earlier and lived around 0.5 day less than asexual females. Also, sexual females emerged with a lower initial egg load, although these wasps tend to have larger eggs than asexual females. Asexual females may enjoy greater longevity and higher developmental plasticity which suggests a higher degree of synchronization with pest population dynamism. 5. The results suggest that sexual wasps, in contrast to asexual wasps, invest more in egg size than in egg load. This study suggests strain‐specific adaptations of L. fabarum to different instars of the black bean aphid by which the allocation of nutritional resources to various functions differs between strains. 6. Furthermore, differences in life history traits between strains can greatly influence the population dynamics of each strain, and hence their effectiveness in suppressing pest populations.     

Host-selection behaviour by genetically identical aphids with different plant preferences

The behaviour of summer and autumn winged forms of the black bean aphid, Aphis fabae Scopoli (Homoptera: Aphididae), was compared on two plants utilized at different stages of the insect’s life cycle. Adult autumn migrants (gynoparae) are monophagous, colonizing spindle (Euonymus europaeus), whereas polyphagous summer winged aphids (alate virginoparae) are associated with a variety of herbaceous plants, including broad bean (Vicia faba). When aphids from a single clone were given access to a spindle leaf and a bean seedling in choice tests, many virginoparae settled and larviposited on both plant species over 24 h. By contrast, gynoparae showed a clear preference for spindle, with 93.5% of settled adults and 98.3% of larvae on this plant species. Close‐up video monitoring showed that gynoparae discriminated beans from spindle within a 5‐min period, whereas virginoparae behaved similarly on both plant species. For gynoparae, the major behavioural difference on the two plants appeared after a brief (epidermal) stylet penetration, with many insects taking flight within a few seconds of stylet withdrawal from bean. Factors detected during stylet insertion by gynoparae must therefore inhibit take‐off on spindle. Electrical recording experiments showed that aphids often punctured a cell membrane during brief probes on both plant species, and intracellular stylet activities always included a waveform associated with ingestion. When gynoparae puncture spindle cells their behaviour is probably modified by intracellular metabolites detected via gustation of ingested epidermal cell sap. These cues may inhibit the take‐off reflex which otherwise follows probing.     

The induction of normal and teratoid viviparae by a juvenile hormone and kinoprene in two species of aphids

ABSTRACT. Topical application of a juvenile hormone (JH1) and the JH mimic, kinoprene, to short-day, ovipara-producers of Megoura viciae usually leads to the production of oviparous/viviparous intermediate forms in the progeny sequence, in place of the expected sexual females (oviparae). The ovaries of these abnormal forms may contain embryos rather than the haploid yolky eggs of oviparae; 'mixed' ovaries containing both haploid eggs and embryos are also observed. The intermediates range in form from winged (alate) to wingless (apterous). The fully alate individuals usually contain only parthenogenetic ovaries but differ from the naturally occurring alate viviparae in that they are invariably infertile, have fewer antennal sense organs and often bear pheromone releasing glands on the metathoracic tibiae. The hormonally induced production of normal viviparae is difficult in this species but has been achieved by rearing short-day aphids on kinoprene-treated bean plants.
In Aphis fabae similar oviparous/viviparous teratomorphs have been reported and, in addition, single JH1 treatments were shown to induce normal viviparae at the end of the progeny sequence. Multiple applications, beginning prenatally and continuing through the postnatal development of the gynopara (winged ovipara-producer), showed that the numbers of viviparae born were related to the earliness of the treatment and to the dosage. The results are compared with the effect of a switch in photoperiod and discussed in relation to the endocrine control of aphid polymorphism.     

Sieve element occlusion provides resistance against Aphis gossypii in TGR-1551 melons

Feeding behavior and plant response to feeding were studied for the aphid Aphis gossypii Glover on susceptible and resistant melons(cv.Iroquois and TGR-1551,respectively).Average phloem phase bout duration on TGR-1551 was<7% of the duration on Iroquois.Sixty-seven percent of aphids on TGR-1551 never produced a phloem phase that attained ingestion(EPG waveform E2)in contrast to only 7% of aphids on Iroquois.Average bout duration of waveform E2(scored as zero if phloem phase did not attain E2)on TGR-1551 was<3% of the duration on Iroquois.Conversely,average bout duration of EPG waveform El(sieve element salivation)was 2.8 times greater on TGR-1551 than on Iroquois.In a second experiment,liquid nitrogen was used to rapidly cryofix leaves and aphids within a few minutes after the aphids penetrated a sieve element.Phloem near the penetration site was then examined by confocal laser scanning microscopy.Ninety-six percent of penetrated sieve elements were occluded by protein in TGR-1551 in contrast to only 28% in Iroquois.Usually in TGR-1551,occlusion was also observed in nearby nonpenetrated sieve elements.Next,a calcium channel blocker,trivalent lanthanum,was used to prevent phloem occlusion in TGR-1551,and A.gossypii feeding behavior and the plants phloem response were compared between lanthanum-treated and control TGR-1551.Lanthanum treatment eliminated the sieve element protein occlusion response and the aphids readily ingested phloem sap from treated plants.This study provides strong evidence that phloem occlusion is a mechanism for resistance against A.gossypii in TGR-1551.     

The effects of host plant species on adult oviposition and larval performance of the aphid predator Aphidoletes aphidimyza

1. Although preference–performance relationships in insects are typically studied in a bi-trophic context, it is well known that host plants can affect both the preference and performance of natural enemies of herbivorous insects. 2. This study presents evidence from field and laboratory studies that two species of milkweeds, the putatively less defended Asclepias incarnata and the putatively more defended Asclepias syriaca, differentially affect adult oviposition and larval performance in Aphidoletes aphidimyza, an aphid-feeding predatory midge, independent of aphid density. 3. Host plant species affected predatory fly larvae abundance by a factor of 50 in the field and a factor of 8 in the laboratory. Larval and adult emergence rates in our laboratory studies provided strong evidence for reduced performance on A. syriaca. Oviposition in choice and no-choice settings provided some evidence for preference for A. incarnata, and a potentially suppressive effect of A. syriaca. 4. The results provide limited support for the hypothesis that natural selection can lead to positive correlations between adult oviposition preferences and larval performance upon various food sources, even when predatory insects oviposit onto host plants of their herbivorous prey. 5. Preference and performance are not perfectly aligned in this system, however, because ovipositing females do not reject A. syriaca entirely. Potential explanations for mismatches between preference and performance in this system include the neural constraints associated with being a generalist, adaptive time-limited foraging strategies, and unique evolutionary histories of laboratory colonies compared with wild insects.     

Infection of Sentinel Cotton Aphids (Homoptera: Aphididae) by Aerial Conidia ofNeozygites fresenii(Entomophthorales: Neozygitaceae)

Uninfected adultAphis gossypii(Homoptera: Aphididae) apterae (sentinel aphids) on cotton leaves were exposed for 8 h to the air over a commercial cotton field in Louisiana during the night of 1–2 July 1995. At 0015 h there were 90,437 primary conidia/m³air of the fungusNeozygites fresenii(Entomophthorales: Neozygitaceae) at the midfield position as determined from Rotorod samples. Forty-eight percent (n = 106) of the sentinel aphids exposed for 8 h at midfield were infected by aerial conidia ofN. fresenii.Exposure of sentinel aphids outside the cotton field, at 10 and 100 m downwind and 10 m upwind, resulted in 34.8% (n = 131), 24.0% (n = 129), and 17.4% (n = 146) infected aphids, respectively. These data demonstrate that wind-dispersed aerial conidia ofN. freseniiare infective and rapidly and efficiently disperse the pathogen throughout aphid populations within and between fields.     

取食转Bt基因棉花上的棉蚜对丽草蛉发育和繁殖的影响

为明确转Bt基因抗虫棉对捕食性天敌的生态效应 ,比较了 2种转Bt基因抗虫棉 (GK-1 2和新棉99B)和 1种常规棉上的棉蚜Chrysopaformosa对丽草蛉Aphisgossypii发育和繁殖的影响。结果表明 ,(1 )与取食常规棉泗棉 3号上棉蚜的对照相比 ,取食转Bt基因抗虫棉GK- 1 2上棉蚜的第 1代和第 2代丽草蛉 ,其幼虫期和茧期的死亡率、幼虫和茧的发育历期、茧重及成虫性比等均与对照无显著差异 ;但第 1代成虫的产卵量减少了 2 88 0粒 ,与对照差异显著 (P <0 . 0 1 ) ;第 2代成虫所产卵的孵化率为 64. 0 % ,显著低于对照的 77. 7% (P <0 0 1 )。 (2 ) 2个品种的Bt棉对丽草蛉发育和繁殖的影响也略有差异。与取食GK 1 2上棉蚜的个体相比 ,取食新棉 99B上蚜虫的第 1代丽草蛉 ,其幼虫发育历期缩短了 0 . 6d(P <0 0 1 ) ,茧期缩短了 0 . 7d(P <0 . 0 1 ) ,茧重降低了 1 . 2mg(P <0 .0 1 ) ,幼虫期和茧期的死亡率、茧重以及成虫性比等则无显著差异 ;雌成虫产卵前期、产卵期、产卵量和寿命等繁殖学特性也无显著差异 ,但其成虫所产卵的孵化率为 65. 0 % ,显著低于取食GK- 1 2上棉蚜的处理 (72 . 7% ,P <0. 0 1 )。分别取食 2种Bt棉上的棉蚜 ,对第 2代丽草蛉的发育和繁殖的影响差异则较小。     

棉蚜抗氧化乐果品系的羧酸酯酶基因突变

用氧化乐果对室内敏感品系棉蚜Aphis gossypii (Glover)进行抗性选育,经24代筛选,抗性指数达到124.7倍。以α-乙酸萘酯（α-NA）为底物,比较了氧化乐果敏感和抗性品系棉蚜羧酸酯酶的比活力,发现抗性品系羧酸酯酶比活力明显小于敏感品系。对这两个品系的羧酸酯酶基因进行了克隆,通过对抗性和敏感品系羧酸酯酶基因核苷酸序列及推导的氨基酸序列比较,发现抗性品系有4个氨基酸残基发生了替代 (His¹⁰⁴→Arg, Ala¹²⁸→Val, Thr³³³→Asp, Lys⁴⁸⁴→Arg)。对其蛋白质三维结构分析推测只有His¹⁰⁴→Arg的替代是位于其活性中心。棉蚜氧化乐果敏感和抗性品系羧酸酯酶基因cDNA全长的GenBank登录号分别为AY485216和AY485214。     

Selecting arthropod biological control agents against arthropod pests: Can the science be improved to decrease the risk of releasing ineffective agents?

With greater emphasis being placed on management of the risks attached to natural enemy releases for biocontrol programs and the need to justify research budgets, the efficient selection of effective natural enemies is increasingly important. Historically there has been little agreement regarding how or whether this can be accomplished. Recent studies have demonstrated that there is good correspondence between insect host-finding behavior and attack rates in well-designed laboratory studies and their performance of this behavior in the field. Success in measuring efficacy of candidate agents remains somewhat of an art due to the multitude of factors influencing efficacy, but will be improved by attention to: (1) characterization of natural enemy candidates using morphological taxonomy or genetic markers at the onset of a program, (2) climatic matching candidate agents when possible, and (3) evaluations in semi-field or field cage conditions following quarantine evaluations whenever possible before proceeding with widespread releases. The application of these principles is discussed in regard to US biocontrol programs for Bemisia tabaci (Gennadius), Lygus spp., and Aphis glycines Matsumura. Proper project planning and interdisciplinary cooperation will enhance the chances for a successful project.