3rd Instar Stage Research Articles

Impact of hot events at different developmental stages of a moth: the closer to adult stage, the less reproductive output.

Hot days in summer (involving a few hours at particularly high temperatures) are expected to become more common under climate change. How such events at different life stages affect survival and reproduction remains unclear in most organisms. Here, we investigated how an exposure to 40 °C at different life stages in the global insect pest, Plutella xylostella, affects immediate survival, subsequent survival and reproductive output. First-instar larvae showed the lowest survival under heat stress, whereas 3rd-instar larvae were relatively heat resistant. Heat exposure at the 1st-instar or egg stage did not influence subsequent maturation success, while exposure at the 3rd-instar larval stage did have an effect. We found that heat stress at developmental stages closer to adult stage caused greater detrimental effects on reproduction than heat stress experienced at earlier life stages. The effects of hot events on insect populations can therefore depend critically on the timing of the event relative to an organism’s life-cycle.

Molecular Characterization and Expression Profiles of Polygalacturonase Genes in Apolygus lucorum (Hemiptera: Miridae).

Polygalacturonase (PG) is an enzyme in the salivary glands of piercing-sucking mirid bugs (Hemiptera: Miridae) that plays a key role in plant feeding and injury. By constructing a full-length cDNA library, we cloned and characterized 14 PG genes from the salivary glands of Apolygus lucorum, a pestiferous mirid bug in cotton, fruit trees and other crops in China. BLAST search analysis showed that the amino acid sequences deduced from transcripts of the PG genes were closely related to PGs from other mirid bugs. Phylogenetic analysis showed that the PGs of mirid bugs had six main branches, PG1-PG6 (Genbank accession numbers: KF881899~KF881912). We investigated the mRNA expression patterns of the A. lucorum PG genes using real-time PCR. All 14 PGs were expressed significantly higher in the salivary glands than in other tissues (head, thorax, abdomen, leg and wing). For eggs and nymphs, the expression levels of these PGs were much higher in the 5th instar stage than in the egg, and 1st and 3rd instar stages. The PG expression levels in 1-day-old adults were very low, and increased in 5, 20 and 30-day-old adults. Additionally, PG expression levels were generally similar between males and females. The possible physiological functions of PGs in A. lucorum were discussed.

Use of Daniovision™ to Measure Activity in 3rd Instar Drosophila melanogaster Larvae

The noncompetitive GABAA receptor antagonist picrotoxin (PTX) decreases activity in 3rd instar Drosophila larvae (Eur J Neurosci, 2006). The purpose of these studies was to replicate the data obtained by Stilwell et al. using an automated data acquisition/data reduction system, Daniovision™ by Noldus.Larvae were extracted from food (Carolina Biologic Supplies 4‐24) in 20% sucrose at the 3rd instar stage. The larvae were randomly placed into vials containing vehicle (20% sucrose + 0.3% DMSO) or PTX from 0.03‐3 mM: n = 20‐30 larvae/treatment. After incubation for 2‐24 hr, individual larvae were placed in separate wells of a 6‐well culture plate previously coated with 2% agar, then placed in the Daniovision™ apparatus. The activity of each larva was digitized and recorded for 5 minutes using Ethovision software.PTX reduces 3rd instar larvae activity in a concentration‐dependent manner, consistent with findings reported by Stilwell et al. Incubation in 1 mM PTX for 4 or 24 hours decreased activity, with consistent reduction produced by 3 mM, variably by 0.3 mM, and never by 0.03 mM. PTX, 0.03‐3 mM, did not alter activity in a mutant strain, Rdl, known to have a point mutation in the PTX binding site on the GABAA receptor conferring a lower affinity for PTX.We have shown that an automated system can be used to quantify activity in 3rd instar Drosophila melanogaster larvae. As human observation and review of videos is not required, and multi‐well plates can be used, we have refined an in vivo high‐throughput screen for anti‐seizure compounds.Supported by funds from the University of Saint Joseph.

Identification and expression of PBAN/diapause hormone and GPCRs from Aedes aegypti

Neuropeptides control various physiological functions and constitute more than 90% of insect hormones. The pheromone biosynthesis activating neuropeptide (PBAN)/pyrokinin family is a major group of insect neuropeptides and is well conserved in Insecta. This family of peptides has at least two closely related G-protein-coupled receptors (GPCRs) activated by PBAN and a diapause hormone (DH). They have been shown to control several biological activities including pheromone production and diapause induction in moths. However, beyond some moth species, the biological function(s) of PBAN/pyrokinin peptides are largely unknown although these peptides are found in all insects. In this study we identified and characterized PBAN/pyrokinin peptides and corresponding GPCRs from the mosquito, Aedes aegypti. Ae. aegypti PBAN mRNA encodes four putative peptides including PBAN and DH, and is expressed in females and males during all life stages. The PBAN receptor (PBAN-R) and the DH receptor (DH-R) were functionally expressed and confirmed through binding assays with PBAN and DH peptides. These receptors are differentially expressed from eggs to adults with the relative gene expression of the PBAN-R significantly lower during the 4th instar larval (L4) and pupal (P1–P2) stages compared to the 2nd and 3rd instar larval stages (L2 and L3). However, DH-R expression level is consistently 4–10 times higher than the PBAN-R in the same period, suggesting that PBAN-R is downregulated in the late larval and pupal stages, whereas DH-R stays upregulated throughout all developmental stages. PBAN/pyrokinin mRNA expression remains high in all stages since it produces PBAN and DH peptides. This study provides the foundation for determining the function(s) of the PBAN/pyrokinin peptides in mosquitoes and establishes data critical to the development of methods for disruption of these hormone actions as a novel strategy for mosquito control.

Determination by LC-MS of Juvenile Hormone Titers in Hemolymph of the Silkworm,Bombyx mori

Juvenile hormone (JH) I, II and III in the hemolymph of the silkworm, Bombyx mori were quantified by liquid chromatography-mass spectrometry (LC-MS). JHs were treated with methanol and trifluoroacetic acid to convert into JH methoxyhydrines (JH-MHs). The key to the analytical condition for JH-MHs was the addition of 5 µM sodium acetate to the eluting solution. Each JH-MH was observed as the sodium adduct ion with good sensitivity. This improved method enabled the titration of JH I, II and III in hemolymph of the silkworm to be monitored from the 3rd instar through to the early pupal stage. A peak of JH I was observed immediately after ecdysis in the 3rd and 4th instar stages. The JH I titer sharply decreased on day 1 and reached the lowest level before ecdysis, but there was no peak at the beginning of the 5th stadium, and no apparent increase was observed until pupation.

The peculiar visual brain of the split-eyed whirligig beetle Dineutus sublineatus

Event Abstract Back to Event The peculiar visual brain of the split-eyed whirligig beetle Dineutus sublineatus Chan Lin1, 2* and Nicholas J. Strausfeld2, 3 1 University of Arizona, Graduate Interdisciplinary Program in Entomology & Insect Science, United States 2 University of Arizona, Center for Insect Science, United States 3 University of Arizona, Department of Neuroscience, United States Whirligig beetles (Coleoptera: Gyrinidae) are aquatic insects living on the water surface. They are equipped with two separate pairs of compound eyes, an upper pair viewing above the water and a lower pair viewing downwards beneath the water line. Little is known about how their optic lobes serve the split eyes. Using reduced silver-staining, immunolabeling and fluorescent tracer injections, we found that their elaborate optic lobes are split into two halves: separated upper and lower laminas; upper and lower medullas; and a bilobed partially split lobula. Visual relay neurons from the upper medulla send axons to the central brain where they provide the exclusive afferent supply to both ipsilateral and contralateral calyces of the paired mushroom bodies. The whirligig beetle is the only insect species so far found to be so equipped [1]. Lobula plate neuropil, which in other insects plays a major role in mediating stabilized flight, is found only in conjunction with the lower lobe of the lobula. Investigations of the larval visual system reveal a precious lobula plate that is supplied by three larval laminas serving the three dorsally located stemmata (single-lens larval eyes), which are adjacent to the developing upper compound eye [2]. Because the whirligig larvae are subaquatic ambush predators, it is theorized that the precocious development of a lobula plate may be employed for detecting movement by potential prey items, as has been reported previously from observations of larval tiger beetles (Cicindela) that are also ambush predators [3, 4]. In D. sublineatus, the precocious lobula plate appears to degenerate during pupal metamorphosis and, as a result, the adult whirligig beetle lacks the upper lobula plate. Other adult optic neuropils, including the lamina, medulla and lobula, begin developing alongside the larval optic neuropils as early as the 3rd instar larval stage. How this early development of adult neuropils contributes to the split optic lobes and how a new lower lobula plate is developed during pupal metamorphosis are presently under investigation. The unique organization and development scheme of the whirligig beetle’s optic lobes suggest distinct functional differences between the upper and the lower compound eyes. Acknowledgements The study was supported by the University of Arizona Regents’ Fund, the Air Force Office of Scientific Research (AFOSR FA95501010299) (to NJS), and stipends from the Taiwan Government Scholarship for Study Abroad and the University of Arizona’s Center for Insect Science (to CL).

Effect of Binodoxys communis parasitism on flight behavior of the soybean aphid, Aphis glycines

Many aphid species possess wingless (apterous) and winged (alate) stages, both of which can harbor parasitoids at various developmental stages. Winged aphids bearing parasitoid eggs or young larvae can potentially still engage in long-distance flights and thereby facilitate parasitoid dispersal, which has important implications for biological control of aphids by parasitoids. In this study, we determined the effect of parasitism by Binodoxys communis (Hymenoptera: Braconidae) on wing development and flight of the summer alate stage of the soybean aphid, Aphis glycines (Hemiptera: Aphididae), and quantified the effect of aphid flight duration on subsequent B. communis development. Parasitism by B. communis was allowed at alatoid 3rd (L3) and 4th instar (L4) nymphal stages of A. glycines and subsequent aphid flight was measured using a computer-monitored flight mill. Only 25% of aphids parasitized as L3 alatoid nymphs produced normal winged adults, compared to 100% of L4 alatoids. While flight performance of aphids that had been parasitized as 4th-instar alatoid nymphs 24 or 48h prior to testing was similar to that of unparasitized alates of identical age, it declined sharply for alates that had been parasitized as 4th-instar alatoid nymphs 72 and 96h prior to testing. Parasitoid larval and pupal development times, percent mummification and adult emergence rates did not differ between treatments in which aphids had flown over varying durations. Our results have implications for natural biological control of A. glycines in Asia and classical biological control of the soybean aphid in North America.

Divergence of larval resource acquisition for water conservation and starvation resistance in Drosophila melanogaster

Laboratory selection experiments have evidenced storage of energy metabolites in adult flies of desiccation and starvation resistant strains of D. melanogaster but resource acquisition during larval stages has received lesser attention. For wild populations of D. melanogaster, it is not clear whether larvae acquire similar or different energy metabolites for desiccation and starvation resistance. We tested the hypothesis whether larval acquisition of energy metabolites is consistent with divergence of desiccation and starvation resistance in darker and lighter isofemale lines of D. melanogaster. Our results are interesting in several respects. First, we found contrasting patterns of larval resource acquisition, i.e., accumulation of higher carbohydrates during 3rd instar larval stage of darker flies versus higher levels of triglycerides in 1st and 2nd larval instars of lighter flies. Second, 3rd instar larvae of darker flies showed ~40h longer duration of development at 21°C; and greater accumulation of carbohydrates (trehalose and glycogen) in fed larvae as compared with larvae non-fed after 150h of egg laying. Third, darker isofemale lines have shown significant increase in total water content (18%); hemolymph (86%) and dehydration tolerance (11%) as compared to lighter isofemale lines. Loss of hemolymph water under desiccation stress until death was significantly higher in darker as compared to lighter isofemale lines but tissue water loss was similar. Fourth, for larvae of darker flies, about 65% energy content is contributed by carbohydrates for conferring greater desiccation resistance while the larvae of lighter flies acquire 2/3 energy from lipids for sustaining starvation resistance; and such energy differences persist in the newly eclosed flies. Thus, larval stages of wild-caught darker and lighter flies have evolved independent physiological processes for the accumulation of energy metabolites to cope with desiccation or starvation stress.

꽃매미(Lycorma delicatula)의 발육단계별 표피탄화수소 비교

Aliphatic cuticular hydrocarbons (CHCs) of different developmental stages of the spot clothing wax cicada, Lycorma delicatula (Hemiptera: Fulgoridae) were analyzed using GC and GC-MS. The numbers of carbons in the major CHCs of each developmental stage 32, 33, 28, 38, 37 in the egg, 1st, 2nd, 3rd, and 4th instar nymphal stages, and adults, respectively. The cuticle of Lycorma delicatula contains mainly methyl-branched 9-methylheptacosane (15.11%) in the egg stage, and a high proportion of n-heptacosane in nymphal stages (15.75, 22.42, 25.04, and 23.11 % in the 1st, 2nd, 3rd and 4th instars, respectively). In contrast, male and female adults had high proportions of n-nonacosane (13.42 and 16.55%). The chemical constituents of CHCs were classified into five groups (n-alkanes, monomethylalkanes, dimethylalkanes, trimethylalkanes, olefins) and group profiles of each developmental stage were compared. Egg surface was composed mainly monomethylalkanes (45.39%), a saturated hydrocarbon. Nymph CHCs consisted primarily of n-alkanes (37.63 to 46.12%). There was a difference between adult male and female CHCs. However, both contained n-alkanes and monomethylalkanes. CHCs with trimethyl or double bonded structure were rare in all stages.

Molecular and functional analysis of Drosophila single-minded larval central brain expression

Developmental regulatory proteins are commonly utilized in multiple cell types throughout development. The Drosophila single-minded ( sim) gene acts as master regulator of embryonic CNS midline cell development and transcription. However, it is also expressed in the brain during larval development. In this paper, we demonstrate that sim is expressed in three clusters of anterior central brain neurons: DAMv1/2, BAmas1/2, and TRdm and in three clusters of posterior central brain neurons: a subset of DPM neurons, and two previously unidentified clusters, which we term PLSC and PSC. In addition, sim is expressed in the lamina and medulla of the optic lobes. MARCM studies confirm that sim is expressed at high levels in neurons but is low or absent in neuroblasts (NBs) and ganglion mother cell (GMC) precursors. In the anterior brain, sim + neurons are detected in 1st and 2nd instar larvae but rapidly increase in number during the 3rd instar stage. To understand the regulation of sim brain transcription, 12 fragments encompassing 5′-flanking, intronic, and 3′-flanking regions were tested for the presence of enhancers that drive brain expression of a reporter gene. Three of these fragments drove expression in sim + brain cells, including all sim + neuronal clusters in the central brain and optic lobes. One fragment upstream of sim is autoregulatory and is expressed in all sim + brain cells. One intronic fragment drives expression in only the PSC and laminar neurons. Another downstream intronic fragment drives expression in all sim + brain neurons, except the PSC and lamina. Thus, together these two enhancers drive expression in all sim + brain neurons. Sequence analysis of existing sim mutant alleles identified three likely null alleles to utilize in MARCM experiments to examine sim brain function. Mutant clones of DAMv1/2 neurons revealed a consistent axonal fasciculation defect. Thus, unlike the embryonic roles of sim that control CNS midline neuron and glial formation and differentiation, postembryonic sim, instead, controls aspects of axon guidance in the brain. This resembles the roles of vertebrate sim that have an early role in neuronal migration and a later role in axonogenesis.

A comparison of the effect of two diatomaceous earth formulations on Plodia interpunctella (Hübner) and the effect of different commodities on diatomaceous earth efficacy

The efficacy of two diatomaceous earth formulations was tested on five commodities; maize, wheat, birdseed, sunflower and barley, against Plodia interpunctella (Lepidoptera: Pyralidae). Exposure to DE began at either the egg stage or 3rd instar stage and the reduction in emergence to adult was noted. There was no significant difference between the freshwater and marine (Protect-It) DE. When eggs were placed on treated diet, the LD90 was 135, 143 and 805 ppm for maize, wheat and birdseed, respectively. When 3 rd instars were placed on diet, LD 90 was 382, 444, and 1156 ppm for maize, sunflower and birdseed respectively. Keywords : DE, Wheat, Maize, Birdseed, Sunflower, Indian meal moth

Role of serotonergic neurons in the Drosophila larval response to light

BackgroundDrosophila larval locomotion consists of forward peristalsis interrupted by episodes of pausing, turning and exploratory behavior (head swinging). This behavior can be regulated by visual input as seen by light-induced increase in pausing, head swinging and direction change as well as reduction of linear speed that characterizes the larval photophobic response. During 3rd instar stage, Drosophila larvae gradually cease to be repelled by light and are photoneutral by the time they wander in search for a place to undergo metamorphosis. Thus, Drosophila larval photobehavior can be used to study control of locomotion.ResultsWe used targeted neuronal silencing to assess the role of candidate neurons in the regulation of larval photobehavior. Inactivation of DOPA decarboxylase (Ddc) neurons increases the response to light throughout larval development, including during the later stages of the 3rd instar characterized by photoneutral response. Increased response to light is characterized by increase in light-induced direction change and associated pause, and reduction of linear movement. Amongst Ddc neurons, suppression of the activity of corazonergic and serotonergic but not dopaminergic neurons increases the photophobic response observed during 3rd instar stage. Silencing of serotonergic neurons does not disrupt larval locomotion or the response to mechanical stimuli. Reduced serotonin (5-hydroxytryptamine, 5-HT) signaling within serotonergic neurons recapitulates the results obtained with targeted neuronal silencing. Ablation of serotonergic cells in the ventral nerve cord (VNC) does not affect the larval response to light. Similarly, disruption of serotonergic projections that contact the photoreceptor termini in the brain hemispheres does not impact the larval response to light. Finally, pan-neural over-expression of 5-HT1ADro receptors, but not of any other 5-HT receptor subtype, causes a significant decrease in the response to light of 3rd instar larvae.ConclusionOur data demonstrate that activity of serotonergic and corazonergic neurons contribute to the control of larval locomotion by light. We conclude that this control is carried out by 5-HT neurons located in the brain hemispheres, but does not appear to occur at the photoreceptor level and may be mediated by 5-HT1ADro receptors. These findings provide new insights into the function of 5-HT neurons in Drosophila larval behavior as well as into the mechanisms underlying regulation of larval response to light.

Dual photoperiodic regulation to enable univoltine life cycle in alpine silver-Y moth, Syngrapha ottolenguii (Noctuidae: Plusiinae) without obligatory diapause

Syngrapha ottolenguii (Noctuidae: Plusiinae) is a typical Japanese alpine moth with adults appearing from mid to late summer. Field and laboratory studies show that this species has a univoltine cycle in 1 year, although one generation can be completed in 60 days at 16L-8D and 20°C. We found two strategies—short-day-induced prolongation of 2nd and 3rd instar larval stages for winter, and long-day-induced arrestment of reproductive maturation in adults for summer to enable the univoltine life history without obligatory diapause in the severe alpine climate. As a result, oviposition is delayed into autumn, and the late-hatching, cold-tolerant larvae overwinter under deep snow. Larvae before and after overwintering develop very slowly due to their unique behavior of hiding from the sun's radiant heat.

Molecular cloning, expression pattern and comparative analysis of chitin synthase gene B in Spodoptera exigua

The chitin synthase (CHS) gene B (4781 bp) of Spodoptera exigua (SeCHSB) was cloned by reverse-transcription PCR (RT-PCR) and 3'/5' RACE from the midgut. SeCHSB contains an open reading frame of 4572 nucleotides, encoding a protein of 1523 amino acids with a predicted molecular mass of approximately 174.6 kDa. Alignment of SeCHSB with class B CHSs of other insects showed a high degree of conservation in the putative catalytic domain region. The structure of the SeCHSB gene was analyzed and was found to be the same as that of Manduca sexta CHSB (MsCHSB), including 23 exons and 22 introns but without alternative exons. Southern blot analysis revealed that SeCHSB was a single copy gene and the presence of only two chitin synthase genes in S. exigua. Further investigation indicated that SeCHSB was specifically expressed in the midgut, and its transcript existed constitutively in the midgut from the 3rd instar larval stage to prepupae and reached highest expression on the 1st day of the fifth instar larval stage. These data suggest that SeCHSB is very important in midgut formation and development. Chitin synthase gene comparisons between different classes of insects using software tools revealed some interesting aspects of the similarity and divergence of the gene in the Class Insecta.

飼料混入法によるBacillus thuringiensis製剤のカイコ検定

A silkworm assay using the 3rd instar stage of silkworm, Bombyx mori and a diet incorporation method has been utilized for the quality control of Bacillus thuringiensis (Bt) products in Japan since 1973. The potency of test sample relative to a standard was calculated based on lethal activity (LC50). The LC50 values were usually estimated by probit analysis on the mortality at the levels of 5–6 doses. In the present study the author tried simpler silkworm assays based on the lethal activity of Bt products against the 2nd instar of silkworms using 1–2 doses. It was shown that the potency of the sample relative to the standard based on assays with 1–2 concentrations is similar to that based on assays with six concentrations.

Particle Size Distribution in Milled Sorghum Grains of Different Corneousness

An actin gene (BPH-Actin3) from the important rice pest brown planthopper, Nilaparvata lugens, was cloned and gene expression was characterized at different development stages. The gene was 1461bp with an open reading frame of 1131bp coding for a 376 amino acids protein, with 330 nucleotides of the 3'-untranslation region (3'-UTR). The amino acid sequence deduced from the nucleotide sequence showed higher similarities to other insect muscle actins (94-95%) than those to non-muscle actins (87-93%). The 3'-UTR contains several AU-rich elements (AREs) AUUUA/UAAAU and one extended ARE UAAAAAU, which may function in regulating mRNA decay. Northern blot and RT-PCR studies showed BPH-Actin3 expressed at brown planthopper full larval stages with the highest mRNA levels at 3rd and 4th instar stages, but not expressed at egg and adult stages. Because the 3rd and 4th instars are the key development stages for brown planthopper wing-form determination, it was thought BPH-Actin3 might play important roles in brown planthopper wing development.

A Comparison of the Development Rate of Protophormia Terraenovae (Robineau-Desvoidy) Raised under Constant and Fluctuating Temperature Regimes

ABSTRACTExperiments were conducted to compare development rates of the blow fly species Protophormia terraenovae (Robineau-Desvoidy) (Diptera Calliphoridae) at constant and fluctuating temperatures. Protophormia terraenovae were raised from egg to adult outdoors under naturally fluctuating temperatures. Minimum times to reach five stages of development were noted (1st, 2nd, and 3rd instar, pupae, and adult). A data logger recorded temperature every 30 minutes. Once the adult stage was reached, the overall mean temperature during the experiment was calculated (19.7°C ± 0.1 °C). Next, P. terraenovae were raised from egg to adult within an incubator in the laboratory at a constant temperature of 20°C ± 0.1°C. Accumulated degree hours (ADH) were calculated for both experiments, at all five stages of development. Protophormia terraenovae raised under a constant temperature regime reached 1st, 2nd, and 3rd instar stages significantly faster than those raised under a fluctuating temperature regime (P = 0.016, t = 3.99, df = 4; P = 0.007, t = 6.79, df = 3; P = 0.043, t = 2.92, df = 4, respectively). At the pupae and adult stages, there was no difference in the development rate between the two temperature regimes (P < 0.05).

Life history of Milnesium tardigradum Doyère (tardigrada) under a rearing environment.

A strain of carnivorous tardigrade, Milnesium tardigradum, was reared in water on agar plates at 25 degrees C. The monogonont rotifer Lecane inermis was presented as a food source. This rearing system permitted detailed observation of tardigrade behaviour. Daily measurements of body length allowed the growth rate and moulting cycle of this species to be determined. The life history of M. tardigradum raised under these conditions included up to seven periods of moult. The first and second moults occurred at intervals of 4-5 days, and individuals reached reproductive maturity at the 3rd-instar stage; the first period of egg laying accompanied the third moult. The most rapidly developing animal in the study population laid eggs 12 days after hatching. The egg-laying intervals or moulting intervals of adult animals were around 6-10 days. The mean clutch size was 6.9 eggs. All tardigrades in this laboratory population were female and reproduced by parthenogenesis. The duration of the embryonic stage ranged from 5-16 days. The most long-lived female survived for 58 days after hatching, and laid a total of 41 eggs in 5 separate clutches. The entire life cycle of tardigrades reared under these conditions was recorded and photographed. A brief description of the embryonic development of M. tardigradum was also reported.

Comparative Toxicities of Pyriproxyfen and Thiamethoxam against the Sweetpotato Whitefly, Bemisia tabaci (Homoptera: Aleyrodidae)

This study was conducted to determine the comparative toxicities of pyriproxyfen and thiamethoxam on the sweetpotato whitefly, Bemisia tabaci biotype B. Ovicidal effect of pyriproxyfen (100 ppm) showed 94.5%, which was ≈ 8 higher times than that of thiamethoxam (50 ppm) at the recommended concentration. The nymphal mortalities of both insecticides treated on the 3rd instar stage were over 85%. Thiamethoxam was very effective against adults, but the activity of pyriproxyfen was relatively low. Longevity and fecundity of newly emerged adults from the treated pupae of two chemicals were adveresely affected. Unlike pyriproxyfen, thiamethoxam highly showed root up-take systemic effect on nymphs and adults of B. tabaci. Pyriproxyfen and thiamethoxam showed residual effects against B. tabaci and particularly, thiamethoxam maintained high control effect with over 90% up to 7 days after treatment. In the control efficacy test on B. tabaci, the control values of pyriproxyfen and thiamethoxam at 9 days after treatment were 92.0 and 99.3%, respectively.

Host age choice for parasitism by Lysiphlebia mirzai and its effect on the development and reproduction of brown citrus aphid

The effects of host age andparasitism by Lysiphlebia mirzaiShuja-Uddin (Hymenoptera: Braconidae) on the development, survivorship,reproduction, and life table parameters ofbrown citrus aphid, Toxoptera citricida(Kirkaldy) (Homoptera:Aphididae) were evaluated at 25 ± 1 °C, 80 ± 5% RH, and a photoperiodof 14:10 (L:D) h. The results showed that theduration from initial parasitization tomummification was independent of the aphid ageat the time of parasitization with a mean of6.0 d. Aphids parasitized at the 1st and 2ndinstar stages and 17% of those parasitized atthe 3rd instar stage failed to reach adulthood,while the rest of the aphids parasitized at the3rd and 4th instar stages and as adults reachedmaturity and produced a number of offspringthat increased with age at parasitization. Thelongevity and fecundity of parasitized aphidswere strongly correlated with the aphid age atparasitization. Aphids parasitized at the 1stand 2nd instar stages did not contribute to thepopulation growth of the aphids. The netreproductive rate (Ro) of the aphidsparasitized at the 3rd and 4th instar andadult stages were only 9, 20 and 43% of thatfor nonparasitized aphids, respectively. Hostage preference experiments involving all fiveaphid stages showed L. mirzai couldattack and parasitize all life stages of browncitrus aphid. Parasitism was highest in the2nd instar in a no-choice test, while in achoice test parasitism in the 2nd and 3rdinstars was similar. A relatively high rate ofparasitism was also observed in the 1st instarnymphs in both choice and no-choice tests. Theresults suggest that L. mirzai haspotential as a biocontrol agent of the browncitrus aphid and warrants a furtherevaluation.