Temporal changes in the egglaying behaviour of the Hessian fly

Responses of mated female Hessian flies were investigated by analysing the behaviour of individual flies in wheat and oats. The behavioural repertoire of such females included: flying, alighting on leaves, arching of the body so that the tip of the abdomen touched the leaf surface, antennation, movements of the tip of the abdomen across the leaf at right angles to leaf veins, sitting with the ovipositor straight but still extended, and sitting with the ovipositor telescoped into the body. After alighting, females on wheat showed a higher frequency of transitions from arching to antennation and a lower frequency of transitions from arching to abdomen straight than females on oats. During the first 5 min of observations, individuals released into arenas with wheat arched and antennated 2–3 times more frequently than females released into oats. Time allotted to behaviours also differed; during the first 5 min, females in wheat spent 50 percent more time arching, whereas females in oats spent 50 percent more time sitting. Females in wheat also stayed longer and laid 4 times more eggs than females in oats. Temporal changes in egglaying were monitored by quantifying hourly rates of egglaying in no-choice assays for several hours following mating at 9:00 am. During the first and second hours post-mating, egglaying occurred infrequently. However, during the third hour post-mating (11:00 am to noon) females on wheat laid 5 times more eggs than females on oats. Rates of egglaying decreased on wheat but increased on oats during the fourth hour, and then during the fifth hour, decreased on both wheat and oats. Changes in egglaying responses were also evident when behaviours of individual females were measured 1–3 h vs. 3–7 h post-mating. Females deprived of host plants and released into wheat or oats later in the day showed higher frequencies of arching and antennation and laid more eggs before leaving the arena.

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Résumé Les réactions de femelles préalablement accouplées de Mouches de Hesse ont été examinées en analysant le comportement de femelles isolées sur blé et sur avoine. Le répertoire comportemental de ces femelles comprenait: le vol, l'atterrissage sur feuille, la flexion du corps de sorte que l'extrémité de l'abdomen touchât la surface de la feuille, l'antennation, les mouvements de l'extrémité de l'abdomen sur la feuille à angle droit des nervures, le repos avec la tarière droite et encore dévaginée, le repos avec la tarière télescopée à l'intérieur du corps. Sur blé plus que sur avoine, les femelles après atterrissage ont présenté une fréquence plus élevée de passage de la flexion à l'antennation que de la flexion à l'abdomen droit. Durant les 5 premières minutes d'observation, les individus libérés dans des enceintes avec blé fléchirent et antennèrent 2 à 3 fois plus que ceux libérés sur avoine. Les durées des différentes séquences différaient aussi: sur blé, pendant les 5 premières minutes, les femelles passèrent plus de 50% du temps à fléchir, tandis que sur avoine elles passèrent plus de 50% du temps en repos. Les femelles restèrent aussi plus longtemps sur les feuilles de blé et y pondirent 4 fois plus d'oeufs que sur avoine.Les femelles de M. destructor ont montré une plasticité du seuil d'acceptation. Pendant les premières heures de ponte, elles ont été très sélectives et refusèrent, ou ne pondirent que quelques oeufs sur avoine, mais acceptèrent volontiers le blé. La discrimination s'est poursuivie tant que les femelles ont eu accès au blé en même temps qu'à l'avoine. Cependant, quand les femelles ont été privées de blé pendant plusieures heures, l'acceptation de l'avoine a augmenté. Cet accroissement de l'acceptation a eu lieu à peu près au moment où les femelles sur blé pondaient leurs derniers oeufs.

     

Physical features of grass leaves influence the placement of eggs within the plant by the Hessian fly

Hessian fly eggs are more likely to be found on adaxial rather than abaxial surfaces of wheat leaves. These leaf surfaces differ in their physical features: the adaxial side of the leaf has parallel grooves and ridges while the abaxial side is relatively smooth. We used leaf models to investigate the relationship between Hessian fly egglaying and these physical features. When both sides of a green paper leaf model were treated with a wheat leaf extract, but only one side of the model was scored with parallel grooves, the grooved side received more eggs than the smooth side. As the number of grooves per surface increased from 0 to 10, eggs per model increased. When grooves and the wheat leaf extract were tested together and separately, the grooves significantly increased egg numbers in the presence, but not the absence, of wheat extract. In contrast, wheat extract increased egg numbers both in the absence and presence of grooves. Molding techniques were used to recreate the physical features of the adaxial and abaxial leaf surfaces of five grasses. For four of the grass genotypes (a triticale, two common wheats, and a durum wheat), patterns of egglaying on real leaves and molded models were similar, i.e., adaxial leaf surfaces and adaxial molded models were preferred over abaxial leaf surfaces and abaxial models. On the fifth grass, oat, preferences for the adaxial side of real leaves and for adaxial models were not as obvious. We conclude that the adult female Hessian fly obtains information about the leaf surface through her tactile and/or kinesthetic senses and uses this information when making egglaying decisions.     

Leaf growth signals the onset of effective plant resistance against Hessian fly larvae

For plant resistance that is induced rather than constitutive, the precise timing of a sequence of events must be considered (i.e., initial detection of the insect by the plant's surveillance systems, up-regulation of signaling and defense pathways, achievement of effective levels of defense, and finally down-regulation of signaling and defense). Here, we provide a timeline for the interaction between resistant wheat ( Triticum aestivum L.) (Poaceae) and the Hessian fly, Mayetiola destructor (Say) (Diptera: Cecidomyiidae). To create this timeline, we measured the daily growth of the third, fourth, and fifth leaves of susceptible and resistant plants. Because each leaf had a different spatial relationship to the site of larval attack (i.e., the sheath epidermal cells of the third leaf) and a different pattern of growth relative to the 3–5 days that larvae attacked resistant plants, we learned different things from each leaf. The third leaf shows how quickly responses of susceptible and resistant plants diverge (i.e., 36–60 h after initial larval attack). The fourth leaf shows that, for both susceptible and resistant plants, negative effects of larval attack extend beyond the third leaf. These negative effects are more severe for susceptible plants, but even in resistant plants continue for several days after larvae have died. The fifth leaf is interesting because it shows how rapidly the resistant plant recovers from larval attack. Thus, 204–348 h after initial attack, a time when the fourth leaf of resistant plants is showing reduced growth and the fifth leaf of susceptible plants is showing zero growth, the fifth leaf of resistant plants shows a small increase in growth. Grasses with resistance gene-mediated resistance may have a two-fold strategy, using resistance mechanisms to stop Hessian fly larvae from further attack and tolerance mechanisms to protect resources for future plant growth.     

Hessian fly resistance gene H13 is mapped to a distal cluster of resistance genes in chromosome 6DS of wheat

H13 is inherited as a major dominant resistance gene in wheat. It was previously mapped to chromosome 6DL and expresses a high level of antibiosis against Hessian fly (Hf) [Mayetiola destructor (Say)] larvae. The objective of this study was to identify tightly linked molecular markers for marker-assisted selection in wheat breeding and as a starting point toward the map-based cloning of H13. Fifty-two chromosome 6D-specific microsatellite (simple sequence repeat) markers were tested for linkage to H13 using near-isogenic lines Molly (PI 562619) and Newton-207, and a segregating population consisting of 192 F_2:3 families derived from the cross PI 372129 (Dn4) × Molly (H13). Marker Xcfd132 co-segregated with H13, and several other markers were tightly linked to H13 in the distal region of wheat chromosome 6DS. Deletion analysis assigned H13 to a small region closely proximal to the breakpoint of del6DS-6 (FL 0.99). Further evaluation and comparison of the H13-linked markers revealed that the same chromosome region may also contain H23 in KS89WGRC03, an unnamed H gene (H_WGRC4) in KS89WGRC04, the wheat curl mite resistance gene Cmc4, and a defense response gene Ppo for polyphenol oxidase. Thus, these genes comprise a cluster of arthropod resistance genes. Marker analysis also revealed that a very small intercalary chromosomal segment carrying H13 was transferred from the H13 donor parent to the wheat line Molly.Mention of commercial or proprietary product does not constitute an endorsement by the USDA.     

Combined effects of host-plant resistance and intraguild predation on the soybean aphid parasitoid Binodoxys communis in the field

Soybean varieties that exhibit resistance to the soybean aphid Aphis glycines have been developed for use in North America. In principle, host-plant resistance to soybean aphid can influence the interactions between the soybean aphid and its natural enemies. Resistance could change the quality of soybean aphids as a food source, the availability of soybean aphids, or resistance traits could directly affect aphid predators and parasitoids. Here, we focus on the effect of soybean aphid resistance on the interactions between soybean aphids, the parasitoid Binodoxys communis (Hymenoptera: Braconidae), and predators of these two species. We determined whether host-plant resistance affected within-season persistence of B. communis by releasing parasitoids into resistant and susceptible soybean plots. We observed higher B. communis densities in susceptible soybean plots than in resistant plots. There were also higher overall levels of intraguild predation of B. communis in susceptible plots, although the per-capita risk of intraguild predation of B. communis was affected neither by plant genotype nor by aphid density. We discuss these effects and whether they were caused by direct effects of the resistant plants on B. communis or indirect effects through soybean aphid or predators.     

Brush border membrane binding properties of Bacillus thuringiensis Vip3A toxin to Heliothis virescens and Helicoverpa zea midguts

The binding properties of Vip3A, a new family of Bacillus thuringiensis insecticidal toxins, have been examined in the major cotton pests, Heliothis virescens and Helicoverpa zea. Vip3A bound specifically to brush border membrane vesicles (BBMV) prepared from both insect larval midguts. In order to examine the cross-resistance potential of Vip3A to the commercially available Cry1Ac and Cry2Ab2 toxins, the membrane binding site relationship among these toxins was investigated. Competition binding assays demonstrated that Vip3A does not inhibit the binding of either Cry1Ac or Cry2Ab2 and vice versa. BBMV protein blotting experiments showed that Vip3A does not bind to the known Cry1Ac receptors. These distinct binding properties and the unique protein sequence of Vip3A support its use as a novel insecticidal agent. This study indicates a very low cross-resistance potential between Vip3A and currently deployed Cry toxins and hence supports its use in an effective resistance management strategy in cotton.     

Induction of actin gene expression in the mosquito midgut by blood ingestion correlates with striking changes of cell shape

Ingestion of a blood meal by the female mosquito Anopheles gambiae (L., Diptera: Culicidae), results in a dramatic distention of the midgut epithelium. Here, we report that these events correlate with a transient increase of actin mRNA and protein abundance. The newly synthesized actin may provide a pool of actin protein needed to remodel epithelial cell cytoarchitecture. We also document changes in midgut epithelial cell morphology. Upon blood ingestion, the columnar cells flatten accompanied by the loss of microvilli on the lumenal side and the unfolding of the labyrinth on the basal side. These changes correlate with the large increase of epithelial surface area needed to accommodate the blood meal. Actin gene expression, actin synthesis and cell morphology all return to the pre-feeding state by 24 h after blood intake.     

Effects of diet-deprivation and physical stimulation on the feeding behaviour of the larvae of the silkworm, Bombyx mori

Continuous observations of larvae of the silkworm, Bombyx mori, revealed that feeding occurred at regular intervals throughout larval development. To investigate possible factors influencing meal-timing, the behaviours of diet-deprived Bombyx larvae were also analysed. Diet-deprivation resulted in longer durations of the first meals after diet replacement, but did not affect feeding patterns. Furthermore, long-term diet-deprivation promoted wandering behaviour and a consequent delay in feeding after diet replacement. Under diet-deprivation conditions, meal-starts appeared to be inducible by defecation and physical stimulation. However, stimulation-induced meal-starts were dependent on the time elapsed since the larvae's previous meals. Provided that more than 1h had elapsed since their previous meals, larvae could be induced to feed by defecation and tapping. At less than 1h post-meal, larvae were less likely to begin feeding after defecation or physical stimulation. Activated locomotions such as wandering and feeding were observed in the long-term diet-deprived larvae only after diet blocks were replaced, while long-term diet-deprived larvae did not show activated locomotion during the absence of diet blocks. Collectively, these data suggest that a combination of elevated locomotion activity and the presence of diet may be necessary for the initiation of feeding in diet-deprived larvae.     

The host range of the male-killing symbiont Arsenophonus nasoniae in filth fly parasitioids

The Son-killer bacterium, Arsenophonus nasoniae, infects Nasonia vitripennis (Hymenoptera: Pteromalidae), a parasitic wasp that attacks filth flies. This gammaproteobacterium kills a substantial amount of male embryos produced by an infected female. Aside from male death, the bacterium does not measurably affect the host, and how it is maintained in the host population is unknown. Interestingly, this bacterial symbiont can be transmitted both vertically (from mother to offspring) and horizontally (to unrelated Nasonia wasps developing in the same fly host). This latter mode may allow the bacterium to spread throughout the ecological community of filth flies and their parasitoids, and to colonize novel species, as well as permit its long-term persistence.We tested 11 species of filth flies and 25 species of their associated parasitoids (representing 28 populations from 16 countries) using diagnostic PCR to assess the bacterium’s actual host range. In addition to 16S rRNA, two loci were targeted: the housekeeping gene infB, and a sequence with high homology to a DNA polymerase gene from a lysogenic phage previously identified from other insect symbionts. We identified infections of A. nasoniae in four species of parasitoids, representing three taxonomic families. Highly similar phage sequences were also identified in three of the four species. These results identify the symbiont as a generalist, rather than a specialist restricted solely to species of Nasonia, and also that horizontal transmission may play an important role in its maintenance.     

Evidence for a novel cryoprotective protein from freeze-tolerant larvae of the goldenrod gall fly Eurosta solidaginis

Third-instar larvae of the goldenrod gall fly Eurosta solidaginis (Diptera: Tephritidae) from populations in northern North America transition from freeze-susceptible to freeze-tolerant just prior to the onset of winter. While studies have documented the accumulation of carbohydrate cryoprotectants during this transition, protein cryoprotectants common to other freeze-tolerant species have not been reported in the gall fly. Using larvae collected from a population in Madison County, NY, which changes from freeze-susceptible to freeze-tolerant in early October, we assayed for the presence of factors that could preserve the catalytic activity of the cold-labile enzyme, rabbit muscle lactate dehydrogenase. Freezing this enzyme with a heat-stable, hydrophilic fraction derived from homogenates of both freeze-tolerant larvae and those in the process of becoming freeze-tolerant preserved between 70% and 80% of this enzyme's activity. Neither a comparable solution of bovine serum albumin nor the naturally-occurring carbohydrates (glycerol, sorbitol, or trehalose) conferred this level of cryoprotection. The putative cryoprotective protein from gall fly larvae did not bind to a weak anion exchanger, implying that its character may be cationic.     

Predicting occurrence of the fungal symbiote Harpella colonizing black fly larvae in coastal streams of Alabama and Mississippi, USA

The environmental conditions governing symbioses are poorly known in aquatic systems. Stream conditions associated with the distribution of the black fly (Simuliidae) midgut symbiote Harpella were investigated in southern Alabama and Mississippi streams. Stream conditions that were most useful in predicting the distribution of Harpella spp. in the study area were dissolved oxygen and water temperature. Presence of Harpella species in streams was associated with higher dissolved oxygen and decreased water temperature compared to streams where Harpella spp. was absent. Stream conditions associated with the distribution of Harpella spp. in other regions of the world vary according to conditions other than those elucidated here, indicating that geography, host species, and stream conditions play important roles in the spatial distribution of Harpella species.     

H9, H10, and H11 compose a cluster of Hessian fly-resistance genes in the distal gene-rich region of wheat chromosome 1AS

H9, H10, and H11 are major dominant resistance genes in wheat, expressing antibiosis against Hessian fly [(Hf) Mayetiola destructor (Say)] larvae. Previously, H9 and H10 were assigned to chromosome 5A and H11 to 1A. The objectives of this study were to identify simple-sequence-repeat (SSR) markers for fine mapping of these genes and for marker-assisted selection in wheat breeding. Contrary to previous results, H9 and H10 did not show linkage with SSR markers on chromosome 5A. Instead, H9, H10, and H11 are linked with SSR markers on the short arm of chromosome 1A. Both H9 and H10 are tightly linked to flanking markers Xbarc263 and Xcfa2153 within a genetic distance of 0.3–0.5 cM. H11 is tightly linked to flanking markers Xcfa2153 and Xbarc263 at genetic distances of 0.3 cM and 1.7 cM. Deletion bin mapping assigned these markers and genes to the distal 14% of chromosome arm 1AS, where another Hf-resistance gene, Hdic (derived from emmer wheat), was also mapped previously. Marker polymorphism results indicated that a small terminal segment of chromosome 1AS containing H9 or H10 was transferred from the donor parent to the wheat lines Iris or Joy, and a small intercalary fragment carrying H11 was transferred from the resistant donor to the wheat line Karen. Our results suggest that H9, H10, H11, Hdic, and the previously identified H9- or H11-linked genes (H3, H5, H6, H12, H14, H15, H16, H17, H19, H28, and H29) may compose a cluster (or family) of Hf-resistance genes in the distal gene-rich region of wheat chromosome 1AS; and H10 most likely is the same gene as H9.Mention of commercial or proprietary product does not constitute an endorsement by the USDA.     

Differential gene expression of the honey bees Apis mellifera and A. cerana induced by Varroa destructor infection

Varroa destructor mite is currently the most serious threat to the world bee industry. Differences in mite tolerance are reported between two honey bee species Apis mellifera and Apis cerana. Differential gene expression of two honey bee species induced by V. destructor infection was investigated by constructing two suppression subtractive hybridization (SSH) libraries, as first steps toward elucidating molecular mechanisms of Varroa tolerance. From the SSH libraries, we obtained 289 high quality sequences which clustered into 132 unique sequences grouped in 26 contigs and 106 singlets where 49 consisted in A. cerana subtracted library and 83 in A. mellifera. Using BLAST, we found that 85% sequences had counterpart known genes whereas 15% were undescribed. A Gene Ontology analysis classified 51 unique sequences into different functional categories. Eight of these differentially expressed genes, representative of different regulation patterns, were confirmed by qRT-PCR. Upon the mite induction, the differentially expressed genes from both bee species were different, except hex 110 gene, which was up-regulated in A. cerana but down-regulated in A. mellifera, and Npy-r gene, which was down-regulated in both species. In general, most of the differential expression genes were involved in metabolic processes and nerve signaling. The results provide information on the molecular response of these two bee species to Varroa infection.     

Isolation of a Drosophila melanogaster desiccation resistant mutant

Mutagenesis provides a powerful way of isolating genetic and physiological processes underlying complex traits, but this approach has rarely been applied to investigating water balance in insects. Here, we describe the isolation of a desiccation-resistant mutant of Drosophila melanogaster. Mutagenesis of a desiccation sensitive line resulted in the isolation of a mutant with two-fold higher resistance. The mutant was partially dominant and mapped to the second chromosome. Mutant flies showed lower rates of water loss, and had a higher water content, but showed no change in body mass, glycogen content, hemolymph volume or water content tolerated at death from desiccation. These physiological differences are contrasted to changes in lines of D. melanogaster mass selected for altered stress resistance. Isolation of this mutant provides an opportunity to identify a gene involved in water balance in insects.