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.     

Ultrastructural changes in the midguts of Hessian fly larvae feeding on resistant wheat

The focus of the present study was to compare ultrastructure in the midguts of larvae of the Hessian fly, Mayetiola destructor (Say), under different feeding regimens. Larvae were either fed on Hessian fly-resistant or -susceptible wheat, and each group was compared to starved larvae. Within 3 h of larval Hessian fly feeding on resistant wheat, midgut microvilli were disrupted, and after 6 h, microvilli were absent. The disruption in microvilli in larvae feeding on resistant wheat were similar to those reported for midgut microvilli of European corn borer, Ostrinia nubilasis (Hubner), larvae fed a diet containing wheat germ agglutinin. Results from the present ultrastructural study, coupled with previous studies documenting expression of genes encoding lectin and lectin-like proteins is rapidly up-regulated in resistant wheat to larval Hessian fly, are indications that the midgut is a target of plant resistance compounds. In addition, the midgut of the larval Hessian fly is apparently unique among other dipterans in that no peritrophic membrane was observed. Ultrastructural changes in the midgut are discussed from the prospective of their potential affects on the gut physiology of Hessian fly larvae and the mechanism of antibiosis in the resistance of wheat to Hessian fly attack.     

The role of vision in the host plant-finding behaviour of the Hessian fly

Abstract. After mating, female Hessian flies, Mayetiola destructor (Say), sit for several hours before taking flight and exhibiting host-finding behaviours. Observation of these behaviours indicated that females used both chemical and visual cues to find oviposition sites, and that visual cues from plants consisted of both spectral (colour) and spatial information. Females oriented to and were stimulated to land on targets reflecting wavelengths in the region of 530-560nm (either alone or in combination with UV) but were inhibited by wavelengths from 400 to 500 nm. This spectral discrimination was probably mediated by photoreceptors located in the medio-frontal zone of the compound eyes. The spatial patterning of targets also influenced orientation during flight; targets with vertical rather than horizontal contour lengths and a higher density of vertical contour lengths were approached and landed on more frequently.     

Factors influencing the onset of egglaying in a cecidomyiid fly

Abstract The timing of the onset of egglaying in the Hessian fly, Mayetiola destructor (Say), is influenced by several exogenous and endogenous factors. Mated females initiated egglaying 48 h earlier than virgins and laid 3–4 times more eggs before dying. The effects of mating on the onset of egglaying were further modified by several other factors whose effects were measured in hours rather than days. Increases in ambient temperatures experienced by mated females shortened the post-mating pre-ovipositional transition phase; however, the effects of temperature were not linear throughout the temperature range. Age of females at the time of mating also influenced the onset of egglaying. Females that mated 1 , 2 and 3 h after eclosion spent 190 , 160 and 120 min in the post-mating transition phase, respectively. Effects of age were also observed when females were mated over the three calling periods that comprise the 3-day lifespan of the adult female. Linear regressions of transition times on time of mating had similar slopes for first and second day post-eclosion females but were offset such that first-day females mated late in the morning had similar transition times to second-day females mated early in the morning. By the third day post-eclosion, transition times showed no significant changes when females were mated throughout the calling period. Possible mechanisms underlying the effects of mating, temperature, and female age on post-mating pre-oviposition transition times are discussed.     

Avoidance of occupied hosts by the Hessian fly: oviposition behaviour and consequences for larval survival

Abstract 1. Unoccupied wheat plants and wheat plants occupied by conspecific eggs or larvae were presented to ovipositing female Hessian flies in choice tests.
2. The presence of conspecific eggs on the leaf surfaces of wheat plants did not appear to have any effect on the responses of ovipositing Hessian fly females.
3. The presence of conspecific larvae at the base and nodes of wheat plants for 1, 6, or 11 days had significant effects on Hessian fly oviposition. Eggs oviposited on plants were inversely proportional to larval densities and days of larval occupation.
4. Feeding by Hessian fly larvae is associated with several changes in wheat plants. One of these changes, the growth arrestment of the plant, was measured by recording the heights of plants used in oviposition tests. Plant heights were inversely proportional to both larval densities and days of occupation. Plant heights were directly proportional to eggs oviposited on plants.
5. The consequences of adult female avoidance of plants occupied by conspecific larvae were investigated by allowing females to oviposit on unoccupied plants and 1-day, 6-day, and 11-day larval occupied plants, then scoring at the end of the first larval instar the survival of the offspring that resulted from this oviposition.
6. Survival during the first larval instar was 88% for the offspring of females that oviposited on unoccupied plants, decreasing to 82, 31, and 4% on the 1-day, 6-day, and 11-day occupied plant treatments. On these four plant treatments, a positive correlation was found between larval performance (i.e. survival) and the preferences of ovipositing females.
7. On the four plant treatments, relationships between first-instar larval density and first-instar larval survival varied significantly. On unoccupied plants, survival was inversely proportional to density. On plants oviposited on at 6 days of larval occupation, survival was directly proportional to density.     

The role of adult learning in the acceptance of host fruit for egglaying by the Queensland fruit fly, Dacus tryoni

Evidence presented indicates that exposure of wild Queensland fruit files, Dacus tryoni (Froggatt), to a given host fruit type (e.g. pear) for 3 days causes females to attempt oviposition to a greater degree in that fruit type than in other fruit types (e.g. tomato, grape). The effects of exposure to a particular fruit type proved reversible, suggesting that D. tryoni females were capable of learning. Females exposed to pear for 3 days appeared to retain the effect of such exposure on acceptance of tomato for up to 4 days but appeared to retain the effect on acceptance of grape for less than 2 days. The possible significance of prior experience of females with a particular fruit type on future ability to discriminate among varying-quality specimens of that type is discussed.

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Résumé Les éléments apportés montrent que l'exposition de D. tryoni Froggat à un type de fruit déterminé (par exemple, la poire) pendant 3 jours, conduit la femelle à tenter de pondre à une plus haute fréquence dans ce type de fruit que dans d'autres (par example; tomate ou raisin). Les effects de l'exposition à un type particulier de fruit étant réversibles, ceci suggère que les femelles de D. tryoni sont capables d'apprentissage. Des femelles exposées à des poires pendant 3 jours ont conservé l'effet d'une telle exposition pendant 4 jours en présence de tomates, mais moins de 2 jours en présence de raisin. La discussion porte sur la signification possible de la connaissance antérieure d'un type particulier de fruit sur l'aptitude ultérieure des femelles à distinguer parmi des spécimens de ce type, mais de qualités différentes.

     

Oviposition behaviour of Dasineura brassicae on a high- versus a low-quality Brassica host

The oviposition behaviour of the brassica pod midge, Dasineura brassicae Winn. (Diptera: Cecidomyiidae), on a preferred host, Brassica napus L. (summer oilseed rape) was compared to that on a nonpreferred, less suitable host for larval growth, Brassica juncea (L.) Coss & Czern (brown mustard). The experiments were done under field conditions with wild females.The number of landing females was significantly higher on B. napus than on B. juncea, indicating host differences in olfactory and/or visual stimuli. After landing, the behaviour differed in that females stayed longer and laid more egg batches on B. napus than on B. juncea plants. The probability that oviposition would occur after landing and the potentially adjustable egg batch size were similar on the high- and the low-quality host.A larger egg load on B. napus than on B. juncea can thus be attributed mainly to a higher landing rate and more repeated ovipositions occurring on B. napus.

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Comportement de ponte de Dasineura brassicae sur des Brassica de qualites élevée et basse

Résumé La comparaison porte sur le comportement de ponte de D. brassicae Winn. (Dept. Cecidomyiidae) sur Brassica napus L., hôte préféré, et sur B. juncea L., hôte non-préféré, qui convient moins au développement larvaire. Les expériences réalisées en champ ont porté sur des femelles sauvages.Le nombre de femelles qui atterrissent sur B. napus est significativement plus élevé que sur B. juncea, ce qui indique des différences entre les stimuli olfactif et visuel des plantes-hôtes. Aprés atterrisage, le comportement diffère en ce que les femelles restent plus longtemps et déposent plus de pontes sur B. napus que sur B. juncea. La probabilité pour que la ponte suive l'atterrissage et les tailles des ooplaques potentiellement ajustables sont semblables sur les hôtes de qualité élevée ou basse.Une charge supérieure en oeufs sur B. napus que sur B. juncea peut ainsi être principalement attribuée à un taux d'atterrissage plus élevé et à une plus grande fréquence de ponte sur B. napus.

     

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.     

Oviposition preferences of the Hessian fly and their consequences for the survival and reproductive potential of offspring

1. The relationship between oviposition preference and offspring performance was investigated experimentally for the Hessian fly Mayetiola destructor (Say) using 10 grass genotypes that represented five different genera and six different species. Oviposition preferences were quantified in a choice test using arrays of 200–400 plants. Offspring performance was estimated by recording survival during three phases of the insect–plant association and by measuring wing length, a correlate of adult reproductive potential. Density effects were examined for all offspring variables, and were taken into account when offspring performance was compared across the 10 grasses. 2. Egg counts from the oviposition choice test revealed a consistent ranking of plants: 18ITSN triticale > Otane bread wheat = Caldwell bread wheat = Stacy bread wheat > 3424 bread wheat = PND durum wheat = Fleet barley = Valetta barley = Matua brome grass > Awapuni oat. 3. Survival and adult wing length varied significantly on the 10 plant types. Survival was ranked: Otane bread wheat > 3424 bread wheat = Fleet barley = Matua brome grass > Caldwell bread wheat = Valetta barley > 18ITSN triticale = PND durum wheat = Stacy bread wheat > Awapuni oat. Adult male and female wing lengths were greatest on Otane, the bread wheat that also provided the best survival. 4. For Hessian flies on each of the 10 plant types, data on survival, wing length, and wing length–fecundity relationships were combined into a single fitness measure. When these fitness measures were compared with egg counts, no overall pattern emerged. On seven of the 10 plant types, there was a positive linear relationship between egg counts and offspring fitness. On the other three plant types, egg counts were high while fitness was low. Possible reasons why Hessian fly females lay eggs on plants that are poor hosts for their offspring are discussed.     

Development of polymorphic microsatellite markers in Hessian fly, Mayetiola destructor (Say)

A microsatellite library was prepared from size-selected genomic DNA of Hessian fly (Mayetiola destructor). Approximately 81% of recovered clones hybridized with microsatellite motif-specific probes. Subsequently, 2350 clones were sequenced. Sixty-two individual flies from laboratory strains were used to test for reliability and polymorphism in 50 of the microsatellites by gel electrophoresis; 18 were further tested with capillary electrophoresis. Of these, 17 behaved as a polymorphic single locus appropriate for population analysis.     

Virulence of Hessian fly (Diptera: Cecidomyiidae) in the Fertile Crescent

The Hessian fly, Mayetiola destructor (Say), is an important insect pest of wheat (Triticum spp.) in North Africa, North America, southern Europe and northern Kazakhstan. Both wheat and this pest are believed to have originated from West Asia in the Fertile Crescent. The virulence of a Hessian fly population from Syria against a set of cultivars carrying different resistance genes, in addition to other effective sources with unknown genes, was determined in the field and laboratory at the International Center for Agricultural Research in the Dry Areas (ICARDA) during the 2005/2006 cropping season. Only two resistance genes (H25 and H26) were effective against the Syrian Hessian fly population, making it the most virulent worldwide. This high virulence supports the hypothesis that Hessian fly coevolved with wheat in the Fertile Crescent of West Asia. The ICARDA screening programme is using this Hessian fly population to identify new resistance genes to this pest.     

Distribution,population dynamics and damage of Hessian fly,Mayetiola destructor (Diptera: Cecidomyiidae) in North Tunisia

A three years survey and monitoring studies (2013–2014–2015) were carried out through 4 regions of north Tunisia in order to follow the evolution of the distribution, the frequency of occurrence and damage caused by the Hessian fly Mayetiola destructor (Say) to bread wheat (Triticum aestivum L.) and durum wheat (Triticum durum Desf). Moreover, the effectiveness of resistance genes H3, H5, H6, H7, H8, H9, H10, H11, H12, H13, H14, H15, H22, H23, H25 and H26 to protect wheat from Hessian fly attack was assessed in natural field and under controlled laboratory conditions at INRAT-Kef Station. Results showed that Hessian fly was detected in 60.33% and 51.5% of all sampled durum and bread wheat fields, respectively. This pest was more frequent with a higher percentage of infestation in semi-arid regions. Indeed, during 2013, infestation rate attained 12.39% in Kef region against 0.9% registered in Bizerte region. In order to update information about the annual number of generations, we surveyed the population dynamic of Hessian fly in Kef region. Three generations of the fly were counted annually on wheat, with two complete and one incomplete generation. This insect affects host plant growth at different developmental stages. Plant height was the most affected parameter followed by shoot dry weight and tiller number. Field investigations on host resistance revealed that among the 16 tested resistance genes, and only three were strictly effective (H22, H25 and H26). The resistance genes H5, H9, H13 and H9H13 have also conferred high levels of protection against Hessian fly. This work indicated that H22, H25 and H26 genes could be incorporated into Tunisian wheat varieties and released to farmers to manage the threat due to Hessian fly attacks.     

Genes encoding a group of related small secreted proteins from the gut of Hessian fly larvae [Mayetiola destructor （Say）]

A group of related genes has been isolated and characterized from the gut of Hessian fly larvae [Mayetiola destructor （Say）]. Members in this group appear to encode proteins with secretary signal peptides at the N-terminals. The mature putative proteins are small, acidic proteins with calculated molecular masses of 14.5 to 15.3 kDa, and isoelectric points from 4.56 to 4.88. Northern blot analysis revealed that these genes are expressed predominantly in the gut of Hessian fly larvae and pupae. Two related genes, GIOK1 and GIOK2, were isolated as tandem repeats. Both genes contain three exons and two introns. The intron/exon boundaries were conserved in terms of amino acid encoding, suggesting that they arose by gene duplication. The fact that the frequency of this group of clones in a gut cDNA library higher than that of total cDNA clones encoding digestive enzymes suggested that this group of proteins may perform an important function in the gut physiology of this insect. However, the exact functions of these proteins are as yet known since no sequence similarity could be identified between these proteins and any known sequences in public databases using standard methods.     

The effect of an oviposition deterring pheromone on egglaying in Pieris brassicae

A laboratory study was conducted in order to determine the influence of the oviposition deterring pheromone (ODP) upon the distribution of eggbatches and eggs by Pieris brassicae females. This pheromone is known to be associated with eggs. Butterflies were offered a choice between cabbage leaves treated in various ways with the ODP and control leaves. The presence of intact conspecific eggs on the treated leaf appeared to have a moderate deterrent effect upon oviposition. An aqueous solution of the ODP, obtained by washing eggs in distilled water was found to have a somewhat higher deterrent effect. Most effective in deterrence of oviposition, however, appeared to be a washing of P. brassicae eggs in methanol. Such a methanol solution can be stored at low temperatures for at least three years without loosing activity. Application of eggwash to either the upper or lower surface of the leaf does not make any difference to females. Percentage deterrence was found to increase with the concentration of eggwash. At very low concentrations no significant difference could be observed anymore in the numbers of eggbatches and eggs laid on control and treated leaf. On the other hand, even very high concentrations of methanol eggwash do not fully protect cabbage leaves against oviposition. Washing P. brassicae eggs seven times consecutively in methanol, a series of pheromone solutions is obtained, all of them were found to possess a high deterrent activity. Although percentage deterrence slowly decreases in subsequent washings, the seventh eggwash sprayed onto cabbage leaves still resulted in less than one quarter of the total number of eggbatches and eggs being laid on the treated leaf.

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Résumé Des expériences de laboratoire ont été réalisées pour déterminer d'influence d'une phéromone dissuasive de la ponte (ODP) sur la distribution des ooplaques et des oeufs de Pieris brassicae. Cette phéromone est connue comme associée aux oeufs. Les papillons ont eu le choix entre des feuilles de chou traitées de différentes façons avec ODP et des feuilles témoins. La présence d'oeufs intacts de la même espèce sur les feuilles a un effet dissuasif modéré sur la ponte. Une solution aqueuse d'ODP, obtenue par lavage des oeufs à l'eau distillée est quelque peu dissuasive. Le lavage des oeufs de P. brassicae au méthanol est apparu comme le plus dissuasif. Une telle solution au méthanol peut être stockée à basse température au moins 3 ans sans perte de son pouvoir. Les applications de l'eau de rinçage sur les faces supérieures ou inférieures des feuilles induisent le même comportement des femelles. L'effet dissuasif augmente avec la concentration de l'eau de rinçage; aux très faibles concentrations, aucune différence significative n'a pu être observée avec les témoins quant au nombre d'ooplaques et d'oeufs. Par ailleurs, même aux très hautes concentrations du méthanol, l'eau de rinçage n'inhibe pas totalement la ponte sur les feuilles de chou. En lavant 7 fois consécutives les oeufs de P. brassicae dans le méthanol, on obtient une série de solutions de phéromones, dont chacune possède un fort pouvoir dissuasif. Bien que l'effet dissuasif diminue lentement avec des rinçages successifs, la pulvérisation du septième rinçage sur les feuilles de chou réduit encore à moins du quart le nombre total d'ooplaques et des oeufs pondus sur la feuille traitée.

     

The influence of a shortage of hosts on the specificity of oviposition behaviour in species of Dacus (Diptera, Tephritidae)

ABSTRACT. When deprived of their preferred hosts for up to 16 days prior to behaviour assays, three relatively specialized tephritid flies, D. cacuminatus (Hering), D. cucumis French and D. jarvisi (Tryon), retain strong preferences for their particular hosts. Moreover, in the absence of the preferred hosts, D. cacuminatus , and to a lesser extent D. cucumis , will not accept fruits that are outside their normal host range. D. jarvisi readily accepts other fruits in the absence of its preferred host, Planchonia careya , but in common with the other two shows no increase in the number of eggs laid with increasing periods of deprivation. None of these species accumulate oocytes when deprived of fruits.
In contrast, the highly polyphagous D. tryoni Frogg. lays more eggs and oviposits readily into a previously unacceptable fruit after 4 days without access to hosts. This change in behaviour is associated with a marked increase in the number of mature eggs carried by females.
These results suggest an important difference between the generalist and more specialized species in the physiological control of oocyte maturation. In D. tryoni there appears to be no inhibition of oocyte development once the primary follicle has matured, whereas in the other species each ovariole contains no more than one mature egg.
In D. tryoni , the change in behaviour which accompanies this increase in egg load, may influence its propensity to accept unusual fruits, and may help to explain its rapid acceptance of most cultivated fruits introduced to Australia.     

Oviposition behavior of the cabbage root fly,Delia radicum (L.), influenced by host plant extracts

An ethanolic extract of cabbage leaves (Brassica oleraceavar. capitata,Golden Acre)and derived fractions were tested on natural and surrogate leaves in order to study the oviposition behavior of the cabbage root fly Delia radicum(Diptera: Anthomyiidae). On surrogate plastic leaves coated with a thin layer of paraffin wax and treated with 0.1 gram leaf equivalent (gle) of an ethanolic raw cabbage extract, the females displayed the same sequence of behavioral patterns as on a natural host plant. The quantified oviposition behavior correlated well with the actual number of eggs laid. The extract-treated surrogate leaves received at least as many eggs as natural leaves with a similar surface area. Previous exposure to surrogate or natural leaves seemed not to induce a specific preference. The three fractions (hexane, butanol, and water) of the raw extract stimulated the oviposition behavior. This was taken as evidence for the presence of a multicomponent mixture or a chemical pattern in the cabbage leaves stimulating oviposition. At the tested concentration each fraction alone could stimulate in some individuals the complete behavior. No effect of volatile components of the raw extract could be detected. This is thought to be due to the extraction procedure, which limits the production of attractive, volatile compounds, such as isothiocyanates.     

Oviposition and larval performance of Rabdophaga terminalis on Salix spp. with special consideration to bud size of host plants

Females of the gall midge Rabdophaga terminalis (H. Loew) (Diptera: Cecidomyiidae) are very selective in their choice of host plants at oviposition. In preference trials, eggs were laid almost exclusively on S. alba and S. fragilis. One single oviposition occurred on S. viminalis but none on S. triandra, S. daphnoides or S. smithiana. Significantly more eggs were laid on S. alba than on S. fragilis. No differences were detected between clones of the same species regarding oviposition in laboratory trials. Within the species of S. alba, larger buds were preferred. However, this did not explain the preference of S. alba to S. fragilis. There was agreement between plant species selected by the females and survival of the larvae. No galls developed when eggs were transferred to species that were not oviposited on. There was no difference between S. alba and S. fragilis in larval growth, but after two weeks of development there was a significantly higher proportion of larvae in cocoons and pupae on S. alba. There was a negative linear relationship between weight of larvae and larval number per gall, indicating larval competition. The negative slope was steeper for S. alba than for S. fragilis when larvae were weighed after two weeks of development. There were some discrepancies between laboratory and field data on infestation of S. alba and S. fragilis. Higher infestation levels were related to denser stands in the field.

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Résumé Etude de la ponte et des performances larvaires de Rabdophaga terminalis (Diptera; Cecidomyiidae) sur plusieurs espèces de saules avec examen particulier de l'influence de la taille des bourgeons.La ponte et les performances larvaires de la cécidomyie galliforme, Rabdophaga terminalis (H. Loew) ont été étudiées sur plusieurs espèces et clones de saules cultivés en Suède. Les femelles sélectionnent avec soin les plantes hôtes lors de la ponte. Dans des essais préférentiels, les oeufs ont été pondus presque exclusivement sur S. alba et S. fragilis; une ponte a été observée sur S. viminalis et aucune sur S. triandra, S. daphnoïdes ou S. smithiana. Significativement plus d'oeufs ont été pondus sur S. alba que sur S. fragilis. Les essais au laboratoire n'ont pas permis de déceler des différences entre clones de la même espèce. Chez S. alba, les plus gros bourgeons étaient préférés, mais ceci ne permet pas d'expliquer la préférence pour S. alba par rapport à S. fragilis. Il y a coïncidence entre les plantes choisies par les femelles et al survie des larves; il n'y avait pas développement de galles quand des oeufs étaient transférés sur des espèces qui n'avaient pas reçu de pontes. La croissance larvaire sur S. alba et S. fragilis ne présentait pas de différences, mais après 2 semaines de développement il y avait significativement plus de larves en cocons et pupes sur S. alba. La corrélation entre le poids des larves et le nombre de larves par cellule était linéaire et négative, ce qui indique une compétition larvaire; la pente était plus raide pour S. alba que pour S. fragilis quand les larves étaient pesées au bout de 2 semaines de développement. Il y a eu quelques discordances entre les résultats au laboratoire et les données de terrain sur la contamination de S. alba et S. fragilis. Les plus fortes contaminations étaient observées à l'extérieur sur pépinières denses.