A quantitative comparison of foliage development among allopatric ferns,Dryopteris crassirhizoma,D. coreano-montana andD. filix-mas

A quantitative comparison was conducted on the foliage development during sporophyte development of three allopatric ferns in cool temperate and subalpine regions of Hokkaido and Tirol, European Alps. The foliage development ofDryopteris crassirhizoma, D. coreano-montana andD. filix-mas was quantitatively described by the leaf development (NV, number of veins); NV correlates the leaf-shape complexity from a circle (DI, L/2(3.14×S)^1/2). Nearly similar patterns were detected on frequency distribution of fertile leaves, fertility increase and number of leaves in threeDryopteris ferns which exhibit funnel-shaped foliage arrangements in mature sporophyte. No difference was found in number of leaves, maximum NV, fertility rate and leaf-shape parameters among three ferns. A positive difference was found only on changes in order of pinnae with maximum number of costa branches (NVP) and the DI of outline of pinnae betweenD. crassirhizoma andD. filix-mas. These allopatricDryopteris ferns seem to have a similar foliage structure, in spite of some sympatricDryopteris ferns capable of producing putative hybrids (D. austriaca andD. amurensis; D. tokyoensis andD. monticola) having different foliage structures in Hokkaido. Contribution No. 3346 from the Institute of Low Temperature Science, Hokkaido University.     

Quantitative comparison of foliage development amongDryopteris monticola,D. tokyoensis and a putative hybrid,D. kominatoensis in Northern Japan

Developmental leaf architecture was quantitatively described in terms of measurements of various parameters on leaf blade from different size of sporophytes inDryopteris monticola, D. tokyoensis and a putative hybrid,D. kominatoensis in the natural site of Hokkaido, to compare the ontogenetic differentiation in foliage structure among allied ferns. The morphological stage of leaf and sporophyte was tentatively quantified by the number of midrib branches of the leaf (NV, number of veins), which exhibited a significant correlation to the leaf-shape complexity from a circle (DI=marginal length/2×(3.14×square)^1/2) of leaf blade. D. kominatoensis showed intermediate values between others in following characters; DI increase, maximum NV (also blade length), maximum number of costa branches of pinnae (NVMP), number of costa branches of the lowest pinna (NVLP), difference between NVMP and NVLP (NVMP-NVLP), during heteroblastic leaf development. A larger number of leaves per sporophyte was found inD. kominatoensis than in others. The fertility rate (%) and initiation of fertility (IF) in the relative developmental stage (RDS) ofD. kominatoensis shifted to that ofD. tokyoensis, while the order of pinnae with NVMP shifted to that ofD. monticola. Even in the intermediate characters inD. kominatoensis, slight shifts in characters to those of putative parents were found during heteroblastic leaf development. Contribution No. 3145 from the Institute of Low Temperature Science, Hokkaido University.     

Life history characteristics ofPolystichum tripteron with special reference to its leaf venation

An intra-species comparison of the life history of various populations ofPolystichum tripteron was undertaken in Hokkaido and Honshu in Japan with respect to some leaf-size characters and fertility during sporophyte development. The developmental process of sporophytes was quantitatively estimated by counting the number of venation (NV: number of midrib branches of the leaf). The mean NV of the fertile leaves decreased slightly with increasing altitude on Mt. Teine near Sapporo and with increasing latitudes from Honshu to Hokkaido. The blade length was longer at any NV in Hokkaido populations than in those of southern Honshu. Longer blade (BL) and pinna length (PL) and lesser number of pinnules of the lowest pinna (NPLP) versus NV were observed in leaf populations from Hokkaido than in those from southern Honshu. The maximum values of lowest pinna length (LPL), NV, number of costa branches (NVLP) and number of pinnule (NPLP) were larger in southern Honshu than in Hokkaido. In the course of leaf-shape formation represented by the ratio of PL to BL versus NV, the Kyoto population seemed to be more differentiated into long-lanceolate fronds than did the Hokkaido population. Initiation of fertility in the sporophyte development and the maximum NV seemed to decrease with increasing altitudes and latitudes in Japan. Contribution No. 2885 from the Institute of Low Temperature Science, Hokkaido University.     

Quantitative expression of fern leaf development and fertility inPolystichum tripteron (Aspidiaceae)

To elucidate the quantitative and qualitative expression of fern development, various features of leaf-size and morphology were examined on leaves ofPolystichum tripteron (Aspidiaceae) in Japan. Among ten parameters, the number of branches of the leaf midrib (NV) proved to be the most successful for discrimination between fertile and sterile leaf populations. In the phase-change from sterile to fertile leaves, the NV parameter also gave the strongest correlation, increasing with fertility (r = 0.983), and is therefore a useful tool for research into the life history characteristics of ferns.Contribution no. 2751 from the Institute of Low Temperature Science, Hokkaido University.     

Short-term damage-induced increases in tobacco alkaloids protect plants

Summary Leaf damage significantly increases the alkaloid content in undamaged leaves on damaged field-grown wild tobacco plants. Although field-grown pot-bound plants fail to exhibit the same damage-induced increase in alkaloid content, the ability to respond to leaf damage is restored 6 days after removing plants from their pots. Freshly hatched Manduca sexta larvae reared individually in the laboratory on the high-alkaloid foliage of damaged plants released from their pots gain less weight and eat less (57.2% and 45.7% of controls, respectively) than larvae fed low-alkaloid foliage from undamaged released plants. Moreover, larvae grow equally well on the foliage of damaged and undamaged pot-bound plants. The higher chlorophyll contents characteristic of damaged released plants did not negate the effects of the increased alkaloid contents on larval growth. Undamaged leaves from undamaged field-grown plants stem-fed nicotine solutions had elevated leaf nicotine and nornicotine contents. Larvae reared on these artificially induced leaves gain only 38.5% of the weight gained by larvae reared on low-alkaloid foliage. These results demonstrate that damage-induced increases in leaf alkaloids protect induced foliage from attack and are sufficient to explain the decreased growth of caterpillars on the foliage of damaged plants.     

胡杨枝芽生长特征及其展叶物候特征

以5个不同发育阶段的胡杨(Populus euphratica Oliv.)个体为研究对象,观测记录了枝芽展叶物候、枝芽生长特征和叶形变化的空间分布规律。结果表明:不同发育阶段的胡杨个体以及同一个体树冠的不同层次,其枝芽生长及其展叶物候期表现出不同的时空特征。随着树龄的增加和树冠层次的增高(由基向顶),当年新生枝条长度、枝条叶片数和叶形指数逐渐减小,但叶面积和叶片干重逐渐增大。5个不同发育阶段胡杨个体均表现出展叶物候始于树冠顶层,依次向下结束于树冠基部;展叶物候期共性表现在枝芽萌动期均在4月上旬,起始展叶期集中在4月中旬,展叶终期则在5月上旬到下旬;树龄较大的个体其枝芽萌动期、起始展叶期、展叶终期较树龄较小的个体早;其枝芽萌动期到展叶终期的时间进程较树龄较小的个体短;不同发育阶段的个体枝芽萌动期出现的时间较为离散,起始展叶期和展叶终期出现的时间较为集中。相关分析表明,出叶周期与枝条长度、枝条叶片数量和叶形指数呈极显著正相关,与叶面积和叶片干重呈显著负相关。     

INTERPOPULATION DIFFERENCES IN HOST PREFERENCE AND THE EVOLUTION OF LEARNING IN THE BUTTERFLY,BATTUS PHILENOR

The host-discrimination behavior of the adult female pipevine swallowtail butterfly (Battus philenor) was investigated for two populations, an east Texas population that uses two host species with different leaf shapes and a Virginia montane population that uses one host species with a single leaf shape. While Texas and Virginia females exhibited similar chemotactile responses after landing on various host species, butterflies from each population landed more frequently on certain host species used by that particular population. Despite this difference in searching behavior, Texas and Virginia populations were equally capable of learning to search for the leaf shape of a particular host species in artificial enclosure arrays. In addition, learning of leaf-shape preference was confounded equally when each population was introduced into arrays containing all the host species found in both populations. The lack of differentiation in learning of leaf-shape preference between populations that differ in host breadth and host preference argues against the specific hypothesis that learning of leaf-shape preference represents a local adaptation that permits foraging butterflies in the east Texas population to respond to seasonal changes in the relative quality or abundance of host species that differ in leaf shape. Three hypotheses are proposed to explain the apparent absence of interpopulation genetic variation in learning traits. One hypothesis supposes that learning of leaf-shape discrimination is mediated by the same physiological mechanisms that permit females to learn to discriminate among suitable and unsuitable conspecific plants. Selection for restriction of learning of leaf-shape preference in the Virginia montane population may therefore be constrained by selection for learning of other types of discrimination behavior.     

EARLY LEAF ONTOGENY AND SHOOT DEVELOPMENT IN BROWNEA ARIZA (LEGUMINOSAE)

Brownea ariza Benth. (Leguminosae: Caesalpinioideae) shows early shoot tip abortion and subsequent renewal growth from the pseudoterminal bud. This species is unusual in that the entire shoot system is formed before flushing from the bud occurs, shoot tip abortion occurs during flushing, and the aborting portion contains three to six leaves as well as primordial structures varying from hood to peg shape. This study focused on the morphological changes from initiation of scale and foliage leaf primordia in the “resting” renewal bud through bud elongation to flushing and bud abortion. Scanning electron microscopy revealed that embryonic scale leaves are hood-shaped while foliage leaf primordia show early segmentation into leaflets and stipules. No transitional stages were observed. Bud scales and foliage leaves show opposite developmental trends. In bud scales, length at maturity increases from first to last formed, while length decreases in sequentially formed foliage leaves. Early in leaf development the stipules keep pace with the elongation of the rachis. When the bud reaches about one half of its final length the leaf rachis begins to exceed the lengths of its stipules. This young rachis terminates in a distinct mucro that persists until maturity at which time it abscises. Growth patterns indicate that mucro and rachis are a single developmental unit. The early abortion of a shoot tip containing several leaves cannot be easily rationalized. Previous suggestions have involved maintenance of form and ecological adaptation. We add the possibility of elimination of cell progeny encumbered by mutations. From this and other studies of this group, it is clear that at maturity leaves of different species may look alike, e.g., Hymenaea and Colophospermum are bifoliolate; Brownea, Saraca, and others are multifoliolate. However, early stages of leaf ontogeny are quite diverse and may be of systematic value, since these early differences are lost or masked by later development.     

Cellular basis of developmental plasticity observed in heterophyllous leaf formation of Ludwigia arcuata (Onagraceae)

When heterophyllous plants of Ludwigia arcuata Walt. (Onagraceae) were transferred from aerial condition to submergence, young developing leaves were matured into leaves with intermediate shape between aerial-type and submerged-type, showing spatulate shape (spoon-shaped). This change was also induced by the exposure of plants to ethylene. On the other hand, when the plants were transferred from submergence to aerial conditions, young developing leaves were matured into intermediate-type leaves with elliptic shape (spearhead shape). Anatomical analysis revealed that the formation of spatulate leaf was caused by the reduction of the number of epidermal cells aligned in the leaf transverse direction in the basal region of the leaf while the tip regions remained as before and did not respond to this treatment. During development, the ethylene-induced spatulate leaves showed that three types of alterations in epidermal cell division were involved in this process. Changes in the distribution of cell divisions in leaf lamina were detected by the first day of ethylene exposure, and changes in the orientation of cell division planes were detected by the second day. However, changes in the number of cells aligned in the leaf transverse direction were not detected by this time. Three days after ethylene exposure, frequency of cell divisions changed, and by the time changes of cell numbers aligned in the leaf transverse direction were observed. Thus, the formation of intermediate-type leaves in L. arcuata was ascribed to the alterations of cell division patterns which was induced by ethylene.     

Comparative life history of five HokkaidoPolystichum ferns with reference to leaf development in relation to altitudinal distribution

The temperate fernsPolystichum craspedosorum, P. retroso-paleaceum, P. tripteron, P. braunii andP. microchlamys are distributed widely in Hokkaido: on 13 Hokkaido mountains their average altitudinal distributions are 450, 479, 570, 689 and 964 m above sea level, respectively. The developmental stage of the sporophytic leaf is expressed by the “number of venation” (NV, the number of veins branching from the midrib of the leaf), which, inPolystichum ferns, is itself a qualitative expression of the phase-change from sterile to fertile leaf production and is more discriminatory than leaf area, length or dry weight. Usually, the developmental stage structure of the fertile leaf expressed by NV in the fivePolystichum ferns showed a normal distribution. Among the fourPolystichum ferns that grow in the forest understory of Hokkaido's cool temperate regions, a good correlation was found between the mean altitude of vertical distribution and the maximum NV of the leaf (r=−0.993) and the initiation of maturity in the relative developmental stage (r=0.991) of the ferns.Polystichum craspedosorum found on cliffs, however, matures at much earlier stage and has the smallest maximum NV. In the developmental stage expressed by the NV, the initiation of fertility and maximum NV seem to be correlated with altitudinal distribution and habitat in populations ofPolystichum ferns in Hokkaido. Contribution No. 2694 from the Inst. of Low Temp. Sci., Hokkaido University.     

Development of shoot inHydrangea macrophylla I. Terminal and axillary buds

The structure of shoots, in particular of winter buds, ofHydrangea macrophylla was examined. The non-flower-bearing shoot is usually composed of a lower and an upper part, between which a boundary is discernible by means of a distinctly short internode. This internode is the lowermost of the upper part, and it is usually shorter than the internodes immediately above and below, although the internodes tend to shorten successively from the proximal to the distal part of the shoot. Variations exist in the following characters among the terminal bud, the axillary bud on the lower part of the shoot and the axillary bud on the upper part: (1) length of bud; (2) character of the outermost pair of leaf primordia; (3) degree of development of secondary buds in the winter bud; and (4) the number of leaf primordia. Usually, the terminal bud contains several pairs of foliage leaf primordia with a primordial inflorescence at the terminal of the bud, but the axiallary bud contains only the primordia of foliage leaves in addition to a pair of bud scales.     

Changes in the fauna of the stony substratum of lakes in the english lake district

Development of foliage structure in Phragmites australis (Cav.) Trin. ex Steudel stands in three Scottish lochs in 1975 was studied. Both tagged and harvested shoots were utilized to monitor the seasonal changes in the chlorophyll content, net leaf number, rate of shoot elongation, leaf production, leaf fall and leaf area increase, and individual leaf size in the reed-stands from the three study areas. Quantitative measurements of the number of leaf and leaf surface area in 25 cm stratified layers in the shoots were also made during active canopy development from May to August.     

HETEROPHYLLIC DEVELOPMENT IN MUEHLENBECKIA (POLYGONACEAE)

Flowering shoots of Muehlenbeckia platyclados Meisn. bear only reduced scale leaves which resemble the membranous sheath portion (ochrea) of leaves of other members of the Polygonaceae. Shoots propagated from cuttings bear enlarged foliage leaves with distinct lamina, petiole, and ochrea zones. The developmental basis for this heterophylly is explored in order to determine whether scale leaves resemble foliage leaves in their pattern of ontogeny or are developmentally unique. SEM and histological analyses have shown that scale leaves and foliage leaves are distinctive from inception. The scale leaf arises as a collarlike growth and extends over the shoot apex as a hooded sheath without evidence of blade initiation. By contrast, the first stage of foliage-leaf ontogeny is the differentiation of the distal lamina from the future leaf base. As the foliage-leaf ochrea encircles the stem axis, the lamina grows erect and projects from the abaxial surface of the sheath. Lamina reduction coupled with ochrea elaboration in intermediate leaf types indicate a homology between the entire scale leaf and foliage-leaf ochrea. Despite this homology, the production of the bladeless scale leaf does not involve a mere suppression of the foliage-leaf lamina. Erect growth of the saccate ochrea of the foliage leaf contrasts with the hooded expansion of the scale. Early histological differences, including contrasting rates of cell differentiation, also distinguish the two organs. This disparity in modes of growth and differentiation from inception results from separate, predetermined courses of ontogeny. Unlike other plants studied, leaf size and degree of leaf elaboration decrease with shoot meristem enlargement in Muehlenbeckia. Leaf packing does increase with shoot development and may contribute to variations in leaf morphology. It is concluded that the peculiarities of the heterophyllic leaf sequence in Muehlenbeckia are a property of the shoot system as a whole.     

Leaf variation in a tree of Pourouma tomentosa (Cecropiaceae) in French Guiana

In the flora of French Guiana we find considerable within-plant variation in leaf form. We observed entire, two-lobed, and three-lobed leaves within five separate levels (tiers) of the canopy of a single individual ofPourouma tomentosa subsp.maroniensis. Five branches from each of the five tiers of the tree were collected around the axis of the trunk. From these branches five secondary branchlets were selected and all leaves excised with information recorded as to nodal position, number of leaf nodes, and fertility status of the main branch. This design produced 1015 leaves representing about 20 m² of foliar area and about 2.4 kg of blade dry weight. Our objectives were to determine if statistically significant patterns exist for leaf variation and to suggest improvements for future, general collections. The four lower tiers had 62% entire, 10% 2-lobed, and 28% 3-lobed leaves, in contrast to the top tier with 38% entire, 11% 2-lobed, and 51% 3-lobed leaves. The top tier had no fertile branches. in the lower tiers, fertile branches produced 68% entire leaves whereas nonfertile branches produced only 46% entire leaves. In the top tier, lobed leaves made up 73% of surface area, while in the lower tiers, lobed leaves made up only 48% of total surface area. We selected a random subset of 75 leaves from the 1015, for morphometric analysis using two-way ANOVA (tier×leaf type). The boundaries of leaf images were digitized and rendered into Fourier coefficients, yielding leaf surface area and two variables that quantify aspects of shape: dissection index and leaf complexity. The Fourier coefficients were averaged by tier and by leaf type to reconstruct synthetic, average leaf images. Logistic regression was used to predict the position of leaves on the tree and to provide visualization of the relationships between leaf position on the tree and leaf morphological variables. Within the tree crown, leaf surface area and leaf specific mass (LSM) increases with height, although leaf shape does not change with height. LSM does not vary with leaf form; and sun leaves are larger than shade leaves on this tree. We conducted computer sampling experiments based on exact randomization to simulate the process of obtaining all leaf shapes present in an individual tree when making field collections of varying numbers of duplicates. This also points out the importance of noting the presence of within-tree variation in leaf form on herbarium labeds. Failure to recognize leaf variation can lead to incorrect delimitation of species as well as cause overestimates of the number of species in diversity studies.     

Changes in chloroplast number during pea leaf development

Protoplasts were prepared from pea (Pisum sativum L.) leaves throughout development and their contents spread in a monolayer to determine the number of chloroplasts per cell. This approach permitted the rapid analysis of more than 100 cells at each stage of development. The average number of chloroplasts per cell increased from 24±10 to 64±20 during greening and expansion of the first true foliage leaves; all cells containing chloroplasts apparently increase their chloroplast number. A parallel increase in the amount of DNA per nucleus was not observed. As the leaves senesced the chloroplast number gradually decreased to 44±12. We have correlated these changes with our previous results on the percentage of chloroplast DNA per cell. Chloroplast multiplication resulted in a 2.7-fold dilution (from 272 to 102) of the number of copies of the chloroplast DNA molecule per plastid.     

Morphogenetic effect of phenylboric acid on various leaf-shape mutants in the tomato, duplicating the effect of thelanceolate gene

Summary Treatment of germinating tomato seeds ofnormal (La ⁺/La ⁺),lanceolate (La ⁺/La) and several other leaf-shape mutants with phenylboric acid (PBA) duplicates the action of theLa gene with respect to the following: 1) Causes an increase in the level of activity of the four oxidative enzymes tyrosinase, laccase, peroxidase and catalase; 2) causes a corresponding change in leaf form; 3) shows a concentration effect similar to the dosage effect exhibited by theLa gene with respect to both the increase in the activity of oxidative enzymes and a change in leaf form; 4) causes changes, when applied to plants carrying any of several leaf-shape mutants, similar to those caused by theLa gene when the latter is in combination with these leaf shape mutant genes. Based on previous evidence and the current evidence, it is suggested that the primary action of PBA as well as of theLa gene, is to cause the increase in the level of activity of the four oxidative enzymes and the latter in turn, among other factors, determine the shape and size of the leaf in the tomato.     

Characterization of induced resistance in tomato plants

We have characterized, using several types of bioassays, the resistance induced in young tomato plants by feeding of the corn earworm, Helicoverpa zea. Beet armyworm larvae, Spodoptera exigua, and leafminers, Liriomyza trifolii, were used to assay the induced resistance. In whole-plant experiments, damage localized to a single leaflet of fourleaf tomato plants induced a systemic increase in resistance such that beet armyworm larvae confined to previously damaged (induced) plants grew at a rate about half that of larvae raised on control plants and consumed less leaf tissue from induced plants than from control plants. In experiments using excised leaves, beet armyworm larvae suffered increased mortality when reared on leaves from induced plants. The strength of this induced resistance varied spatially relative to the damaged position; moreover, the spatial distribution of induced resistance changed over a three-week period following damage. Other experiments demonstrated that the mechanisms of induced resistance in tomato foliage involves both a decrease in larval preference for and a decrease in the nutritional value of induced foliage. Induction also retarded the oviposition and/or early development of leafminers. Thus, induced resistance has relatively severe effects on the biology of subsequent herbivores. These data should allow us to begin to elucidate cause-effect relationships between induced resistance and induced chemistry in tomato plants.     

A culture unit system for the study of responses of mycorrhizal and non-mycorrhizal seedling to treatments

The time-dependence of Mn accumulation was confirmed in potato foliage (Solanum tuberosum. L.cv. Norland) grown in solution culture. Older leaves grown at 0.61 mM Mn had substantially higher Mn concentrations than younger leaves and stem samples. Levels of Mn in older leaves increased steadily from 4000 µg g^–1 at one week to 8–10,000 µg g^–1 at 6 weeks, but were relatively constant in the emerging leaves. Even foliage grown at low Mn levels (0.01 mM Mn) had 4 fold gradients in Mn concentration from younger (40 µg g^–1) to older leaves (180 µg g^–1).At 0.61 mM Mn, concentrations of 3–4000 µg g^–1 in the youngest fully-developed leaves did not bring about any decline in yield, and levels of up to 5000 µg g^–1 occurred in individual potato leaves before Mn toxicity symptoms were observed. Potato foliage grown at the high Mn had similar leaf numbers, but showed an increased stem length and smaller leaves than foliage grown at 0.01 mM Mn. In particular, the leaf area of the middle and lower leaf fractions were affected by the high Mn level.The ability of rapidly growing plants to withstand high concentrations of Mn is discussed in relation to the pattern of dry matter and Mn accumulation shown by potato foliage.     

Shoot morphology of Aucuba japonica incurred by anisophylly: ecological implications

Anisophylly, having leaves different in size and/or shape, was quantified in adult Aucuba japonica and simulations were carried out to evaluate the effects of anisophylly on the extent of self-shading at the single-shoot level as well as at the whole-canopy level. Clear anisophylly was observed in the individual after switching from the single-stemmed juvenile stage to the multi-stemmed adult stage. In such plants, leaf area in the canopy abruptly increased. The effective display of adult foliage involved a variety of morphological changes in addition to anisophylly, most prominently reduction in leaf size compared to juveniles. The simulation results indicate that diversity of leaf size and shape is an effective means of minimizing self-shading as well as allowing the efficient exploitation of a larger canopy volume in adult plants. Anisophylly also increased the biomass use efficiency of individual plants at maturity. Taken together, having diverse leaf forms is superior to having a single leaf form for maximizing area acquisition and for efficiently filling the acquired area. We therefore conclude that the anisophylly expressed in A. japonica is adaptive.     

Diamondback moth oviposition: effects of host plant and herbivory

The oviposition behaviour of Plutella xylostella L. (Lepidoptera: Plutellidae) on Chinese cabbage (Brassica rapa L. Pekinensis, cv. Wombok), canola (Brassica napus L. cv. Thunder TT), and cabbage (Brassica oleracea L. Capitata, cv. sugarloaf) (Brassicaceae) was studied in the laboratory. In no‐choice experiments moths laid most eggs on the stems and lower three leaves of cabbage plants, the lower three leaves of canola plants, but on the upper three leaves of Chinese cabbage plants. The effects of conspecific herbivore damage to foliage could be replicated by mechanical damage. When foliage was damaged, injured cabbage and canola plants were preferred for oviposition over intact conspecifics, whereas injured Chinese cabbage plants were less preferred than intact conspecifics. However, when root tissue was damaged, intact cabbage and canola plants were preferred over injured conspecifics, whereas moths did not discriminate between root‐damaged and intact Chinese cabbage plants. Injury to upper leaves significantly affected the intra‐plant distribution of eggs. In cabbage and canola plants, injury to leaf 6 significantly increased the number of eggs laid on this leaf, resulting in a significant decrease in the number of eggs laid on the lower foliage/stem of plants, whereas in Chinese cabbage plants it significantly decreased the number of eggs laid on leaf 6. Following oviposition on intact plants, neonate larvae established the vast majority of feeding sites on leaves 5–8 in all three host plants, indicating that larvae moved a considerable distance from preferred oviposition sites in cabbage and canola plants. The growth rate of neonates fed on leaf‐6 tissue was significantly greater than that of those fed on leaf‐1 tissue; >90% of larvae completed development when fed exclusively on leaf‐6 tissue but no larvae completed development when fed exclusively on leaf‐1 tissue. The study demonstrates the complex and unpredictable interactions between P. xylostella and its host plants and provides a basis from which we can begin to understand observed distributions of the pest in Brassica crops.