Preference for plants damaged by conspecific larvae in ovipositing cabbage root flies: influence of stimuli from leaf surface and roots

In laboratory dual-choice assays females of the cabbage root fly, Delia radicum, prefer for oviposition plants with roots damaged by conspecific larvae to undamaged controls. Cauliflower and kale plants were inoculated with root fly eggs (25 per plant) and the hatching larvae were allowed to feed on the roots for various periods of time (1–17 days). After 4 (cauliflower) or 5 (kale) days of larval feeding the oviposition preference was most pronounced and flies laid between 64% and 68% of their eggs near plants with damaged roots. Later, with increasing damage but fewer surviving, and thus actively feeding, larvae, the magnitude of the preference declined. The preference for plants already damaged by conspecific larvae may contribute to the previously observed aggregated distribution of D. radicum eggs in Brassica crop fields.Further experiments revealed that the sensory cues inducing this oviposition preference originate from the complex consisting of the damaged roots, the surrounding substrate (soil) and associated microbes, rather than from the aerial plant parts. In choice assays using the root-substrate complex of damaged and control plants (aerial parts removed), the observed preference for damaged roots was similar to that found for the entire plant but was more pronounced. The damaged roots alone, compared to control roots, received up to 72% (cauliflower) and 75% (kale) of the eggs. By contrast, surrogate leaves sprayed with methanolic leaf surface extracts from the most preferred plants which had been damaged were not discriminated from surrogate leaved sprayed with extracts of the respective control plants. Analysis of glucosinolate levels in methanolic leaf surface extracts revealed that root damage resulted in enhanced concentrations of indole-glucosinolates on the leaf surface in kale but not in cauliflower. Although indole-glucosinolates are oviposition stimulants for the cabbage root fly, the induced changes were apparently too small to influence oviposition behaviour.     

Oviposition‐induced plant cues: do they arrest Trichogramma wasps during host location?

Plants can defend themselves against herbivorous insects before the larvae hatch from eggs and start feeding. One of these preventive defence strategies is to produce plant volatiles, in response to egg deposition, which attract egg parasitoids that subsequently kill the herbivore eggs. Here, we studied whether egg deposition by Pieris brassicae L. (Lepidoptera: Pieridae) induces Brussels sprouts plants to produce cues that attract or arrest Trichogramma brassicae Bezdeko (Hymenoptera: Trichogrammatidae). Olfactometer bioassays revealed that odours from plants with eggs did not attract or arrest parasitoids. However, contact bioassays showed that T. brassicae females were arrested on egg‐free leaf squares excised from leaves with 72 h‐old egg masses, which are highly suitable for parasitisation. We tested the hypothesis that this arresting activity is due to scales and chemicals deposited by the butterflies during oviposition and which are thus present on the leaf surface in the vicinity of the eggs. Indeed, leaf squares excised from egg‐free leaves, but contaminated with butterfly deposits, arrested the wasps when the squares were tested 1 day after contamination. However, squares from egg‐free leaves with 72 h‐old butterfly deposits had no arresting activity. Thus, we exclude that the arresting activity of the leaf area near 72 h‐old egg masses was elicited by cues from scales and other butterfly deposits. We suggest that egg deposition of P. brassicae induces a change in the leaf surface chemicals in leaves with egg masses. A systemic induction extending to an egg‐free leaf neighbouring an egg‐carrying leaf could not be detected. Our data suggest that a local, oviposition‐induced change of leaf surface chemicals arrests T. brassicae in the vicinity of host eggs.     

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.     

Complementary Behaviors of Maternal and Offspring <Emphasis Type="Italic">Spodoptera littoralis</Emphasis>: Oviposition Site Selection and Larval Movement Together Maximize Performance

The selection of oviposition and feeding sites within cotton plants by Spodoptera littoralis was investigated in the field in 2 years, 2007 and 2008. The female moths exhibited significant oviposition preference for young leaves (YL), particularly the 3rd and 4th leaves from top. The larvae originating from egg batches deposited on YL fed mostly in situ for about 5 days, after which they gradually moved their feeding site toward fully expanded or mature leaves on the same individual plant or on neighboring plants. Larvae hatching from batches deposited on fully expanded leaves (FE) fed in situ only for about 2 days, after which they moved toward younger leaves, where they fed for about 3 more days. After the fifth day, however, larvae of the two groups dispersed mainly downward and outward from their hatching site until the end of a 12-day observation. Larvae hatching from eggs deposited on mature or pre-senescent leaves (MP) moved mainly horizontally to other plants after a slight upward shift. The YL and FE larvae grew significantly faster than MP larvae, both in the field and in a laboratory experiment. In the laboratory experiment, the larval period was shorter and the pupal weight was higher when the animals were offered young leaves or young and fully expanded leaves, than when the animals were offered mature and pre-senescent leaves during the first 5 days after hatching. Possible causes and advantages of the exhibited oviposition preference, as well as the apparent ability of larvae to correct for small egg misplacements made by the females, are discussed.     

Diamondback moth performance and preference for leaves of Brassica oleracea of different ages and strata

The preference–performance hypothesis predicts that moth behaviour links plant variations with caterpillar attack and distribution, and the plant‐age hypothesis states that specialist herbivores are more successful in exploring younger plant tissue. We integrated these predictions to investigate underlying mechanisms by which moths and caterpillars of Plutella xylostella L. (Lepidoptera: Plutellidae) track and exploit within‐plant variability of leaf age and stratification. We measured leaf proteins, glucosinolates and fibre, as well as larval choice, developmental performance, and moth oviposition preference with regard to leaf age classes (young, mature and senescent) of three varieties (collard, cauliflower and cabbage) of the main host plant Brassica oleracea L. Larvae consistently fit the prediction that specialist herbivores prefer and perform better on young, upper leaves that have the highest protein level, despite the highest content of defence compounds. Conversely, moths laid more eggs on fibrous and less nutritious leaves from the lower and senescent stratum. We argue that the leaf stratification of host plants imposes conflicting selective pressures concerning offspring feeding and protection on adult females. If egg mortality is catastrophic on the upper nutritious leaves in a particular microclimatic context (e.g. sun, heat, winds, drought or rain‐washing), then oviposition preference will remain for the suboptimal lower and senescent leaves. The ability of larvae to spread upwards over the plant to access the more nutritious leaf stratum is critical when eggs are preferentially laid on the protective low‐quality leaves.     

Choice of oviposition sites by Manduca sexta and its consequences for egg and larval performance

The preference‐performance hypothesis predicts that female insects should prefer to lay eggs in locations that enhance offspring performance. This study examines the choices of females regarding where to oviposit within plants, focusing on the hawkmoth Manduca sexta L. (Lepidoptera: Sphingidae) and its host Datura wrightii Regel (Solanaceae) in the southwestern USA. Smaller Datura leaves provide cooler microclimates for eggs (which may lead to faster embryonic development, shortening their exposure to egg predators) and more nitrogen for larvae. In contrast, large leaves reach temperatures that are stressfully high (which slows embryonic development) and provide less nitrogen for larvae. Thus, we would expect females to oviposit on small leaves. To examine whether leaf size influences female preference and offspring performance, we used laboratory and field studies to address the following questions. (1) On what size leaves do females typically oviposit? (2) Does the distribution of eggs in nature differ from that expected by chance? And (3) how does leaf size affect survival or growth of eggs and larvae? We find that oviposition choices of females do not lead to the highest probability of offspring survival. Females lay eggs on larger leaves, likely due to the greater accessibility of those leaves; however, eggs are more likely to hatch on small leaves. Larvae grow faster on large leaves, but larvae are also surprisingly mobile, suggesting that the consequences of oviposition site are minor once eggs have hatched. Larval mobility was seen only in the field, not in the laboratory, emphasizing the importance of field studies for predicting real‐world performance. Although females' leaf choices are potentially risky for eggs, the threats of high temperature and predation may vary sufficiently in space and time that there is no consistent selection for strong preferences. Furthermore, the fitness consequences for eggs and larvae largely offset each other and offspring are sufficiently mobile to cope with the conditions where they are laid.     

Within-plant distribution of onion thrips (Thysanoptera: Thripidae) in onions

Two aspects of the within-plant distribution of Thrips tabaci Lindeman (Thysanoptera: Thripidae) on onion, Allium cepa L., plants were investigated: 1) diurnal variations in the distribution of adults and larvae between basal and upper sections of onion leaves, and 2) between-leaf and within-leaf distribution of the eggs. The diurnal investigations showed that higher proportions of larvae than of adults congregated at the basal sections of plants, particularly when plants were young and thrips density was low. As plants matured and thrips density increased, the larvae became more dispersed. Regardless of plant size, there were always more adults in the upper than basal plant sections. There were no clear time-windows during the 24-h diurnal cycle when more thrips were in the upper plant parts. T. tabaci eggs were laid everywhere in the plant. Leaves of intermediate ages had more eggs than older or younger leaves. Within leaves, the white leaf sheath received the least eggs and leaf tips received slightly more eggs than leaf sheaths. The highest egg density was found between the green leaf base and the leaf tips. Regardless of plant size, more than half of all eggs were laid above the basal sections. The percentage increased to >95% in mature plants. Except when plants were small the outer leaves were preferred over inner leaves and upper leaf sections preferred over lower leaf sections as egg-laying sites by adults. Implications of the results in the management of T. tabaci are discussed.     

The influence of leaf age on the oviposition preference of Chrysophtharta bimaculata (Olivier) and the establishment of neonates

1 The degree of discrimination shown by a herbivore when selecting oviposition sites has been suggested as a key factor to understanding herbivore population dynamics. Chrysophtharta bimaculata (Coleoptera: Chrysomelidae) is a primary pest of Tasmanian eucalypt forests and can cause severe defoliation. Previous work suggests that females show discrimination when selecting oviposition sites. Our aim was to test the degree of oviposition discrimination exhibited by C. bimaculata with regards to leaf toughness, a character that is critical to neonate survival. 2 We conducted an experiment examining the leaf toughness critical for neonate survival and found that significant larval mortality occurs above a toughness of 46.9 g. We also determined that the maximum toughness of leaves upon which larvae established in the field was 48.2 g, supporting the laboratory result. 3 Field surveys showed that although the majority of eggs were laid on leaves suitable for larval establishment, many eggs were laid on unsuitable, tougher leaves. However, all eggs were normally placed within 20 cm of suitable leaves and glasshouse trials demonstrated the neonates could move this distance without mortality occurring. 4 We conclude that egg batch distribution and larval performance of C. bimaculata will influence the population dynamics of C. bimaculata in two ways. Firstly, the availability of expanding/newly expanding leaves of eucalypt hosts will determine larval carrying capacity. Secondly, at a more localized level, the deposition of large numbers of egg batches on both suitable and unsuitable leaves followed by successful neonate migration increases the risk of resource depletion and poor larval development.     

Diamondback moth egg susceptibility to rainfall: effects of host plant and oviposition behavior

Oviposition patterns of the diamondback moth (DBM), Plutella xylostella L. (Lepidoptera: Plutellidae), differ between common cabbage (Brassica oleracea L. var. capitata) and Chinese cabbage (Brassica rapa L. var. pekinensis) (Brassicaceae) host plants. This study shows that the moth prefers to oviposit on adaxial rather than abaxial leaf surfaces and petioles of both host plants. More eggs were laid in leaf veins than on leaf laminas of both host plants, especially in Chinese cabbage, where 94.6% of eggs were laid in veins. On Chinese cabbage, very few eggs were laid in clusters (≥2 eggs), whereas on common cabbage approximately 30% of eggs were laid in groups of 2 or more eggs. Removal of wax from common cabbage leaves dramatically increased the number of eggs laid singly on the leaf lamina of treated plants, suggesting that leaf waxes affect how eggs are distributed by ovipositing DBM. Eggs were most susceptible to removal by rainfall from the plant surface immediately (<1 h) after oviposition and when close to hatching (>72h old) whereas they were least susceptible 24 h after oviposition. Eggs laid on common cabbage plants were more susceptible to simulated rainfall than eggs laid on Chinese cabbage plants. On common cabbage plants, egg susceptibility to rainfall on different plant parts ranked adaxial leaf surfaces>petioles = abaxial leaf surfaces>stem, but there was no difference in egg susceptibility to rainfall on the various plant parts of Chinese cabbage. Furthermore, on common cabbage plants, eggs laid on both adaxial and abaxial leaf surfaces were afforded significant protection from the effects of rainfall by leaves higher in the plant canopy. On common cabbage plants, oviposition patterns reduce the potential impact of rainfall on eggs, possibly reducing the effect of this important abiotic mortality factor in the field.     

Oviposition site selection by Mansonia mosquitoes on water lettuce

Abstract. 1. Viable Mansonia egg masses occur in nature on both the upper and under surfaces of Pistia stratiotes (L.) leaves. Upper-surface masses were from Mansonia dyari Belkin, Heinemann & Page, but lower-surface oviposition was attributable to both M. dyari and M. titillans Walker.
2. Upper-surface egg masses were often out of water but were concentrated near a wet-dry stain line on the leaf. Lower-surface masses were laid underwater within 3 mm of the leaf edge, except for those oviposited through fenestrations caused by insect damage.
3. Oviposition varied seasonally and masses were most numerous between August and December when water lettuce plants were large and crowded. Egg masses were clumped on plants and leaves and concentrated on mature or mature-old leaves that subtended mean angles of 28–34° from the horizontal.
4. On intact plants in cages, M. dyari laid egg masses on both leaf surfaces in approximately the same proportions as observed in nature. On detached leaves floating flat on the water, M. dyari laid all masses on under surfaces.
5. At 20 and 25°C, egg development of M. dyari required 17.4 and 8.8 days (means), these being significantly longer than the mean times for M. titillans. Some larvae from eggs that hatched in the absence of water survived 72 h in the eggshell.
6. Upper-surface oviposition by M. dyari may be an adaptation to the crowded growth of water lettuce, the mosquito's favoured host plant, whose leaves are largely out of water. Leaf ageing and subsidence cause submergence of most upper-surface eggs by the time of hatching.     

柳蓝叶甲的生物学特性室内观察

在实验室条件下(27±0.5℃,12 D:12 L)研究了柳蓝叶甲Plagiodera versicolora的生物学特性。结果表明,幼虫每隔2~3 d蜕皮1次,共蜕皮2次。成虫产卵前期4 d,世代周期17 d。产卵具有一定的周期性,约10 d为1个周期。叶龄对幼虫的生长发育和成虫的产卵行为有极显著的影响。当幼虫以成熟叶为食料时,其生长发育速率明显减慢,各龄期延长,蛹重较轻;成虫以成熟叶或老叶为食料时产卵几乎完全被抑制,而以幼叶为食料时几乎每天均能产卵。此外,柳蓝叶甲产出卵表面化合物对产卵行为有极为显著的影响。卵表面的有机提取物对成虫产卵具有显著的引诱作用;相反,卵表面的水提取物对产卵有一定的驱避作用。     

Oviposition by herbivorous insects induces changes in optical and mechanical properties of <Emphasis Type="Italic">Prunus avium</Emphasis> leaves

This study of animal–plant interaction focused on the impact of oviposition by an insect on the leaves of Prunus avium (cherries). We examined whether the oviposition by Caliroa cerasi affects leaf mechanical and spectral traits in P. avium. Three cultivars of P. avium were studied. Infested leaves had from 1 to 18 eggs and exhibited higher leaf dry mass per area (LMA) than leaves without eggs. Leaf dry weight and LMA were positively correlated with egg number per leaf. Infested leaves tended to have higher number of trichomes. Leaf thickness and material and structural resistance tended to increase in infested leaves. The reflectance across all wavelengths (500–700 nm) in leaves with larger number of eggs was higher compared to leaves without eggs. Photosynthetic performance was reduced and oxidative activity was increased in leaves with eggs. Extrafloral nectaries increased with increasing the number of eggs per leaf and thus play an important role in defense against herbivores by providing nectar rewards that attract their depredators. These responses to oviposition may be beneficial for the plants in terms of resistance to feeding larvae.     

Distribution ofChilo partellus (Lepidoptera: Pyralidae) egg batches on maize

Distribution ofChilo partellus egg masses was studied in field, greenhouse, and laboratory experiments. The eggs were laid in batches mainly on the lower side and the lower leaves of the plant. The egg batch size ranged from 1 to 169 eggs, with a median of 33.5 eggs per batch (average, 40.5). Oviposition ofC. partellus is described at two levels. The first level, choice of oviposition plants, followed a random distribution. The second level, number of egg batches per plant, followed an aggregated distribution in the field, where more than one egg batch was deposited on the same plant by the same female, which was found on 25% of the oviposition plants. A mechanism for egg-layingC. partellus females to perceive preceding oviposition or injured plants could not be detected. Oviposition site choice seemed to be mediated by tactile stimuli.     

Temporal changes in olfactory and oviposition responses of the diamondback moth to herbivore‐induced host plants

Temporal changes in the pre‐ and post‐alighting responses of mated female diamondback moth, Plutella xylostella L. (Lepidoptera: Plutellidae), to two species of Brassica (Brassicaceae) host plants induced by larval feeding were studied using olfactometer and oviposition assays. Females displayed strong olfactory and oviposition preferences for herbivore‐induced common cabbage (Brassica oleracea var. capitata L. cv. sugarloaf) plants over intact plants; these preferences decreased with time and disappeared by the 7th day after induction. In herbivore‐induced common cabbage plants, eggs were clustered near feeding damage on the younger leaves (leaves 5–7), whereas in intact plants, eggs were clustered on the stem and lower leaves (leaves 1–4) . However, as the time interval between larval feeding and oviposition increased, more eggs were laid on the lower leaves of induced plants. This demonstrates a change in egg distribution from the pattern associated with induced plants to that associated with intact plants. In contrast, females displayed strong olfactory and oviposition preferences for intact Chinese cabbage [Brassica rapa ssp. pekinensis (Lour.) Hanelt cv. Wombok] plants over induced plants; these preferences decreased with time and disappeared by the 5th day after induction. More eggs were laid on the upper leaves (leaves 4–6) than on the lower leaves (leaves 1–3) of intact Chinese cabbage plants at first, but the distribution changed over time until there were no significant differences in the egg count between upper and lower leaves by the 4th day post induction. For both host plant species, pre‐alighting responses of moths were reliable indicators of post‐alighting responses on the first 2 days post induction. The results suggest that temporal changes in a plant's profile (chemical or otherwise) following herbivory may influence attractiveness to an insect herbivore and be accompanied by changes in olfactory and oviposition preferences.     

Host plant conspicuousness and the distribution of eggs and larvae in the butterfly,Anthocharis scolymus (Lepidoptera: Pieridae)

We investigated how the distribution pattern of eggs and larval on the host plant, Turritus glabra, was influenced by the oviposition behavior of the pierid butterfly Anthocharis scolymus. Females searched for the host plants visually and they frequently approached taller host plants with sparse surrounding vegetation. After encountering host plants, oviposition behavior of females was independent of host plant characteristics such as height, density, and type of surrounding vegetation. A female laid eggs singly on a host plants. Most females appeared to lay their eggs regardless of the presense of eggs on the host plant. Consequently egg and larva tended to be abundant on conspicuous host plants as measured by height or relative isolation from other plants. However, overcrowding of eggs on an individual host decreased the survival rate of larvae.     

Factors influencing adult female oviposition in the citrus leafminer Phyllocnistis citrella

1 The citrus leafminer (CLM) Phyllocnistis citrella Stainton (Lepidoptera: Gracillariidae) is a serious pest in most citrus‐growing regions of the world. The influence of leaf length, citrus species or variety, leaf colour tone and temperature on CLM oviposition was studied from field observations and laboratory experiments. The spatial distribution of eggs on leaves was also examined. Field data were obtained from 1100 samples collected in eastern Spain for 7 years. 2 Significant differences in oviposition rate were found among citrus species in ‘no choice’ laboratory experiments. This tendency was not apparent in the field due to the confounding effect of such factors as the intensity of new flushes and adult CLM abundance. Leaf colour tone and air temperature in the range studied (18–27°C) had no effect on CLM egg‐laying. 3 The distribution of eggs among leaves was random for population densities lower than four eggs per leaf, but became strongly aggregated above this, when not all eggs could survive and complete development. 4 The CLM developmental stage found on leaves depended on the leaf length, and most of the egg‐laying occurred only on leaves that were 10–25 mm long. These leaves had the highest CLM stages in the field and thus give the best estimate of CLM oviposition.     

Ovipositing female house flies provision offspring larvae with bacterial food

Symbiotic bacteria on house fly eggs, Musca domestica L. (Diptera: Muscidae), provide ovipositional cues for conspecific female flies and curtail the growth of fungi that compete with fly larval offspring for resources. Because bacteria are also essential dietary constituents for developing larvae, we tested the hypothesis that egg‐derived bacteria support development of larvae to adults. From house fly eggs, we isolated and identified 12 strains of bacteria, eight and four of which were previously shown to induce and inhibit oviposition, respectively. When larvae were provisioned with a total dose of 10⁶–10⁷ colony‐forming units of bacteria from either the oviposition‐inducing or inhibiting group, or from both groups together, significantly more larvae completed development. Thus, egg‐associated bacteria could be a fail‐safe mechanism that ensures a bacterial food supply for larval offspring, particularly if the resource selected by parent females is poor in bacterial food.     

甘蔗、玉米气味对亚洲玉米螟成虫产卵和幼虫取食的影响

【目的】农作物间套作对害虫的影响很大程度上取决于害虫的行为反应,通过研究玉米/甘蔗套作系统中植物气味对亚洲玉米螟Ostrinia furnacalis(Guenee)行为的影响,将为利用化学生态手段防治套作田中的害虫提供依据。【方法】通过昆虫触角电位实验、成虫产卵和幼虫取食实验,测定了甘蔗、玉米植株及二氯甲烷漂洗物对亚洲玉米螟成虫产卵、幼虫取食的影响。【结果】亚洲玉米螟成虫在甘蔗植株上的落卵量(卵粒数、卵块数)与玉米植株差异不显著,取食甘蔗植株的幼虫数量显著低于玉米植株。亚洲玉米螟对甘蔗、玉米叶片漂洗物均可产生EAG反应,且在同一浓度下的反应值之间无显著差异。成虫产卵量(卵粒数、卵块数)在0.1 gE/mL浓度的甘蔗和玉米漂洗物间差异不显著;幼虫对经甘蔗叶片漂洗物处理过的饲料的相对取食率均低于65.00%,显著低于玉米漂洗物处理的饲料。【结论】甘蔗和玉米气味对亚洲玉米螟产卵的影响没有差异,但甘蔗气味会导致初孵幼虫表现出很强的逃逸行为。     

Performance of a spring-feeding moth in relation to time of oviposition and bud-burst phenology of different host species

Abstract. 1. As a spring-feeding moth committed to immature foliage, the autumnal moth Epirrita autumnata (Lepidoptera, Geometridae) must have egg hatch synchronised with the bud-burst of its host plants. Due to large individual variation in the length of the pupal period, however, E. autumnata populations exhibit a prolonged period of flight and oviposition. Because the timing of oviposition in autumn is associated with the timing of egg hatch in the following spring, the time window for egg hatch expands and more potential hosts may become attainable. This suggestion was evaluated under field conditions by rearing E. autumnata eggs and larvae on four different hosts.
2. The performance of E. autumnata was measured by using estimates for fecundity (pupal mass) as well as survivorship of eggs and larvae. Based on the availability of foliage and phenological synchrony between larval and leaf development, early-laid eggs and the larvae originating from them were predicted to perform better on the hosts that have early-flushing leaves. On the late-flushing hosts, the larvae that hatched later were predicted to perform better than the larvae that hatched earlier. Half of the trials were exposed to predators and parasitoids, while the rest were conducted inside mesh-bags preventing larval dispersal and mortality due to natural enemies.
3. The results of the experiment did not support the simple predictions. In particular, host-plant quality and natural enemies appeared to operate discordantly between early- and late-laid eggs. Larvae from the late-laid eggs had rapid development during the larval stages and pupated at the same time and with the same pupal mass as the larvae hatched from the early-laid eggs.
4. The results indicate an occurrence of several, unknown selective forces in E. autumnata populations maintaining variation in the length of the pupal period, timing of oviposition, and timing of egg hatch.