The effects of physiological factors and host plant experience on the ovipositional activity of the sweet potato whitefly, Bemisia tabaci

Both egg load and levels of vitellogenin and vitellin increased when Bemisia tabaci Gennadius (Homoptera: Aleyrodidae), were deprived of host plants. These increases resulted in significant increases in rates of oviposition. There was no difference in total fecundity between whiteflies temporarily deprived of hosts and a control treatment that had continuous access to hosts. The results of previous exposure to a preferred host, melon (Cucumis melo), and a non-preferred host, cotton (Gossypium hirsutum), were also examined. B. tabaci deposited significantly more eggs during a 6-h period on melon than on cotton, regardless of host species they were previously confined to. In addition, whiteflies previously exposed to cotton, deposited more eggs than females previously exposed to melon. This higher rate of oviposition resulted in a low egg load as well as lower levels of vitellogenin and vitellin. Conversely, a low rate of oviposition led to high egg load and high levels of vitellogenin and vitellin. Individuals from the same treatment exhibited variation in egg load, which was negatively and significantly correlated with previous oviposition activity. We conclude that the effects of previous host plant exposure on oviposition were, in part, due to behavioral differences that are not related to the reproductive physiology.     

The pollen beetle, Meligethes aeneus, changes egg production rate to match host quality

Motivation-based models dominate current theory concerning host plant selection for oviposition by herbivorous insects. A female searching for a host plant will be more likely to accept a host which is of inferior quality for her offspring if motivation is high, e.g. a large eggload or long time since last oviposition. This implies that insects will accumulate eggs if exposed to hosts of low acceptability and after a time lay eggs on such hosts. An alternative strategy for insects when exposed to less acceptable hosts is to stop producing, instead of accumulating, eggs. Thus, resources would be saved until a more acceptable host is found. If this hypothesis is true, a herbivorous insect would cease egg production when exposed to hosts of low acceptability and resume egg production when exposed to hosts of high acceptability. Previous exposure should not affect oviposition rate when an insect encounters a new host of a different quality. In an earlier study pollen beetles, Meligethes aeneus (F.) (Coleoptera: Nitidulidae), did not accumulate eggs in the absence of high quality hosts. In this study we monitored the daily oviposition rate of female pollen beetles on hosts plants of low (Sinapis alba L.), intermediate (Brassica nigra Koch) or high (B. napus L.) acceptability over a 5-day period. Individuals were then switched to an oviposition resource of a different acceptability. Beetles moved from high- to low-acceptability plants reduced their oviposition rate considerably. In the opposite case, low to high acceptability, the rate of oviposition increased markedly after the switch. When M. aeneus were moved from the high-acceptability host to that of intermediate acceptability oviposition rate was modified accordingly. However, when moved to the intermediate host from a host of low acceptability oviposition on B. nigra was much less than would normally be expected. A possible mechanism for this finding is discussed. M. aeneus, by adjusting oviposition rate to host acceptability, maximizes the average host quality for offspring, even at the cost of a lower egg-laying rate. Received: 5 October 1998 / Accepted: 20 April 1999     

The effect of host acceptability on oviposition and egg accumulation by the small white butterfly, Pieris rapae

The influence of host‐plant acceptability on oviposition rate, egg load, internal fat storage and longevity was studied in the small white butterfly, Pieris rapae L. (Lepidoptera: Pieridae). Newly emerged females and males were presented with either cabbage (Brassica oleracea L. var. gemmifera), which is a highly acceptable host for the small white, or wallflower (Cheiranthus cheiri L.), which is much less acceptable for oviposition. Individuals were dissected when 3, 6 and 9‐days‐old. Females kept on cabbage contained fewer mature eggs than those kept on wallflower and there was no change in the load of mature eggs over the time course studied. The number of immature eggs carried did not vary with host plant species, but did fall significantly between days 6 and 9. The body fat content of individuals declined with increasing age, but the decline was slower for individuals kept on the host of low acceptability. Individuals that were allowed to spend their natural lifespan on cabbage showed similar oviposition patterns over time, where the oviposition rate started high and gradually reduced until death. However, considerable differences in oviposition pattern were found in individuals kept on wallflower, varying from that found on cabbage to no oviposition at all. The implications of these findings are discussed in the light of existing oviposition theories. This leads to the conclusion that in one species the premises of existing theories on optimization of oviposition are not mutually exclusive but rather play in concert.     

Reduced realised fecundity in the pine looper Bupalus piniarius caused by host plant defoliation

1. Whether the potential fecundity of herbivorous insects is realised or not may depend on female behaviour, which in turn may be influenced by host plant acceptability. Female Bupalus piniarius were observed to discriminate against needles growing out the year following defoliation (current‐year needles) of its host plant Pinus sylvestris. 2. It was hypothesised that the discriminatory behaviour was due to current‐year needles being less secure as a substrate. Field and laboratory experiments were designed to test this hypothesis and to estimate the discrepancy between potential and realised fecundity when females were offered defoliated branches. 3. In a laboratory oviposition experiment, B. piniarius females were exposed to branches bearing either current‐year needles only or both mature and current‐year needles. Daily oviposition rate, egg batch size, longevity, and mature eggs and fat retained at death were recorded for each female. In field experiments, the rate at which eggs dropped from expanding needles and the capacity of neonate larvae hatching from the dropped eggs to colonise a tree were assessed. 4. Significantly fewer eggs were laid when females were exposed to defoliated branches. 5. Twenty‐six and 16% of the eggs laid on current‐year needles dropped from the needles in 1998 and 1999 respectively, whereas no eggs dropped from mature needles in 1998 and only one egg (< 1%) dropped in 1999. 6. A very small proportion of larvae hatching on the forest floor (simulated egg drop) was able to recolonise host trees. 7. These results emphasise the importance of oviposition behaviour on realised fecundity when analysing insect population dynamics. In the case of B. piniarius, egg placement, although a minor detail during the normal course of events, became of key importance when defoliation deprived females of their preferred egg attachment site.     

Host selection by Homalodisca vitripennis: the interplay between feeding, egg maturation, egg load, and oviposition

For some phytophagous insects, egg maturation may be dependent on adult feeding. Accordingly, rates of egg maturation may be dependent on the quality and quantity of available food sources. In turn, oviposition behavior could be affected by diet quality via changes in egg load (number of mature eggs carried by a female). Experiments were conducted to determine whether adult feeding may affect oviposition behavior of the glassy-winged sharpshooter, Homalodisca vitripennis. No-choice tests demonstrated that eggs accumulated in glassy-winged sharpshooter abdomens as time since last oviposition increased largely as a function of feeding plant species. In choice tests, glassy-winged sharpshooter females were observed most frequently on the plant species that imparted the greatest egg maturation rate in no-choice tests. Direct tests of the effects of egg load on glassy-winged sharpshooter oviposition behavior found that females were more likely to deposit eggs as egg load increased. Similarly, acceptance of a low-ranked oviposition plant species by female glassy-winged sharpshooters increased with egg load and time since last oviposition. The results indicate that adult feeding affected glassy-winged sharpshooter egg maturation, plant species varied in quality for providing nutrients for egg maturation, and egg load affected oviposition behavior. Thus, the quantity and quality of available feeding plant species may affect glassy-winged sharpshooter egg maturation rates, which in turn may affect the plant species female glassy-winged sharpshooters select for oviposition.     

Influence of host deprivation on egg load and oviposition behaviour of Brachymeria intermedia, a parasitoid of gypsy moth

Abstract. Mated female Brachymeria intermedia (Hymenoptera: Chalcididae) deprived, since emergence, from pupae of their host Lymantria dispar (Lepidoptera: Lymantriidae), accumulated eggs but had a very low rate of hostacceptance. Parasitoids that were host-deprived after encountering pupae early in life also accumulated eggs, but maintained a high acceptance rate. Thus early exposure to hosts promoted active reproductive behaviour. Total egg production depended on the total number of pupae encountered, indicating that B.intermedia adjust their egg production to host availability. Hence, in B. intermedia both the physiological state of the parasitoid (age and egg load) and the informational state (in this case host-availability and experience) interact to shape oviposition behaviour.     

Effect of host deprivation on egg quality,egg load,and oviposition in a solitary parasitoid,Chetogena edwardsii (Diptera: Tachinidae)

Solitary parasitoids are limited to laying one egg per host because larvae compete within hosts. If host encounter rate is low, females should not increase the number of eggs/host in response. The tachinid fly, Chetogena edwardsii,was used to evaluate the effect of host deprivation on egg accumulation, oviposition behavior, and egg quality in a solitary parasitoid. Females deprived of hosts for 2– 7 days accumulate about 1 day's supply of eggs. Egg output of deprived females once hosts are restored does not differ from that of control females. Deprived females retain one egg in the uterus where it undergoes embryogenesis. Maggots emerging from retained eggs are more likely to survive in hosts molting in 40 h or less after receipt of an egg than are maggots emerging from eggs fertilized shortly before oviposition. Egg retention is a consequence of host deprivation that permits females to broaden the range of hosts they can exploit to include soon-to-molt hosts and possibly multiply parasitized hosts.     

Influence of host age and host deprivation on longevity, egg load dynamics and oviposition rate in Microplitis rufiventris

Adult size, longevity, egg load dynamics and oviposition ofMicroplitis rufiventris Kok. which began their development in the first, second, third （preferred hosts） or fourth （non-preferred hosts） instar larvae of Spodoptera littoralis （Boisd.） were studied. The parasitoid size was largely determined by the initial host size at parasitism. Non-ovipositing females derived from older hosts lived for longer periods than those derived from younger ones. However, the ovipositing females, irrespective of their size, lived for almost the same periods. At emergence, the oviducts of adult females contain a significant amount of mature eggs available for oviposition for a few hours on eclosion day. Egg load increases during the early phase of adult life. The amount of additional mature eggs and rate of egg maturation per hour was greater for wasps derived from preferred hosts compared with those in females derived from non-preferred hosts. The pattern of egg production in M. rufiventris females depended on the availability of hosts for parasitization. Host-deprived females depleted the egg complement with aging; the longer the host deprivation, the lower the oviduct egg load. Marked reduction in both realized or potential fecundity of host-deprived females was observed following host availability. Host privation for more than 3 days induced a marked deficit fecundity pattern through the female＇ s life. The realized fecundity was determined by the interaction among host availability, the number of eggs that are matured over the female＇ s life span, oviposition rate and host size from which the female was derived. These results suggest that： （i） M. rufiventris wasp is a weak synovigenic species; （ii） the maturation of additional eggs is inhibited once the maximum oviduct egg load is reached; （iii） the egg load of the newly emerged female is significantly less than the realized fecundity; and （iv） because M. rufiventris females oviposit fewer eggs when they begin depleting their egg supply at 3 days, augmentative releases will require release immediately following emergence to ensure the highest parasitization rate in the field.     

Behavioural plasticity in relation to egg and time limitation: the case of two fly species in the genus Anastrepha (Diptera: Tephritidae)

Reproductive opportunities in insects that deposit their eggs in discrete resource patches are frequently limited because the availability of oviposition substrates is often spatially and temporally restricted. Such environmental variability leads individuals to confront time‐ or egg‐limitation constraints. Additionally, species with different oviposition strategies (i.e. single egg layers vs clutch layers) commonly deal with different structural and ecological characteristics of larval host plants. To test the hypothesis that oviposition strategies such as laying eggs singly or in batches (clutches) are related to these constraints (i.e. egg vs time limitation), we compared the lifetime oviposition patterns of two closely related sympatric species of Anastrepha (Diptera: Tephritidae) with different oviposition strategies. We exposed five cohorts of A. obliqua and A. ludens females, over the course of their adult lifetimes, to three conditions of “habitat quality” (measured as host density per cage): unpredictable habitat quality (host density varied randomly from day to day between 1, 5, 15, 30 and 60 hosts/cage), low habitat quality (fixed density of one host/cage) and high habitat quality (fixed density of 60 hosts/cage).
Responses to host density conditions were strikingly different in the two species. (1) Frequency of host visits and oviposition events increased in A. obliqua but not in A. ludens when host densities increased. (2) Anastrepha ludens females accepted low quality hosts (i.e. fruits on which eggs had already been laid and were therefore partially covered with host marking pheromone) significantly more often than A. obliqua females did. (3) Females of A. obliqua adjusted their oviposition activity to variations in host density, whereas A. ludens females exhibited a constant oviposition pattern (i.e. did not respond to variations in host density). Based on the above, it is likely that in A. obliqua oviposition is governed by egg‐limitation and in A. ludens by time‐limitation constraints. We discuss the relationship between the oviposition strategies of each fly species and the fruiting phenology and density of their native host plants. We also address the possible influence of oogenesis modality and parasitism by braconid wasps in shaping oviposition behaviour in these insects.     

Oviposition site selection in Cactoblastis cactorum (Lepidoptera): constraints and compromises

Summary Oviposition by Cactoblastis cactorum on Opuntia ficus-indica and O. aurantiaca was assessed from the positioning of egg sticks on plants in the field. The number of egg sticks laid on O. ficus-indica plants was affected by: (1) plant size; (2) moth emergence near the plant; (3) cladode condition; and (4) plant conspicuousness. These factors contributed towards the clumping of egg sticks on plants. There was no apparent oviposition preference for one of the two host plant species despite the fact that egg predation was higher and fecundity lower on O. aurantiaca. The selection of a site for oviposition on the host plants was influenced by: (1) cladode condition; (2) height above ground; and (3) shelter from wind during oviposition. Succulent cladodes were the favoured sites for oviposition. The evidence suggests that in C. cactorum, oviposition site selection is largely the net result of a compromise between oviposition behaviour selected for increasing the probability of juvenile survival and oviposition behaviour selected for increasing the probability of laying the full complement of eggs. In addition, environmental and physiological factors such as wind and wing-loading, are thought to place constraints on the range of sites available for oviposition.     

The effect of egg load on superparasitism by the snowberry fly

In studies conducted with fruits of the host plant, Symphoricarpus albus (L.), we examine the influence of egg load on the oviposition behaviour of Rhagoletis zephyria Snow (Diptera:Tephritidae). By altering the availability of exogenous protein, three classes of females with progressively increasing egg loads were produced, while keeping confounding factors such as age, experience, and mating status constant. Flies from all three classes were randomly presented with either a pheromone marked fruit, or with an unmarked fruit. Results indicate that increased egg load led to a greater propensity to accept, or superparasitize, the pheromone marked fruit. Upon dissection it was revealed that females which superparasitized had a mean egg load of 19.5 eggs (n=22), while females which rejected marked fruit had a mean egg load of 13.5 eggs (n=26). These results are consistent with the theory of adaptive superparasitism.     

Motivation models fail to explain oviposition behaviour in the diamondback moth

Abstract. It is widely accepted that previous experience and internal physiological factors (such as egg‐load) affect host‐plant discrimination during oviposition by phytophagous insects. However, there is some debate as to how these factors interact in a mechanistic sense to control acceptance. The role of learning and host deprivation in host acceptance by adult diamondback moths (Plutella xylostella L.) was investigated. In the first experiment, we tested whether experience of a lower ranked host cabbage increased acceptance of a higher ranked host as predicted by a hierarchy threshold model. Moths trained on cabbage were over three times more likely to accept cabbage during testing than untrained moths. There was no effect of cabbage training on acceptance of cress, indicating that the effect of training was species‐specific. In a second experiment, designed to test the prediction of motivation models that insects become less discriminating when deprived of oviposition opportunities, depriving females of host plants for 2 nights significantly increased female egg‐load (×2.3). Host deprivation did not decrease discrimination between the preferred host cress and cabbage. Cabbage and cress plants were equally likely to have been accepted by nondeprived moths after 1 night of exposure, yet moths deprived of hosts for 2 nights strongly preferred cress when tested during the first 20 min of the scotophase. During this 20‐min period, previous host deprivation increased acceptance of host plants generally but did not decrease discrimination between hosts. These data contradict the expectation that there is an inverse relationship between host species discrimination and the failure of an insect to find hosts as found in existing oviposition acceptance models. As an alternative, the Incremental Acceptance Model of host acceptance behaviour is presented, in which responsiveness to a host is a function of the recent encounter rate with host‐specific stimuli, and the oviposition reflex is regulated by nonspecific cues such as egg‐load.     

Do Golden Egg Bugs (Phyllomorpha laciniata: Heteroptera, Coreidae) Require Conspecifics for Oviposition?

Golden egg bug (Phyllomorpha laciniata) females lay eggs on the bodies of conspecifics of both sexes. We investigated to what extent reproduction depended on the availability of conspecifics as oviposition substrate and the acceptability of the host plant as an alternative oviposition substrate in the absence of conspecifics. Mated females were placed in experimental enclosures each containing a sprig of fresh host plant. Each experimental female was subjected to one of three treatments: isolated from conspecifics (solitary), paired with another female, or paired with a male. Solitary females laid a few eggs on the host plant but then stopped laying eggs, and solitary females laid significantly fewer eggs than those enclosed with another female or a male. Females enclosed with a male laid no more eggs than those enclosed with a female. When two previously isolated females were later enclosed together, they soon renewed oviposition. Females in nature contained significantly more oviducal eggs than did females that were enclosed with other females for a short period. Thus the availability of suitable conspecifics as oviposition substrate stimulates the deposition of mature eggs, and reproduction depends on the presence of conspecifics of either sex as oviposition substrate.     

Intraspecific variability in egg maturation patterns and associated life‐history trade‐offs in a polyembryonic parasitoid wasp

1. Life‐history theory predicts a trade‐off between the resources allocated to reproduction and those allocated to survival. Early maturation of eggs (pro‐ovigeny) is correlated with small body size and low adult longevity in interspecific comparisons among parasitoids, demonstrating this trade‐off. The handful of studies that have tested for similar correlations within species produced conflicting results. 2. Egg maturation patterns and related life‐history traits were studied in the polyembryonic parasitoid wasp, Copidosoma koehleri (Hymenoptera: Encyrtidae). Although the genus Copidosoma was previously reported to be fully pro‐ovigenic, mean egg loads of host‐deprived females almost doubled within their first 6 days of adulthood. 3. The initial egg‐loads of newly emerged females were determined and age‐specific realised fecundity curves were constructed for their clone‐mate twins. The females' initial egg loads increased with body size, but neither body size nor initial egg load was correlated with longevity and fecundity. 4. The variation in initial egg loads was lowest among clone‐mates, intermediate among non‐clone sisters and highest among non‐sister females. The within‐clone variability indicates environmental influences on egg maturation, while the between‐clone variation may be genetically based. 5. Ovaries of host‐deprived females contained fewer eggs at death (at ～29 days) than on day 6. Their egg loads at death were negatively correlated with life span, consistent with reduced egg production and/or egg resorption. Host deprivation prolonged the wasps' life span, suggesting a survival cost to egg maturation and oviposition. 6. It is concluded that adult fecundity and longevity were not traded off with pre‐adult egg maturation.     

野外条件下广聚萤叶甲对豚草的产卵选择

为探究影响广聚萤叶甲Ophraella communa LeSage选择豚草产卵的环境因素, 在南京城郊于2009年6月23日至9月1日豚草生长季节, 跟踪调查了60个豚草斑块上落卵数量动态, 运用跨栏模型分析了影响叶甲产卵以及产卵数量的因素。结果表明： （1）产卵发生随季节延长、 豚草被取食程度增大、 株高增长、 暴露环境中斑块增大而增加, 但随遮蔽环境中豚草斑块增大、 开花、 开花后季节延长、 季节延长情况下被取食程度增大、 开花后被取食程度增大等因素而降低; （2）落卵数量随季节延长、 豚草被取食程度增大、 暴露环境、 开花期被取食程度增大、 开花期株高增长等因素而增加, 但随豚草开花、 季节延长情况下被取食程度增大而减小; （3）落卵量随季节延长而增大的幅度在豚草营养生长期明显大于开花期, 在暴露环境中随季节延长而呈明显直线增大, 但在遮阴环境中先直线增加, 于10周后趋缓。研究结果说明, 影响产卵发生与落卵数量的因素不完全一致, 产卵发生与落卵数量主要受因子之间互作的影响, 而较少受到单因素的独立影响。     

Oviposition site selection of the Alcon blue butterfly at the northern range margin

Female oviposition decisions in insects may strongly affect offspring growth and survival, and thus determine population performance. In this study, we examined oviposition site selection in the xerophilous ecotype of the endangered myrmecophilous butterfly Phengaris (=Maculinea) alcon (Lepidoptera, Lycaenidae) in Estonia, at the northern distribution margin of both the butterfly and its host plant, Gentiana cruciata L. Egg distribution on individual host plants appeared to be highly uneven: plants carrying high egg loads contrasted to a high proportion of host plants without any or with a few eggs. Host plant use for oviposition was strongly dependent on plant characteristics and environmental context. Host plant height relative to the surrounding vegetation rather than the absolute height of host plants was a key factor determining the use of particular host plant individuals for oviposition. In particular, plants protruding above surrounding vegetation had a higher probability of being used for oviposition, and carried more eggs. Additionally, the number of eggs laid on individual host plants was positively associated with the presence of flowers and the number of shoots. More aggregated host plants received fewer eggs than those with less conspecifics around. Feeding damage by wild herbivores, found in a substantial proportion of the butterfly’s host plants, strongly reduced the number of eggs on individual plants. Our results underline the need to assure that butterfly’s host plants do not become overgrown by surrounding vegetation. Best practices for opening vegetation around host plants may need further studies that explicitly account for butterfly’s host ants—their abundance in relation to vegetation height and their response to opening vegetation.     

Egg performance on an egg-carrying bug. Experiments in the field

Selection of oviposition sites has direct influence on female fitness. Differences in offspring survival among sites should favour females to select oviposition sites with the highest survival. Golden egg bug females ( Phyllomorpha laciniata; Coreidae, Heteroptera) use conspecifics as oviposition substrates. Most eggs are laid on the back of the bug but they can be found on all body parts. Females never carry their own eggs, and males commonly carry eggs received without copulation with the donor. We examined differences in egg survival relative to paternity to the egg, host sex and body size and attachment of an egg on a host's body in the field. We also studied which bugs received eggs. Egg loss was surprisingly common: 30–80% of recaptured individuals lost eggs during a six-day period. Unexpectedly, host's paternity to the eggs did not affect egg survival. Also, egg loss did not differ among hosts in respect to other parameters studied. Males received more eggs than females, but survival of the eggs was not better on a male's back than on a female's back. Since egg loss is common in the golden egg bug, we suggest that female oviposition strategy to lay eggs on conspecifics is not perfect. This is due to active behaviour of potential hosts (for example, rejected oviposition attempts) or lack of suitable oviposition substrates (conspecifics) in the field. Since eggs do not survive unless carried, females may be acting opportunistically, doing the best job possible by laying eggs on available conspecifics.     

A general model for host plant selection in phytophagous insects

We develop a general theoretical framework for exploring the host plant selection behaviour of herbivorous insects. This model can be used to address a number of questions, including the evolution of specialists, generalists, preference hierarchies, and learning. We use our model to: (i) demonstrate the consequences of the extent to which the reproductive success of a foraging female is limited by the rate at which they find host plants (host limitation) or the number of eggs they carry (egg limitation); (ii) emphasize the different consequences of variation in behaviour before and after landing on (locating) a host (termed pre- and post-alighting, respectively); (iii) show that, in contrast to previous predictions, learning can be favoured in post-alighting behaviour--in particular, individuals can be selected to concentrate oviposition on an abundant low-quality host, whilst ignoring a rare higher-quality host; (iv) emphasize the importance of interactions between mechanisms in favouring specialization or learning.     

Counterstrategy to Egg Dumping in a Coreid Bug: Recipient Individuals Discard Eggs from Their Backs

The golden egg bug, Phyllomorpha laciniata Vill. (Heteroptera: Coreidae), is the only terrestrial insect in which females oviposit on the backs of female and male conspecifics. Eggs do not survive unless carried by a bug. Herein, I report laboratory observations that egg-carrying individuals actively brush their backs against the host plant seemingly in an effort to rub off eggs. Egg scraping is more common among individuals carrying many eggs than among those carrying only a few eggs. The most recently received eggs were rubbed off first. Females did not avoid laying eggs on the backs of egg-loaded individuals, nor did bugs carrying several eggs resist oviposition attempts more often than unloaded ones. Some males were likely to have fertilized the eggs they scraped off their backs. Laboratory results of active egg removal correspond with egg loss in the field, suggesting that egg scraping may explain egg loss in nature. The data indicate a cost of egg carrying to an individual and an evolutionary arms race between oviposition and discarding behavior.     

Oviposition Site Selection by the Regal Fritillary, Speyeria idalia, as Affected by Proximity of Violet Host Plants

Selection of oviposition sites by female regal fritillary butterflies, Speyeria idalia (Drury), in relation to the location and abundance of their larval food plant, Viola pedatifida G. Don, was studied in Kansas tallgrass prairie. To identify potential cues that females use to select oviposition microsites, we compared plots in which eggs were laid with paired control plots in terms of violet abundance, distance from plot center to the nearest violet plant, plant species composition and relative abundance, plant diversity (Shannon's index), and average plant canopy height. No significant differences occurred between control and oviposition sites for any of these variables (P > 0.15). Violets were present in only 30% of the 1-m-diameter oviposition plots, compared with 24% of the corresponding controls. Furthermore, eggs were never laid directly on violets even when they were present nearby. These data imply that S. idalia females do not preferentially orient to or oviposit on their larval food plant. Nevertheless, female S. idalia did not oviposit randomly, for they invariably chose microsites near the ground that were shaded by the grass/forb overstory and usually deposited eggs on the underside of dead vegetation. We speculate that environmental stresses such as high temperatures and intense solar insolation during the egg stage or harsh overwintering conditions experienced by first-instar larvae impact survival and influence choice of oviposition sites. High fecundity (more than 2000 eggs in some individuals) may allow this species to use a conditional, sweepstakes strategy, i.e., producing and spreading many eggs over prairie that harbors host plants to compensate for low egg and larval survivorship.