Prey Stage Research Articles

Consequences of size structure in the prey for predator–prey dynamics: the composite functional response

1. Current formulations of functional responses assume that the prey is homogeneous and independent of intraspecific processes. Most prey populations consist of different coexisting size classes that often engage in asymmetrical intraspecific interactions, including cannibalism, which can lead to nonlinear interaction effects. This may be important as the size structure with the prey could alter the overall density-dependent predation rates. 2. In a field experiment with damselfly and dragonfly larvae, 16 treatments manipulated the density of a small prey stage, the presence of large conspecific prey and the presence of heterospecific predators. 3. Size structure in the prey (i.e. when both prey stages were present) decreased the impact of the predator on overall prey mortality by 25-48% at mid and high prey densities, possibly due to density-dependent size-structured cannibalism in the prey. The predation rates on small prey stages were determined by the interaction of large prey and predators. Predation rates increased with prey density in the absence of large prey, but predation rates were constant across densities when large conspecifics were present. 4. The functional response for unstructured prey followed a Holling type III model, but the predation rate for size-structured prey was completely different and followed a complex pattern that could not be explained with any standard functional response. 5. Using additional laboratory experiments, a mortality model was developed and parameterized. It showed that the overall prey mortality of size-structured prey can be adequately predicted with a composite functional response model that modelled the individual functional responses of each prey stage separately and accounted for their cannibalistic interaction. 6. Thus, treating a prey population as a homogeneous entity will lead to erroneous predictions in most real-world food webs. However, if we account for the effects of size structure and the intraspecific interactions on functional responses by treating size classes as different functional groups, it is possible to reliably predict the dynamics of size-structured predator-prey systems.

Coexistence and stability of predator–prey model with Beddington–DeAngelis functional response and stage structure

We present a predator–prey model of Beddington–DeAngelis type functional response with stage structure on prey. The constant time delay is the time taken from birth to maturity about the prey. By the uniform persistence theories and monotone dynamic theories, sharp threshold conditions which are both necessary and sufficient for the permanence and extinction of the model as well as the sufficient conditions for the global stability of the coexistence equilibria are obtained. Biologically, it is proved that the variation of prey stage structure can affect the permanence of the system and drive the predator into extinction by changing the prey carrying capacity: Our results suggest that the predator coexists with prey permanently if and only if predator's recruitment rate at the peak of prey abundance is larger than its death rate; and that the predator goes extinct if and only if predator's possible highest recruitment rate is less than or equal to its death rate; furthermore, our results also show that a sufficiently large mutual interference by predators can stabilize the system.

Some Ecological and Biological Studies on Typhlodrompis swirskii (Athias-Henriot) (Acari: Phytoseiidae)

Relative humidity of 70 to 85% proved to be the most suitable for Typhlodrompis swirskii (Athias-Henriot) at 25oC as itaccelerated development (10.0 & 10.8 days) and increased female fecundity (13.0 & 12.0 eggs/♀/10 days) onEutetranychus. orientalis immatures. Low temperature (5 & 9oC) prolonged egg incubation and decreased hatchabilityas well as female survival. After one to four weeks, egg hatchability ranged from 90 to 50% and from 100 to 64% andfemale survival from 50 to 0% and from 80 to 10% at 5 and 9oC, respectively. Multiple mating due to male companythrough the whole female longevity or sporadically for 12 hours every 5 days increased female fecundity and longevityas it averaged 47.0 & 35.0 eggs and 37.6 & 35.0 days compared with 25.0 eggs and 29.2 days for once mated female.For food attraction and /or kairomone emitted that affects predator, T. swirskii females showed greater percentage ofattractance in a shorter period to more advanced prey stage and to mites than insects tested. Also fed females showedmore attraction than 24 starved females and the latters better than 48 hours starved ones. E. orientalis adults gave thegreatest percentage attraction (60%) in the shortest time (3.20 minutes) for fed female, while castor been pollens gavethe smallest (1%) and the longest time (121.6 minutes). Host plants of different leaf texture, affected female fecundity,averaging the greatest (15.8 eggs/♀/10 days) on smooth leathery leaf of grape fruit, while coarse reticulated leaf ofguava resulted in the least number of deposited eggs (10.8 eggs/♀/10 days).

Control Measures of Tetranychs urticae Koch on Two Cucumber Cultivars in Plastic Houses

Biological control of Tetranychus urticae Koch different stages on two cucumber cultivars (Sahm & Heikal) grown inplastic houses in Nubaria District, Beheira Governorate, during 2004&2005 seasons was studied. Four predatorphytoseiid mites; Phytoseiulus macropilis (Banks), Neoseiulus californicus (McG.), N. cucumeris (Oudemans), and N.zaheri (Yousef and El-Borolossy) were used against T. urticae different stages. N. californicus and P. macropilis gavethe highest reduction percentages of T. urticae different stages (97.36 & 97.51 % adults; 98.49 & 98.45% immaturesand 99.36& 98.59% eggs) in Sahm cultivar, while in Heikal cultivar the percentages were 87.14 & 92.50 %; 98.50 &97.38 % and 97.87&97.85%, respectively during 2004. Similar results were obtained, during 2005. Chemical control byspraying the two compounds Vertemic & Ortus proved that Vertemic was the best in reducing T. urticae different stagesby 89.55, 95.37 & 94.00% of the aforementioned successive prey stages. Integrated pest control, showed that releasingN. californicus and P. macropilis after spraying Vertemic gave in general the high reduction of T. urticae differentstages but less than Vertemic alone. However using the two predators alone and not integrated with acaricides gave thehighest reduction percentages.

A phytoseiid predator from the tropics as potential biological control agent for the spider mite Tetranychus urticae Koch (Acari: Tetranychidae)

The two-spotted spider mite Tetranychus urticae Koch (Acari: Tetranychidae) is one of the most important pests of many crops in temperate and tropical climates. Chemical control is the main method of combating this mite, but it is less preferred due to the development of resistance as well as environmental problems associated with the use of pesticides. Biological control of spider mites has been tried as a logical alternative method for chemical control. Studies have been conducted in different countries to assess the effect and potential of natural enemies for controlling the pest. The predatory mite Phytoseiulus macropilis (Banks) (Acari: Phytoseiidae) was found associated with spider mites in strawberry crops in the state of Minas Gerais, Brazil. Earlier studies suggested that P. macropilis was able to control spider mites, but predation and oviposition rates have not been measured so far. We measured predation and oviposition on strawberry with spider mites as prey in the laboratory. The predator fed on all prey stages and showed capacity to control local prey populations on leaf disks. The oviposition rate of P. macropilis is similar of the most used predatory mite Phytoseiulus persimilis and the predation rate is higher than that of the latter. Our results suggest that P. macropilis is a promising candidate to control two-spotted spider mites in the tropics and other areas.

Impact of Prey Size on Prey Capture Success, Development Rate, and Survivorship inPerillus bioculatus(Heteroptera: Pentatomidae), a Predator of the Colorado Potato Beetle

Nymphs of Perillus bioculatus F., a specialist pentatomid predator of the Colorado potato beetle, Leptinotarsa decemlineata (Say), are smaller than comparable instars of their prey. In laboratory experiments, P. bioculatus fed small prey exhibited greater capture success, increased survivorship, and faster development to adulthood than individuals fed large prey. An increase of potato beetle prey stage by one instar lowered capture success and survival by 82 and 80%, respectively. Although multiple P. bioculatus are commonly found feeding on a single prey in the field, laboratory survival rates, and development times did not differ significantly between Perillus bioculatus reared individually and in groups. P. bioculatus presented with two prey sizes most commonly attacked the instar that was easiest to capture and that maximized survival. In the absence of augmentative release programs, P. bioculatus is unable to regulate L. decemlineata populations. At the study site in Yakima, Washington, L. decemlineata completes one to three generations per year in potato fields, never reaching stable age distribution before the end of the growing season. Consequently, small, easily captured prey are present only episodically. Developing P. bioculatus must therefore feed on large prey during much of the growing season, limiting their capacity to grow and survive, which is hypothesized as one reason for their failure to regulate L. decemlineata populations. Typically, invulnerable prey stages stabilize predator–prey dynamics. The evidence presented here suggests that prey refuges can also destabilize predator–prey interactions by limiting the capacity of predators to numerically respond and to regulate prey populations.

Impact of Prey Size on Prey Capture Success, Development Rate, and Survivorship in <I>Perillus bioculatus</I> (Heteroptera: Pentatomidae), a Predator of the Colorado Potato Beetle

Abstract Nymphs of Perillus bioculatus F., a specialist pentatomid predator of the Colorado potato beetle, Leptinotarsa decemlineata (Say), are smaller than comparable instars of their prey. In laboratory experiments, P. bioculatus fed small prey exhibited greater capture success, increased survivorship, and faster development to adulthood than individuals fed large prey. An increase of potato beetle prey stage by one instar lowered capture success and survival by 82 and 80%, respectively. Although multiple P. bioculatus are commonly found feeding on a single prey in the field, laboratory survival rates, and development times did not differ significantly between Perillus bioculatus reared individually and in groups. P. bioculatus presented with two prey sizes most commonly attacked the instar that was easiest to capture and that maximized survival. In the absence of augmentative release programs, P. bioculatus is unable to regulate L. decemlineata populations. At the study site in Yakima, Washington, L. d...

Effects of Bt maize on Frankliniella tenuicornis and exposure of thrips predators to prey‐mediated Bt toxin

AbstractAs a part of a risk assessment procedure, the impact of Bt maize expressing Cry1Ab toxin on the thrips Frankliniella tenuicornis (Uzel) (Thysanoptera: Thripidae) was investigated, and the potential risks for predators feeding on thrips on Bt maize were evaluated. The effects of Bt maize on F. tenuicornis were assessed by measuring life‐table parameters when reared on Bt and non‐Bt maize. The content of Cry1Ab toxin in different stages of F. tenuicornis reared on Bt maize and the persistence of the toxin in adults where determined in order to evaluate the possible exposure of predators when feeding on thrips. In addition, Chrysoperla carnea (Stephens) (Neuroptera: Chrysopidae) was used as a model predator to assess how the behaviour of prey and predator may influence the exposure of a natural enemy to the Bt toxin. Life‐table parameter results showed that F. tenuicornis was not affected when it was reared on Bt maize. This indicates that the potential for prey quality‐mediated effects on predators is low. Bt content was highest in thrips larvae and adults, and negligible in the non‐feeding prepupal and pupal stages. The persistence of the Cry1Ab toxin in adult F. tenuicornis was short, resulting in a decrease of 97% within the first 24 h. Predation success by young C. carnea larvae varied among the thrips stages, indicating that exposure of predators to Bt toxin can additionally depend on the prey stage. When combining the current knowledge of the susceptibility of major thrips predators with our findings showing no potential for prey quality‐mediated effects, relatively low toxin content in thrips as well as short persistence, it can be concluded that the risks for predators when feeding on thrips in or next to Bt maize fields are negligible.

Prey stage preference and functional response of Euseius hibisci to Tetranychus urticae (Acari: Phytoseiidae, Tetranychidae)

The aims of this study were: (a) determine the prey stage preference of female Euseius hibisci (Chant) (Phytoseiidae) at constant densities of different stages of Tetranychus urticae Koch (Tetranychidae), (b) assess the functional response of the predator females to the varying densities of eggs, larvae, or protonymphs of T. urticae, and (c) estimate the functional response of E. hibisci when pollen of Ligustrum ovalifolium was present as well. We conducted experiments on excised pieces of strawberry leaf arenas (Fragaria ananassa) under laboratory conditions of 25+/-2 degrees C, 60+/-5% RH and 12 h photophase. Our results indicated that the predator consumed significantly more prey eggs than other prey stages. Consumption of prey deutonymphs and adults was so low that they were excluded from the non-choice functional response experiments. The functional response on all food items was of type II. The two parameters of the functional response were estimated for each prey type by means of the adjusted non-linear regression model. The highest estimated value a' (instantaneous rate of discovery) and the lowest value of Th (handling time, including digestion) were found for the predator feeding on prey eggs, and a' was lowest and Th highest when fed protonymphs. Using the jack-knife method, the values for the functional response parameters were estimated. The values of a' and Th produced by the model were similar among all prey types except for the eggs, which were different. Using pollen simultaneously with prey larvae decreased the consumption of the latter over the full range of prey densities The suitability of this predator for biological control of T. urticae on strawberry is discussed.

Feeding Preference of Three Lady Beetle Predators of the Hemlock Woolly Adelgid (Homoptera: Adelgidae)

In a laboratory study, we tested the feeding preferences of three coccinellid predators of hemlock woolly adelgid, Adelges tsugae Annand, an introduced pest of hemlock in the eastern United States. The species tested were Sasajiscymnus tsugae Sasaji & McClure (formerly Pseudoscymnus tsugae) from Japan, Scymnus ningshanensis Yu & Yao from China, and Harmonia axyridis (Pallas), a generalist species introduced from Asia that is currently widespread in eastern hemlock, Tsuga canadensis Carriere, forests. We measured the feeding preference of each beetle species when given the choice of A. tsugae and either 1) Pineus strobi (Hartig) on Pinus strobus L.; 2) Adelges laricis Vallot on Larix decidua Mill.; 3) Adelges cooleyi (Gillette) on Pseudotsuga menziesii (Mirb.) Franco; or 3) Paraprociphilus tessellatus (Fitch) on Alnus serrulata (Ait.) Willd. We evaluated beetle preference for adults, nymphs, and eggs of each prey species. Generally, when adult or nymphal prey stages were compared, S. tsugae preferred A. tsugae adults to P. strobi, A. cooleyi, A. laricis, and P. tessellatus. S. ningshanensis showed less preference between adelgid species, but it did not prefer P. tessellatus nymphs. When preferences for adelgid eggs were assayed, S. tsugae and S. ningshanensis showed no preference between A. tsugae and A. cooleyi or P. strobi, but S. tsugae did prefer A. tsugae to A. laricis. Larvae of S. tsugae were unable to survive on P. tessellatus nymphs. H. axyridis adults readily consumed both A. tsugae and P. tessellatus, but H. axyridis larvae did not complete their life cycle on A. tsugae. Our host range tests suggest that S. ningshanensis and S. tsugae may feed on several species of Adelgidae and that A. tsugae is often preferred.

Prey consumption preferences of Serangium parcesetosum Sicard (Col., Coccinelidae) for different prey stages, species and parasitized prey

Serangium parcesetosum Sicard (Col., Coccinellidae) is considered one of the important predators of whiteflies. However, knowledge about its preferences for different prey stages, species and parasitized prey is still lacking in the literature. The present work investigated the preferences of S. parcesetosum for different stages of B. tabaci, different prey species and B. tabaci parasitized by Encarsia formosa Gahan (Hym., Aphelinidae) by prey consumption at different temperatures in the laboratory. Results showed that L2 and L4 predatory instars of S. parcesetosum preferred puparia to nymphs and eggs of Bemisia tabaci (Genn.) (Hom., Aleyrodidae). The mean daily prey consumption was 5.1–9.0, 4.5–6.2 and 3.6–4.3 by L2 and 6.4–9.7, 5.5–8.5 and 2.5–7.5 by L4 for puparia, nymphs and eggs, respectively. Adult females, however, indicated a significantly greater preference for both puparia and nymphs, consuming a daily mean of 6.4–7.5 puparia and 5.1–6.7 nymphs, but only 3.0–4.7 eggs. At 18 and 30 °C, all S. parcesetosum stages tested significantly preferred B. tabaci and Trialeurodes vaporariorum Westwood (Hom., Aleyrodidae) over the other three prey species offered. At both temperatures, all predatory stages preferred B. tabaci to T. vaporariorum, the L2 instar at 18 °C, showing significantly more preference for B. tabaci than T. vaporariorum. In contrast, very few individuals were consumed from Aphis gossypii Glover (Hom., Aphididae), Frankliniella occidentalis (Pergande) (Thys., Thripidae) and Tetranychus urticae Koch (Acari, Tetranychidae). At 18 °C, a daily mean of 7.5–8.0, 6.6–9.0 and 6.7–8.1 B. tabaci as well as 5.3–6.4, 5.4–7.8 and 5.6–6.3 T. vaporariorum was consumed by L2, L4 and adult females, respectively, while at 30 °C, L2, L4 and adult females consumed a mean of 9.3, 8.8–9.7 and 8.3–9.7 B. tabaci/day as well as 8.3–9.0, 7.8–9.1 and 5.5–8.4 T. vaporariorum/day, respectively. S. parcesetosum L2 and L4 instars as well as adult females and males at both studied temperatures showed a significant tendency to avoid B. tabaci puparia after 5 days of parasitism by E. formosa and preferred to feed on unparasitized whiteflies. At 18 °C, the mean daily consumption was 8.7 and 0.2 (L2), 11.1 and 0.6 (L4), 12.1 and 1.0 (♀♀) as well as 10.5 and 0.2 (♂♂), while at 30 °C the means were 15.9 and 0.5 (L2), 19.8 and 1.0 (L4), 18.9 and 1.2 (♀♀) as well as 17.4 and 0.6 (♂♂) from unparasitized and parasitized B. tabaci puparia, respectively.

Daily consumption and predation rate of differentStethorus punctillum instars feeding onTetranychus urticae

Laboratory experiments were conducted to evaluate the prey stage preference and the daily consumption of each stage of the coccinellid predatorStethorus punctillum Weise (Coleoptera: Coccinellidae) feeding on the two-spotted spider miteTetranychus urticae (Koch) (Acari: Tetranychidae). Groups of different life stages of the prey were offered (eggs, larvae, nymphs and adults). The prey preference varied with the stage ofS. punctillum. First larval instars had no significant preference among theT. urticae stages offered. Second larval instars consumed significantly more spider mite larvae in comparison with nymphs. In contrast, third larval instars indicated a strong preference for mite eggs. Significantly fewerT. urticae larvae were consumed by the fourth larval instars ofS. punctillum, in comparison with the three other mite stages. Finally, adult predators consumed significantly more mite eggs than the other stages offered. This preferential trend was similar for all adults tested, whether during the pre-oviposition or the oviposition period.

Predatory abilities of Amphibolus venator (Klug) (Hemiptera: Reduviidae), a predator of stored-product insect pests

The predatory abilities of Amphibolus venator (Klug) on the stored-product insect pest Tribolium confusum Jacquelin du Val were examined. A. venator adults (5–15 days old) were starved for 3 days and then introduced individually into plastic containers containing different prey densities (3, 5, 10, 15 or 20) of last-instar larvae, pupae or adults of T. confusum. The assay was carried out at 25°C and 30°C for 1 day. The number of T. confusum killed by A. venator during 10 days was also investigated a prey density of 10 individuals. A. venator attacked all stages tested: mature larvae, pupae and adults. A. venator targeted mature larvae preferentially to the other stages. The number of prey killed by A. venator increased at high prey density, and the functional response of A. venator exhibited Holling's Type II response for all the prey stages. Females tended to kill more prey than males. Predation by A. venator was more effective at 30°C than at 25°C.

Multi‐predator effects across life‐history stages: non‐additivity of egg‐ and larval‐stage predation in an African treefrog

AbstractThe effects of multiple predators on their prey are frequently non‐additive because of interactions among predators. When prey shift habitats through ontogeny, many of their predators cannot interact directly. However, predators that occur in different habitats or feed on different prey stages may still interact through indirect effects mediated by prey traits and density. We conducted an experiment to evaluate the combined effects of arboreal egg‐stage and aquatic larval‐stage predators of the African treefrog, Hyperolius spinigularis. Egg and larval predator effects were non‐additive – more Hyperolius survived both predators than predicted from their independent effects. Egg‐stage predator effects on aquatic larval density and size and age at hatching reduced the effectiveness of larval‐stage predators by 70%. Our results indicate that density‐ and trait‐mediated indirect interactions can act across life‐stages and habitats, resulting in non‐additive multi‐predator effects.

Seasonal abundance and synchrony between Laricobius nigrinus (Coleoptera: Derodontidae) and its prey, the hemlock woolly adelgid (Hemiptera: Adelgidae)

AbstractLaricobius nigrinus Fender, native to the Pacific Northwest, is being evaluated as a potential biological control agent of the hemlock woolly adelgid, Adelges tsugae Annand, in the eastern United States. Members of the genus Laricobius feed exclusively on adelgids. Adelges tsugae is found on hemlocks (Tsuga sp.) in North America and Asia, but is considered only a pest of eastern [Tsuga canadensis (L.) Carrière] and Carolina (Tsuga caroliniana Engelmann) hemlocks in eastern North America. This is the first detailed study of the life history of L. nigrinus and its interaction with A. tsugae. Results of a 2-year field study conducted in a seed orchard in British Columbia on the seasonal abundance of L. nigrinus and its prey, A. tsugae, revealed that (i) the sistens generation of A. tsugae matures 2-3 months earlier than previously reported in Virginia and Connecticut, (ii) no A. tsugae sexuparae were observed, which differs from findings in Virginia and Connecticut, (iii) L. nigrinus adults undergo an aestival diapause that coincides with diapausing first instar A. tsugae sistens, and (iv) oviposition and subsequent larval development of L. nigrinus coincides with oviposition by the A. tsugae sistens adults, indicating good synchrony between L. nigrinus and suitable prey stages of A. tsugae.

Interspecific infanticide deters predators

It is well known that young, small predator stages are vulnerable to predation by conspecifics, intra‐guild competitors or hyperpredators. It is less known that prey can also kill vulnerable predator stages that present no danger to the prey. Since adult predators are expected to avoid places where their offspring would run a high predation risk, this opens the way for potential prey to deter dangerous predator stages by killing vulnerable predator stages. We present an example of such a complex predator–prey interaction. We show that (1) the vulnerable stage of an omnivorous arthropod prey discriminates between eggs of a harmless predator species and eggs of a dangerous species, killing more eggs of the latter; (2) prey suffer a minor predation risk from newly hatched predators; (3) adult predators avoid ovipositing near killed predator eggs, and (4) vulnerable prey near killed predator eggs experience an almost fourfold reduction of predation. Hence, by attacking the vulnerable stage of their predator, prey deter adult predators and thus reduce their own predation risk. This provides a novel explanation for the killing of vulnerable stages of predators by prey and adds a new dimension to anti‐predator behaviour.

Functional and numerical responses do not always indicate the most effective predator for biological control: an analysis of two predators in a two‐prey system

Summary Functional and numerical responses are key components in the selection of predators for biological control. We examined the relevance of these responses for predicting the effectiveness of generalist predators, taking into account effects of alternative prey and multiple predators. Our system involved two acarine predators of two prey species on apple. Responses were measured on leaf discs in the laboratory, and predictions assessed on small potted apple trees. In particular, we tested three hypotheses. Hypothesis I: the species with the higher predatory responses will be more effective in limiting prey populations. Neither predator had a consistently higher functional response, which depended on prey stage and species. Amblyseius fallacis had a (approximately two times) higher ovipositional response than Typhlodromus pyri. We therefore hypothesized that A. fallacis would be more effective in controlling prey. No evidence was found to support this hypothesis. Hypothesis II: alternative prey reduce the functional response of predators to target prey. Alternative prey did or did not reduce the functional response to target prey, depending on the predator, stage and species of alternative prey. The only consistent trend for both predators was that the predation of Panonychus ulmi deutonymphs was reduced when Tetranychus urticae was present. Hypothesis III: the predator species with the highest mean ovipositional response will out‐compete the other predator species. The number of predators observed in the mixed predator treatments depended on the prey composition. Although A. fallacis had a higher ovipositional response, it was never more abundant. Intraguild predation probably played a role in determining predator abundance, although prey composition altered intraguild effects. These results highlight the complex nature of predator and prey interactions. Because of these interactions, functional and numerical assays on single predator–single prey systems in simplified laboratory environments do not allow predictions of the growth of mixed populations in realistic habitats, or of the effectiveness of predators as biological control agents in the field.

Do functional responses of predatory arthropods reach a plateau? A case study of Orius insidiosus with western flower thrips as prey

AbstractParameters determining the functional and numerical response of Orius insidiosus to the density of second instar larvae of the western flower thrips (WFT), Frankliniella occidentalis, were estimated with the aim to be used in models calculating adequate release ratios of predators vs prey. Especially when the prey population must decrease immediately after predator release and the time to suppression must be short, it is of crucial importance to know whether the functional response reaches a plateau or keeps on increasing with prey density within the range of densities that are realistic for the prey. Such plateaus may arise from constraints on the time budget or from constraints on gut‐fullness‐associated motivation to attack the prey. Estimates of the plateau for O. insidiosus based on prey handling times by far exceed realistic values. In addition, motivation constraints did not apply, because the level of gut fullness above which attack ceases coincides with gut capacity. This implies that the predation rate keeps on increasing linearly with the square root of the density of WFT‐larvae and does not reach a plateau within the realistic range of thrips densities (0–20 WFT per cm2). Such plateaus are likely to occur for smaller‐sized predators and smaller‐sized stages of the same predator and they may also occur when the prey stage offered has better capacities to escape or resist attack. We argue that the presence and level of plateaus in functional responses are of importance for determining initial predator‐to‐prey ratios.

EFFECTS OF PHOTOPERIOD AND PREY TYPE ON DIAPAUSE TENDENCY AND PREOVIPOSITION PERIOD IN PERILLUS BIOCULATUS (HEMIPTERA: PENTATOMIDAE)

AbstractAttempts at using Perillus bioculatus (F.) for control of Colorado potato beetle, Leptinotarsa decemlineata (Say), have been hampered by an incomplete understanding of the predator’s over-wintering biology. This study determined the effects of photoperiod and life stage of prey (Colorado potato beetle) on tendency for adult females to enter reproductive diapause, duration of the preoviposition period, and mortality of females. Perillus bioculatus showed an increasing tendency to enter diapause rather than to initiate reproductive activities as day length decreased. Females that were fed large beetle larvae (mid to late fourth instar) showed a significant increase in the number of individuals entering diapause compared with females that were fed a mix of beetle eggs and small larvae (first to third instar). Probit analysis was used to estimate the photoperiod that caused 50% of females to enter diapause; these estimates were 15L:9D for females feeding on large larvae, and 14.5L:9.5D for females feeding on eggs and small larvae. Females that were fed large larvae also showed a longer preoviposition period and had a slightly significant higher rate of mortality than those fed eggs and small larvae.

Resolving Discrepancies between Deterministic Population Models and Individual‐Based Simulations

This work ties together two distinct modeling frameworks for population dynamics: an individual-based simulation and a set of coupled integrodifferential equations involving population densities. The simulation model represents an idealized predator-prey system formulated at the scale of discrete individuals, explicitly incorporating their mutual interactions, whereas the population-level framework is a generalized version of reaction-diffusion models that incorporate population densities coupled to one another by interaction rates. Here I use various combinations of long-range dispersal for both the offspring and adult stages of both prey and predator species, providing a broad range of spatial and temporal dynamics, to compare and contrast the two model frameworks. Taking the individual-based modeling results as given, two examinations of the reaction-dispersal model are made: linear stability analysis of the deterministic equations and direct numerical solution of the model equations. I also modify the numerical solution in two ways to account for the stochastic nature of individual-based processes, which include independent, local perturbations in population density and a minimum population density within integration cells, below which the population is set to zero. These modifications introduce new parameters into the population-level model, which I adjust to reproduce the individual-based model results. The individual-based model is then modified to minimize the effects of stochasticity, producing a match of the predictions from the numerical integration of the population-level model without stochasticity.