The non-lethal effects of predators and the influence of food availability on life history of adult Chironomus tentans (Diptera: Chironomidae)

1. We used a laboratory experiment to determine effects of a predator (other than straightforward prey consumption) and food availability, during the larval stage, on adult size, age at emergence and fecundity of Chironomus tentans. 2. Predator presence and decreased food availability resulted in reduced adult emergence. 3. Predator presence and food availability resulted in smaller size and greater age at emergence of male and female chironomids. There were no significant interactions between effects of predator presence and food availability. 4. Predator presence had no significant effect on fecundity. 5. Smaller size and greater age at emergence can have important implications for adult survival, size and age at first reproduction and, thus, intrinsic rate of population growth.     

Effects of Mesopredators on Nest Survival of Shrub-Nesting Songbirds

ABSTRACT Although nest predation is often the single largest source of mortality in avian populations, manipulative studies to determine predator impacts on nest survival are rare, particularly studies that examine impacts of mid-size mammalian predators (hereafter, mesopredators) on nest survival of shrub-nesting birds. We quantified nest survival and identified nest predators of shrub-nesting songbirds within 4 large (approx. 40-ha) exclosures and 4 control sites within a longleaf pine (Pinus palustris) ecosystem. During 2003–2006, we located and monitored 535 shrub nests (222 with videography) for 4,804 nest-days to quantify daily nest survival and document predation events. We found no support for a treatment effect, suggesting mesopredators had little impact on daily nest survival (0.9303 in controls and 0.9260 in exclosures) of shrub-nesting songbirds. For the 5 most commonly monitored species, daily nest survival within species was constant. Our analysis suggested that shrub nests were most vulnerable during the nestling stage and presence of cameras on nests increased survival with the increase in survival being more pronounced during the incubation stage. We filmed 107 nest predation events, identifying predators at 88 nests. Of these 88 nests, snakes caused 33%, red imported fire ants (hereafter fire ants, Solenopsis invicta) 28%, raptors 17%, corvids 8%, mesopredators 6%, and small mammals 8% of nest predations. Cause-specific nest predation in controls and exclosures did not differ from expectation, providing evidence that compensatory predation did not occur. Nest predators differed from expectation with regard to nest stage; fire ants and raptors only depredated nests during the nestling stage. Presence of cameras had no effect on nest abandonment. Fire ants were the most prevalent nest predator, and nest predation by fire ants was only observed on nestlings, potentially reducing likelihood of renesting. Magnitude and timing of fire ant predation suggests that fire ants may be the most influential nest predator of shrub-nesting birds within the longleaf pine ecosystem. Our data suggest that controlling mesopredators will have no effect on nest success of shrub-nesting birds within longleaf pine forests.     

Effects of management for productivity on adult survival of Snowy Plovers

Understanding the factors contributing to variation in demographic parameters and their influences on population growth is fundamental to effective conservation of small populations, but this information is often not available. Among shorebirds, population growth is generally most sensitive to changes in adult survival so understanding the factors affecting this vital rate is important. We used a long-term mark–resight dataset and Program MARK to examine the effect of management actions, initiated to improve nesting productivity, on adult survival in a threatened population of Snowy Plovers (Charadrius nivosus) in Oregon, USA. Apparent adult survival averaged 0.71 ± 0.01 (SE), but increased from 1990 to 2014. This increase coincided with a decline in use of protective nest exclosures, but initiation of lethal nest predator management. The unexpected apparent benefit to adult survival of removal of nest predators and the negative effect of protective nest exclosures highlight the importance of understanding how management practices at one life cycle stage may have unintended consequences at other life stages. Our 25-year analysis adds to our knowledge of an intensively managed, threatened species at the northern limit of its range, but, more importantly, knowledge of the negative effect of exclosure use and the positive effect of predator management on adult survival can help inform conservation of less well-studied species with similar life histories.     

Cover,not caging,influences chronic physiological stress in a ground‐nesting bird

Predator exclosures (‘nest cages’) around nests are increasingly used to enhance hatching success of declining ground‐nesting birds. However, such exclosures are contentious and have been suggested to have detrimental effects on the species which they aim to protect. This study examines whether exclosures increase physiological stress of incubating birds, a hitherto unrecognised and untested potential drawback of exclosures. Red‐capped plover Charadrius ruficapillus hatching success was radically altered and significantly higher for nests with exclosures (96.2%) compared with those without (6.8%). Chronic physiological stress in parents (as measured by the heterophil/lymphocyte [H/L] ratio in blood) did not vary between nests with and without exclosures, or between the sexes. However the absence of vegetative cover at the nest site was associated with a 62.7% elevation in H/L ratio, indicating that incubating birds which place their nests in the open are subject to increased levels of chronic stress. The results from this study demonstrate the fundamental importance of predation for the nesting success of this species and confirm that chronic stress levels are not a detrimental side effect of exclosure use.     

Influence of predator density on nonindependent effects of multiple predator species

Interactions between multiple predator species are frequent in natural communities and can have important implications for shared prey survival. Predator density may be an important component of these interactions between predator species, as the frequency of interactions between species is largely determined by species density. Here we experimentally examine the importance of predator density for interactions between predator species and subsequent impacts on prey. We show that aggressive interactions between the predatory shore crabs Carcinus maenas and Hemigrapsus sanguineus increased with predator density, yet did not increase as fast as negative interactions between conspecifics. At low density, interactions between conspecific and heterospecific predators had similar inhibitory impacts on predator function, whereas conspecific interference was greater than interference from heterospecifics at high predator density. Thus the impact of conspecific interference at high predator density was sufficient in itself that interactions with a second predator species had no additional impact on per capita predation. Spatial and temporal variability in predator density is a ubiquitous characteristic of natural systems that should be considered in studies of multiple predator species.     

Evidence for the Predator Attraction Hypothesis in an amphibian predator–prey system

Many species possess damage-released chemical alarm cues that function in alerting nearby individuals to a predator attack. One hypothesis for the evolution and/or maintenance of such cues is the Predator Attraction Hypothesis, where predators, rather than prey, are the “intended” recipients of these cues. If a predator attack attracts additional predators, these secondary predators might interfere with the predation event, providing the prey with a better chance to escape. In this study, we conducted two experiments to explore this hypothesis in an amphibian predator/prey system. In Experiment 1, we found that tiger salamanders (Ambystoma mavortium) showed a foraging attraction to chemical cues from wood frog (Lithobates sylvaticus) tadpoles. Salamanders that were experienced with tadpole prey, in particular, were strongly attracted to tadpole alarm cues. In Experiment 2, we observed experimental encounters between a tadpole and either one or two salamanders. The presence of the second predator caused salamanders to increase attack speed at the cost of decreased attack accuracy (i.e., increasing the probability that the tadpole would escape attacks). We also found that the mere presence of visual and chemical cues from a second predator did not affect this speed/accuracy trade-off but did cause enough of a distraction to increase tadpole survival. Thus, our findings are consistent with the Predator Attraction Hypothesis for the evolution and/or maintenance of alarm cues.     

Nest exclosures do not improve Streaked Horned Lark nest success

ABSTRACT Improving the conservation status of rare and declining species often requires multiple strategies targeted at several vital rates. We report on one of several ongoing management actions intended to benefit the declining population of Streaked Horned Larks (Eremophila alpestris strigata). To improve Streaked Horned Lark fecundity, we employed predator exclosures (wire cages) around nests (N= 33 exclosed and 32 not exclosed) in 2009 and 2010 at two sites in Oregon and two in Washington with the goal of excluding larger birds, the primary lark nest predators. We found no statistically significant effect of exclosures on nest success. For exclosed nests, lower rates of nest predation (exclosed = 12%, unexclosed = 48%) were offset by higher rates of nest abandonment (exclosed = 27%, unexclosed = 0%). Nest abandonment was likely caused by a variety of factors including American Kestrels (Falco sparverius) perching on exclosures, and predation of adults associated with exclosed nests. Our results suggest that the current exclosure design does not improve Streaked Horned Lark fecundity and may negatively affect adult survival. To improve exclosure effectiveness, we recommend modifications that prevent kestrels from perching on exclosures and deny their access to the nest. We also recommend that modifications be applied in an adaptive management framework that includes close monitoring to assess their effectiveness, and subsequent adaptation that might include continued structural modification of exclosures or discontinued use on some or all sites.     

Behavioral Response of Corophium volutator to Shorebird Predation in the Upper Bay of Fundy,Canada

Predator avoidance is an important component of predator-prey relationships and can affect prey availability for foraging animals. Each summer, the burrow-dwelling amphipod Corophium volutator is heavily preyed upon by Semipalmated Sandpipers (Calidris pusilla) on mudflats in the upper Bay of Fundy, Canada. We conducted three complementary studies to determine if adult C. volutator exhibit predator avoidance behavior in the presence of sandpipers. In a field experiment, we monitored vertical distribution of C. volutator adults in bird exclosures and adjacent control plots before sandpipers arrived and during their stopover. We also made polymer resin casts of C. volutator burrows in the field throughout the summer. Finally, we simulated shorebird pecking in a lab experiment and observed C. volutator behavior in their burrows. C. volutator adults were generally distributed deeper in the sediment later in the summer (after sandpipers arrived). In August, this response was detectably stronger in areas exposed to bird predation than in bird exclosures. During peak predator abundance, many C. volutator adults were beyond the reach of feeding sandpipers (>1.5 cm deep). However, burrow depth did not change significantly throughout the summer. Detailed behavioral observations indicated that C. volutator spent more time at the bottom of their burrow when exposed to a simulated predator compared to controls. This observed redistribution suggests that C. volutator adults move deeper into their burrows as an anti-predator response to the presence of sandpipers. This work has implications for predators that feed on burrow-dwelling invertebrates in soft-sediment ecosystems, as density may not accurately estimate prey availability.     

Effects of predator exclusion on nest and hatchling survival in the gopher tortoise

Gopher tortoise (Gopherus polyphemus) populations are declining throughout the Southeast, and high levels of predation on nests and juveniles have been suggested as a potential contributor to this decline. Therefore, we documented gopher tortoise nest success and hatchling survival relative to mammalian predator control. We used 4, large (approx. 40-ha) fenced, predator exclosures to exclude mid-sized mammalian predators: bobcat (Lynx rufus), raccoon (Procyon lotor), Virginia opossum (Didelphis virginianus), fox (Urocyon cinereoargenteus and Vulpes vulpes), coyote (Canis latrans), nine-banded armadillo (Dasypus novemcinctus), and skunk (Mephitis mephitis); 4 unfenced plots served as controls. We monitored nests for survival through hatching and used radio-telemetry to examine hatchling survival. We radio-tracked 40 hatchlings for up to 329 days, but we were only able to track 8 individuals from a single nest at an unfenced plot because of high nest predation. Mean nest survival was greater at exclosures than at unfenced controls (F_{1, 2} = 45.80, P = 0.0001). Hatchling survival differed (χ² = 5.839, P = 0.016) between unfenced plots (37.5%) and exclosures (74.4%), suggesting that mammals also were significant predators of hatchlings. The number of juvenile (<13 cm in diameter) and subadult tortoise burrows (13–21.9 cm) increased over a 6-year period in exclosures, providing further support for an effect of excluding mammalian predators on nest and juvenile tortoise survival. © 2012 The Wildlife Society.     

Nest Predation Management: Effects on Reproductive Success in Endangered Shorebirds

Abstract Many species have suffered population declines through loss of suitable habitat. In addition, current agricultural land use and human settlements favor generalist predators, which pose an increasing threat to ground-nesting bird species such as shorebirds (waders). During the last 2 decades, nest exclosures have been used to control nest-predation rates and often improved hatching success. We evaluated the effectiveness of protective nest-cages to boost reproductive success in the endangered southern dunlin (Calidris alpina schinzii) and ultimately to halt the population decline. We found that exclosures successfully increased the survival probability of nests and, thereby, the number of hatchlings, without markedly elevating the predation rate on incubating adults. Nest exclosures did not, however, translate into an increased number of fledglings and recruits produced/breeding adult in the population, showing that factors other than nest survival are also important for population development. Our results highlight that conservation efforts aimed only at removing high nest-predation pressure may be insufficient to preserve declining species such as the southern dunlin.     

Nest‐site selection and demography of Wilson's Plovers on a North Carolina barrier island

Despite concerns about their population status, information about the habitat preferences, population size, and vital statistics of Wilson's Plovers (Charadrius wilsonia) is currently lacking. We compared habitat characteristics of nest sites and unused sites and examined factors affecting nest success on a barrier island in North Carolina in 2010 and 2011. We monitored 83 nests with cameras and added heart‐rate monitors in artificial eggs to 36 of these nests for a concurrent study of the effects of jet overflights; predator exclosures were placed around 17 of the nests with cameras. Wilson's Plovers used interdune areas, flats, and isolated dunelets on flats more than expected based on availability, and nests were located closer to dense vegetation than unused sites. Nests in interdune areas had higher daily survival rates than nests on flats, but distance to dense vegetation did not affect nest survival. Nests without cameras, heart‐rate monitors, or exclosures had a 35% predicted probability of hatching at least one egg. Exclosed nests had higher daily survival rates than nests without exclosures, but daily survival rates were lower for nests with cameras or heart‐rate monitors and for nests initiated later in the season. Daily survival rates also declined as nests aged. The predicted probability of fledging was 74%, resulting in a reproductive output of 0.78 fledglings/pair. Apparent annual adult survival was 77%, and the apparent annual survival rate for birds banded as chicks was 42%. Additional research is needed throughout the range of Wilson's Plovers to determine if populations are stable or decreasing, and to predict the productivity rates needed to maintain current populations. However, our results suggest that in our study area, predator removal and protection of sparsely vegetated overwash habitats will likely have the greatest impact on reproductive output.     

Raccoon Removal on Sea Turtle Nesting Beaches

Abstract: Predator removal can be an effective strategy for reducing mortality rates of prey species. Because removal programs must continue indefinitely to remain effective, trapping creates a source—sink dynamic that can alter predator spatial distribution and demography. We investigated the intraspecific effects of predator removal by comparing 2 Florida, USA, raccoon (Procyon lotor) populations that are managed to decrease sea turtle egg mortality. Long-term removal created an extremely male-biased population (>10:1), but the proportion of juveniles did not differ between sites. Stable isotope analyses indicate that raccoons on the removal beach originated from inland habitats. Our results suggest that adult males dominate the recolonization of removal areas and the presence of juveniles on the beach is due to predispersal behavior. Because raccoons are highly omnivorous and mobile, intensive management at a small scale may have broader impacts across the landscape that predator-removal programs should consider.     

Effects of predator treatments,individual traits,and environment on moose survival in Alaska

We studied moose (Alces alces) survival, physical condition, and abundance in a 3-predator system in western Interior Alaska, USA, during 2001–2007. Our objective was to quantify the effects of predator treatments on moose population dynamics by investigating changes in survival while evaluating the contribution of potentially confounding covariates. In May 2003 and 2004, we reduced black bear (Ursus americanus) and brown bear (U. arctos) numbers by translocating bears ≥240 km from the study area. Aircraft-assisted take reduced wolf (Canis lupus) numbers markedly in the study area during 2004–2007. We estimated black bears were reduced by approximately 96% by June 2004 and recovered to within 27% of untreated numbers by May 2007. Brown bears were reduced approximately 50% by June 2004. Late-winter wolf numbers were reduced by 75% by 2005 and likely remained at these levels through 2007. In addition to predator treatments, moose hunting closures during 2004–2007 reduced harvests of male moose by 60% in the study area. Predator treatments resulted in increased calf survival rates during summer (primarily from reduced black bear predation) and autumn (primarily from reduced wolf predation). Predator treatments had little influence on survival of moose calves during winter; instead, calf survival was influenced by snow depth and possibly temperature. Increased survival of moose calves during summer and autumn combined with relatively constant winter survival in most years led to a corresponding increase in annual survival of calves following predator treatments. Nonpredation mortalities of calves increased following predator treatments; however, this increase provided little compensation to the decrease in predation mortalities resulting from treatments. Thus, predator-induced calf mortality was primarily additive. Summer survival of moose calves was positively related to calf mass (β > 0.07, SE = 0.073) during treated years and lower (β = −0.82, SE = 0.247) for twins than singletons during all years. Following predator treatments, survival of yearling moose increased 8.7% for females and 21.4% for males during summer and 2.2% for females and 15.6% for males during autumn. Annual survival of adult (≥2 yr old) female moose also increased in treated years and was negatively (β = −0.21, SE = 0.078) related to age. Moose density increased 45%, from 0.38 moose/km² in 2001 to 0.55 moose/km² in 2007, which resulted from annual increases in overall survival of moose, not increases in reproductive rates. Indices of nutritional status remained constant throughout our study despite increased moose density. This information can be used by wildlife managers and policymakers to better understand the outcomes of predator treatments in Alaska and similar environments. © 2011 The Wildlife Society.     

No evidence of nonlinear effects of predator density,refuge availability,or body size of prey on prey mortality rates

Predator density, refuge availability, and body size of prey can all affect the mortality rate of prey. We assume that more predators will lead to an increase in prey mortality rate, but behavioral interactions between predators and prey, and availability of refuge, may lead to nonlinear effects of increased number of predators on prey mortality rates. We tested for nonlinear effects in prey mortality rates in a mesocosm experiment with different size classes of western mosquitofish (Gambusia affinis) as the prey, different numbers of green sunfish (Lepomis cyanellus) as the predators, and different levels of refuge. Predator number and size class of prey, but not refuge availability, had significant effects on the mortality rate of prey. Change in mortality rate of prey was linear and equal across the range of predator numbers. Each new predator increased the mortality rate by about 10% overall, and mortality rates were higher for smaller size classes. Predator–prey interactions at the individual level may not scale up to create nonlinearity in prey mortality rates with increasing predator density at the population level.     

Influence of Population Reduction on Predator Home Range Size and Spatial Overlap

ABSTRACT The increasing populations of red foxes (Vulpes vulpes), raccoons (Procyon lotor), and striped skunks (Mephitis mephitis) in the Intermountain West have contributed to low waterfowl recruitment in recent decades. This effect prompted the need for predator removal at many waterfowl refuges, such as the Bear River Migratory Bird Refuge (BRMBR) in the Great Salt Lake ecosystem. Our study examined the effects of the removal of predatory mammals at the BRMBR on the home range size and spatial overlap of the remaining populations of red foxes, raccoons, and striped skunks. The removal of predators through traps, snares, and night-shooting created a lower predator population during the predators' rearing and dispersal seasons. Predator removal did not result in a change of home range size for red foxes, raccoons, or striped skunks. In all species, home ranges were of similar size during the rearing and dispersal seasons and there were no differences among sexes. After predator removal, the proportion of a home range that overlapped with that of another conspecific decreased in foxes but increased in raccoons. However, predator removal did not change the proportion of inter-specific home range overlap between foxes and raccoons. These findings indicate that home range sizes of these mammalian predators were not constrained by their population densities prior to predator management. In this situation, predator control may be only temporarily successful in reducing predator populations. Managers may achieve more permanent reduction in predator population by decreasing food and shelter resources, thereby reducing the carrying capacity of the landscape.     

Competitive interactions among two specialist predators and a generalist predator of hemlock woolly adelgid, Adelges tsugae (Hemiptera: Adelgidae) in south-western Virginia

1 Competitive interactions among two specialist predators, Laricobius nigrinus and Sasajiscymnus (Pseudoscymnus) tsugae, and a generalist predator, Harmonia axyridis Pallas, of hemlock woolly adelgid, Adelges tsugae were evaluated in hemlock stands in south‐western Virginia. The two specialist predators are part of a biological control program for A. tsugae, and the potential for competition among these species and previously established generalist predators in the field is unknown. 2 Adult predators were evaluated in branch cages during spring and summer at two field sites infested with A. tsugae. Using females only in 2003 and sexual pairs in 2004, predator survival and net reproduction were examined, as well as their feeding and impact on A. tsugae when present alone and in conspecific and heterospecific groupings. 3 Predator survival was not affected by the presence of additional predators. Total feeding was greater for all species when placed in predator groupings, suggesting that interactions do not significantly interfere with feeding activity. Net reproduction per predator was negatively affected by conspecifics, but unaffected by heterospecifics, indicating that direct or indirect intraspecific interference may occur. In spring, L. nigrinus showed the greatest impact on A. tsugae, and H. axyridis had the greatest impact during summer. 4 These results suggest that it would be beneficial to utilize multiple predator species combinations over single species when implementing biological control for A. tsugae. Low‐density releases are also recommended to reduce intraspecific interference.     

Food availability and nest predation influence life history traits in Audouin's gull, Larus audouinii

The effects of food availability and nest predation on several life history traits such as adult survival, dispersal, and reproductive performance were assessed in an Audouin's gull (Larus audouinii) colony during the period 1992–1997. The amounts of fish discarded from trawlers were used as a measure of food availability, and a trawling moratorium which partially overlapped with the breeding season of the gulls was taken into account. The effects of nest predation were assessed in 1994, when a terrestrial predator entered the colony and remained for the whole breeding season preying on both eggs and chicks. Using the moratorium and the predatory event as natural experiments, several hypotheses were tested: (a) food supply would affect breeding performance but not adult survival (independently of age and sex), since gulls are long-lived and adult survival is the most sensitive demographic parameter in their population dynamics; (b) the predator would trigger breeding dispersal (although gulls are mostly philopatric, they are known to abandon their natal colony after breeding failure instigated by events such as this). If breeding dispersal occurs, the rate is expected to be higher in females than in males, and higher in new breeders than in more experienced breeding birds, as is usually recorded in colonial seabirds. Probabilities of resighting and survival were estimated separately, using capture-recapture models. As expected, changes in food availability did not affect adult survival, whereas they influenced egg volume, clutch size, and breeding success. Local adult survival was estimated to be 0.908 (SD = 0.007) for males and females, and it did not change significantly with the age of individuals (range 3–8 years). The predator significantly decreased breeding success, and caused the dispersal of a number of adults probably to breed in another colony; this rate was estimated at an average of 0.10 (SD = 0.02). As expected, inexperienced breeders dispersed significantly more (14%) than more experienced breeders (8%) after the predator event, but dispersal was not sex biased. Recapture probabilities after the predator event suggest that birds that left the colony still had not returned. Results confirm that population dynamics of ground-nesting seabirds are sensitive to terrestrial predation, even when predation caused only a partial breeding failure. Received: 16 July 1998 / Accepted: 16 November 1998     

The Feeding Behaviour of a Sit and Wait Predator Ranatra dispar (Heteroptera: Nepidae): The Effect of Prey Density and Age Structure on the Number of Prey Eaten

Functional response experiments were performed in the laboratory to examine the effect of prey density (as observed in the field) on feeding behaviour, and to measure handling-times and attack-rates for each instar and adult of Ranatra dispar Montandon (Heteroptera: Nepidae) feeding on five size-classes of its common prey, Anisops deanei Brooks (Heteroptera: Notonectidae). The most generally applicable response was the Type 2, although for both the predator fifth instar and adult female and male feeding on the two smallest prey sizes, the asymptote or plateau was not observed even at the highest prey density given. Generally, the handling-time increased as prey-size increased, and decreased as the predator size increased. The attack-rate surface was far more complex. For the first two predator instars (I and II), the maximum attack-rate occurred on the smallest prey sizes (1 and 2). The maximum attack-rate for predator instar III was almost the same for prey sizes 1 and 2, that of predator instar IV was greater for prey size 2, while in the three largest predator sizes (V, female and male), the maximum attack-rate was found for prey size 3. Predator instar V had the largest attack-rate values over all prey sizes, and both the predator adult female and male had lower attack-rates for various prey sizes than instars V, IV and, to some degree, III. The results support the suggestion that small predator instars will usually compete with large instars for prey, unless they are spatially or temporally separated. Observations in the field indicate that a distinct age-specific spatial distribution exists in R. dispar and the prey, A. deanei, with the smallest individuals being found predominantly in the shallow (littoral zone) water, while the larger individuals are found in the deeper water.     

Application of predator-associated cues to control small brown planthoppers: non-consumptive effects of predators suppress the pest population

Predator non-consumptive effects (NCEs) have been well studied in many ecosystems and NCEs can alter the behavior, morphology and life history of prey, producing strong trait-mediated indirect effects (TMIEs) on host plants. However, studies involving the application of NCEs to control pests in the field, and instances of combined laboratory bioassay and field practice are rare. Here, we examine the development, reproduction and behavior of small brown planthoppers, Laodelphax striatellus (Fallén), when exposed to predator cues from caged predators (Paederus fuscipes Curtis), or predator body extracts (in solvents with different polarities) in the laboratory. Field foliage sprays of these extracts were also used to test their effects on the L. striatellus population and rice plant biomass. Nymph development and egg hatch rate in L. striatellus were not influenced, but adult longevity was shorter, and fecundity and weight gain were lower, when nymphs were exposed to the predator cues. Adults exposed to predator cues also gained less weight and laid fewer eggs. The poorer developmental and reproductive performances might result from lower activity levels observed in threatened L. striatellus. The field foliage sprays of predator cues decreased L. striatellus abundance and increased rice plant biomass, suggesting their possible application for pest control. Predator cues extracted using chloroform increased stronger NCEs and TMIEs, indicating their non-polar characteristics. Our studies advance the understanding of how NCEs shape the life history and behavior of L. striatellus and improve rice growth, laying new foundations for future research on novel pest control materials and methods.

     

Gregariousness affects performance and defensive reactions in swallowtail caterpillars

1. Group living in caterpillars may enhance individual performance due to sharing of costs associated with individual tasks when dealing with biotic or abiotic ecological factors. 2. In the gregarious caterpillar Battus polydamas archidamas (Papilionidae) egg clusters and caterpillar groups vary in size. We hypothesized that individual survival would be higher in larger groups and that group living would enhance individual performance: shorter development time and/or reduced frequency of (presumably costly) defensive reactions in larvae and larger adult size. We also tested whether the group size conferring the highest survival to laboratory-reared caterpillars matched the most frequent egg clutch size in the field. 3. We collected egg clutches in the field and reared caterpillars in groups of 1, 6, 10, and 14 individuals. We quantified larval survival and stage duration as well as adult mass under laboratory conditions, excluding natural enemies. We also recorded the frequency of larval defensive reactions (thrashing and osmeterium display) against a tactile stimulus of first-instar larvae. 4. Group living enhanced caterpillar survival, particularly during the first instars, when caterpillars are 100% gregarious. Groups of intermediate size reduced larval development time but group living did not affect adult mass. Individual caterpillars in groups showed defensive reactions less frequently than solitary individuals, revealing a cost-saving feature of gregariousness for this swallowtail species. The most frequent clutch size in the field (9–10 eggs) did not match the larval group with highest survival (14 individuals), but did match the group with shortest development time.