TY - JOUR
AU1 - Harshaw, Lauren
AU2 - Chrisawn, Charlie
AU3 - Kittinger, Benjamin
AU4 - Carlson, Jessica
AU5 - Metz, Grace
AU6 - Smith, Leslie
AU7 - Paradise, Christopher J.
AB - Abstract Treeholes are detritus-based communities, and resource quantity and quality play a large role in structuring such communities. The primary resource is leaf litter, but decaying invertebrates also are a resource to treehole inhabitants. These communities are subject to a variety of disturbances, which may affect resources or cause widespread mortality. When dead inhabitants decay, they provide a potentially high-quality resource to survivors or subsequent colonists. We predicted that variation in decaying larvae (0, 7.3, and 29.2 mg/liter) and leaf litter (1, 5, and 10 g/liter) would influence the performance of populations of Aedes triseriatus (Say), the eastern treehole mosquito. We tested this prediction in field mesocosms, which were subjected to a freezing event causing widespread mortality of the scirtid beetle Helodes pulchella Guerin. We then added a cohort of first instar mosquitoes to mesocosms, and we monitored their development from March until June 2005. At the highest leaf litter level, survival, adult mass, and time to complete development were unaffected by decaying scirtids, and they were different from treatments with lower levels of leaf litter. In treatments with 1 and 5 g/liter leaf litter and decaying scirtids, mosquito survival and adult mass were higher than in treatments with 1 and 5 g/liter leaf litter and no decaying scirtids. At 5 g/liter leaf litter, a higher mass of dead scirtids was required to significantly increase adult mass. Faster decay of carcasses and release of limiting nutrients likely spur growth of microorganisms, upon which mosquitoes feed. Invertebrate populations in high-disturbance communities may be subject to high mortality, and mosquitoes hatching after the disturbance will benefit, but only when other resources are limiting. Aedes triseriatus, Helodes pulchella, resource quantity and quality, leaf litter, treeholes The state and availability of resources can have a variety of density-dependent effects at both the population and community levels (Naeem 1988, Hunter and Price 1992, Walker et al. 1997, Srivastava and Lawton 1998, Paradise 1999). Allochthonous plant material represents the major input of energetic resources to many freshwater detritus-based habitats (Petersen and Cummins 1974, Fish and Carpenter 1982, Paradise and Dunson 1997, Walker et al. 1997, Wallace et al. 1997). Drowned terrestrial arthropods represent another source of energy and nutrients; they may be a critical source of protein to these habitats (Daugherty et al. 2000, Yee and Juliano 2006), and such high-quality resources may be limited temporally or due to competition (Wallace and Merritt 2004). In water-filled treeholes or other phytotelmata, these two types of inputs can be highly heterogeneous (Fish and Carpenter 1982, Kitching 2000, Daugherty and Juliano 2002, Paradise 2004, Yee and Juliano 2006), and, in addition, larvae inhabiting such habitats may die and decompose, providing nutrients to survivors and enhancing growth of microorganisms (Daugherty et al. 2000). Southeastern U.S. treeholes are dominated numerically by larvae of the eastern treehole mosquito Aedes triseriatus (Say) (Lounibos 1983; Bradshaw and Holzapfel 1984; Harlan and Paradise 2006; Burkhart et al., unpublished data), a filter feeder and browser that consumes small particulate matter and microbes (Merritt et al. 1992). The scirtid beetle Helodes pulchella (Guerin) is also a common resident of southeastern U.S. treeholes and is a leaf shredder (Barrera 1996, Paradise 2004). Scirtids can potentially affect treehole communities, and growth of Ae. triseriatus, in one of four ways. First, particulate or dissolved organic matter increases as scirtids shred leaf litter, because not all particles are consumed by scirtids (Daugherty and Juliano 2002). Second, as scirtids process litter they also may increase the surface area available for microorganism growth. This can be important because microbes form a significant part of the diet of treehole detritivores (Maguire 1971, Walker et al. 1991, Daugherty et al. 2000, Kaufman et al. 2000). Third, fecal production by scirtids could increase resource availability as resources are changed from litter to feces (Daugherty and Juliano 2003). Fourth, dead scirtids, as they decay, could provide resources to microbes and other insects (Daugherty et al. 2000). Scirtid and Ae. triseriatus densities are positively correlated in natural treeholes, and both tend to be in higher abundance in larger habitats that collect more leaf litter (Paradise 1997, Daugherty and Juliano 2001, Paradise 2004), suggesting the potential for interaction. Initially, we set out to test hypotheses regarding the effects of scirtid shredding on populations of Ae. triseriatus under conditions of varying leaf litter levels and densities of scirtid beetle larvae. A freeze in January 2005 killed all or most of the scirtids that we added to our mesocosms the previous November. We used this as an opportunity to determine the effects of variation in different kinds of resources (leaf litter and decaying scirtids) on populations of Ae. triseriatus in a field experiment. Mosquito larval growth is known to be affected by resource levels (Fish and Carpenter 1982, Léonard and Juliano 1995, Walker et al. 1997, Paradise 1999), but most studies have examined plant detritus as the resource. Exceptions exist, such as the studies of Daugherty et al. (2000) and Yee and Juliano (2006), which showed positive effects of invertebrate carcasses on growth of container-breeding mosquitoes. In addition, there have been studies in other analogous container habitats, such as pitcher plants, where invertebrates comprise the primary resource (Maguire 1971, Heard 1994, Kitching 2000). Decaying invertebrate carcasses could thus be an important resource for container-breeding larvae, but past studies have not tested for facilitative effects of carcasses in cases of limiting plant detritus, and they have all been laboratory studies. Given that disturbances, such as drought, flooding, or freezing are common in treeholes (Bradshaw and Holzapfel 1988, Jenkins et al. 1992, Paradise 1997, Aspbury and Juliano 1998, Paradise 2004), larval mortality can be high (Aspbury and Juliano 1998). Animals that die and decay in treeholes could contribute higher levels of limiting nutrients, such as nitrogen, to microbes and surviving insects than decomposing vegetation, and they could decompose more quickly than leaves (Yee and Juliano 2006). The effects of decaying insect carcasses on surviving larvae or larvae that hatch and develop postdisturbance are not well known. The disturbance that occurred during the initial phase of this field mesocosm experiment allowed us to ask how the resulting high mortality of one species affected the subsequent growth and survival of a species that colonized the containers after the disturbance. Materials and Methods We created mesocosms using 7.62-cm internal diameter polyvinyl chloride (PVC) pipe cut into 11-cm lengths. We affixed fiberglass window screening to the inside of the pipe by overlapping it beyond the two ends (Paradise 2006). The screen created a textured inner surface and darkened the interior, promoting insect oviposition and allowing scirtids to crawl to the top for air. We used silicon caulk to seal on an end cap, which held the overlapping screen in place at the bottom. At the top, a PVC coupling that was sawed in half sealed the overlapping screen in place, and the coupling and screen were caulked in place. The total capacity of each mesocosm was ≈540 ml. We attached mesocosms in pairs to a frame with expandable polyurethane foam. Frames were ≈50 cm in width by 35 cm in height by 25 cm in depth, and they were made using 1.5-cm PVC pipe. The back end of the frame was left open for attachment to trees. We flushed mesocosms several times in the laboratory over 3 wk to remove any volatile chemicals. The frames were tied to trees with nylon clothesline in a hardwood forest on the Davidson College Ecological Preserve (DCEP, Davidson, NC; 30° 30′ 30″ N, 80° 49′ 45″ W) in August and September 2004. We glued fiberglass window screen (2-mm mesh) to the top of each frame, ≈25 cm above the mesocosms, to reduce the amount and size of debris that dropped into mesocosms (Paradise 2006). Finally, we wrapped each frame and the trunk of its tree in 2.5-cm mesh wire for protection, and we made a hinged door on the front of the cage. One of 10 treatment combinations was randomly assigned to each mesocosm. We used three levels of leaf litter crossed with three levels of scirtid density, all within the natural ranges found in treeholes (Paradise 2004), with five replicates of each treatment combination. We eliminated the treatment with high scirtid density and low leaf litter, because that combination leads to low scirtid survival (Burkhart et al., unpublished data), yielding eight treatment combinations. The three levels of leaf litter added were 1, 5, and 10 g of dried red oak, Quercus rubra L., leaves per liter (low, intermediate, and high, respectively), collected in September 2004. We then added medium-sized scirtids (mostly second instar) that were collected from a large basal treehole on the Davidson College Ecological Preserve at three densities: 0, 20 (7.3 ± 0.5 mg), and 80 (29.2 ± 2.2 mg; none, low, and high, respectively). We obtained estimates of dry mass from two sets of 20 larvae set aside for this purpose. The final two treatments consisted of three mesocosms each supplied only with 3 g/liter of dried treehole sediment and water, with one set containing 20 scirtids per liter and the other set with no scirtids. We have observed scirtids in treeholes with little or no leaf litter, so the latter two treatments were used to determine whether scirtids facilitated mosquitoes in the absence of leaf litter. The experiments conducted comply with the current laws of the United States of America. In late October 2004, leaf litter, a small aliquot of filtered treehole water, and ≈500 ml of distilled water to within 2 cm of the top were added to each mesocosm, which were then covered with thick plastic secured with cable ties. On 8 November 2004, scirtids were added at the appropriate densities. Mesocosms were then covered with no-see-um netting secured with cable ties. The netting allowed gas exchange, but it prevented colonization by insects. The mesocosms remained in this state through the winter. Unusually cold weather in January 2005 froze the water in all containers solid, an unlikely event for our containers in North Carolina. Most, if not all, scirtids died as a result. In early March 2005, water from a set of mesocosms set out as oviposition traps was brought back to the laboratory, from which first instars of mosquitoes were collected. The eggs laid the previous autumn had hatched under warm, wet conditions in late February. We then added 25 first instars to each mesocosm. No-see-um netting was left on the mesocosms to prevent escape of emerging mosquitoes or colonization by other insects. We observed mesocosms weekly to track development of mosquitoes, and we added distilled water to maintain constant water levels. When mosquito larvae reached the fourth instar, we began to observe mesocosms more frequently, once every 2 to 3 days. When adults began to emerge, we checked each mesocosm every other day, and we used an aspirator to extract adults. There was a small air space above the water and below the screen lid in which adults rested. We gently removed the cable tie and lifted the screen to insert the aspirator tube for extraction of adult mosquitoes. This method was ≈98% effective, with very few adults escaping. Species and sex of the adults were identified before extraction as a precaution in case any adults escaped. Captured adults were returned to the laboratory, where we froze, dried, weighed on a Mettler MT5 microbalance (Mettler Instrument Corp., Hightstown, NJ), and we identified them as to their species and sex (Slaff and Apperson 1989). When mosquito emergence had essentially stopped in early June 2005, we removed all water and leaf litter from each mesocosm, and we carefully looked through all of it to extract remaining mosquitoes and scirtids. All scirtids had died, and we found no remaining mosquito larvae or pupae. The wet masses of leaf litter and coarse particulate organic matter (CPOM > 1 cm2) were measured using an Acculab Pocketpro 250B portable digital balance (Acculab, Edgewood, NY). We brought all leaf litter and coarse particulate matter back to the laboratory to measure dry mass of leaf litter. More than 98% of mosquitoes extracted were Ae. triseriatus, with the remainder being Aedes japonicus (Theobald). It is possible that some Ae. triseriatus were, in fact, Aedes hendersoni Cockerell, but our observations of fourth instars in other experiments indicate that it is uncommon in our study area and containers (using Slaff and Apperson 1989). We analyzed for effects of the invasive Ae. japonicus by using analysis of variance (ANOVA) to compare mesocosms from the same treatment combination with and without A. japonicus. There was no pattern to the occurrence of A. japonicus, and there was no effect of A. japonicus on any A. triseriatus response variable. In computing cumulative measures, such as proportion survival or total biomass, we eliminated A. japonicus individuals from the analysis. We then recalculated proportion survival based on the new total number of Ae. triseriatus, and we rescaled biomass using the new proportion survival to estimate the number of males and females that would have emerged if all 25 first instars were Ae. triseriatus, and multiplying that by the average biomass of males and females. We performed this for 16 mesocosms that produced either one or two Ae. japonicus. We analyzed the arcsine-transformed proportion survival using a one-way ANOVA (Minitab, Inc. 2000), with treatment combination (plant detritus level, dead scirtid level) as a fixed effects factor. We could not analyze interactions in this experiment because of the less than factorial design—not every level of scirtid density was crossed with every level of resource. For mass of Ae. triseriatus adults and length of their larval developmental period, we used a nested repeated measures ANOVA, using measurements on mosquitoes within each mesocosm as a random effects factor nested within treatment, and the leaf litter/scirtid density treatment combination as a fixed effects factor. This is because multiple measurements were made from each mesocosm—the individual mosquitoes are the measurement units, not the replicate mesocosms. We also used date of collection as a random effects factor for the mass ANOVAs. Mass was log transformed to achieve a normal distribution. For each mosquito response variable, we ran the models with and without the two sediment treatments. Although we were interested in the effects of sediment and the possible facilitation of dead scirtids in limiting detritus habitats, some responses of mosquitoes in sediment treatments were far different from those in leaf litter treatments, and this may unduly influence the statistical results. For each ANOVA, Tukey pairwise comparisons were performed (Minitab, Inc. 2000). Finally, we analyzed the arcsine-transformed proportion leaf litter mass lost using a one-way ANOVA, and we graphically examined the absolute change in leaf litter dry mass. We used a Bonferroni correction for the number of response variables (adjusted α = 0.05/6 = 0.0083). All data were tested for univariate normality and heteroscedasticity, and transformations were used where appropriate, as noted above. Results In total, 852 mosquitoes emerged from 46 mesocosms, which is a 74% experiment-wise emergence yield. Of those 852 mosquitoes, 830 were Ae. triseriatus and 22 were Ae. japonicus. Thus, 97.4% of the total emerging mosquitoes were Ae. triseriatus. Analysis of mesocosms with Ae. japonicus yielded no trends in terms of effects on Ae. triseriatus (data not shown). Twenty adult mosquitoes escaped while extracting them from mesocosms, but all of them were judged to be Ae. triseriatus before opening mesocosms. Of the 810 Ae. triseriatus brought back to the laboratory, we were able to measure the mass of 752 adult Ae. triseriatus (309 females and 443 males). Survival of A. triseriatus was equivalent to emergence and was significantly affected by treatment, and the differences among leaf litter treatments were the same with or without the sediment treatments included in the analysis (Tables 1 and 2; Fig. 1). The three treatments with the highest level of leaf litter (10 g/liter) had ≥80% survival of mosquitoes (Fig. 1). The two treatments with the highest level of both leaf litter and dead scirtids had the highest average survival, and these treatments had significantly higher survival than the two treatments without scirtid carcasses and with the lowest levels of plant detritus (3 g/liter sediment and 1 g/liter leaf litter). The only other treatment with >80% total survival was intermediate leaf litter (5 g/liter) with no scirtids (Fig. 1). Table 1 Statistical results of ANOVAs on all 10 treatment combinations for adult Ae. triseriatus response variables Open in new tab Table 1 Statistical results of ANOVAs on all 10 treatment combinations for adult Ae. triseriatus response variables Open in new tab Fig. 1 Open in new tabDownload slide Average proportion survival for Ae. triseriatus adults across ten combinations of resources (n = 3 for sediment treatments; n = 5 for leaf litter treatments). Similar letters above bars indicate statistical equivalence for all ten treatments. The letters above leaf litter treatments also indicate statistical equivalence for ANOVA with just those treatments. Open bars represent treatments without dead scirtids, gray bars represent treatments with low densities of dead scirtids (20 per liter), and black bars represent treatments with high densities of dead scirtids (80 per liter). Sed, sediment, and numbers in x-axis labels refer to leaf litter treatment level. Error bars are ± 1 SE. The length of the developmental period for males was significantly different among treatments, as was mass for both males and females (Tables 1 and 2). The pattern of differences among treatments was the same with or without sediment included in the analysis, although pairwise comparisons are shown for ANOVAs with all 10 treatments only (Figs. 2 and 3). Males from the sediment treatment were in between the low and intermediate leaf litter treatments in terms of size and emergence date (Fig. 2a). However, there was no effect of scirtids on mosquito mass, either males or females, in the presence of sediment, in comparison with sediment alone (Fig. 2). Scirtid carcasses significantly enhanced mass of mosquitoes when leaf litter was low or intermediate (1 or 5 g/liter), although a high density of scirtid carcasses was required to make a significant difference at 5 g/liter, compared with 5 g/liter and no dead scirtids (Fig. 2). This was true for both males and females. In addition, adults from high leaf litter (10 g/liter) and 5 g of leaf litter and 80 dead scirtids per liter were significantly larger than all other treatments, except for females from 5 g of leaf litter and 20 scirtids per liter. Scirtid carcasses did not enhance mass in high leaf litter treatments. Scirtid carcasses lead to shorter developmental periods only for males within sediment treatments and at 5 g of leaf litter/liter when density of scirtid carcasses was high (Fig. 3a). Average developmental periods for females, however, did not vary with leaf litter amount or density of scirtid carcasses; they were all within a day of each other (Fig. 3b). Fig. 2 Open in new tabDownload slide Average dry mass of Ae. triseriatus adults for each treatment combination (n ranges from 13 to 47 for females and from 15 to 66 for males, pooled across replicates). Similar letters above bars indicate statistical equivalence for all ten treatments. The letters above leaf litter treatments also indicate statistical equivalence for ANOVA with just those treatments. Open bars represent treatments without dead scirtids, gray bars represent treatments with low densities of dead scirtids (20 per liter), and black bars represent treatments with high densities of dead scirtids (80 per liter). Sed, sediment, and numbers in x-axis labels refer to leaf litter treatment level. (a) Males. (b) Females. Error bars are ± 1 SE. Fig. 3 Open in new tabDownload slide Average developmental period of A. triseriatus adults for each treatment combination (n ranges from 13 to 47 for females and from 15 to 66 for males, pooled across replicates). Similar letters above bars indicate statistical equivalence for all ten treatments. The letters above leaf litter treatments also indicate statistical equivalence for ANOVA with just those treatments. Open bars represent treatments without dead scirtids, gray bars represent treatments with low densities of dead scirtids (20 per liter), and black bars represent treatments with high densities of dead scirtids (80 per liter). Sed, sediment, and numbers in x-axis labels refer to leaf litter treatment level. (a) Males. (b) Females. Error bars are ± 1 SE. Table 2 Statistical results of ANOVAs on leaf litter treatment combinations only for adult Ae. triseriatus response variables Open in new tab Table 2 Statistical results of ANOVAs on leaf litter treatment combinations only for adult Ae. triseriatus response variables Open in new tab Generally, treatments with heavier adults also had higher cohort survival, with at least 70% survival. The relationship between mass and survival led to significantly higher total biomass from treatments with high leaf litter in comparison with the two sediment treatments and the low leaf litter treatment with no dead scirtids (Fig. 4; Tables 1 and 2). In addition, presence of scirtid carcasses significantly enhanced total mosquito production in the 1 g of leaf litter/liter treatment. Fig. 4 Open in new tabDownload slide Average cumulative biomass production of A. triseriatus emerging from mesocosms (n = 3 for sediment treatments; n = 5 for leaf litter treatments). Similar letters above bars indicate statistical equivalence for total adult biomass. The letters above leaf litter treatments also indicate statistical equivalence for ANOVA with just those treatments. Open bars represent treatments without dead scirtids, gray bars represent treatments with low densities of dead scirtids (20 per liter), and black bars represent treatments with high densities of dead scirtids (80 per liter). Sed, sediment, and numbers in x-axis labels refer to leaf litter treatment level. Error bars are ±1 SE. No scirtids were alive at the end of the experiment (June 2005). We found that the proportion of leaf litter mass lost did not vary within a leaf litter level—scirtids did not survive long enough to significantly affect leaf litter decay. But the proportion of mass lost was higher for low leaf litter than for high leaf litter and the intermediate leaf litter/no scirtid treatment (F = 8.71; df = 7, 32; P < 0.001) (Fig. 5). Fig. 5 Open in new tabDownload slide Average proportional mass lost for each leaf litter treatment combination (n = 5 per treatment). Open bars represent treatments without dead scirtids, gray bars represent treatments with low densities of dead scirtids (20 per liter), and black bars represent treatments with high densities of dead scirtids (80 per liter). Error bars are ± 1 SE. Discussion Our mesocosms were exposed to a disturbance that allowed us to examine how growth of a cohort of mosquitoes is affected by quantity and type of resource, decaying leaf litter and insect carcasses. We demonstrated that the presence of decaying scirtids had a positive impact on A. triseriatus under conditions of limiting litter availability. The facilitation here is primarily on adult size; developmental period was unaffected by scirtid carcasses within a leaf litter level. Leaf litter quantity is highly variable, over time and among treeholes (Carpenter 1983, Kitching 1987, Kitching and Beaver 1990, Paradise 2004). Plant detritus is low in quality, in that it often has low levels of nutrients, such as nitrogen (Kitching 2000). Furthermore, treeholes are subject to a high frequency of disturbances, such as freezing and drought, and this can affect survival of individuals (Kitching 1987, Bradshaw and Holzapfel 1988, Jenkins et al. 1992, Paradise 1997). Our experimental design simulated the situation where mosquito eggs are laid above the waterline, overwinter, and hatch in spring when rains fill treeholes. Mosquitoes with such a strategy thus avoid freezing in ice during the winter. Scirtids, however, overwinter as larvae (Barrera 1988, Paradise 1997). It is likely that significant scirtid mortality occurred during the hard freeze in January 2005, because we observed very few scirtids at the time of mosquito addition, and no scirtids were recovered from any mesocosm. Furthermore, scirtid effects on Ae. triseriatus are due to carcass decay, because we did not observe any scirtid effects on leaf decay. Other disturbance scenarios exist, including situations where freezing or drought occurs after mosquito eggs have hatched (Bradshaw and Holzapfel 1988, Aspbury and Juliano 1998). A majority of early instars of mosquitoes would then be killed, as would any overwintering larvae. These decaying carcasses would then provide nutrients to microorganisms and other insects that survive or colonize thereafter. The decaying animal carcasses resulting from such disturbances might be essential in providing nutrients and enhancing growth of microorganisms, which may then enhance growth of insect detritivores (Daugherty et al. 2000, Kaufman et al. 2000). How frequently large numbers of larvae die as a result of disturbance before or after mosquito egg hatch is unknown, but either freezing followed by warm weather and rains, or a drought followed by rain would have the same beneficial effect to mosquito populations. High levels of detritus can produce many large mosquitoes (Fish and Carpenter 1982, Walker et al. 1997, Paradise 2000), and we confirm that in our high leaf litter treatments. High leaf litter availability increases size and decreases developmental time of individual larvae and increases production of entire mosquito cohorts (Fish and Carpenter 1982, Carpenter 1983, Léonard & Juliano 1995, Walker et al. 1997, Paradise 1999). We obtained similar results in our leaf litter treatments in the absence of decaying scirtids, at least for adult mosquito mass. Mosquitoes reared under conditions of high leaf litter, regardless of the number of decaying scirtids added, were larger than adult mosquitoes that emerged from most other treatments, and combined with high proportion survival in those high detritus treatments, produced more total biomass. As we predicted, decaying scirtids did not enhance mosquito growth at high leaf litter, because the positive effects of decaying invertebrate carcasses is much lower when detritus is abundant. At high leaf litter levels, abundance of dissolved nutrients and microorganisms may be sufficient to allow high growth rates of insect larvae without additions of animal detritus (Kaufman et al. 2000). Our prediction that survival, growth rates, and adult size of mosquitoes would be enhanced in treatments with decaying scirtids, in comparison to equivalent leaf litter treatments without beetles, was strongly supported for mass of adults only. Developmental time was not as strongly affected, likely due to the overall slow development of all cohorts. The reason for this is the cool spring temperatures, especially cooler nights, experiences in March and April in North Carolina. This prevented water temperatures from rising, leading to slow growth of larvae. Within the low and intermediate leaf litter levels, presence of scirtids had a density-dependent effect on adult mass; mosquitoes were significantly larger when scirtid carcasses were present, compared with the same resource level in the absence of scirtids. Treeholes have been found to contain very little or no leaf litter (Paradise 1997, Walker and Merritt 1988), suggesting severe resource limitations. Overall, low quantities of plant detritus, especially without any decaying scirtid carcasses, lead to low production of mosquito populations, supporting the contention that those conditions are limiting to mosquito growth, and likely to be limiting to other treehole inhabitants. At the two lower levels of leaf litter, the masses of mosquitoes were similar to the next higher leaf litter treatments only when supplemented with decaying scirtids. More insects decaying provides more resources, in the form of nutrients and microorganisms, to growing mosquitoes (Yee and Juliano 2006). The benefits to mosquitoes of being in a habitat where high densities of decaying invertebrate carcasses occur are thus mostly size benefits, at least in the conditions of our experiment. Female size and fecundity in mosquitoes are positively related, and larger females have higher adult survival, produce more eggs (Livdahl 1984, Hawley 1985), and have a higher probability of completing the blood-feeding cycle (Haramis 1985). Additionally, large males tend to live longer than small males, all else being equal (Benjamin and Bradshaw 1994). Female mosquitoes experience greater fitness benefits than males by achieving large size, but male fitness is only marginally affected by mass and is more significantly affected by time to pupation (Lounibos et al. 1993). Males are known to minimize time to pupation and pupate at smaller mass under conditions of low resources (Kleckner et al. 1995), but we only observed effects on mass. We conclude that substantial fitness benefits are conferred to Ae. triseriatus larvae inhabiting a container with a high density of decaying larvae, but only when leaf litter levels are below a level that completely fills the treehole. Disturbances that cause high mortality of larvae, such as a freeze or drought, could provide substantial nutrients and energy to subsequent colonists. The benefit is not observed under conditions of high leaf litter; this condition by itself is sufficient to lead to high survival and large individual size of a cohort of mosquito larvae. This effect is not altogether surprising, given the strong leaf litter effects found in other experiments (Fish and Carpenter 1982, Léonard and Juliano 1995, Walker et al. 1997). Differences in adult mass and cohort survival caused by variability in quantity and quality of resources will thus have dramatic consequences on population growth. We conclude that widespread mortality in detritus-based communities subject to extreme disturbances provides those high-quality resources to populations of insect larvae that hatch after a disturbance. Acknowledgements We thank Duncan Berry, John Burkhart, Ben Kegan, Stella Kenyi, and Shawn Villalpando for assistance in the field and with data management and Davidson College for permission to work on the Davidson College Ecological Preserve. This research was supported by National Science Foundation (NSF) grant DEB-0315208 to C.J.P., NSF-REU grant DBI-0139153 to the Davidson College Department of Biology, and a Davidson College Faculty Study and Research grant to C.J.P. References Cited Aspbury A. S. Juliano S. A. . 1998 . Negative effects of habitat drying and prior exploitation on the detritus resource in an ephemeral aquatic habitat . Oecologia (Berl.) 115 : 137 – 148 . Google Scholar Crossref Search ADS WorldCat Barrera R. 1988 . Multiple factors and their interactions on structuring the community of aquatic insects of treeholes . Ph.D. dissertation, The Pennsylvania State University , State College, PA . Barrera R. 1996 . 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Google Scholar Crossref Search ADS PubMed WorldCat © 2007 Entomological Society of America This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/), which permits non-commercial reuse, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial re-use, please contact journals.permissions@oup.com © 2007 Entomological Society of America
TI - Decaying Invertebrate Carcasses Increase Growth of Aedes triseriatus (Diptera: Culicidae) When Leaf Litter Resources Are Limiting 
JF - Journal of Medical Entomology
DO - 10.1093/jmedent/44.4.589
DA - 2007-07-01
UR - https://www.deepdyve.com/lp/oxford-university-press/decaying-invertebrate-carcasses-increase-growth-of-aedes-triseriatus-QNbA01wUPT
SP - 589
EP - 596
VL - 44
IS - 4
DP - DeepDyve
ER -