Egg Abundance Research Articles

Spatial ecology and growth in early life stages of bay anchovy Anchoa mitchilli in Chesapeake Bay (USA)

The bay anchovy Anchoa mitchilli is the most abundant fish in Chesapeake Bay (USA) and is a vital link between plankton and piscivores within the trophic structure of this large estuarine ecosystem. Baywide distributions and abundances of bay anchovy eggs and larvae, and larval growth, were analyzed in a 5 yr program to evaluate temporal and spatial variability based on research surveys in the 1995-1999 spawning seasons. Effects of environmental variability and abundance of zooplankton that serve as prey for larval bay anchovy were analyzed. In the years of these surveys, 97.6% of eggs and 98.8% of larvae occurred in the polyhaline lower bay. Median egg and larval abundances differed more than 10-fold for surveys conducted in the 5 yr and were highest in the lower bay. Within years, median larval abundance (ind. m-2) in the lower bay was generally 1-2 orders of magnitude higher than upper-bay abundance. Salinity, temperature, and dissolved oxygen explained 12% of the spatial and temporal variability in egg abundances and accounted for 27% of the variability in larval abundances. The mean, baywide growth rate for larvae over the 5 yr period was 0.75 ± 0.01 mm d-1, and was best explained by zooplankton concentration and feeding incidence. Among years, mean growth rates ranged from 0.68 (in 1999) to 0.81 (in 1998) mm d-1 and were fastest in the upper bay. We identified environmental factors, especially salinity, that contributed to broadscale variability in egg and larval production.

Composition, Abundance and Distribution of Fish Eggs in Sarawak Exclusive Economic Zone (EEZ) of the South China Sea

Fish eggs are categorised as ichthyoplankton and most pelagic eggs are distributed in or just below the photic zone. The study of the fish egg is crucial in understanding the dynamics of fish populations, but information on fish eggs in the Sarawak exclusive economic zone (EEZ) is still lacking. This study reports the fish eggs composition, abundance and distribution at 38 stations within three zones in the Sarawak EEZ. The eggs were sampled from 19 August to 6 October 2015 using a bongo net (330 μm and 500 μm mesh-size), obliquely towed at a speed of 2 to 3 knots for 20 min. Selected physicochemical water parameters were also collected according to depth profile. Preserved fish eggs were identified to the family level. Density and diversity of fish eggs were calculated. The influence of environmental factors on fish egg abundance according to zone was tested with canonical correspondence analyses (CCA). A total of 3,935 fish eggs belonging to 6 orders and 12 families were successfully collected whereby Carangidae, Clupeidae and Scombridae showed high abundance (>10 %). Highest mean density was recorded at inner neritic zone while the Jaccard’s dissimilarity index ranged from 0 % to 25 % among the three zones. Based on CCA, the abundance of Labridae, Malacostidae, Muraenidae, Scombridae and Sphyraenidae were influenced by environmental factors. The findings of this paper are useful for future fishery management in Sarawak EEZ

Mixed-Species Gardens Increase Monarch Oviposition without Increasing Top-Down Predation.

Simple SummaryThe North American monarch butterfly is an iconic insect that has recently declined by over 80%, largely due to habitat loss. The primary approach to mitigate population declines is to plant milkweed, the primary host plant that monarch caterpillars feed and develop on. Recently, researchers have focused on optimizing monarch conservation habitats (i.e., milkweed plantings) in urban green spaces by studying habitat design and plant species selection. In many cases, as plant diversity increases, predatory and parasitic insect diversity increases and insect herbivore colonization and establishment decrease. We compared milkweed monocultures to a mixture of milkweed and other wildflower species to see what effects plant diversity have on monarchs and potential predators. We found that monarchs laid 22% more eggs on milkweed planted in mixed-species plots than milkweed in monoculture. We also found more predators in the mixed-species plantings, but this did not affect monarch disappearance rates. These results can be used to create evidence-based guidelines for monarch conservation habitats.Monarch butterfly populations have declined by over 80% in the last 20 years. Conservation efforts focus on the creation of milkweed habitats to mitigate this decline. Previous research has found monarchs lay more eggs per milkweed stem in urban gardens than natural habitats and recent work identified specific garden designs that make urban gardens more attractive to monarchs. Increasing plant diversity can reduce specialist insect herbivore colonization via bottom-up (e.g., plant) and top-down (e.g., predation) regulatory factors. Although this is beneficial for pest management efforts, it contradicts conservation efforts. In this study, we explored if adding multiple flowering species to garden-sized milkweed plantings affected monarch oviposition or top-down regulation of larvae. We compared monarch egg abundance, natural enemy abundance and richness, and biological control of monarch larvae in milkweed monocultures and milkweed mixed with four additional wildflower species. We found that monarchs laid 22% more eggs on sentinel milkweed plants in mixed-species plots with no effect of plant diversity on monarch survival. We also found higher natural enemy richness, wasp, and predatory bug abundance in the mixed-species plots and this did not translate to higher biological control rates. Our results provide more evidence that plant selection and habitat design are important for monarch conservation.

Influence of Abiotic Environmental Factors on the Abundance of Cod Eggs and Cod Larvae in the Southeastern Baltic Sea in 2016

The characteristics of the abiotic environmental parameters obtained during in situ observations and significant for the survival of cod eggs and larvae (water salinity, water temperature, and oxygen content) are presented for the Baltic Sea for 2016. Cod eggs were present in ichthyoplankton during the entire spawning season (March–August). In July and August 2016, the abundance of cod larvae exceeded the long-term average value for the Gdansk Deep. The thickness of the reproductive layer, suitable for cod reproduction, calculated from vertical localization of 11‰ isohaline and 2 mL/L isooxygene, was sufficient for cod egg survival. Layers with acute vertical density gradients were noted in the upper part of the halocline in March–August and also in the surface water layer in the summer period. It is assumed that the lower boundary of the pycnocline in the surface water layer could serve as a food-rich zone of cod larvae concentration.

Resource pulses increase the diversity of successful competitors in a multi‐species stream fish assemblage

AbstractFood resources are often patchily distributed through space and time and are classified as resource pulses when hyperabundant. Resource pulses can benefit growth, reproduction, and abundance of various consumers. Yet, it is relatively unknown how such resources are partitioned among competing consumers and how this is influenced by the magnitude of the pulse. Here, we examined how the magnitude of a pulsed resource influences resource partitioning among diverse sizes and species of consumers in a natural setting over small spatial and temporal scales. We focused on salmon egg subsidies to stream fish consumers. We experimentally added different quantities of pink salmon eggs to five meter long experimental stream sections. Egg additions spanned three orders of magnitude from 6 to 3575 eggs. Stream fish (egg consumers) were captured and gastric lavaged at each experimental section to determine how many eggs each individual fish consumed. We modeled taxon‐specific individual egg consumption as a function of egg availability, individual mass, community composition, number of competitors, and stream velocity using hurdle models in a Bayesian framework. We found that there were diminishing returns for increasing egg abundance increasing egg consumption (i.e., type II functional response) for individual size classes of fish, but that higher egg numbers were needed to benefit diverse consumers. Top models indicated that egg availability and individual fish characteristics (size and taxon) drove egg consumption, while community characteristics (species composition and number of competitors) were not supported. Our results suggest that resource pulses can provide rare opportunities for less dominant sizes and species of fish to consume abundant resources. The current paradigm in the stream fish literature suggests that stream fish communities are structured by dominance hierarchies; however, dominance hierarchies may be less influential where pulsed resources comprise a large portion of the resource base.

Meteorological variables associated with the temporal oviposition rate of Aedes aegypti (Diptera: Culicidae) in Resistencia city, Chaco province, Northeastern Argentina

Aedes aegypti is the main vector of dengue virus in South America. In the last fifteen years, Argentina has suffered three large dengue outbreaks: one in 2009, another one in 2016 and the current 2020 outbreak, with 26,000, 66,000 and more than 43,000 confirmed cases, respectively. These outbreaks are associated with the circulation of the virus in neighboring countries due to the constant movement of people across the frontier. In 2009, the main province affected was Chaco province, with 11,037 confirmed cases (50% of total cases). Thus, the aim of this study was to characterize the temporal oviposition rate of Aedes aegypti in Resistencia, the capital city of this province, in relation to meteorological variables. Mosquitoes were sampled weekly, from April 2015 to March 2017, using ovitraps located in houses randomly selected within the urban area. Oviposition rate was evaluated by means of the total number of eggs collected per week and the proportion of positive ovitraps per week. The coefficient of variation for these two indicators was estimated for the whole study period and then compared using the Wilcoxon Pair test. A generalized linear model (GLM) was performed to infer association between meteorological variables and oviposition rate without time lag and with a time lag of 1 to 4 weeks, considering the biology of this mosquito species. Comparisons between the coefficient of variation of egg number versus the proportion of positive ovitraps showed significant differences, being the former more variable than the latter. The most significant time lag was 2 weeks for the minimum temperature. The number of Ae. aegypti eggs increased 4.05 times when the minimum temperature increased 1°C two weeks before, and decreased 0.69 times with an increase of 1 unit in relative humidity. No eggs were collected when the temperature was below 8°C. The oviposition rate was associated with the increase in the critical minimum temperature (over 8°C) and the weekly frequency of precipitation and dissociated with relative humidity. The maximum oviposition rate was recorded between November and January of both years. The GLM could not explain the relation between meteorological variables and the proportion of positive ovitraps. The peaks of Ae. aegypti egg abundance occurred simultaneously with dengue autochthonous cases recorded in Chaco province, resulting in a good indicative of the period of greatest epidemiological risk.

Climatic variables limit population abundance of Neoleucinodes elegantalis: Important neotropical tomato pest

The small tomato borer, Neoleucinodes elegantalis (Guenée) (Lepidoptera: Crambidae), is a significant pest of tomato crops in Central and South America, where its occurrence and abundance is dependent on environmental factors. The aim of this study was to determine the effects of climate variables on the abundance of N. elegantalis in open-field tomato cultivation. The population density of N. elegantalis was sampled weekly after tomato fruits reached a diameter ≥0.5 cm until the final harvest, over 15 commercial tomato fields. Egg abundance and mortality, larval abundance and mortality, and pupae abundance was determined within each sample. Rain, photoperiod, wind speed, temperature, and relative humidity was monitored daily. The highest densities of N. elegantalis eggs, larvae, and pupae occurred between March and July. After July, N. elegantalis density was drastically reduced. Path analysis revealed that temperature, rainfall, and photoperiod had a significant and direct effect on N. elegantalis egg abundance, which indirectly affected larval and pupal densities. The path coefficient indicated a negative correlation between the number of N. elegantalis eggs and the photoperiod, while air temperature and rainfall had a positive effect on theses densities. This study improves our understanding of how climate influences N. elegantalis population dynamics. This information will assist in the development of more sustainable pest-management programs for tomato fields, allowing farmers to monitor and adopt control methods when populations rise.

Beach restoration improves habitat quality for American horseshoe crabs and shorebirds in the Delaware Bay, USA

Beach nourishment is commonly conducted to protect human infrastructure but rarely for the primary purpose of improving wildlife habitat. To improve horseshoe crab spawning and shorebird feeding habitat in the Delaware Bay, New Jersey (USA), we removed 2000 t of shoreline rubble and placed sand on 16 ha of degraded shoreline spanning 8 beaches. Horseshoe crab egg cluster abundance varied annually, seasonally and spatially. Beaches restored using sand with grain size fractions similar to native sand had horseshoe crab egg cluster abundances matching or exceeding those of high-quality reference beaches. Deeper sand with a higher coarse-grain fraction resulted in the highest egg cluster abundance across all sites and beaches, while finer-grained sand used on a subset of restored beaches was associated with lower egg cluster abundances. These patterns were also reflected in shallow egg availability for shorebirds, with egg cluster abundance correlating positively with shallow egg abundance. Over time, sand placed on beaches moved cross-shore and longshore, and overwashed into marshes. Longshore sand movement nourished adjacent beaches and ebb shoals at creek mouths. Such shoals attract spawning horseshoe crabs and have high densities of surface eggs available for shorebird feeding, but experience high attrition of egg clusters. This study demonstrates that investments in beach restoration provide important benefits for horseshoe crabs and shorebirds. Outcomes can be further improved by expanding project scope and integrating other coastal restoration strategies. Restoration will be critical for the conservation of coastal species as sea levels rise and current and past coastal management practices continue to degrade habitats.

Horizontal distribution affects the vertical distribution of native and invasive container-inhabiting Aedes mosquitoes within an urban landscape.

The vertical dimension constitutes an important niche axis along which mosquitoes may adjust their distribution. Here, we evaluated whether the vertical distribution of container-inhabiting Aedes mosquitoes differs along a gradient of anthropogenic land-use intensity within an urban landscape. Using a pulley system, we hung oviposition cups at three heights (ground level, 4.5, and 9 m) and in three habitats: forest, park, and a built environment. We hypothesized that mosquito abundance and diversity would be highest in the least disturbed forest habitat, decrease in the park, and be lowest at the UNC-Greensboro campus. We also expected Aedes albopictus (Skuse) and Ae. triseriatus (Say) to mainly oviposit at ground level and Ae. hendersoni (Cockerell) at canopy height. Aedes albopictus was the most common species (68.8%) collected in all three habitat types and was the only species found in the built environment. In that habitat, Ae. albopictus exhibited a bimodal distribution with the lowest activity at the intermediate height (4.5 m). Aedes triseriatus (28.9%) did not differ in egg abundance between the forest and park habitats but did exhibit diverse vertical habitat use while avoiding the canopy in the park habitat. Aedes hendersoni (2.3%) was the most sylvatic species and oviposited only at ground level. Our results indicate that the vertical distribution of mosquitoes is affected by the type of habitat in which they occur, and that this variation could be driven via local-scale modification of microclimatic factors.

The Abundance and Distribution of the Early Life Stages of Sardine (Sardina pilchardus) in Central of the Aegean Sea (Sığacık Bay) and their Interactions with Certain Environmental Factors

The study was carried out on a monthly basis at 16 stations between January 2017 and December 2017 in the Sigacik Bay, Izmir, Turkey. For ichthyoplankton sample collections, vertical (350 μm) plankton tows were carried out using a WP-2-type plankton net with a mouth area of 0.255 m2. Depth, temperature, oxygen, pH, salinity, zooplankton volume and chlorophyll-a values were detected at each research station in the study. The eggs and larvae of the sardine samples were obtained during the period between December and February, the maximum being in February (mean temperature 15.29 ± 0.57 °C). The mean abundance values of all sardine eggs and larvae in all stations were 78 individuals·10 m−2. The egg diameter values in sardines were in the range of 1.40–1.69 mm and the oil globule diameter values were in the range of 0.12–0.18 mm. The majority of sardine eggs and larvae were found at the depths of 25–75-m at the stations. The correlation between the abundance of sardine eggs and larvae and environmental variables was determined using the Principal Component Analysis (PCA). There was a positive correlation between sardine eggs and dissolved oxygen (r: 0.75) and a negative correlation between larvae and salinity (r:-0.75). It was concluded that sardine does not prefer Sigacik Bay as a spawning area. However, further ichthyoplanktonic studies considering the fluctuations of pilchard stocks in Sigacik Bay should be carried out for a longer period to better clarify the issue.

Temporal variation of the effects of landscape composition on lacewings (Chrysopidae: Neuroptera) in vineyards

Abstract Increasing landscape heterogeneity, both in terms of composition and configuration, can promote natural enemies and biological control in agricultural landscapes. However, relatively poor information exists about the effects of landscape heterogeneity on lacewings, which are a major group of predators. Furthermore, temporal changes of landscape effects on natural enemy dynamics remain largely unexplored. Here, we investigated how landscape composition and configuration affect lacewings and their biological control potential on leafhoppers. Lacewings and leafhoppers were sampled from April to July in 10 vineyards located in southwestern France. The vineyards were selected along a gradient of a proportion of semi‐natural habitats in the landscape. The proportion of semi‐natural habitats positively affected the abundance of adults and eggs, as well as species richness, of lacewings, alone or in interaction with the sampling month. Landscape configuration was never found to enhance abundance or species richness of lacewings. Finally, the predator–prey ratio increased through time but did not respond to landscape composition or configuration. Our study highlights that the proportion of semi‐natural habitats increases both abundance and diversity of lacewings in vineyard landscapes but that this effect varies over time. This result indicates the need to assess the variability of landscape effects over time to maximize biological pest control services in agricultural landscapes.

Spatial variation of ostracod (Crustacea, Ostracoda) egg banks in temporary lakes of a tropical flood plain

Ostracods are microcrustaceans that produce resting eggs under adverse conditions. In this study we evaluated the spatial variation of ostracod resting eggs in different regions of temporary lakes in a Brazilian flood plain. Based on the homogenisation effect of flood pulses on aquatic communities in flood plains, we hypothesised that the composition and abundance of ostracod eggs in the centre of temporary lakes would be similar to those in edge regions. Samples were collected from the centre and edge regions of five temporary lakes. Sediment was oven dried, rehydrated and hatching was monitored in germinating chambers. Twelve ostracod species hatched from the egg banks during our experiments. The abundance and species composition were similar between the two regions of the lakes. Flood events may be responsible for the homogenisation of the egg banks as a result of the connection of lakes with principal river channels. During flooding, water masses powerfully enter lakes and can redistribute sediments. This study shows that egg banks have the potential to contribute to the maintenance of local biodiversity and the resilience of biodiversity of temporary lake ecosystems.

Effects of Argentine ants (Hymenoptera: Formicidae) on myrmecophilous lycaenid butterfly, Narathura bazalus (Lepidoptera: Lycaenidae), in western Japan

AbstractEffects of the invasive Argentine ant, Linepithema humile (Mayr), on a myrmecophilous butterfly, Narathura bazalus (Hewiston), were investigated in the field in western Japan. Larvae of N. bazalus were attended by workers of Argentine ants in invaded parks and of ten native and one cosmopolitan ant species in uninvaded parks. The abundance of eggs and larvae were not significantly different between invaded and uninvaded parks. Pupal weight and parasitized ratio by tachinid flies were also not different between the two types of parks. These results indicate that the role of Argentine ants for the butterfly might be almost equivalent to the native ants.

Changes in the spawning habitat of two small pelagic fish in the Northwestern Mediterranean

AbstractWe investigated the effects of three sea surface oceanographic variables (temperature, salinity, and chlorophyll a) on the abundance of eggs and larvae of two summer‐spawning species in the NW Mediterranean Sea, the anchovy Engraulis encrasicolus and the round sardinella Sardinella aurita, based on data from ichthyoplankton surveys carried out in the 1980s, 2000s, and 2010s. The environmental data showed an increase in seawater temperature and salinity along time, coupled with a decrease in chlorophyll a (proxy for primary production). These long‐term directional changes in environmental conditions helped explain the important reduction observed in the abundance of eggs and larvae of anchovy, as well as shrinking of spawning habitat in this species. At the same time, the probability of occurrence of round sardinella has increased from practically zero in the 1980s to probabilities near 1 along the coastal area of the study region in the two decades of the 21st century. Given that the trends observed in the environmental variables along the three decades of study are expected to continue during the 21st century, as a consequence of climate change, the spawning habitat of anchovy is expected to continue decreasing, while round sardinella habitat can expand. Considering that anchovy is of high commercial importance in NW Mediterranean fisheries, while round sardinella has very low commercial interest, our results show that the viability of small pelagic fisheries in the area may be compromised.

The influence of meteorological variables on the oviposition dynamics of Aedes aegypti (Diptera: Culicidae) in four environmentally distinct areas in northeast Brazil.

BACKGROUND Fluctuations in climate have been associated with variations in mosquito abundance.OBJECTIVES To analyse the influence of precipitation, temperature, solar radiation, wind speed and humidity on the oviposition dynamics of Aedes aegypti in three distinct environmental areas (Brasília Teimosa, Morro da Conceição/Alto José do Pinho and Dois Irmãos/Pintos) of the city of Recife and the Fernando de Noronha Archipelago northeastern Brazil.METHODS Time series study using a database of studies previously carried out in the areas. The eggs were collected using spatially distributed geo-referenced sentinel ovitraps (S-OVTs). Meteorological satellite data were obtained from the IRI climate data library. The association between meteorological variables and egg abundance was analysed using autoregressive models.FINDINGS Precipitation was positively associated with egg abundance in three of the four study areas with a lag of one month. Higher humidity (β = 45.7; 95% CI: 26.3 - 65.0) and lower wind speed (β = −125.2; 95% CI: −198.8 - −51.6) were associated with the average number of eggs in the hill area.MAIN CONCLUSIONS The effect of climate variables on oviposition varied according to local environmental conditions. Precipitation was a main predictor of egg abundance in the study settings.

Short-Term, Large-Area Survey of Container Aedes spp. (Diptera: Culicidae): Presence and Abundance is Associated with Fine-scale Landscape Factors in North Carolina, USA.

Container Aedes mosquitoes are responsible for the transmission of anthroponotic and zoonotic viruses to people. The surveillance and control of these mosquitoes is an important part of public health protection and prevention of mosquito-borne disease. In this study, we surveyed 327 sites over 2 weeks in late June and early July in 2017 in North Carolina, USA for the presence and abundance of Aedes spp. eggs in an effort to better target potential Ae. aegypti collections. We examined the ability of 2 types of landscape data, Light Detection And Ranging (LIDAR) and National Land Cover Database (NLCD) to explain the presence and abundance of eggs using principal component analysis to deal with collinearity, followed by generalized linear regression. We explained variation of both egg presence and abundance for Aedes albopictus (Skuse) and Aedes triseriatus (Say) using both NLCD and LIDAR data. However, the ability to make robust predictions was limited by variation in the data. Increased sampling time and better landscape data would likely improve the predictive ability of our models, as would a better understanding of oviposition behavior.

Ихтиопланктон Юго-Восточной Балтики в летний сезон: современные изменения в распределении и численности икры и личинок массовых видов рыб

The aim of ichthyoplankton studies in July 2019 was to monitor the distribution and estimate the abundance of: 1) eggs and larvae of mass pelagophilous fish species (cod, sprat) in deep-water areas; 2) larvae of small-sized benthic fish species inhabiting the shallow coastal zone of the South-Eastern Baltic Sea (the exclusive economic zone of the Russian Federation). It was noted, the main concentrations of cod and sprat eggs were in the northern part of the area (southern slope of Gotland Deep). Aggregations with a noticeably lower abundance of eggs were observed in the Gdansk basin. In July 2019, the average abundance of cod eggs (3.4 ind./m2) was higher than in the years without strong North Sea advections according to observations in the 1990–2000. Although the reproduction of sprat was nearing completion, in July its eggs dominated the ichthyoplankton assemblage of the deep-water zone, tenfold exceeding the numbers of cod eggs. In the composition of the ichthyoplankton of the shallow-water zone, 7 species of fish larvae were found, among which the sand goby dominated in numbers. Its small-sized larvae were most abundant above depths from 20 to 40 m, which made it possible to identify this depth range as an area of intensive spawning of the species. The decrease in the number of sand goby larvae in the 2010s, compared to the beginning of the 2000s, could be associated with the spread of the Ponto-Caspian invader round goby in the coastal zone, small-sized fry of which were also found in July 2019 in the ichthyoplankton of the coastal zone.

Importance of hydrological parameters in the distribution of planktonic eggs and larvae in an upwelling zone (Imessouane Bay, Moroccan Atlantic Coast)

The present study aimed to evaluate the spring biodiversity of planktonic eggs and larvae in Imessouane Bay and to assess their variability according to the hydrological parameters of the environment. Twenty seven biological and hydrological samples were taken at three stations during a three-month period (March, April and May 2018). The qualitative study revealed the presence of 26 taxa, divided into six major groups, of those the Arthropod larvae were the most dominant (43.16%). The maximum abundances of planktonic eggs and larvae were recorded during May, as the richest month in terms of diversity (25 taxa). The principal component analysis of the hydrological parameters made it possible to define a temporal organization dominated by 3 groups. The canonical correspondence analysis exhibited that certain environmental parameters are essential factors for the functioning and the spatiotemporal variability of the planktonic communities.

Gloomy Scale (Hemiptera: Diaspididae) Ecology and Management on Landscape Trees

AbstractGloomy scale, Melanaspis tenebricosa (Comstock), is native to the eastern United States and feeds on deciduous trees. In natural areas, it is a background herbivore that typically remains at low densities. Gloomy scale generally responds positively to warming with greater egg production, size, survival, and abundance. In urban areas, which are warmer than surrounding natural areas, gloomy scale is pestiferous on planted trees, particularly red maple (Acer rubrum L.; Sapindales: Sapindaceae) but other native maples as well. They live on the bark and damage host trees by feeding from plant cells and tissues, which deprives the trees of energy and nutrients, reducing the trees’ growth and overall health. Gloomy scales are likely to expand their range beyond the Southeast and become pestilent in new areas with continued climatic warming and urbanization. Here we present a review of the biology, ecology, response to environmental conditions, host range and damage, and management of gloomy scale.

Effect of patch size of the exotic host plant Calotropis procera (Apocynaceae) on herbivory

Abstract Calotropis procera is a xerophytic perennial milkweed shrub native to Asia and Africa, which currently is also widely distributed throughout the Brazilian Caatinga. C. procera is well defended against herbivores, especially with latex and toxic steroidal cardenolides. The goal of this study was to evaluate how patch size of this exotic host plant affect insect herbivory. Eight patches were selected containing a varied number of C. procera individuals (5, 8, 29, 31, 55, 79, 116, and 172 individuals/patch) in the Caatinga. Patches were divided into four categories according to the number of C. procera individuals: very small (5 and 8), small (29 and 31), intermediate (55 and 79), and large (116 and 172). The percentage of herbivory was greater in patch categories with more individuals. Among the herbivorous insects associated with C. procera, larvae of Danaus spp. (Lepidoptera: Nymphalidae) were commonly observed feeding on all patches. These herbivores present specialized behaviors to circumvent the presence of latex on the host leaves. Adult Danaus spp. females probably had higher probability to find large patches of C. procera, leaving a greater abundance of eggs and, consequently, increasing the herbivory by their larvae in these patches. In contrast to immigration tendency, emigration from large patches may be lower, because there is a higher probability of finding resources (e. g. suitable C. procera leaves) inside large patches compared with small patches. We conclude that patch size of the host plant C. procera is a major factor affecting herbivory.