Phyllotreta cruciferae and Phyllotreta striolata responses to insecticidal seed treatments with different modes of action

The strategy used most commonly in western North America to protect seedlings of canola (Brassica rapa L. and Brassica napus L.) from attack by adults of the flea beetles Phyllotreta cruciferae (Goeze) and Phyllotreta striolata (Fabricius) (Coleoptera: Chrysomelidae) involves planting seed coated with insecticide for systemic activity. Previous research determined that the two beetle species responded differently to the most commonly used neonicotinoid seed dressings. However, other insecticides that exploit different modes of action have commercial potential for managing infestations of these pests, but no information exists on their efficacies for these flea beetle species. Studies were conducted to compare effects of the neonicotinoid compounds, thiamethoxam and imidacloprid, to spinosyn and fipronil as systemic seed treatments for reducing feeding damage to canola seedlings and increasing mortality of P. cruciferae and P. striolata. Phyllotreta cruciferae experienced greater mortality and caused less feeding damage than P. striolata to seedlings treated with the neonicotinoid compounds. Mortality increased and feeding damage decreased significantly when beetles fed upon seedlings treated with fipronil, indicating its potential usefulness for control of these pests. However, spinosyn seed treatment was relatively ineffective against either beetle species. Higher rates of P. striolata mortality with fipronil than thiamethoxam suggest that fipronil may provide improved flea beetle control over hundreds of thousands of hectares in western North America where flea beetle populations are dominated by P. striolata, and control with thiamethoxam has been suboptimal.     

Systemic control efficacy of neonicotinoids seeds dressing on English grain aphid (Hemiptera: Aphididae)

English grain aphid, Sitobion avenae (Fabricius) (Hemiptera: Aphididae), is an important pest of wheat (Triticum aestivum L.), and is usually controlled by intensive foliar sprays of pesticides under field conditions. In order to reduce labour costs and increase the utilization of pesticides, neonicotinoids seed treatment was studied as a simple and accurate control technology for S. avenae. We evaluated the mortality of imidacloprid, acetamiprid, thiamethoxam, clothianidin, nitenpyram and dinotefuran to the English grain aphid by seed dressing methods in the laboratory, and found that the toxicity with that LC₅₀ of clothianidin (20.97?a.i.?g/100?kg seeds) and thiamethoxam (28.84?a.i.?g/100?kg seeds) to S. avenae are higher than other neonicotinoids. LC₅₀ values of nitenpyram, imidacloprid and acetamiprid ranged between 120?a.i.?g/100?kg seeds and 210?a.i.?g/100?kg seeds. Dinotefuran showed the lowest toxicity with LC₅₀ value 565.76?a.i.?g/100?kg seeds to English grain aphid. Field plot experiments were conducted to investigate the control efficacy of neonicotinoids seed treatment for the aphid, and the effects on growth of wheat. Field observations indicated that clothianidin and thiamethoxam provided the better control efficacy on the English grain aphid than imidacloprid, and had no influence on wheat seedling emergence. These results showed that seed treatment by neonicotinoids was effective against S. avenae throughout the growth period, furthermore, thiamethoxam and clothianidin were the effective and safe alternative options for S. avenae management in the crop.     

Differences in Phyllotreta cruciferae and Phyllotreta striolata (Coleoptera: Chrysomelidae) responses to neonicotinoid seed treatments

Insecticidal seed treatments are used commonly throughout the Northern Great Plains of North America to systemically protect seedlings of canola (Brassica napus L. and Brassica rapa L.) from attack by the flea beetles Phyllotreta cruciferae (Goeze) and Phyllotreta striolata (F.) (Coleoptera: Chrysomelidae). Here, we investigated differential responses by the two flea beetle species to the neonicotinoid seed treatments thiamethoxam (Helix and Helix XTra) and clothianidin (Prosper 400) in greenhouse experiments. P. cruciferae experienced higher mortality and fed less when exposed to these compounds than did P. striolata. Beetles of the overwintered and the summer generations responded differently when feeding on seedlings that developed with insecticidal seed treatments, with mortality higher for P. cruciferae in May than in August. When the two flea beetle species were held together at equal densities and allowed to feed on seedlings affected by the seed treatments, mortality of P. cruciferae significantly exceeded that of P. striolata. Differences in efficacies of these compounds for these beetles have ramifications for management strategies in regions where these insects occur sympatrically. Competitive release of P. striolata was previously reported to occur when P. cruciferae was excluded from brassicaceous crops; consequently, the consistent use of these seed treatments over millions of hectares of canola cropland may be a factor that contributes to a shift in prevalence of flea beetle pest species from P. cruciferae toward P. striolata.     

Impact of planting dates and insecticide strategies for managing crucifer flea beetles (Coleoptera: Chrysomelidae) in spring-planted canola

Integration of cultural practices, such as planting date with insecticide-based strategies, was investigated to determine best management strategy for flea beetles (Phyllotreta spp.) (Coleoptera: Chrysomelidae) in canola (Brassica napus L.). We studied the effect of two spring planting dates of B. napus and different insecticide-based management strategies on the feeding injury caused by fleabeetles in North Dakota during 2002-2003. Adult beetle peak emergence usually coincided with the emergence of the early planted canola, and this resulted in greater feeding injury in the early planted canola than later planted canola. Use of late-planted canola may have limited potential for cultural control of flea beetle, because late-planted canola is at risk for yield loss due to heat stress during flowering. Flea beetle injury ratings declined when 1) the high rate of insecticide seed treatment plus a foliar insecticide applied 21 d after planting was used, 2) the high rate of insecticide seed treatment only was used, or 3) two foliar insecticide sprays were applied. These insecticide strategies provided better protection than the low rates of insecticide seed treatments or a single foliar spray, especially in areas with moderate-to-high flea beetle populations. The foliar spray on top of the seed treatment controlled later-emerging flea beetles as the seed treatment residual was diminishing and the crop became vulnerable to feeding injury. The best insecticide strategy for management of flea beetle was the high rate of insecticide seed treatment plus a foliar insecticide applied at 21 d after planting, regardless of planting date.     

Comparative evaluation and economic potential of ecorational versus chemical insecticides for crucifer flea beetle (Coleoptera: Chrysomelidae) management in Canola

From 2001 to 2004, field studies were conducted to evaluate the effect of the ecorational insecticides SpinTor (spinosad), BotaniGard (Beauveria bassiana), Neemix (azadirachtin), and Surround (kaolin) against crucifer flea beetle on canola, Brassica napus L., at the cotyledon stage. The ecorational treatments were compared with a standard foliar chemical insecticide, Capture (bifenthrin), and the chemical seed treatment insecticide Helix XTra (thiamethoxam). This study indicated that flea beetle injury was lower for Helix XTra, Capture, and the ecorational insecticide SpinTor. SpinTor was less effective when flea beetle populations were relatively high (200-300 per trap-week). Yields for chemical insecticide treatments were always greater than SpinTor, with differences being the smallest (68-374 kg/ha) at low levels of flea beetle feeding injury. Differences were greatest when canola seedling injury was high (775-1,364 kg/ha). Yield differences between the conventional insecticides and BotaniGard, Neemix, and Surround were 119-439 and 61-2,248 kg/ha at low and high flea beetle feeding injury, respectively. Although yield differences between SpinTor and chemical insecticides were relatively small at lower levels of flea beetle injury, net losses ranged from $47 to $151/ha when SpinTor was used as an alternative to a standard chemical seed treatment, Helix XTra. This suggests that SpinTor would not be a viable alternative to the chemical insecticide. Net losses ranged from $30 to $266/ha when BotaniGard, Neemix, and Surround were used as alternatives to the seed treatment.     

Tamarins and Dung Beetles: An Efficient Diplochorous Dispersal System in the Peruvian Amazonia

Dung beetles fulfill several key functions in ecosystems but their role as secondary seed dispersers is probably one of the most complex ones. Various factors, such as seed characteristics, dispersal pattern induced by the primary disperser, season, and habitat, can affect the seed–beetle interaction. Particularly little is known about the fate of seeds primarily dispersed in small feces. The aim of this study was to investigate the effects of these factors on the dung beetle community (species composition, number and size of individuals) and its consequences on burial occurrence and depth of seeds primarily dispersed by two tamarin species. We captured dung beetles in a Peruvian rain forest with 299 dung‐baited pitfall traps to characterize the dung beetle community. Seed burial occurrence and depth were assessed by marking in situ 551 dispersed seeds in feces placed in cages. Among these seeds, 22.5 percent were buried by dung beetles after 2 d. We observed a significant effect of the amount of dung, season, time of deposition, and habitat on the number of individuals and species of dung beetles, as well as on seed burial occurrence and depth, while the tamarin species significantly influenced only the number and the size of dung beetles. This seed dispersal loop is particularly important for forest regeneration: small to large seeds dispersed by tamarins in secondary forest can be buried by dung beetles. These seeds can thus benefit from a better protection against predation and a more suitable microenvironment for germination, potentially enhancing seedling recruitment.     

The effect of seed, furrow and stem base spray treatment with iprodione on white rot disease (Sclerotium cepivorum) in spring-sown salad onions

Seed treatment with iprodione at 125 and 150 g a.i./kg was superior to calomel seed treatment at 500 g a.i./kg in reducing disease losses and increasing yields in field experiments with salad onions infected with white rot; iprodione at 50, 62·5 and 100 g a.i./kg and thiophanate-methyl at 150 g a.i./kg were as effective as calomel. Furrow treatment with iprodione or thiophanate-methyl at 0·05 and 0·15 g a.i./m row or calomel at 0·5 g a.i./m row gave similar control as equivalent rates of seed treatment. Neither seed nor furrow treatments gave adequate control with prolonged exposure of the crop to the disease. A single stem base spray of iprodione at 0·0625 g a.i./m row applied 5 wk after drilling, reduced losses from 46% with a standard calomel seed treatment to 20%; increasing the stem base spray concentration to 0·25 g a.i./m row did not improve the control but resulted in a doubling of yields. The most effective control was obtained with iprodione applied as a seed treatment at 62·5 g a.i./kg combined with a single stem base spray at 0·0625 g a.i./m row 5 wk after drilling and this reduced losses to 6% compared with losses of 46% with calomel treated seed and 88% with untreated seed; increasing the stem base spray concentration did not improve control but resulted in higher yields.     

The effect of seed treatment with benzimidazole-based fungicides on infection of the foliage of overwintered salad onions by Botrytis cinerea

Seed treatments of carbendazim (Bavistin 50% W.p.) and thiophanate-methyl (Mildothane 50% W.p.) applied to overwintered salad onions at 250 g a.i./kg seed protected the foliage of plants from infection by Botrytis cinerea during the seasons 1973–1976. Crop establishment and yield were also improved. Seed treatment with calomel was not effective. Chemical analysis of treated non-viable seeds, retrieved from the soil, indicated that 73% carbendazim and 46% thiophanate-methyl remained attached to the seeds after 9 months in the soil. Analyses of onion leaves revealed that each fungicide was represented by similar quantities of carbendazim, 5 μg/g fresh weight in October 1975 reducing to 1 μg/g fresh weight in May 1976. Bioassay tests showed that the fungicide was acropetally distributed and was present in all leaves early in the season (October) but was absent from some new leaves formed in the following spring. Carbendazim-insensitive isolates of B. cinerea occurred after three seasons' use of this chemical. Sensitive isolates failed to grow on agar containing 1 μg/ml benomyl but all insensitive isolates (31 total) grew normally at this concentration and some were capable of growth on agar containing 1000 μg/ml benomyl. The emergence of foliar isolates of the fungus insensitive to the benzimidazole-based compounds used in the treatment of seeds indicated that these fungicides did not provide a permanent solution to the disease problem.     

Alternative management tactics for control of Phyllotreta cruciferae and Phyllotreta striolata (Coleoptera: Chrysomelidae) on Brassica rapa in Massachusetts

The flea beetles Phyllotreta cruciferae (Goeze) and Phyllotreta striolata (F.) (Coleoptera: Chrysomelidae: Alticinae) are significant pests of crops in the Brassicaceae family. From 2001 to 2003, the efficacy of both new and commonly used treatments for the control of flea beetles in brassicas, Brassica rapa L., were evaluated in three small plot, randomized complete block design trials. Row cover and carbaryl (applied as a weekly foliar spray) were found to be the most consistent at reducing damage in comparison with untreated controls in all trials. Two new products that may provide adequate flea beetle control are spinosad (in either conventional or organic formulations) and thiamethoxam. The plant-derived compounds azidiractin and pyrethrin did not protect treated plants from flea beetle feeding. Treatment of plants with kaolin, or removal of the beetles with a vacuum, also did not reduce the level of crop damage. The level of damage at harvest was found to be correlated with population size of flea beetles in each plot, as measured by captures on yellow sticky traps and direct visual counts. Removal of the outer two leaves of individual B. rapa plants reduced the total number of holes per plant by 40%, while only removing 15% of the leaf area.     

Bean leaf beetle (Coleoptera: Chrysomelidae) management for reduction of bean pod mottle virus

Bean pod mottle virus (BPMV) is a management concern for soybean, Glycine max (L.), producers in the North Central states because it can cause yield loss and reduce seed quality by induction of seed coat mottling. The main vector of BPMV is the bean leaf beetle, Cerotoma trifurcata (Forster). An experiment was conducted in 2000 and 2001 at two locations in northwestern and central Iowa to test three insecticide treatments for suppression of bean leaf beetles, and subsequently, BPMV. Treatments of insecticide applications with lambda-cyhalothrin were 1) a single early-season application (23 g [AI] /ha) (2.5 oz/acre) at the VE-VC soybean developmental stage; 2) two early-season applications, the first the same as treatment 1 and a second at the same rate 9-13 d later; 3) a single early-season application the same as treatment 1, followed by a mid-season application (28 g [AI] /ha (3.2 oz/acre) at approximately R2 (flowering, near 15 July); and 4) an unsprayed control. Application of lambda-cyhalothrin after soybean emergence and again as first-generation bean leaf beetles emerged in northwestern Iowa in 2000 (treatment 3) significantly reduced beetle densities through mid-season, BPMV field incidence by 31.5%, and seed coat mottling by 31.2%, compared with the unsprayed control. Similar effects were measured at the same location when insecticide was applied twice at early season (treatment 2). Yield was 453.7 kg/ha (6.74 bu/acre) greater in treatment 2 and 525.20 kg/ha (7.80 bu/acre) greater in treatment 3 than in the unsprayed control at the northwestern site in 2000. At both locations in 2001 fewer treatment effects were observed, which was likely related to lower beetle populations in that year. Early-season insecticide sprays targeted at overwintered beetles on VC-VE reduced the initial population of vector insects and may have contributed to a lower first-generation population because of reduced overwintered beetle oviposition. In 1 year at one location there was a benefit to an additional mid-season insecticide spray, although effectiveness of spraying at this time could vary based on the magnitude of the vector population.     

Effect of forest fragmentation on dung beetle communities and functional consequences for plant regeneration

I compared dung beetle communities and assessed some of their functional effects (dung removal, seed burial, seedling establishment) in continuous forest with those in 1-ha and 10-ha forest fragments in Central Amazonia. I followed the fate of seeds until seedling establishment for three native tree species, using clean seeds and seeds surrounded by dung. The 1-ha fragments had half the number of dung beetle species captured in continuous forest and in 10-ha fragments. The continuous forest sites and the 1-ha fragments had similar number of individuals, but in the 10-ha fragments dung beetles were twice as abundant. Mean beetle size increased with increasing forest area. Dung removal and seed burial rates were higher in continuous forest than in forest fragments. Seed predation rates were higher in the forest fragments. In all sites, the proportion of seedlings established from seeds surrounded by dung vs clean seeds was the same, and it was the same in continuous forest vs fragments. When comparing seeds that remained on the forest floor with seeds buried by dung beetles, a higher percentage of seedlings established from the latter. Conservation programs that aim to maintain the regeneration ability of forest fragments must incorporate all the important components involved in seedling establishment; in Central Amazonia these include dung beetles as secondary dispersers. It is important that studies start measuring directly not only the first-order effects of forest fragmentation on species, but also the higher-order functional effects.     

Sabal palmetto seed size: causes of variation,choices of predators,and consequences for seedlings

High variation in seed size, as is common among angiosperms, may be maintained in a plant species when several factors select for seed size. Variation may also result from differences among adult plants, such as nutrient and water availability or the amount of photosynthetic tissue. In a study of Sabal palmetto seed ecology I found high seed size variation both within- and among-palms, and investigated possible factors maintaining this variation. Seed size was positively correlated with the number of leaves on parent palms. Larger seeds produced more vigorous seedlings that had greater leaf length, area, and mass, and greater root mass. Caryobruchus gleditsiae (Bruchidae: Coleoptera), whose larvae develop within palm seeds, preferentially oviposited on larger seeds, which in turn produced larger beetle offspring. By choosing the largest seeds available, ovipositing beetles thus affect both the quantity and the quality of seeds available for recruitment. I conclude that because beetle predation selects against large seeds, while larger seeds promote seedling vigor, the maintenance of seed size variation may be an adaptation of S. palmetto promoting both seed escape from predators and seedling vigor.     

新烟碱类杀虫剂拌种对马铃薯甲虫幼虫食物利用和生长发育的影响

为研究马铃薯甲虫Leptinotarsa decemlineata（Say）幼虫取食新烟碱杀虫剂噻虫嗪和吡虫啉处理（有效成分18 g/100 kg种薯拌种）播种90 d后马铃薯叶片的消化吸收和生长发育情况,在室内采用重量法测定了幼虫取食量、体重增加量、食物利用率,近似消化率以及蛹重等营养指标。 结果表明：70%噻虫嗪种子处理可分散粉剂拌种后,马铃薯甲虫幼虫的取食量、体重增加量、食物利用率、食物转化率、近似消化率和相对生长率以及蛹重显著低于10%吡虫啉可湿性粉剂拌种和空白对照（P＜0.05）,发育历期显著长于10%吡虫啉可湿性粉剂拌种和空白对照（P＜0.05）;而10%吡虫啉可湿性粉剂拌种后,马铃薯甲虫幼虫的取食量和3～4龄期的体重增加量与空白对照差异显著（P＜0.05）,蛹重、1～2龄幼虫的体重增长量、食物利用率、食物转化率、近似消化率、相对生长率和生长发育历期与空白对照差异不显著（P＞0.05）。 说明70%噻虫嗪种子处理可分散粉剂拌种对马铃薯甲虫幼虫的取食有显著抑制作用,不能很好地满足其生长发育营养物质的需要,幼虫取食其叶片后,近似消化率和相对生长速率显著降低,生长发育历期显著延长。 这有利于减少当季世代数,降低危害。     

Seed treatment for the control of halo-blight of beans (Pseudomonas phaseolicola)

Streptomycin and kasugamycin were applied as soaks, slurries or dusts to dwarf bean seeds either naturally (internally) infected or externally contaminated with Pseudomonas phaseolicola. Slurries of streptomycin (2–5 g a. i./kg seed) or kasugamycin (0–25 g a.i./kg seed) were the most effective treatments against both types of infection and were generally non-phytotoxic at these rates. Combined analysis of eight field experiments made over a 3 yr period showed that on average both compounds applied in slurries reduced primary infection from infected seeds by 98 %. The method thus shows considerable promise as a commercial control treatment.     

Dung beetle activity affects rain forest seed bank dynamics and seedling establishment

Dung beetles relocate vertebrate feces under the soil surface, and this behavior has many ecological consequences. In tropical forests, for example, seeds defecated by mammals that are subsequently buried by dung beetles are less likely to suffer predation. While the effects of dung beetles on the fate of defecated seeds have been relatively well studied, their effect on seeds already buried in the soil has not. To contribute to fill this gap, we designed a study with three objectives: (a) Describe the vertical re‐distribution of soil seeds that occurs due to dung beetle activity; (b) Determine if beetle activity favors establishment of seedlings from the soil seed bank; and (c) Determine if the effect of dung beetles is stronger in sites of recurrent mammal defecation. We carried out three complementary field experiments, one with artificial seeds (plastic beads) of three sizes buried at known depths, one with two species of seeds buried at those same depths, and one with the natural soil seed bank in sites of single vs. recurrent defecation. Buried beads were moved by dung beetles along the vertical axis, both upwards (9.5%) and downwards (11.5%); smaller beads were more frequently moved downwards while the contrary occurred for larger beads. Dung beetle activity caused an increase in seedling establishment, both from experimentally buried seeds and from the natural seed bank. Defecation recurrence had no effect on seedling establishment. We conclude that dung beetle activity affects seed bank dynamics with important consequences for seedling establishment in tropical forests.Abstract in Spanish is available with online material.     

The effect of seed and stem base spray treatment with iprodione on white rot disease (Sclerotium cepivorum) in autumn-sown salad onions

Iprodione applied to seed at 250 g a.i./kg controlled white rot in autumn-sown salad onions until July the following year, and reduced losses during the winter caused by Botrytis spp. At 25–150 g a.i./kg seed, iprodione controlled autumn and spring infections but it was less effective later in the summer. Treatment of autumn-sown onions at 50 g a.i./kg seed followed in March by a single stem base spray at 0.031 g a.i./m row (total rate c. 2.4 kg a.i./ha) gave complete control; seed treatment at 25 g a.i./kg followed by a stem base spray at 0.125 g a.i./m row (c. 4.5 kg a.i./ha) was equally effective. Four stem base sprays of iprodione at 0.075 g a.i./m row/spray (9 kg a.i./ha) applied in spring to plants raised from untreated seed, controlled spring and summer infections but yields were low because of losses caused by infection in the previous autumn. A single stem base spray of iprodione at 0.125 g a.i./m row applied in spring to plants raised from thiophanate-methyl treated seed at 125 g a.i./kg gave complete control and high yields.     

Primary Seed Dispersal by Red Howler Monkeys and the Effect of Defecation Patterns on the Fate of Dispersed Seeds1

The effectiveness of a seed disperser depends on the quantity and quality of dispersal. The quality of dispersal depends in large part on factors that affect the post–dispersal fate of seeds, and yet this aspect of dispersal quality is rarely assessed. In the particular case of seed dispersal through endozoochory, the defecation pattern produced has the potential of affecting the fate of dispersed seeds and consequently, dispersal quality and effectiveness. In this study, I assessed the effects of dung presence and dung/seed densities on seed predation by rodents and secondary dispersal by dung beetles. In particular, I compared seed fates in clumped defecation patterns, as those produced by howler monkeys, with seed fates in scattered defecation patterns, as those produced by other frugivores. I also determined the prevalence of red howler monkeys (Alouatta seniculus) as seed dispersers at the plant community level in Central Amazonia by determining the number of species they dispersed in a 25–month period. I found that dung presence and amount affected rodent and dung beetle behavior. Seed predation rates were higher when dung was present, and when it was in higher densities. The same number of seeds was buried by dung beedes, in dumped versus scattered defecation patterns, but more seeds were buried when they were inside large dung–piles versus small piles. Seed density had no effect on rodent or dung beetle behavior. Results indicate that caution should be taken when categorizing an animal as a high or low quality seed disperser before carefully examining the factors that affect the fate of dispersed seeds. Red howler monkeys dispersed the seeds of 137 species during the study period, which is the highest yet reported number for an Alouatta species, and should thus be considered highly prevalent seed dispersers at the plant community level in Central Amazonian terra firme rain forests.     

Effects of seed manganese concentration on lupin emergence

Seed of narrow-leafed lupin (Lupinus angustifolius L.) produced in Western Australia often has low manganese (Mn) concentration because of low Mn availability in the soil during grain filling. A major problem of lupin production is poor seedling establishment. We tested the hypothesis that low Mn concentration in lupin seeds decreases emergence.The experiment was a factorial design comparing emergence of lupins (cv. Gungurru) grown under glasshouse conditions from seed with 2 different internal Mn concentrations (7 or 35 mg Mn kg^–1 DW) and with 2 external Mn fertiliser treatments (0 or 10 mg MnSO₄.H₂O kg^–1 soil). There were no visible differences between the seeds. Emergence was monitored and plants were harvested 17 days after sowing.Emergence was approximately 60% in all pots sown with low Mn compared to 100% in pots sown with high Mn seed. Application of Mn did not increase the final emergence of low Mn seed. Seed viability was assessed by staining with tetrazolium chloride, a common test used in seed testing laboratories. All high Mn seed were viable while 34% of low Mn seed were completely or partly unstained and therefore were non-viable. We have shown that low Mn supply during seed filling may lead to production of non-viable seed that cannot be visually distinguished from viable seed..     

Dung beetles in a Central Amazonian rainforest and their ecological role as secondary seed dispersers

Abstract 1. The role of several factors that affect the composition of the dung beetle assemblages in an Amazonian rainforest was quantified, together with the effect of these factors on the role that dung beetles play as secondary seed dispersers. 2. A total of 61 dung beetle species was captured during 3360 h of trapping. During nocturnal trapping periods, more dung beetles, of larger mean size, and more species were captured per trap than during diurnal trapping periods. 3. During the rainy season, more dung beetle species were captured per trap than during the dry season, but the number of individuals and their mean size did not vary between seasons. 4. Bait size had a significant effect on the mean number of beetles and mean number of species but not on mean beetle size. As bait size increased from 5, 10, 25, to 50 g, more beetles and more species were captured per trap. 5. Between 6 and 73% of plastic beads, used as seed mimics, were buried by dung beetles at depths that ranged from 0.5 to 7 cm. Both the proportion of beads buried and burial depth decreased with increasing bead size, and increased with increasing amounts of dung surrounding each bead (5, 10, and 25 g). 6. The proportion of buried seeds for three species varying in size between 5 and 27 mm, increased with increasing dung beetle size, using beetles of seven sizes, varying between 10 and 25 mm. 7. Seeds surrounded by dung were buried more often and more deeply when placed on the forest floor during the late afternoon than when placed during the early morning. Seeds were also buried more often when placed on the forest floor during the rainy season than when placed during the dry season, but season had no effect on burial depth. 8. Forests in Central Amazonia hold a rich dung beetle community that plays an active role in secondary seed dispersal, and consequently in plant regeneration. The interaction between seeds and beetles is complex because it is affected by many factors.     

Seed size variation in the palm Euterpe edulis and the effects of seed predators on germination and seedling survival

Intraspecific variation in seed size is common in wild plant populations and has important consequences for the reproductive success of individual plants. Multiple, often conflicting evolutionary forces mediated by biotic as well as abiotic agents may maintain such a variation. In this paper we assessed seed size variation in a population of the threatened, commercially important palm Euterpe edulis in southeast Brazil. We investigated (i) how this variation affects the probability of attack by vertebrate and invertebrate post-dispersal seed predators, and (ii) if seed size influences the outcome of seeds damaged by beetles in terms of seed germination and early survival of seedlings. Euterpe edulis seeds varied in diameter from 8.3 to 14.1 mm. Neither insects nor rodents selected the seeds they preyed upon based on seed size. Seed germination and total, shoot and root biomasses of one-year seedlings were significantly and positively affected by seed size. Root biomass and seedling survival were negatively affected by seed damage caused by a scolytid beetle (Coccotrypes palmarum) whose adults bore into seeds to consume part of the endosperm, but do not oviposit on them. Seed size had a marginally significant effect on seedling survival. Therefore, if any advantage is accrued by E. edulis individuals producing large seeds, this is because of greater seed germination success and seedling vigor. If this is so, even a relatively narrow range of variation in seed size as observed in the E. edulis population studied may translate into differential success of individual plants.