Curculio Research Articles

Pre‐dispersal acorn predation in mixed oak forests: interspecific differences are driven by the interplay among seed phenology, seed size and predator size

Summary1. Pre‐dispersal seed predation (PSP) often occurs in multi‐host–predator systems (e.g. several plant species exposed to a common array of granivorous insects). However, whether the interaction among seed phenology, seed size and predator size accounts for interspecific differences in PSP remains elusive.2. We studied PSP in a mixed‐oak forest with two oaks (the larger‐seeded Quercus humilis and the smaller‐seeded Q. ilex), both depredated by two acorn weevils (the smaller Curculio glandium and the larger C. elephas). We intensively monitored acorn production and infestation phenology and we identified the weevil species depredating acorns by means of DNA taxonomy.3. The minimum acorn size required for infestation was lower for C. glandium than for C. elephas, in accordance with their different body sizes. This resulted in an earlier infestation phenology in C. glandium and the ability of this species to infest both smaller and larger acorns. Above a minimum acorn size threshold, no selection for larger acorns by weevils was observed.4. Initial acorn crop size was similar in the two oaks. Nonetheless, the earlier acorn phenology and the production of larger acorns in Q. humilis favoured the earlier infestation by C. glandium and the predation by both small and large weevils. Smaller acorns of Q. ilex almost excluded infestation by the larger C. elephas.5. Although larger acorns of Q. humilis could better survive infestation (preserve the embryo), higher PSP in this species finally resulted in a lower mature acorn crop size than in Q. ilex.6. Synthesis. In a multi‐host–predator system, smaller‐seeded species may benefit from a reduced PSP because they exclude larger granivorous insects, but also by means of a ‘free‐rider effect’, if larger‐seeded heterospecifics earlier reach a critical size to be depredated. These results also highlight the benefits of a small body size in granivorous insects to depredate seeds earlier and to forage on a wider range of seed sizes. Whether the advantage of ‘being small’ in this antagonistic plant–animal interaction is offset by other processes, or whether it results in a pressure towards seed and insect size reduction, deserves further attention.

Seed germination and seedling vigor of weevil-damaged acorns of red oak

Acorn weevils (Coleoptera: Curculionidae) are well-known predators of oak acorns in the eastern hardwood forest region of the United States. We examined the germination percentage of seeds, as well as the physical characteristics of seedlings, originating from both weevil-damaged and sound acorns of red oak ( Quercus rubra L.) to determine if weevil depredation impacts seedling vigor. Seeds were grown under greenhouse conditions for a period of 8 weeks. X-ray imaging was used as a nondestructive method for determining seed condition prior to germination. The combined data set showed a reduction in germination percentage from 86% for sound acorns to 26% for those damaged by weevils. Seven seedling metrics were evaluated for differences between seedlings originating from sound and those from weevil-damaged acorns. Of these metrics, the number of leaf flushes, total number of leaves, root collar diameter, shoot length, and dry mass were significantly (P < 0.05) different. Two variables, root length and shoot diameter, were not significantly different. Early allocation of resources to root establishment likely explains these findings. Because of reduced stem height and leaf number, seedlings from weevil-damaged acorns are likely to be less competitive in the forest understory than those from sound acorns.

Phylogeographical patterns of a generalist acorn weevil: insight into the biogeographical history of broadleaved deciduous and evergreen forests

BackgroundClimatic changes during glacial periods have had a major influence on the recent evolutionary history of living organisms, even in temperate forests on islands, where the land was not covered with ice sheets. We investigated the phylogeographical patterns of the weevil Curculio sikkimensis (Curculionidae), a generalist seed predator of Fagaceae plants living in both deciduous oak and evergreen forests of Japan. Its genetic structure was compared to that of another host-specific seed predator, C. hilgendorfi, inhabiting only evergreen forests.ResultsWe examined 921 bp of mitochondrial DNA for 115 individuals collected from 33 populations of C. sikkimensis from 11 plant species of three genera, Quercus, Lithocarpus, and Castanopsis. An analysis of molecular variance revealed that a large proportion (almost 50%, P < 0.001) of the total genetic variance could be explained by differences between two geographical regions, the southwestern and northeastern parts of the main islands of Japan. In contrast, no significant genetic differentiation of the weevil was observed among vegetation types of their utilized host plant species. The phylogeographical patterns of the generalist and the host-specific seed predator exhibited a congruent genetic boundary in the Chugoku-Shikoku region.ConclusionOur results suggest that geology and historical environment have contributed to shaping the present genetic structure of C. sikkimensis. The geographical patterns of genetic differentiation in the Chugoku-Shikoku region observed in the two types of Fagaceae-associated Curculio in this study have also been observed in several plant species growing in warm and cool temperate zones of Japan. The occurrence of this common pattern suggests that deciduous oak and evergreen forests of Japan survived together, or adjacent to each other, in small refugia during glacial ages, in the southwestern and northeastern parts of the main islands, although these two types of forests are presently distributed in cool and warm temperate zones of Japan, respectively.

Silvicultural treatment effects on oak seed production and predation by acorn weevils in southeastern Ohio

Oak regeneration failure in the hardwood forests of eastern North America has been well documented. Silvicultural treatments of prescribed burning and canopy thinning (fire surrogate) are being studied as possible management tools to promote oak regeneration in oak dominated forests. We examined oak seed production and predation by acorn weevils (Coleoptera: Curculionidae) from two experimental forests in southeastern Ohio, under four different silvicultural treatments. Treatments consisted of replicate stands that received a prescribed burning, thinning, and thinning followed by a prescribed burn, in addition to an untreated control. Initial thinning and prescribed burning treatments were conducted in winter/spring of 2000–2001, with a second prescribed burn in spring 2005. Within each treatment unit, nine black oak and nine chestnut oak trees were selected for study and two 0.25 m 2 seed fall traps were placed beneath each tree. Seed collections were completed for five seasons from 2001 to 2005. Data were analyzed using a randomized complete block design, utilizing a mixed-model repeated measures analysis. Overall, stand level treatments resulted in only a slight increase in acorn production (in the burn and thin + burn stands) relative to the control; however, this response was species specific. Masting, the intermittent production of large seed crops, was evident in our study though occurrence of a mast event was not influenced by the treatments. Chestnut oak displayed greater yearly, as well as individual variation in seed production than did black oak. Treatments had no effect on predation by acorn weevils. Predation percentages were lowest during mast years for chestnut oak; however, percentages were mostly stable for black oak across all 5 years. Our data suggest that variation due to climate and genotype are more influential in affecting seed production and masting cycles than are stand level disturbances. Thus, stand level management activities are not likely to have a large influence on oak seed production and oak regeneration must be more strongly influenced at other stages of its life history.

Multi-trophic effects of ungulate intraguild predation on acorn weevils

Predators and parasitoids may contribute to controlling the population sizes of phytophagous insects, and this has been shown to benefit plants. Phytophagous insects may also be killed by other herbivores (intraguild predation), usually larger-sized vertebrates that ingest insects accidentally while feeding on common food sources. We studied the intraguild predation on acorn weevils by ungulates and assessed the consequences for weevil populations. Infested acorns are prematurely abscised and the weevil larvae finish their development inside the acorns after being dropped. Our results show that weevil larvae were killed by ungulates eating the infested acorns on the ground. Ungulates did not discriminate between infested and sound acorns, and the probability of a larva being incidentally eaten was inversely related to acorn availability. Thus, predation risk was enhanced by the premature drop of infested acorns when acorn availability on the ground was low. Predation rates on infested acorns were much higher where ungulates were present, and acorn infestation rates were significantly lower. However, ungulates did not provide the oaks any net benefit, since the reduction of infestation rates was not enough to compensate for the large amounts of sound acorns eaten by ungulates. Seed predation is usually studied as a progressive loss of seeds by pre- and post-dispersal predators, but the interactions between them are usually not considered. We show that intraguild predation on insects by large ungulates had an effect on the structure of the foraging guild, as the proportion of acorns predated by insects decreased; however, replicating the same experimental design in different ecological scenarios would increase the strength of these results. In conclusion, the present study shows the importance of considering the multi-trophic interactions between seed predators in order to have a complete picture of granivory.

Acorn Fall and Weeviling in a Northern Red Oak Seedling Orchard

In 2000, we determined levels of damage by acorn weevils (Curculio spp.) and patterns of acorn fall in a northern red oak (Quercus rubra L.) seedling orchard in eastern Tennessee. The mean (±SE) production of acorns among 43 selected trees was 5,930 ± 586 acorns per tree with a maximum production level of 16,969 acorns for one tree. Trees were selected in the spring of 2000 based on abundance of acornets. The mean (±SE) damage level to acorns was 33 (±2) percent (determined by dissection). The floating method for assessing sound acorns overestimated acorn damage by 36 percent overall. Weevils accounted for approximately 66 percent of all damage to acorns. We found that the percentage of weeviled acorns was negatively correlated to total acorn production per tree. The rate of acorn drop was higher in October and November than in September. However, the percentage of acorns damaged by weevils was higher for acorns falling in September than for acorns falling in October or November.

Does the shelterwood method to regenerate oak forests affect acorn production and predation?

The shelterwood system is one of the primary methods currently used to encourage regeneration of oak forests; yet, little is known about its influence on acorn production and predation. We compared acorn production, and predation by insects and mammals in stands of red oak ( Quercus rubra L.) that were regenerated by the shelterwood method (50% canopy removal) to that of uncut (control) stands in the first year of production after the harvest treatment. In each plot, we measured stand and tree characteristics and estimated acorn production by using both acorn traps and a visual crown survey to place trees into productivity classes. Acorns collected in traps were examined to record the external and internal conditions, percentage of cotyledon damaged and the presence of insects. Exclusion cages were used to quantify acorn predation by mammals in harvested and control plots. Oaks in the shelterwood plots produced more acorns than oaks in uncut stands if the acorn crop was rated by the crown survey method, but not when production was measured with acorn traps. We found no evidence that the shelterwood method influenced acorn predation by insects or mammals. Visual examination of the exterior of the pericarp indicated that insects attacked 44% and 47% of the acorns in harvested and control plots, respectively. Most of the damage produced by insects was attributed to pip galls (cynipid wasps) and acorn weevils ( Curculio sp.), which in most cases damaged more than 75% of the cotyledon. Squirrels and chipmunks were the primary mammals responsible for removing 50% of the acorns in the fall-spring whereas mice took 33% of the acorns. Use of the shelterwood method in conjunction with leaving the best acorn producers can be used to create the desired stand structure while maintaining or increasing acorn production and oak regeneration potential in the stand.

The phylogeny of acorn weevils (genus Curculio) from mitochondrial and nuclear DNA sequences: the problem of incomplete data

We considered the contribution of two mitochondrial and two nuclear data sets for the phylogenetic reconstruction of 22 species of seed beetles in the genus Curculio (Coleoptera: Cuculionidae). A phylogenetic tree from representatives found on various hosts was inferred from a combined data set of mitochondrial DNA cytochrome oxidase subunit I, mitochondrial cytochrome b, nuclear elongation factor 1α, and nuclear phosphoglycerate mutase, used for the first time as a molecular marker. Separate parsimony analyses of each data set showed that individual gene trees were mainly congruent and often complementary in the support of clades but the analysis was complicated by failure of PCR amplification of nuclear genes for many taxa and hence missing data entries. When the four gene partitions were combined in a simultaneous analysis despite the missing data, this increased the resolution and taxonomic coverage compared to the individual source trees. Alternative approaches of combining the information via supertree methodology produced a comparatively less resolved tree, and hence seem inferior to combining data matrices even in cases where numerous taxa are missing. The molecular data suggest a classification of the European species into two species groups that are in accordance with morphological characteristics but the data do no support any of the previously recognised American species groups.

Acorn selection by Mexican jays: a test of a tri-trophic symbiotic relationship hypothesis.

By caching acorns, jays serve as important dispersal agents for oak (Quercus) species. Yet little is known about which acorn characteristics affect selection by jays. In the traditional model of jay/oak symbiosis, large, brown, ripe acorns free of invertebrate parasites (e.g., Curculio acorn weevils) are selected by jays. Recently, it has been suggested that a tri-trophic relationship between oaks, jays, and weevils may have evolved to counter the negative dietary effects of acorn tannins. Under the tri-trophic model, jays would preferentially select acorns containing weevil larvae. We tested the assumptions that (1) acorns containing curculionid larvae exist in sufficient quantities to support jay populations and (2) jays can detect, and preferentially select, acorns containing weevil larvae, and investigated the cues by which jays select acorns. Captive Mexican jays (Aphelocomaultramarina) were presented Emory oak (Quercusemoryi) acorns in aviary feeding trials. Large, dense, viable acorns free of curculionid larvae were preferentially selected. Contrary to results of previous research, color did not affect selection. Acorn viability increased and curculionid larval occupancy decreased in adjacent savannas and isolated stands relative to existing oak woodland, perhaps favoring oak recruitment into adjacent lower-elevation grasslands. Our results compel us to reject the tri-trophic model for this system, and are consistent with the traditional jay/oak symbiosis model. Relatively long-distance dispersal of viable acorns favors Emory oak replacement, and spatial patterns of acorn viability and curculionid parasitism suggest expansion of Emory oak into adjacent low-elevation semi-arid grasslands.

Tannins and Partial Consumption of Acorns: Implications for Dispersal of Oaks by Seed Predators

-A common assumption in studies of seed predation is that seeds survive attack and are dispersed only 'when animals fail to find seeds, drop undamaged seeds or fail to recover seeds after they are cached. This study, however, suggests that many acorn consumers consistently eat only a portion of the cotyledon of several species of acorns and thereby permit embryo survival. Several vertebrates [gray squirrels (Sciurus carolinensis), common grackles (Quiscalus quiscula) and blue jays (Cyanocita cristata)] were observed to consume only 30-60% of the cotyledon from the basal portion (cap end) of willow oak (Quercus phellos) acorns. Gray squirrels exhibited a similar preference for the basal end of acorns of several other species of red oaks (Q. rubra, Q. laevis, Q. nigra, Q. palustris and Q. coccinea) from a wide geographic region. In addition, acorn weevil larvae (Curculio sp.) were observed significantly (>35%) more often in the basal portion than in the apical end of Q. alba acorns. Chemical analyses of acorns from two tree species revealed that the concentration of protein-precipitable phenolics (primarily tannins) was 12.5% (Q. phellos) and 84.2% (Q. laevis) higher in the apical portion of the seeds where the embryo is located. Moreover, germination experiments revealed equal or greater germination frequencies for partially consumed acorns than for intact acorns. We suggest that the higher tannin levels may render the apical portion less palatable, and thereby increase the probability of embryo survival after attack by seed consumers.

Blarina brevicauda and Peromyscus leucopus Reduce Overwinter Survivorship of Acorn Weevils in an Indiana Hardwood Forest

We tested the hypothesis that free-ranging white-footed mice (Peromyscus leucopus) and northern short-tailed shrews (Blarina brevicauda) reduce the survivorship of acorn weevils (Coleoptera: Curculionidae) overwintering in forest soils. Field exclosures differentially excluding these and other vertebrate insectivores, in combination with translocation of individual shrews from one site to another, were employed over 2 winters. The presence of small mammals led to a significant reduction in survivorship of weevils, but no effect due to density of shrews or presence of other potential predators (e.g., birds) was detected. These results are consistent with the hypothesis that these small mammals, through their consumption of weevils, have a positive effect on oak populations, and thus can affect forest composition and functioning.

Dietary circumvention of acorn tannins by blue jays : Implications for oak demography.

Blue jays consume large quantities of acorns to fuel energy-demanding caching flights in the fall. Yet blue jays possess no known physiological adaptation to counter the negative effects of a high tannin diet on protein digestion. Dietary experiments were conducted to determine if blue jays could subsist on an acorn-only diet, and if they could not, to determine whether supplements of acorn weevil larvae (Curculio), present inside acorns, enabled them to maintain their mass. Comparative tannin assays also were conducted on Lepidobalanus (low tannin; white oak) and Erythrobalanus (high tannin; pin oak) acorns using radial diffusion assay. Captive jays consumed considerable acorn material, yet were unable to maintain mass on ad lib. acorn-only diets or on an acorn +1.5 g larvae/day supplement. There were no significant differences in mass loss between high and low tannin diets. In contrast, blue jays were able to stabilize mass on a diet of acorns +5.0 g larvae supplement/day. These results suggest that acorn weevil larvae, or perhaps other insects, counteract the effects of acorn tannins in the jay diet allowing jays to subsist largely on acorns during the fall caching season. Oak demographic processes may be partly regulated by a tri-trophic relationship among plant, insect and bird. Acorn weevil larvae, considered damaging to oak populations, may actually facilitate oak recruitment and population vagility in the long-term.

Growth of Live Oak from Seed Hydrothermally Treated to Control Acorn Weevil Larvae

Abstract Live oak (Quercus virginiana Mill.) acorns harvested for commercial seedling production frequently are heavily infested by larvae of Curculio spp. (2). Many nurserymen routinely soak acorns for 30 min in 49°C water to kill weevil larvae before planting the seed (4). Microwave radiation is effective against some stored products pests, but it is too damaging for use against acorn weevil larvae (2). Crocker and Morgan (1) measured the short-term (12-day) effects of hydrothermal treatments of tree-harvested acorns on survival of weevil larvae and seed germination, using 0- to 60-min immersion of the seed in 43.3° to 60.0° baths. Treatment for any of the tested times at a minimum of ≈49° controlled 100% of the weevils; it also produced dosage-related plant mortality and reduction in the short-term growth of seedlings. In the present research, we examined the survival and long-term vigor of acorns that were exposed to a 49° hydrothermal treatment.

Scarifying Agents and Pathogens Screened Against Pecan Weevil Larvae in the Laboratory, 1986

Abstract Pecan weevil larvae were exposed to various scarifying agents, pathogens, and combinations of these 2 groups in 1 pt styrofoam cups. Ten holes were punched in the bottom of the cups for drainage. Pecans infested with weevil larvae and soil were collected from an insecticide free orchard at Byron, Ga., in late Sep. Nuts were held in the laboratory and weevil larvae were collected as they emerged. The soil was sterilized and the soil moisture content was brought to field capacity (13%). Clay was packed in the bottom half of the cups. Topsoil was placed on the clay filling the next quarter of the cup. Treatments were then added to the top soil and 10 mature weevil larvae were placed in each of 8 cups/treatment. Cups were covered with parafilm. Treatments included tests 1 and 2—diatomaceous earth (MN36 and MP78), perlite, sand, vermiculite, and untreated; test 3—Beauveria bassiana ex pecan weevil (in solution and as dry spores on top of the soil), Metarhizium anisopliae ex pecan weevil (in solution), perlite, sand, soil containing dead pecan weevil larvae, vermiculite, and untreated; and test 4—Bacillus thuringiensis tenehrio, Bacillus thuringiensis tenehrio + diatomaceous earth (MN36), Beauveria bassiana + diatomaceous earth (MN36), Metarhizium anisopliae + diatomaceous earth (MN36), soil containing an unknown agent causing disease in the acorn weevil Conotrachelus posticatus Boheman, and untreated. Cups were scored for weevil mortality after 30 days in test 1 and 120 days in tests 2-4. Data were analyzed by analysis of variance and contrasts.

Control of Weevil (Curculio sp.) Larvae in Acorns of the Live Oak (Quercus virginiana) by Heat1

Abstract Mature acorns of the live oak (Quercus virginiana Mill.) were immersed for 0-60 minutes in 43.3 to 60.0°C (110 to 140°F) water baths. Various of those treatments produced up to 100% control of larvae of acorn weevils (Curculio sp.) in the seeds, but reduced acorn germination and radicle length to varying degrees.

The status of Paykull's Curculio fuscirostris (Coleoptera: Curculionidae)

AbstractAlthough Paykull cited Fabricius as author of the name Curculio fuscirostris, several authors have wrongly attributed the name to Paykull, listing it as a synonym of Tychius picirostris (Fabricius) or T. stephensi Schönherr. Paykull's usage, however, was based on a misidentification, so Paykull cannot be cited as author, nor can the name replace any currently in use in Tychius.

Plautus for Production: Captivi, Curculio, Mostellaria, with Five Scenes from Other Comedies. Adapted, with Running Vocabulary and Notes

Plautus for Production: Captivi, Curculio, Mostellaria, with Five Scenes from Other Comedies. Adapted, with Running Vocabulary and Notes

Insect Damage to Acorns in West Virginia and Control Studies Using Granular Systemic Insecticides1

Studies were conducted to determine the kind, extent, and prevalence of insect damage to acorns in West Virginia. The most prevalent and destructive insect was the acorn weevil (Curculio spp.). Acorn insect control studies were also made using granular, systemic insecticides applied (1× and 2× rates of application) on the humus layer around the base of mature oaks. All treatments with phorate and Di-Syston® (O,O-diethyl S-[2-(ethylthio)ethyl] phosphorodithioate) controlled acorn weevils in forest oaks (red and white) to some degree. The average acorn weevil in festation for 3 years in chemically treated oaks was 35% as compared with 58% in untreated oaks. There was considerable evidence that an application of either of these chemicals in early June was more effective than one or more made later in the season and that the lower rate (1×) of application was just as effective as the higher rate (2×). Data from 2 of the 3 years' study indicated that phorate was slightly more effective in controlling acorn weevils in white oaks and that Di-Syston was more effective in red oaks.

Observations on Certain Lepidopterous and Hymenopterous Parasites of Polistes Wasps

In an article entitled “Studies in the Ecology and Behavior of Polistes Wasps” (Bull. Brooklyn Ent. Soc. 33: 224–235, 1938, and 34:36–44, 1939) I state that Lepidopterous parasites, Dicymolomia pegasalis emerged from a nest of Polistes pallipes . This statement brought an inquiry from a friend who wanted to know what the moth had fed upon in its larval stage. Did it, he asked, feed upon the wasp-larva itself, or the larval excrement plastered against the ceiling of the cell or was it perhaps upon the papery material of the nest? This moth belongs to the family Pyralididae, a few of whose members, like those of the Tineidae and a few other families of small moths, have acquired strange and unusual feeding habits. Many species have strayed so far from the generally accepted vegetarian habits of Lepidoptera as to be nothing short of astonishing. Mr. H. I. O'Byrne has called my attention to a few of the most outstanding examples. For example, there are two species belonging to the family Pyralididae, Cryptoses choloepi [1][1] and Bradipodicola hahneli [2][2] which inhabit the fur of living sloths, living continuously in it and causing its matted condition. Then there are two species of moths, Tinea vastella [3][3] and T. orientalis [4][4] that have been bred from the horns of cattle, where they feed upon the horny tissue. The larvae of Zenodochium coccivorella [5][5] and of Euclemensia bassettella [6][6] are internal parasites of the females of Kermes (Coccidae). The caterpillar of the latter species cuts a lid in the Kermes' gall so that it may easily emerge when it becomes adult. Tinea fuscipunctella (Forbes, ibid. , p. 126) breeds in the trash of pigeon nests and Triohophaga tapetzella (Forbes, ibid. , p. 131) is a clothes moth and general scavenger often breeding in owl pellets; while the larvae of Monopis crocicapitella (Forbes, ibid. , p. 132) breed in seeds of absinth and in refuse, and have also been taken in caves in association with bats. The larvae of Valentinia glandulella (Forbes, ibid. , p. 310) are scavengers on acorn weevils, while V. quaintancella (Forbes, ibid. , p. 327) are known to feed on mummy-apples, i. e. , apples entirely black and shriveled up from disease. Pyroderous rileyi (Forbes, ibid. , p. 327) feeds on mummy fruits, rotten cotton-balls and stored corn. We must not forget the notorious wax moths, Galleria mellonella and Achroia grisella which are scavengers in the comb and the wax of the honey-bee, and finally we have certain species such as Aphomia sociella and Vitula edmandsii whose larvae are found in the nests of bumble bees (Forbes, ibid. , p. 631). [1]: #fn-1 [2]: #fn-2 [3]: #fn-3 [4]: #fn-4 [5]: #fn-5 [6]: #fn-6

EXTRACT FROM A REPORT ON THE PLUM CURCULIO, (Conotrachelus nenuphar.)

The accompanying figures shows the curculio in all its stages. a, is the larva, b, the chrysalis, c, the perfect beetle, all magnified, the adjoining lines shows the natural size, d, is a small plum with the curculio (natural size) working on it. One egg is deposited under the crescent cut, and a second incision is being made. I shall now refer to some experiments of my own on this insect which will, I hope, add something to our knowledge of the creature's habits.