Bruchine Beetles Research Articles

Multivariate analysis on blackgram genotypes for bruchine (Callosobruchus maculatus F.) resistance towards selection of parental lines

Black gram (Vigna mungo (L.) Hepper) is one of the most important pulse crops in daily diets. However, black gram production and post-harvest preservation are still tedious due to the losses caused by the storage pest bruchine, Callosobruchus maculatus (F.), both quantitatively and qualitatively. Hence, the present study involves the utilization of the multivariate analysis by effectively understanding variation among the genotypes based on their level of bruchine infestation. The multivariate studies indicated that the traits viz., the total number of adult emergence (AE), seed damage % (SD) and seed weight loss % (SWL) had more variation and with more significant correlation among them. Also, these traits are the most influential principal component traits governing 88% of the variation among genotypes. The divergence analysis showed that the genotype TU 68 found in cluster II would have the potential to create the variation for bruchine infestation among the black gram genotypes involved in the study. As it has scored lesser adult emergence (AE) (7 adults), seed damage % (SD) (14 %) and seed weight loss % (SWL) (17.79 %) than the other genotypes. It shows the resistant nature of the genotype against bruchine beetles. Hence, TU 68 could be utilized in the future hybridization programme as a donor for bruchine resistance.

Host‐plant range expansion to Gymnocladus dioica by an introduced seed predatory beetle Megabruchidius dorsalis

AbstractA seed predatory beetle, Megabruchidius dorsalis (Coleoptera: Chrysomelidae: Bruchinae) native to the Oriental region was first found to utilize a North American Gymnocladus dioica (Fabaceae: Caesalpinioideae) in its introduced area in Central Europe. A maximum of three adult exit holes were found on a single seed. Host‐plants of the bruchine beetle have been reviewed from its native and introduced regions, including a host record of Gleditsia fera from Taiwan. Our review indicated the beetle's strict oligophagy on caesalpinioid Gleditsia species. On the contrary, our finding suggests that the beetle's host‐range extends to the caesalpinioid Umtiza clade. On the plant side, this study provides a counterexample to the enemy release hypothesis that predicts fewer predators/parasites in an organism's range of introduction than in their native range; Gy. dioica is attacked by the seed predator in its introduced region, whereas in its native range it is free from seed predators.

Genetic structure, species limits and evolution of the parasitoid wasp genus Stenocorse (Braconidae: Doryctinae) based on nuclear 3RAD and mitochondrial data

AbstractStenocorse (Braconidae: Doryctinae) is an ectoparasitoid wasp genus widely distributed from southern U.S.A. to central Argentina, which is known to attack over 60 bruchine beetle species that feed on a variety of legumes. This genus currently comprises a single described species, S. bruchivora (Crawford, 1910), though it is probably composed of additional, morphologically similar species. In this study we investigated genetic structure, species limits and evolutionary relationships of sampled populations of Stenocorse obtained along its known geographic distribution, with an emphasis on the Mexican territory. For this, we generated DNA sequences from both the mitochondrial (mt) barcoding locus and nuclear genome data obtained with the 3RAD technique. The Bayesian phylogenetic reconstructions based on the two datasets were mostly congruent, both showing clear geographic structure. Four clusters were recovered with nuclear data, which were also congruent with the geographic distribution of the samples and the species delimitation analyses. We delimited six evolutionary lineages with the two data sources, and three additional species were also delimited with the COI locus alone. Stenocorse probably originated during the mid‐ to early Miocene, and the diversification events that led to its current species distribution probably occurred between the early Pliocene and late Pleistocene. Our species delineation analyses, phylogenetic reconstructions and rearing records suggest that the species of Stenocorse have generalist feeding habits, contrary to what was expected due to host plant specialization of the bruchine species and the cascading effect that this could have in the species diversification of their parasitoids.

When a seed-feeding beetle is a predator and also increases the speed of seed germination: an intriguing interaction with an invasive plant

Bruchine beetles are usually considered seed predators, particularly because these beetles consume the seed embryo and kill the seeds. Previous studies suggest that under certain conditions, these insects do not kill the embryo. In this study, we asked whether the germination speed of seeds of the invasive tree Leucaena leucocephala is enhanced by the seed-feeding beetle Acanthoscelides macrophthalmus (Coleoptera: Chrysomelidae: Bruchinae). We also tested whether differences in germination between attacked and intact seeds could be related to seed size. We finally examined whether the number of larvae per seed affected seed germination and whether seedling emergence patterns were similar to those exhibited by germination. We found that compared to intact seeds, proportionally faster germination occurred in seeds attacked by A. macrophthalmus in 14 of the 26 populations studied. In addition, those populations that presented greater germination speed in the attacked seeds during the evaluation time also had the largest seeds. Similar to the germination experiments, seedling emergence was faster in the attacked compared to the intact seeds. Our findings show that the germination speed of L. leucocephala seeds can be enhanced by A. macrophthalmus. However, this effect is much more intense when a single larva develops inside the seed. In evolutionary terms, it is possible that the selection for larger seeds is favoured, increasing the speed of seed germination and contributing to predator satiation at the seed level. However, this effect could be minimized by the production of many seeds by L. leucocephala plants, causing predator satiation by “masting” effects, which would favour the selection for higher seed numbers.

The role of herbivorous insects and pathogens in the regeneration dynamics of Guazuma ulmifolia in Panama

A significant proportion of the mortality of rainforest trees occurs during early life stages (seeds and seedlings), but mortality agents are often elusive. Our study investigated the role of herbivorous insects and pathogens in the early regeneration dynamics of Guazumaulmifolia (Malvaceae), an important tree species in agroforestry in Central America. We reared pre-dispersal insect seed predators from G.ulmifolia seeds in Panama. We also carried out an experiment, controlling insects and pathogens using insecticide and/or fungicide treatments, as well as seed density, and compared survivorship of G.ulmifolia seeds and seedlings among treatments and relative to untreated control plots. We observed (1) high pre-dispersal attack (92%) of the fruits of G.ulmifolia, mostly by anobiine and bruchine beetles; (2) negligible post-dispersal attack of isolated seeds by insects and pathogens; (3) slow growth and high mortality (> 95%) of seedlings after 14 weeks; (4) low insect damage on seedlings; and (5) a strong positive correlation between seedling mortality and rainfall. We conclude that for G.ulmifolia at our study site the pre-dispersal seed stage is by far the most sensitive stage to insects and that their influence on seedling mortality appears to be slight as compared to that of inclement weather. Thus, the regeneration of this important tree species may depend on effective primary dispersal of seeds by vertebrates (before most of the seed crop is lost to insects), conditioned by suitable conditions in which the seedlings can grow.

An entomocentric view of the Janzen–Connell hypothesis

In 1987, in the first issue of Conservation Biology, Edward O. Wilson wrote about the “little things that run the world” – the importance and conservation of insects (Wilson, 1987). Readers of Insect Conservation and Diversity will no doubt be very familiar with the concept. Sadly, however, this perception is not as widely shared among the rest of the scientific community as it should be, and insects are still comparatively neglected as a prime focus of scientific investigations.

Geographic distribution, large-scale spatial structure and diversity of parasitoids of the seed-feeding beetle Acanthoscelides macrophthalmus.

Bruchine beetles are highly host-specific seed feeders during the larval stage. Although some specific parasitoid families have been recorded attacking bruchine beetles, most studies have been done at small spatial scales. Therefore, the current knowledge about the diversity and the geographic distribution of parasitoid species parasitizing bruchines is scarce, especially at a wide geographic area that extends over large distances through a latitudinal cline (i.e. large-scale spatial structure). The present study determined the species richness and evenness of parasitoids attacking the bruchine beetle Acanthoscelides macrophthalmus feeding on Leucaena leucocephala seeds, examined their geographic distribution, and characterized the large-scale spatial structure in parasitoid species composition. A total of 1420 parasitoids (all Hymenoptera) belonging to four families, five subfamilies and eight species were collected (genera: Horismenus, Paracrias, Urosigalphus, Stenocorse, Chryseida, Eupelmus). Most parasitoid species showed wide spatial distribution, high evenness in species abundance and the species richness estimators were close to stabilization (approximately eight species). Overall, greater similarity was observed in the species composition of plant populations near to each other than those farther apart, revealing a large-scale spatial structure in parasitoid species composition.

The Extent of Seed Predation by Bruchine Beetles (Coleoptera: Chrysomelidae: Bruchinae) in a Heterogeneous Landscape in Southeastern Brazil

In this study, seed predation rates imposed by bruchines and the composition of bruchine species and their host plants were assessed in a heterogeneous landscape in southeastern Brazil. Fruits were collected from 49 plants from 16 species belonging to four families, primarily Fabaceae. The five bruchine species collected emerged from four plant species as follows: Acanthoscelides macrophthalmus (Schaeffer) from Leucaena leucocephala (Lamarck) de Wit, Acanthoscelides sp. from Senna hirsuta (L.) Irwin and Barneby, Ctenocolum podagricus (F.) from Lonchocarpus müehlbergianus Hassler, and Gibbobruchus polycoccus (Fähraeus) and Gibbobruchus speculifer (Gyllenhal) from Bauhinia forficata Link. Bauhinia forficata is here recorded for the first time as a host for G. polycoccus. Only 1/4 of the local flora that was surveyed hosted bruchines. Bruchine and plant species composition varied among habitats, with most beetles found in plants located in the most disturbed habitat. Because of the economic importance of L. leucocephala in the tropics, we compared germination percentages between attacked and unattacked seeds of this species. The unattacked seeds had an average germination rate of 59%, and none of the attacked seeds germinated, showing that the germination of L. leucocephala seeds was drastically affected by predation.

Description and Differentiation of the Four Larval Instars of Acanthoscelides macrophthalmus (Coleoptera: Chrysomelidae: Bruchinae)

Abstract Bionomic data usually hold the key for understanding the life history of the target insect species. Here, we provide morphological characteristics of different larval instars of Acanthoscelides macrophthalmus (Schaeffer), a leucaena bruchine beetle species that is a potential biocontrol agent for the notoriously invasive plant Leucaena leucocephala. The scanning electron micrographs of the head capsule, antenna, clypeolabrum, maxilla, labium, leg, spiracle, and anus of the larval stage of A. macrophthalmus also are provided for the first time for this species, with most of the traits reflecting the taxonomic placement of A. macrophthalmus in the genus Acanthoscelides. Successive instars are determined accurately by using a model of the distribution of the width of the larval head capsule. Therefore, the data generated from this study represent baseline information for further biological control programs involving A. macrophthalmus.

Larval Competition Reduces Body Condition in the Female Seed Beetle,Callosobruchus maculatus

Early body condition may be important for adult behavior and fitness, and is impacted by a number of environmental conditions and biotic interactions. Reduced fecundity of adult females exposed to larval competition may be caused by reduced body condition or shifts in relative body composition, yet these mechanisms have not been well researched. Here, body mass, body size, scaled body mass index, and two body components (water content and lean dry mass) of adult Callosobruchus maculatus (Fabricius) (Coleoptera: Chrysomelidae: Bruchinae) females exposed to larval competition or reared alone were examined. Experimental females emerged at significantly smaller body mass and body size than control females. Additionally, scaled body mass index and water content, but not lean dry mass, were significantly reduced in experimental females. To our knowledge, these are the first results that demonstrate a potential mechanism for previously documented direct effects of competition on fecundity in female bruchine beetles.

Increased Productivity and Reduced Seed Predation Favor a Large‐seeded Palm in Small Atlantic Forest Fragments

ABSTRACTLarge‐seeded plants are especially vulnerable to the loss of seed dispersers in small forest fragments. The palm Attalea humilis goes against this trend by reaching high abundances in small remnants. Productivity, seed dispersal and seed predation of A. humilis were investigated in two large (2400 and 3500 ha) and three small (19, 26 and 57 ha) Atlantic Forest fragments in southeastern Brazil. Palms in the small fragments produced more female inflorescences, resulting in a higher fruit production in these places. Seed dispersal rates were higher in the large fragments, where scatter hoarding was more frequent. Scolytine beetles were the main seed predators and damaged a larger number of seeds in small fragments, but predation by rodents and bruchine beetles was low irrespective of fragment size. As scolytines do not necessarily kill the seeds, low predation by bruchines and rodents, together with its own high productivity, allow A. humilis to be more abundant in small fragments despite the scarcity of its main dispersers. This increased abundance, by its turn, can increase competitive interactions between A. humilis and other plants in small fragments. Thus, abundance patterns of A. humilis are a good example of fragmentation affecting the balance of ecological interactions in a complex way, emphasizing the role of preserving ecological processes for conserving biodiversity in fragmented tropical landscapes.Abstract in Portuguese is available at http://www.blackwell‐synergy.com/loi/btp.

Parasitoid attack of the seed-feeding beetle Bruchus loti enhances the germination success of Lathyrus japonicus seeds

Hard seeds of some legume species can germinate after seed-feeding insects bore through the seed coat and consequently break seed dormancy. Larvae of bruchine beetles are the main seed feeders attacking many legume species. Boring of the hard seed coat by bruchine beetle larvae enhances the germination percentage of legume species, but consuming too much of a single seed may reduce the chances the seed will survive. We hypothesise that the early mortality of bruchine larvae due to parasitism contributes positively to seed germination because larvae are killed before consuming too large a quantity of the seed. Here, we tested this hypothesis using Lathyrus japonicus seeds and Bruchus loti, the main seed feeder attacking this plant. B. loti larvae were mainly parasitised by two species of idiobiont parasitoids—Pteromalus sp. and Dinarmus sp. The seeds from which Pteromalus wasps emerged germinated more successfully than did the seeds from which B. loti adults emerged. B. loti larvae parasitised by the two wasp species consumed the seeds less intensively than did unparasitised larvae. Thus, the results of experiments supported our hypothesis. However, the germination success varied significantly between the seeds from which Pteromalus and Dinarmus wasps emerged. The difference in the size of seeds the two wasp species chose for parasitism may have influenced the germination percentage.

Evolutionary diversification of bruchine beetles: climate-dependent traits and development associated with pest status

A number of insect species infest human households and stored foods and products, leading to their designation as pests. Until recently, little was known about the factors driving the evolution of pests that feed on stored dry foods. Here, I review the effects of changes in climate and species interactions on the evolution and ecology of beetles that feed on dried seeds/grains. My review focuses on evidence that the host utilization by part of the species in the subfamily Bruchinae (Chrysomelidae) is a preadaptation for utilizing stored dry seeds and grains, thus leading to their status as a pest. These and other stored product pest beetles retain a higher percentage of water in their body, relative to the water content of their diet, than beetles that feed on fresh crops. I review the studies that have documented adaptation, acclimation and polyphenetic response to high temperatures and desiccation and/or made direct comparisons between these traits between developmental stages, populations and among higher taxonomic groups. Finally, I review evidence for the effects of environmental change on insect host-parasitoid and competitor assemblages.

Over‐wintering stage polymorphism of a bruchine beetle: geographical variation in optimal diapause strategy

Abstract 1. Most temperate insects undergo diapause at a specific developmental stage to overcome severe winters. The bruchine beetle Bruchidius dorsalis in a warmer region in Japan, however, has diverse over‐wintering stages – non‐diapausing larvae, diapausing larvae, and diapausing adults, whereas in a cooler region, it over‐winters only as the final instar larva or adult in diapause.2. The geographical pattern of over‐wintering stages in 12 populations was investigated over a wide range along the mainland of Japan. It revealed that a distinct geographical pattern of over‐wintering stages exists in relation to temperature conditions. In regions with warmer climates, the proportion of non‐diapausing larvae increased and B. dorsalis had a more complex over‐wintering stage structure.3. Life cycles were also compared between two areas of Japan by field experiments. In the cooler area, the first generation over‐wintered in the diapausing larval or adult stage. Conversely, in the warmer area, diapause was induced later and some of the first‐generation adults produced second‐generation offspring before over‐wintering.4. Based on the geographical cline of climates and the differences in cold hardiness among stages, we can demonstrate that the over‐wintering stage variation among and within populations results from an adaptive timing of diapause induction in each region, because the late larval or adult diapauses protect pupae or eggs – which unlike other stages are not cold hardy – from being produced late in the season.

Dissecting the evolutionary impacts of plant invasions: bugs and beetles as native guides

AbstractThe introduction of plants into new biogeographical realms is a main repercussion of human trade. The responses of native insects to alien plants may provide insight into how invaders influence ecological processes in their new communities. We illustrate this point with results from our field and lab studies of seed‐feeding insects on alien plants. Soapberry bugs (Jadera, Leptocoris) have colonized several species of weedy invasive plants (sapindaceous trees and vines) in the United States and Australia. After initial reduction in physiological performance, they evolved behavioral, morphological, physiological and life history adaptations permitting more efficient exploitation of those hosts. Those changes occurred quickly, in fewer than 100 generations (ca. 30–50 years). The underlying genetic changes are surprisingly complex, and also involve loss of function on native hosts. Contrasting with this is the bruchine beetle (Stator limbatus) on seeds of leguminous trees. Large numbers of S. limbatus oviposit on an alien tree in Arizona, but few offspring survive. The main influence on larval survival is a maternal effect determined by the host the mother experiences as her eggs mature. Adaptive plasticity in egg size and composition may ultimately permit successful exploitation of novel resources. Together, these studies show that both complex genetic and developmental factors influence the integration of ecological and evolutionary processes in environments altered by anthropogenically initiated plant invasions. Tractable insect study systems may be valuable guides to understanding biotic dynamics in a changing world.

Dinâmica populacional de bruquíneos (Coleoptera, Chrysomelidae) em Senna multijuga (Rich.) H. S. Irwin & Barneby (Caesalpinaceae)

Senna multijuga (Rich.) H. S. Irwin & Barneby (Caesalpinaceae) é uma planta ornamental comum no sudeste do Brasil, suscetível ao dano por bruquíneos predadores de sementes. Com o objetivo de identificar os predadores de suas sementes e determinar seus ciclos populacionais, frutos de cinco árvores foram coletados em 2000 e 2001 e acondicionados em casa de vegetação até a emergência de adultos. Os bruquíneos foram identificados como Sennius crudelis Ribeiro-Costa & Reynaud, 1998, S. puncticollis (Fåhraeus, 1839) e S. nappi Ribeiro-Costa & Reynaud, 1998. Sennius crudelis foi a espécie mais abundante em 2000, seguida por S. puncticollis e S. nappi. Em 2001, Sennius crudelis foi seguida por S. nappi e S. puncticollis. Diferenças foram observadas entre as árvores com relação ao período de frutificação, refletindo na oviposição. O período de emergência dos adultos se inicia em julho tanto em casa de vegetação quan-to no campo. Os resultados demonstraram que as dinâmicas populacionais dos bruquíneos são complexas e a compreensão desses processos contribui para responder a muitas outras questões ecológicas do grupo.