Pioneer-Follower dilemma game in <Emphasis Type="Italic">Acanthoscelides obtectus</Emphasis> (Coleoptera: Bruchidae)

Larvae of Acanthoscelides obtectus show two contrasting behaviors when entering a bean. One is pioneer behavior in which a larva enters the bean through an entrance hole made by itself; the other is follower behavior in which a larva enters the bean through an entrance hole made by a pioneer. Previous studies have shown that the number of followers is much greater than that of pioneers. If there is a cost to being a pioneer, and if larvae can choose either of the two strategies, there is a dilemma: to be a pioneer or not. This dilemma is similar to the chicken game because if all larvae avoid choosing the risky pioneer strategy in favor of the follower strategy, none of the larvae can enter a bean, and they will die. In the present study, in order to investigate whether the larvae of A. obtectus are facing a dilemma of entry order, we experimentally measured the cost to pioneers and tested the flexibility of larval entering strategies. Pioneers’ costs were measured by entrance success rate, and the flexibility of larval strategies was tested by gauging the proportion of pioneers at various larval densities. The entrance success of pioneers was lower than that of followers, and the proportion of pioneers decreased as the number of competing larvae increased. These results suggest that the Pioneer-Follower interaction in A. obtectus satisfies the conditions for a dilemma game: the larvae of A. obtectus are in a dilemma of entry order.     

Histological changes during maturation in male and female cones of the cycad Zamia furfuracea and their significance in relation to pollination biology

The cycad Zamia furfuracea L.Fil. Is pollinated by a curculionid beetle, Rhopalotria mollis Sharp which completes its life cycle in male cones of the cycad, and effectively pollinates female coneS. Idioblasts within parenchyma in both male and female cones appear to contain toxic compounds, including at least one neurotoxin, 2-amino-3-(methylamino) propanoic acid (BMAA), and a toxic glycoside, methylazoxymethanol-/!-primeveroside (macrozamin). Idioblasts appear structurally unmodified in male cones throughout the period of pollen maturation, and feeding weevils consume much of the starch-rich microsporophyll parenchyma tissue, including idioblastS. During this activity no appreciable change in morphology or staining reactions of male-cone idioblasts is detectable. Prior to pollen receptivity, female-cone idioblasts resemble those of male cones. Thereafter, many female-cone idioblasts show marked changes in morphology and content not caused by the weevils themselveS. Idioblast changes in female cones are probably associated with the defence of female-cone resources against predation by animals, including pollinating weevils, and may relate to mobilization of toxinS. Absence of similar morphological changes in male-cone idioblasts is correlated with toxin sequestration, enabling the pollinator to breed and feed without intoxication.     

Rainforest conversion to smallholder cash crops leads to varying declines of beetles (Coleoptera) on Sumatra

Southeast Asian arthropod biodiversity is in rapid decline, but the variability of responses within taxa has received little attention. Using canopy fogging, we collected ~50,000 beetles (Coleoptera) in (1) lowland rainforest, (2) jungle rubber (rubber agroforest), and smallholder monoculture plantations of (3) rubber and (4) oil palm in Sumatra, across two landscapes and seasons. On average, beetle abundance was more than 50%, and biomass over 75%, lower in rubber and oil palm plantations than in rainforest and jungle rubber. This pattern was influenced by landscape and season. Abundance and biomass declines were similar in Chrysomelidae, Elateridae, and Staphylinidae, but differed in Curculionidae, which were most abundant in oil palm due to the introduced oil palm pollinator Elaeidobius kamerunicus. Across beetle families, species richness in monocultures was reduced by at least 70% compared to rainforest, with beetle richness in jungle rubber being similar to rainforest. Community composition in oil palm plantations differed markedly from the other land-use systems for Chrysomelidae and Curculionidae, but less for Elateridae and Staphylinidae. Turnover contributed more to overall beta diversity than nestedness for all families and land-use systems. Likely undersampling of the beetle community in rainforest suggests that declines of beetle density and diversity are much more severe than reported here, especially for beetle families with many concealed species, such as Staphylinidae. This study provides first evidence that negative responses of beetles to tropical land-use change vary among families, and is the first report of its kind from heavily understudied Sumatra.     

An analysis of the pattern of feeding in the Costa Rican weevil, Exopthalmus jekelianus, on the tropical tree, Cedrela odorata

Feeding patterns were recorded and analysed for adult female weevils, Exopthalmus jekelianus (White) (Coleoptera: Curculionidae), feeding on Central American mahogany, Cedrela odorata L., in the field in Costa Rica. The study forms part of an investigation into the relationship between feeding patterns and the fine-scale variation in leaf chemistry occurring within the host plant. The weevils’ feeding patterns were the simplest in temporal structure of any reported to date for an insect herbivore. Weevils spent an average of only 3% of their time feeding during the 10-h observation periods. Meals lasted an average of 2.8 min and occurred at a mean intermeal interval of 84 min. The feeding patterns gave the appearance of a short-term rhythm underlying the onset of feeding (as has been found in locusts and caterpillars), although there were insufficient meals taken by individuals over the 10-h period to test this suggestion. Meals were notable in apparently lacking intrameal pauses and also commencing without preliminary sampling behaviours, such as palpating or biting. Whether the combination of short, infrequent meals, ingested without pauses and not preceded by sampling behaviour, represents an adaptation reducing apparency to natural enemies, or else simply reflects low nutritional needs, is discussed. Correlations between meal durations and following and preceding intermeal intervals suggested that variation in intermeal intervals stemmed largely from variation in meal duration, not vice versa, with variation in meal duration resulting from an external influence such as leaf nutritional and/or allelo-chemistry. The latter suggestion is currently being tested.     

First phylogenetic analysis of Dryophthorinae (Coleoptera,Curculionidae) based on structural alignment of ribosomal DNA reveals Cenozoic diversification

Dryophthorinae is an economically important, ecologically distinct, and ubiquitous monophyletic group of pantropical weevils with more than 1,200 species in 153 genera. This study provides the first comprehensive phylogeny of the group with the aim to provide insights into the process and timing of diversification of phytophagous insects, inform classification and facilitate predictions. The taxon sampling is the most extensive to date and includes representatives of all five dryophthorine tribes and all but one subtribe. The phylogeny is based on secondary structural alignment of 18S and 28S rRNA totaling 3,764 nucleotides analyzed under Bayesian and maximum likelihood inference. We used a fossil‐calibrated relaxed clock model with two approaches, node‐dating and fossilized birth‐death models, to estimate divergence times for the subfamily. All tribes except the species‐rich Rhynchophorini were found to be monophyletic, but higher support is required to ascertain the paraphyly of Rhynchophorini with more confidence. Nephius is closely related to Dryophthorini and Stromboscerini, and there is strong evidence for paraphyly of Sphenophorina. We find a large gap between the divergence of Dryophthorinae from their sister group Platypodinae in the Jurassic‐Cretaceous boundary and the diversification of extant species in the Cenozoic, highlighting the role of coevolution with angiosperms in this group.