Oviposition by the riceinfesting weevil, Oryzophagus oryzae (Costa Lima, 1936) (Coleoptera, Curculionidae): influence of water depth and host-plant characteristics

Following characterization of the egg-laying site, oviposition site selection by the rice-infesting weevil Oryzophagus oryzae (Costa Lima, 1936) (Coleoptera, Curculionidae) was studied in relation to water depth, age and density of rice in outdoor tanks. Experimental units consisted of plastic pots that were filled with different soil amounts to obtain the desired water depths in the tanks. Most eggs were laid in the submerged portions of the leaf sheath within the leaves’ internal air space (aerenchyma). Oviposition rates increased linearly from 10.9 to 54.5 eggs per plant with an increase in water depth from 0 to 12 cm. There was a significant interaction between water depth and host plant age, and tiller density. In water varying from 4 to 12 cm deep, females oviposited significantly more eggs on 60-day old plants (average > 75 eggs per plant) than on 15-day old plants (average < 30 eggs per plant). Oviposition was negligible on 105 and 150-day old plants. Oviposition rates increased with tiller density in the 4-12 cm water depth interval. The dataindicate that females oviposit preferentially on tillering rice plants in relatively deep water, and that egg density is directly related to the number of tillers per plant

Leaf selection and daily variation on feeding and oviposition of Gratiana spadicea (Klug) (Coleoptera, Chrysomelidae, Cassidinae)

Gratiana spadicea(Klug) (Coleoptera, Chrysomelidae) is a monophagous beetle that feeds only on leaves of Solanum sisymbriifolium Lamarck (Solanaceae). We determined the portions of S. sisymbriifolium leaves that are used by the adults as feeding and oviposition sites. Daily variation on larval and adult feeding frequency, and on oviposition, was also registered under laboratory conditions (25oC; 70+10% rh). Larvae and adults were fed with S. sisymbriifolium leaves during photo (14 hours) and scotophase (10 hours). At the end of each phase, it was measured the leaf area they ate and registered position of their feeding marks on leaves. The oothecae were counted and noted, regarding their position on the leaf blade. Larvae and adults of G. spadicea showed feeding activity during photo and scotophase. Oviposition was restricted to photophase. Females leaf consumption rates were greater than those of the males. Adult feeding marks were most frequent on leaf margins. Oothecae were most frequently found near the central vein of the abaxial leaf surface. Daily ingestion rates grew exponentially through the larval stage; fifth instar ingested more than 60% of the total amount of food consumed by the larval stage. The possible adaptive mechanisms involved in such feeding and oviposition patterns are discussed

Conspecific mimics and low host plant availability reduce egg laying by Heliconius erato phyllis (Fabricius) (Lepidoptera, Nymphalidae)

Oviposition response of Heliconius erato phyllis (Fabricius, 1775) (Lepidoptera, Nymphalidae) to variation in host plant availability, Passiflora suberosa Linnaeus (Passifloraceae), and to presence of conspecific eggs and larvae was determined through choice experiments performed under insectary conditions. Freeze dried, painted eggs and larvae were used as mimics for testing presence of conspecific effects. Females laid more eggs on intact P. suberosa shoots without conspecifics than on those with H. erato phyllis egg and first instar mimics in both simultaneous and sequential choice trials. Oviposition response to variation in host plant availability was determined through no-choice trials, under host plant densities varying from 0.3 to 8.3 plants per female. Number of eggs laid per plant decreased exponentially with an increase in plant availability. On the contrary, daily oviposition rates (eggs /female/day) increased with an increase in plant number, and levelled off when the number of plants available for oviposition was greater than potential fecundity of females. Thus, it is inferred from the results that females assess egg and larval load and prefer to lay eggs on shoots free from conspecifics. It is also inferred that they are able to recognize plant abundance and are unwilling to lay more than one egg per shoot even when host availability is scarce, as judged by reduction in daily oviposition rates under low host plant number. The consequences of laying isolated eggs on P. suberosa shoots are discussed from the viewpoint of intraspecific competition in the larval stage of H. erato phyllis

Developmental pathway from leaves to galls induced by a sap-feeding insect on Schinus polygamus (Cav.) Cabrera (Anacardiaceae)

Galling sap-feeding insects are presumed to cause only minor changes in host plant tissues, because they usually do not require development of nutritive tissues for their own use. This premise was examined through comparison of the histometry, cytometry and anatomical development of non-galled leaves and galls of Calophya duvauae (Scott) (Hemiptera: Calophyidae) on Schinus polygamus (Cav.) Cabrera (Anacardiaceae). Cell fates changed from non-galled leaves to galls during the course of tissue differentiation. C. duvauae caused changes in dermal, ground, and vascular systems of the leaves of S. polygamus. Its feeding activity induced the homogenization of the parenchyma, and the neoformation of vascular bundles and trichomes. The histometric and cytometric data revealed compensatory effects of hyperplasia and cell hypertrophy in the epidermis, with hyperplasia predominating in the adaxial epidermis. There was a balance between these processes in the other tissues. Thus, we found major differences between the developmental pathways of non-galled leaves and galls. These changes were associated with phenotypic alterations related to shelter and appropriate microenvironmental conditions for the gall inducer. The nondifferentiation of a typical nutritive tissue in this case was compared to other non-phylogenetically related arthropod gall systems, and is suggested to result from convergence associated with the piercing feeding apparatus of the corresponding gall-inducer