Aspects of the biology and control of three species of acorn weevils infesting oak acorns in Kumaun Himalaya

Abstract

Biology and ecology of three acorn weevils: Dicranognathus nebulosus Redt. (Col., Attelabidae), Sitophilus glandium (Mshl.) (Col., Curculionidae) and Curculio sikkimensis (Hell.) (Col., Curculionidae), which infest acorns of Quercus leucotrochophora A. Camus and Q. floribunda Lindle was studied in the laboratory and in the field. Adults of D. nebulosus and C. sikkimensis laid one egg per infested acorn, and S. glandium laid 0 to 8 (means 5.2 ± 0.47) eggs in an infested acorn of Q. leucotrichophora. Only a single larva of D. nebulosus and C. sikkimensis developed per acorn, and 1 to 5 (mean 3.8 ± 0.3) larvae of S. glandum developed per acorn through the last instar. Larvae of D. nebulosus and S. glandium completed their development in the infested acorn, and C. sikkimensis emerged from the acorn through the last instar and completed its development in the soil. Good synchronization was observed in the life cycle of acorn weevils and phenology of Q. leucotrichophora. An average of 88.7% of acorns were infested by the acorn weevils. Injury to live acorns by weevil larvae reduced germination and seedling growth. Weevil larvae could be controlled by hydrothermal treatment (20 min at 45 °C) of infested acorns in the germination experiments. Zusammenfassung Zur Biologie und Bekämpfung von drei Käferarten in Kumaun Himalaya, Indien, die Eicheln befallen Im Labor und Freiland wurden die Biologie und Ökologie der 3 Käferarten Dicranognathus nebulosus Redt. (Col., Attelabidae), Sitophilus glandium (Mshl.) (Col., Curculionidae) und Curculio sikkimensis (Hell.) (Col., Curculionidae), welche die Eicheln von Quercus leucotrochophora und C. floribunda befallen, untersucht. Die Weibchen von D. nebulosus und C. sikkimensis legten ein Ei pro Eichel ab, während S. glandium 0 bis 8 Eier (i.M. 5) pro Eichel von Q. leucotrochophora ablegte. Somit entwickelten sich von D. nebulosus und C. sikkimensis in einer Eichel nur je 1 Larve. Von S. glandium dagegen gelangten bis zu 5 (i. M. 3) Larven in einer Eichel zum letzten Larvenstadium. Während bei D. nebulosus und S. glandium die Larven ihre Entwicklung in der Eichel vollendeten, verließen die Altlarven von C. sikkimensis die Eichel und beendeten ihre Entwicklung im Boden. Es bestand eine gute Synchronisation zwischen der Phänologie von Quercus leucotrichophora und dem Lebenszyklus der Eichelkäfer. Die 3 Käferarten befielen im Untersuchungszeitraum i. M. 88,7 % der Eicheln von Q. leucotrichophora. Der Befall lebender Eicheln durch die Käferlarven führte zur Verminderung der Keimung und des Sämlingswachstums. Die Käferlarven konnten mit Hilfe einer Hitzebehandlung (20 min bei 45 °C) der Eicheln erfolgreich, d.h. im Sinne der Erhaltung der Keimkraft, bekämpft werden.

An attempt to reconstruct the natural and cultural history of the granary weevil, Sitophilus granarius (Coleoptera: Curculionidae)

“…Several members of this seed-breeding guild, however, mandatorily leave the host as larva and pupate in the leaf litter or in the upper soil layer. This is the case for: Curculio sikkimensis Hell., which breeds in acorns in the Himalayas; Curculio nucum L., the acorn beetle in Middle Europe, and Conotrachelus retentus (Say), which breeds in the seeds of the black walnut (Juglans nigra) in North America (Kaushal et al, 1993;Stamps & Linit, 2002), to name just a few. Other species pupate within parts of their food plant and do not leave them until they are adult beetles.…”

“…S. glandium, S. rugicollis, S. rugosus, S. sculpturatus and S. vateriae breed on the seeds of Quercus incana, Q. leucotrochophora, Q. floribunda and Q. dilatata, as well as on the seeds of trees in the Dipterocarpaceae and Fabaceae families in temperate to subtropical mixed forests of the Orientalis, from the southwest and south sides of the Himalayas all the way to the Indian subcontinent (Marshall, 1920(Marshall, , 1940Weidner, 1983;Kaushal et al, 1993;Nardon et al, 2002). As far as is known in the breeding biology, all species of Sitophilus develop from egg to pupa inside the kernel of their host plants.…”

“…Then the egg cavity is sealed with a clear and sticky secretion. For S. linearis and S. glandium, it is known that the host kernel can hold multiple eggs (Cotton, 1920;Kaushal et al, 1993). With only a few exceptions, for the stored grain pest species S. granarius, S. oryzae and S. zeamais, each kernel only hosts one egg.…”