Observations on Argentine stem weevil mortalities in Volcanic Plateau pastures

Abstract

Recent research at Ruakura has shown that the negative correlation betweenArgentine stem weevil (Lirtronotu bonariasis (Kuschel)) population survival (egg to adult) and egg density was density dependent. Density dependent mortalities could arise from pathogens, predators, parasitoids, larval combat and chemical releases by larvae andlor by the host plant. Large mortalities arising from pathogens, parasitoids, soil invertebrate predators and possibly Carabidae and Staphylinidae predators can be discounted in populations at Wairakei in the central North Island.Even without knowing the causative agent of the population mortality, any considerations for releases of natural enemies for biologcal control of stem weevil should act to augment this existing control. It is recommended that parasitoids be evaluated for release against late larval instar, pupae and adults.

Evidence of density-dependent oviposition behaviour byListronotus bonariensis(Coleoptera: Curculionidae) in Canterbury pasture

“…The mean number of eggs laid/oviposition by L. bonariensis was 1.8 and 1.9 for experiments 1 and 2 respectively and was generally uniform for all manipulated weevil densities. These means were lower than the 2.8 eggs/oviposition observed by Goldson (1982) on L. multiflorum X perenne but fell within the range of 1.5-2.5 eggs/oviposition reported by Prestidge et al (1987) and Barker et al (1989a). The minimum tiller diameter on which L. bonariensis eggs were found was 0.86 mm and agrees with the value of 1.0 mm reported by Pottinger (1961).…”

“…The minimum tiller diameter on which L. bonariensis eggs were found was 0.86 mm and agrees with the value of 1.0 mm reported by Pottinger (1961). The incidence of tillers sustaining superoviposition ranged between c. 3-6% and is comparable to North Island results (Prestidge et al, 1987;Barker et al, 1989a), suggesting that L. bonariensis avoid tillers already occupied by eggs deposited by conspecifics.…”

Argentine stem weevil (Listronotus bonariensis, Coleoptera: Curculionidae) population dynamics in Canterbury, New Zealand dryland pasture

“…Closer to the field environment, McNeill et al (1998) used weevils confined in field plots and again found strong evidence for negative density dependent effects on egg-laying. That Prestidge et al (1987) found a maximum of 3% multiple ovipositions per tiller and Barker et al (1989) 6%, tends to support the Pilkington & Springett (1988) theory. Moreover, that tiller numbers were found to offset unrealised fecundity could well be the result of dilution of the effect of spacing pheromone, particularly if the effect is associated with the frequency of plugged (or unplugged) ovipositional holes.…”

Endophytic microorganisms: a review on insect control and recent advances on tropical plants

“…In addition to the reports mentioned above (Webber, 1981;Funk et al, 1983;Gaynor and Hunt, 1983;Lasota et al, 1983;Barker et al, 1984;Prestidge et al, 1984;Ahmad et al, 1985;Clay et al, 1985a;Claydon et al, 1985;Hardy et al, 1985;Latch et al, 1985a;Johnson et al, 1985), that correlate endophytic fungi with negative effects towards insects, other reports kept accumulating in the following years. Some of them will be presented here but we should keep in mind that most of them refer to the host F. arundinacea and L. perenne.…”

“…These authors also showed that these associations may be complex and factors like the level of nitrogen fertilizers may as well affect attack frequency. With the same insectplant interaction, in New Zealand, Barker et al (1984) and Prestidge et al (1984) observed that plants free of endophytic fungi of the genus Acremonium, nowadays classified as Neotyphodium (in this review both names will be used according to the original reports) are severely attacked. Lasota et al (1983) had also correlated in the white spruce Picea glauca, death rate of the Homoptera Adelges abietis when galls are infected with the endophytic fungus Cladosporium sphaerosperum.…”