Pollen abundance in Late Quaternary sediment cores off West Africa

The pollen record of three marine late Quaternary cores off Senegal shows a juxtaposition of Mediterranean, Northern Saharan, Central Saharan elements, which are considered transported by the trade winds from a winter-rainfall area, and Sahelian, Soudanese, Soudano-Guinean elements, considered transported both by winds and mostly by the Senegal River, and coming from the monsoonal, summer tropical rainfall area of southern West Africa. Littoral vegetation is either the edaphically dry and saline Chenopodiaceae from sebkhas at the time of the main regression, or the warm tropical humid mangrove with Rhizophora during the humid optimum period. Four stratigraphic zones reflect, from basis to top: Zone 4. A semi-arid period with a balanced pollen input. Zone 3. A very arid period with the disappearance of monsoonal pollen, probably from the disappearance of the Senegal River, a very saline littoral plain with Chenopodiaceae, a larger input of northern Saharan pollen from intensified trade winds. Zone 2. A quite humid period, much more so than today, very suddenly established, with a northward extension of the monsoonal areas, a rich littoral mangrove, and weakening of the trade winds. Zone l. A slow and steady evolution toward the present semi-humid conditions with regression of the mangrove, and of the monsoonal areas toward the south. Tentative datations and correlations with the Tchad area suggested: zone 4: 22,500 to 19,000 years BP; zone 3: 19,000 to 12,500 years BP; zone 2: 12,500 to 5,500 years BP; zone 1: 5,500 years BP to top of core. Dinoflagellate cysts display a tropical assemblage with mostly estuarine neritic elements and also a weak oceanic component, mostly in the lower slope core 47. Cosmopolitan taxa dominate the assemblage and only a few species point to more specialized environments. Quantitative variations of the assemblage are the basis of stratigraphy which is not similar to the pollen stratigraphy, and an inshore-outshore gradient has to be taken into account to correlate the three cores.

Acacia nilotica ssp. indica (L.) Willd. ex Del. (Mimosaceae)

Prickly acacia, a Weed of National Significance or WONS, is a serious problem in Queensland particularly the Mitchell grass downs where it was once planted to provide shade for livestock. The chapter summarises current knowledge about the taxonomy, biology, distribution, ecology, impacts and biological control of the weed. Queensland has been trying to achieve biological control of prickly acacia since 1980 when it began foreign exploration in Pakistan. Since then further exploration was undertaken in Kenya, South Africa and presently India. Six insects have been released in Queensland but only two of these are established. Greater emphasis is being placed on climate matching, plant response to herbivory and genotype matching in present work and it is hoped that this approach will allow more rigorous evaluations of agent performance and better understanding of reasons for success or failure of agents.

The introduction and release of Chiasmia inconspicua and C. assimilis (Lepidoptera: Geometridae) for the biological control of Acacia nilotica in Australia

Two geometrid moths Chiasmia inconspicua and Chiasmia assimilis, identified as potential biological control agents for prickly acacia Acacia nilotica subsp. indica, were collected in Kenya and imported into quarantine facilities in Australia where laboratory cultures were established. Aspects of the biologies of both insects were studied and CLIMEX® models indicating the climatically favourable areas of Australia were developed. Host range tests were conducted using an approved test list of 74 plant species and no-choice tests of neonate larvae placed on both cut foliage and potted plants. C. inconspicua developed through to adult on prickly acacia and, in small numbers, Acacia pulchella. C. assimilis developed through to adult on prickly acacia and also in very small numbers on A. pulchella, A. deanei, A. decurrens, and A. mearnsii. In all experiments, the response on prickly acacia could be clearly differentiated from the responses on the non-target species. Both insects were approved for release in Australia. Over a three-year period releases were made at multiple sites in north Queensland, almost all in inland areas. There was no evidence of either insect's establishment and both colonies were terminated. A new colony of C. assimilis was subsequently established from insects collected in South Africa and releases of C. assimilis from this new colony were made into coastal and inland infestations of prickly acacia. Establishment was rapid at one coastal site and the insect quickly spread to other infestations. Establishment at one inland area was also confirmed in early 2006. The establishment in coastal areas supported a CLIMEX model that indicated that the climate of coastal areas was more suitable than inland areas.

The host range and biology of Cometaster pyrula; a biocontrol agent for Acacia nilotica subsp. indica in Australia

Prickly acacia, Acacia nilotica subsp. indica (Benth.) Brenan, a major weed of the Mitchell Grass Downs of northern Queensland, Australia, has been the target of biological control projects since the 1980s. The leaf-feeding caterpillar Cometaster pyrula (Hopffer) was collected from Acacia nilotica subsp. kraussiana (Benth.) Brenan during surveys in South Africa to find suitable biological control agents, recognised as a potential agent, and shipped into a quarantine facility in Australia. Cometaster pyrula has a life cycle of approximately 2 months during which time the larvae feed voraciously and reach 6 cm in length. Female moths oviposit a mean of 339 eggs. When presented with cut foliage of 77 plant species, unfed neonates survived for 7 days on only Acacia nilotica subsp. indica and Acacia nilotica subsp. kraussiana. When unfed neonates were placed on potted plants of 14 plant species, all larvae except those on Acacia nilotica subsp. indica and Acacia nilotica subsp. kraussiana died within 10 days of placement. Cometaster pyrula was considered to be highly host specific and safe to release in Australia. Permission to release C. pyrula in Australia was obtained and the insect was first released in north Queensland in October 2004. The ecoclimatic model CLIMEX indicated that coastal Queensland was climatically suitable for this insect but that inland areas were only marginally suitable.

A systematic approach to biological control agent exploration and prioritisation for prickly acacia (Acacia nilotica ssp. indica)

Agent selection for prickly acacia has been largely dictated by logistics and host specificity. Given that detailed ecological information is available on this species in Australia, we propose that it is possible to select agents based on agent efficacy and desired impact on prickly acacia demography. We propose to use the 'plant genotype' and 'climatic' similarities as filters to identify areas for future agent exploration; and plant response to herbivory and field host range as 'predictive' filters for agent prioritisation. Adopting such a systematic method that incorporates knowledge from plant population ecology and plant-herbivore interactions makes agent selection decisions explicit and allow more rigorous evaluations of agent performance and better understanding of success and failure of agents in weed biological control.

The host range of Isturgia deeraria, an insect considered for the biological control of Acacia nilotica in Australia

The geometrid caterpillar Isturgia deerraria was imported from Kenya into quarantine facilities in Australia as a potential biological control agent for prickly acacia, Acacia nilotica subsp. indica (Benth.) Brenan (family Mimosaceae). The insect was then tested on 30 plant species presented to neonate larvae as a no-choice cut foliage test and 13 plant species presented as a no-choice potted plant test. In these tests the insect was able to complete its life cycle on 13 native Acacia spp. and also on Acacia farnesiana and the exotic ornamental Delonix regia (family Caesalpiniaceae). The tests supported field observations that the insect has a host range spanning many leguminous species and as such the insect could not be considered for release in Australia.

Impact of a biological control agent, Chiasmia assimilis, on prickly acacia (Acacia nilotica ssp. indica) seedlings

A leaf-feeding geometrid, Chiasmia assimilis (Warren), was introduced into northern Queensland from South Africa in 2002 as a biological control agent for the invasive woody weed, prickly acacia, Acacia nilotica subsp. indica (Bentham) Brenan. The insect established in infestations in coastal areas between the townships of Ayr and Bowen where the larvae periodically cause extensive defoliation at some localities during summer and autumn. The impact of this herbivory on a number of plant parameters, including shoot length, basal stem diameter, root length, number of leaves, number of branches, and above and below ground biomass was investigated at one coastal site through an insect exclusion trial using potted seedlings and regular spray applications of a systemic insecticide to exclude the biological control agent. Half the seedlings, both sprayed and unsprayed, were placed beneath the prickly acacia canopy, the other half were placed in full sunlight. Larvae of C. assimilis were found on unsprayed seedlings in both situations. The effects of herbivory, however, were significant only for seedlings grown beneath the canopy. At the end of the five-month trial period, shoot length of these seedlings was reduced by 30%, basal stem diameter by 44%, root length by 15%, number of leaves by 97%, above ground biomass by 87%, and below ground biomass by 77% when compared to sprayed seedlings. Implications are that the insect, where established, may reduce seedling growth beneath existing canopies and in turn may help limit the formation of dense infestations. Crown Copyright (C) 2012 Published by Elsevier Inc. All rights reserved.

Ravenelia acaciae-arabicae and Ravenelia evansii are distinct species on Acacia nilotica subsp. indica in India

The two rust fungi, Ravenelia acaciae-arabicae and R. evansii, were both found on Acacia nilotica subsp. indica in southern (Tamil Nadu) and northern (Gujarat) India. R. acaciae-arabicae has been often incorrectly synonymised with R. evansii, although each has distinctive urediniospores, viz. echinulate in R. acaciae-arabicae and verruculose in R. evansii. Both species are re-described and illustrated from fresh specimens collected in India. Herbarium specimens of R. evansii from South Africa, including the holotype, were also examined. The difficulty in connecting different anamorphic spore stages to either of these teleomorphic rusts is highlighted by the presence of similar aecidia on plants of A. robusta infected with R. evansii in South Africa and on A. nilotica subsp. indica infected with R. acaciae-arabicae in India. It is not known whether these aecidial rusts represent the same species, nor is it known if they represent an aecidial stage of either R. acaciae-arabicae, R. evansii or other rusts.