Letitia Silberbauer
Welcome to my web page. This page describes my current and past research activities in entomology and ecology.
Current Research
My current research focuses on the sources and movement of generalist predatory insects in and around cotton crops. I'm working with Assoc. Prof. Peter Gregg in the Insect Pest Management laboratory at UNE, New South Wales, Australia.
Insect pests of cotton are one of the major problems facing growers. In an era of increasing pesticide resistance in key pests, the use of "soft option" pesticides, combined with an awareness of the needs of beneficial (predatory and parasitic) insects is going to become standard practice. Predatory and parasitic insects can increase the efficacy of anthropogenic pest control if land use practices and pesticide application are sympathetic to the ecological requirements of these insects.
I am investigating some basic questions of the ecology of generalist predators insects in and around cotton; namely where they occur and how much they move around between vegetation types. The eventual outcome will be to provide information to farmers to help them maintain useful populations of beneficials in their crops.
There are two complementary parts to this study. The first is a survey of insects in cotton and in vegetation types near cotton. The second is examining beneficials for pollen using scanning electron microscopy (SEM). I am focusing on six species of Australian native insects known to be predatory on cotton pests: transverse ladybird, Coccinella transversalis, two spotted ladybird, Diomus notescens, nabid bug, Nabis kinbergii, red and blue beetle, Dicranolaius bellulus, green lacewing, Mallada signata, and brown lacewing, Micromus tasmaniae. Samples were taken using a suction sampler; which is the most common method (besides visual sampling) used by agronomists and consultants working in cotton.
I'm using SEM to identify pollen found on the beneficial insects' exoskeletons. Several of the species I'm studying visit flowers as well as prey on insects and pick up pollen as they go. The image here is of a Brown Lacewing after it has been in a sunflower (brown lacewings are normally, um, brown!). As pollen is easily identified to plant family and often to species, and since we have surveyed the vegetation in the areas we're sampling, we can use the pollen to trace the movements of the insects prior to capture. This can be a powerful tool to estimate the distances moved and the number of flowers visited by the insects.
I am funded by the Australian Cotton Cooperative Research Center. For information on cotton growing in Australia, please go to the Australian Cotton CRC home page.
Previous Research
My previous research has concentrated on the behaviour and ecology of allodapine bees and conservation project on lycaenid butterflies.Allodapine bees (Hymenoptera: Apidae)
Allodapine bees are a predominantly southern hemisphere group of stem nesting bees, closely related to carpenter bees (xylocopines and ceratinines). This image is of a female Halterapis nigrinervis, a South African allodapine species.
My PhD research at Melbourne's La Trobe University concentrated on the ecology and sociobiology of a heathland allodapine species, Exoneura bicolor (now called E. robusta). My supervisors were Dr. Michael Schwarz and Dr. Tim New. Exoneura species are particularly interesting because sociality seems to be facultative in most species in the genus. My project examined some of the ecological factors that were influencing social behaviour in E. robusta.
I worked in the Zoology department of the University of the Witwatersrand for a year in Prof. Robin Crewe's laboratory. While there I researched the life cycle and social organisation of a primitive allodapine species, Halterapis nigrinervis. Halterapis spp. are the only allodapine bees to mass-provision their young, a primitive trait. I was interested in determining whether H. nigrinervis was social and whether it showed reproductive differentiation within colonies (i.e. whether the colony was divided into reproductive and non-reproductive females). Since Halterapis is basal in the allodapine lineage, this kind of information can tell us whether sociality is ancestral to allodapines or whether it has undergone independent evolution after allodapines diverged from basal stock.
Brenton Blue Butterfly conservation project (Lepidoptera: Lycaenidae: Orachrysops niobe)
In the summer of 1995/96 David Britton and I were employed by the Endangered Wildlife Trust to assess the population status and conservation priorities for a critically endangered butterfly, the Brenton Blue - Orachrysops niobe, in the Eastern Cape region of South Africa. This butterfly is South Africa's most endangered butterfly, existing as a small population on a tiny block of land in the middle of a housing development at Brenton-on-Sea. This species used to be more widespread, but other colonies have been rendered extinct by loss of habitat through development and changed management practises. Larvae feed on a single plant species, Indigofera errecta, which is itself of restricted distribution, and appear to have a symbiotic relationship with an ant species (a trait common in this group of butterflies).
We were part of a large team consisting of members from the Lepidopterists' Society of Africa (David Edge, Ernest Pringle and Jonathan Ball), South African Museum (Hamish Robertson), and Rhodes University (Roy Lubke) and many locals from Brenton-on-Sea. The project was managed and co-ordinated by the Endangered Wildlife Trust's Conrad Steenkamp.
Click here to see a list of selected publications.