Sub sections:
Pol Chanthy - The influence of climate change on Nezara viridula and its parasitoid, Trichopoda spp.
Soybean is the most economically important legume crop in the world. In the tropics and sub-tropics, green vegetable bug Nezara viridula is a major insect pest world-wide. Serious yield losses can result from green vegetable bug (GVB) feeding as well as reduced seed germination in GVB damaged seeds. Integrated Pest Management (IPM), in which natural occurring biological control mechanisms are used in conjunction with compatible insecticides, is the preferred management strategy for GVB. Two important biological control agents of GVB are the parasitoids Trichopoda spp. and Trissolcus spp.. Pest status and density of GVB is limited by environmental temperature and winter diapause, however, climate change may exacerbate the pest status of GVB. The likely temperature increase of 2.4 – 6.4oC in Australia may shorten the life cycle of GVB allowing more generations and damaging populations on soybean crops. GVB may also become a year round pest as increased temperature may remove its winter diapause. While GVB may adapt to climate change, predators and parasites may not be able to survive changes in temperature and rainfall and changes in the life cycle of the GVB host. The aims of this project are to measure the effect of changed temperature and moisture thresholds on GVB and Trichopoda spp. life cycles and the ability of the parasitoid to parasitize GVB.
The parasitoid flies and their hosts, green vegetable bugs were obtained from Breeza in North-Western NSW and Grafton on the North Coast of NSW. Breeza (Gunnedah) represents a dry climate (618 mm annual average rainfall) compared to Grafton (1053 mm). Grafton is also more humid with average annual 3pm relative humidity of 53% compared to 46% at Breeza (Gunnedah). Average annual maximum temperature is similar at both sites (26oC) but minimum temperature is higher at Grafton (13.6oC) compared to 10.9oC at Breeza (Gunnedah).
An experiment was conducted under controlled conditions to determine the effects of combination of two factors, temperature and humidity regimes on the developmental stages of Trichopoda spp. and to examine whether the two populations of Trichopoda spp. are different under the effects of temperature and humidity. The experiment was laid out as factorial design with two factors, temperature (25, 30, 33, and 36°C) and humidity (30-40% RH and 70-80% RH) and three replications. The temperature was considered as the main factor for this experiment. Saturated salt solution was used to maintained humidity regimes in incubators. Magnesium Chloride was used for the higher humidity regime, whereas Lithium Chloride was used for the low humidity regime. The data of this experiment is being analysed.
In relation to the effects of climate change, a study of insect physiology: Discriminating temperature of green vegetable bug (GVB) was conducted. The objective of this study was to determine whether the discriminating temperature of GVBs from different climatic gradients is different between these two populations. The results of this study showed that the discriminating temperature of green vegetable bug was about -7 °C under cold condition and there were no significant differences of discriminating temperature between these two populations. Similarly, there were no significant differences in discriminating temperature between two populations of green vegetable bug under hot conditions. The discriminating temperature of green vegetable bug under high temperature was about 40 °C. In relation to this study, the effects of acclimatisation temperature on discriminating temperature of GVB populations will be conducted in order to determine whether acclimatisation temperature increases or decreases survival discriminating temperature of GVB.