Life table parameters

The development of a laboratory rearing method for B. cockerelli enabled the basic demographic parameters of this species to be determined. These parameters can underpin useful applications: analyzing population stability and structure, estimating extinction

probabilities, predicting life history evolution, predicting outbreak in pest species, and examining the dynamics of colonizing or invading species (Vargas et al. 1997, Haghani et al. 2006). Demographic information may also be useful in constructing population models (Carey 1993) and understanding interactions with other insect pests and natural enemies (Omer et al. 1996). Life table parameters such as reproduction, fecundity, oviposition, and lifespan for B. cockerelli were determined on potato at a constant temperature of 25°C (Chapter 3). While there have been some studies to determine the life history parameters of TPP at different temperatures and on different plant species (eg. Yang and Liu 2009, Yang et al. 2010), the data in my study are among the most extensive established for TPP. While temperature is the most important factor in determining the rate of development, the host plant species is also important to life history. Different host plant species often vary in suitability for specific insects in terms of their effects on survival, development, and reproductive rate (Yang and Liu 2009). For example, development time was shorter and survival greater when B. cockerelli were fed on eggplant compared with bell pepper (Yang and Liu 2009). Under laboratory conditions in this current study it was determined that potato is a better host plant for B. cockerelli immatures than tomato, based on shorter developmental times (Chapter 2, Tran et al. 2012). Along with the studies of Yang et al. (2010) and Yang and Liu (2009), I further confirmed that potato is a better host plant for B. cockerelli immatures than eggplant and bell pepper.

With respect to TPP survivorship and mortality on potato in laboratory studies, the highest mortality occurred during the egg stage (29%) followed by the first instar (17%) in my study, as is known for many insects (Begon and Mortimer 1981, Win et al. 2011). Over 94% of the 5th _{instar TPP successfully became adults. The pre-oviposition period was 7.9} days (141 DD) with a range from 6-11 days (107-197 DD). Interestingly, the oviposition period, 43.6 days (780 DD), with a range from 19-80 days (340-1432 DD) in my study is similar to that of Yang et al. (2010) who reported that the oviposition period of TPP reared on potato was 43.9 days. Such a long oviposition period may partly explain why there are always overlapping generations of psyllids in the field over a single growing season. Collett (2000) reported that growth and development of other psyllid nymphs occur throughout most of the year. The total developmental period for pre-adult stages was 23.02 days at 25°C, whereas adults lived as long as 51.47 days, and 34.13 days for female and male respectively

at this temperature. Such adult longevity may help explain why, along with other cardiaspine psyllid species (brown lace lerp) studied by Collett (2000), TPP is likely to have overlapping generations in the field in favorable environments.

A mean maximum oviposition rate of 21.7 eggs per day was observed for one female of B. cockerelli (Table 3.4). The mean total oviposition of one female was 388 eggs (Chapter 3). The levels of fecundity of TPP observed in this study is very close to that determined by Yang et al. (2010) who reported a total individual fecundity (of TPP reared on potato at 26.7 ±2°C) of 400 eggs. Data presented here falls within the range of cardiaspine psyllid species reported as ranging from 45 to 700 eggs per female by Collett (2000). The net reproductive rate or the average number of offspring a female would have during her lifetime is an

important indicator of population dynamics (Varley and Gradwell 1970, Kumral et al. 2007). It is a key statistic that summarizes the physiological capability of an animal relative to its reproductive capacity (Kumral et al. 2007). Comparison of net reproductive rate often provides considerable insight beyond that available from the independent analysis of individual life history parameters (Liu et al. 2004). For example, the net reproductive rate may reflect the potential of a certain host plant to increase TPP fitness and therefore population size. The net reproductive rate (Ro) of B. cockerelli on potato was found to be 73.2±4.5, indicating that B. cockerelli is capable of increasing its population numbers hugely within a generation despite a high mortality rate (46%) in the egg and first instar stage. The net reproductive rate observed in this study was higher than that reported by Yang and Liu (2009) on bell pepper (R0 = 59), and on tomato (R0 = 7 - 12.40) reported by Madriz et al. (2011) but lower than that reported by Yang and Liu (2009) for TPP reared on eggplant (R0 = 84.51). With respect to its potato host, the net reproductive rate (R0 = 73.2) observed in this study was much lower than the R0 =102.9 observed in the study by Yang et al. (2010) of TPP on potato. The difference may be due to the difference between the temperatures used in two studies. The current study was carried out at 25°C while the study by Yang et al. (2010) was carried out at 26.7°C. The cohort life table in this study was constructed based on an unlimited food supply in the environment free from natural enemies. Therefore, predators or parasitoids are not included as mortality factors on TPP development. Further studies are needed to elucidate more specifically the importance of mortality factors as a result of natural

enemy populations and their ability to provide biological control for TPP on crops under field and glasshouse conditions.