The development of integrated pest management for Brassica crops in DPRK and its improvement in Australia

Objective 1. Demonstration of the principles of IPM in Brassica crops under DPRK conditions.
Trials to demonstrate the principles of IPM were performed in summer white cabbage (Brassica oleracea) and autumn Chinese cabbage (Brassica campestris) crops at two locations, Oryu Co farm in Pyongyang and Tae Sung Co farm in Sariwan, in 2003. Pieris rapae, Plutella xylostella, Mammestra brassicae, Brevicorryne brassicae, Agrotis sp. and Phylotretta vittata were identified as the major pests of the white cabbage crop and M. brassicae, B. brassicae, Agrotis sp., Phaedon brassica,P. vittata and Athalia collibre were identified as the major pests of the Chinese cabbage crop. The major parasitoids attacking immature Pieris rapae were Apanteles glomeratus and P. puparum, while the major parasitoids attacking P. xylostella were the larval parasitoids Cotesia plutellae and Oomyzus sokolowskii and the pupal parasitoid Diadromus collaris. Several species of parasitoid were reared from immature M. brassicae but these have yet to be identified.
DPRK team members, farm managers and farm engineers were impressed by the results of IPM strategies, founded upon threshold based Bacillus thuringiensis intervention tactics, on crop yields. Crop scouting procedures at Tae Sung Co farm have been modified in line with protocols introduced by project personnel. At both trial sites farm managers expressed enthusiasm for the research and communicated that they would like further supplies of Bacillus thuringiensis to treat Brassica crops that are not currently part of the study. At provincial meetings in the autumn of 2003, the engineer from Tae Sung Co farm informed other engineers from in the province of last year's trials, resulting in the basic concepts of IPM being discussed among over 200 engineers.

Objective 2. Wide-scale surveying for natural enemies of key insect pests in Brassica crops in DPRK
Surveys for natural enemies of the key insect pests was limited to the experimental sites at Oryu Co farm, on the outskirts of Pyongyang, and Tae Sung Co farm in Sariwan, 70 km south of Pyongyang, in 2003. Problems associated with transport of collected material from the field to the laboratory and subsequent rearing of collected pests and natural enemies resulted in the information regarding natural enemy abundance being qualitative rather than quantitative. Local facilities have been greatly improved during the year and such problems should be avoidable in the future.

Objective 3. Assessment of the impact of natural enemies on key insect pests
A preliminary natural enemy exclusion experiment performed in June- July 2003 indicated that the impact of natural enemies on the P. xylostella population at Oryu Co farm was low. Larger scale, replicated experiments at three sites over coming years of the project will test this preliminary finding and examine the impact of pest management practice on natural enemy efficacy.

Objective 4. Determination of EIL/ ETs for key pests at different crop growth stages
EIL/ETs employed in the project to date are based on the "standard insect" threshold system developed in ACIAR project "CS2/1998/089: Improvement of Integrated Pest Management of Brassica Vegetable Crops in China And Australia". Mammestra brassicae, which has been identified as a significant pest of Brassica crops in DPRK, moves between host plants. Its relative foliage consumption is yet to be quantified but preliminary data indicates that the number of plants which can potentially become infested by larvae from a single egg mass is equal to approximately 25% of the number of eggs in an egg mass.

Objective 5. Analysis and interpretation of project data
Detailed discussions regarding analysis and interpretation project data collected to date have been held in DPRK during the two project visits to DPRK.

Objective 6.Investigation of endemic natural enemies of early season Brassica pests and the potential for the release of mass reared beneficial insects in Australia
The first record of egg parasitism of Crocidolomia pavonana in Australia has been recorded. Molecular techniques have identified the parasitoid as Trichogramma pretiosum. Although the parasitoid's rate of egg mass discovery was high it is unlikely that T. pretiosum will prove an effective biological control agent of the pest as it had no significant impact on pest mortality. Electron micrographs suggest that this may be due in part to egg morphology and egg mass structure. Crocidolomia pavonana suffers only minor mortality due to larval predation and parasitism, future studies will examine the mortality factors operating on the soil dwelling pupal stages.

Objective 7. Refining IPM practices to minimise early season chemical insecticide use in Australian Brassica crops.
Treatment of seedling roots with imidacloprid provided significant protection against attack by Hellula hydralis larvae for approximately four weeks after transplanting and resulted in both improved yields and a reduction in the foliar application of insecticides. The field trial was initiated early in the season (mid February) but egg masses of C. pavonana were not sampled in the study crop until late March. Consequently, the effectiveness of the strategy to contribute to the control of C. pavonana was not effectively tested in the field in this year's study. The recent dramatic increase in the silverleaf whitefly, Bemisia tabaci, abundance in south-east Queensland is yet to be proven as a serious economic threat to Brassica growers. However, imidacloprid treatment of seedling roots significantly reduced B. tabaci infestations by up to 7-fold when compared to seedlings subject to standard practice and up to 3-fold when compared to seedlings treated weekly with insecticides currently registered for whitefly control

Objective 1. Demonstration of the principles of IPM in Brassica crops under DPRK conditions.
In 2004Trials to demonstrate the principles of IPM were performed in a summer white cabbage (Brassica oleracea) crop at three sites (Oryu Co-farm, Tae Sung Co-farm and Ssang Un Co-farm) and an autumn Chinese cabbage (Brassica campestris) crop at a single site, Tae Sung Co-farm. Pieris rapae, Plutella xylostella and Mamestra brassicae were the major pests of the summer white cabbage crop and M. brassicae and P. rapae were identified as the major pests of the autumn Chinese cabbage crop. As in 2003, DPRK team members, farm managers and farm engineers were impressed by the results of IPM strategies in 2004. These strategies are based on applications of Bacillus thuringiensis when pest thresholds are reached. In 2004 yields in summer white cabbage crops were significantly higher when managed by the IPM strategy than when managed by standard co-farm practice. At all three trial sites members of work teams not currently involved with the project have expressed a desire to become involved in the project and have requested supplies of Bacillus thuringiensis to treat their Brassica crops.

Objective 2. Wide-scale surveying for natural enemies of key insect pests in Brassica crops in DPRK
Surveys for natural enemies of the key insect pests have been limited to the three experimental sites at Tae Sung, Oryu and Ssang Un co-farms. At all three sites, the major parasitoids attacking Pieris rapae larvae were Cotesia glomeratus and Cotesia rubecula while Pteromalus puparum was the major parasitoid of P. rapae pupae. The major parasitoids attacking P. xylostella larvae were Cotesia plutellae and Oomyzus sokolowskii while Diadromus collaris was the major parasitoid which attacked P. xylostella pupae. The important P. xylostella larval parasitoid, Diadegma semiclausum, was not detected at any of the study or survey sites for the second successive year; it appears that this is parasitoid is absent form the area of study.

Objective 3. Assessment of the impact of natural enemies on key insect pests
Natural enemy exclusion studies at two sites studied in 2004 indicated that natural enemies had a significant impact on experimental pest populations at one site, Ssang Un Co-farm but not at the other, Tae Sang co-farm. At Ssang Un Co-farm natural enemy activity was significantly greater on a crop managed by IPM than on a crop managed by standard co-farm practice.

Objective 4. Determination of EIL/ ETs for key pests at different crop growth stages
EIL/ETs employed in the project to date are based on the "standard insect" threshold system developed in ACIAR project CS2/1998/089. These thresholds need to be refined for local conditions and for the inclusion of M. brassicae which has voracious and highly mobile larval stages. Preliminary studies to quantify food consumption rates of M. brassicae and its movement between plants have been carried out but need to be repeated and refined.

Objective 5. Analysis and interpretation of project data
Detailed discussions regarding analysis and interpretation project data collected to date have not been possible during the reporting period because of logistical problems of organising visits between Australia and DPRK. A 7-10 day project meeting will be convened in Hangzhou, China in November 2005 and the large volumes of project data collected to date will be analysed, interpreted and discussed.

Objective 6. Investigation of endemic natural enemies of early season Brassica pests and the potential for the release of mass reared beneficial insects in Australia
In the reporting period research has concentrated on the mortality factors impacting on Crocidolomia pavonana in southeast Queensland. Egg parasitism by Trichogramma pretiosum was far lower in 2005 than in 2004. Field collections and natural enemy exclusion studies have demonstrated that C. pavonana suffers limited mortality due to larval predation and parasitism; low numbers of several species of hymenopteran and tachinid parasitoids were reared from field collected larvae in 2005 and these are currently awaiting identification at the University of Queensland insect collection. In natural enemy exclusion studies to examine the mortality of soil dwelling pupal stages of C. pavonana no significant mortality could be attributed to natural enemies. Temperature-developmental rate studies conducted in the laboratory indicate that C. pavonana may be near the edge of its distribution in southeast Queensland, this might in part explain the apparent lack of any specific and effective natural enemies at the study sites.

Objective 7. Refining IPM practices to minimise early season chemical insecticide use in Australian Brassica crops.
Studies of the effectiveness of treating Brassica seedling roots with imidacloprid were successfully completed in 2003 and 2004. The strategy provided significant protection against attack by Hellula hydralis for approximately 4 weeks and against the silverleaf whitefly, Bemisia tabaci for considerably longer. Laboratory and computer simulation modelling studies have examined the potential suitability of different strains of the entomopathogenic fungus Zoophthora radicans for incorporation into IPM programmes for Brassica pests in southeast Queensland. The studies indicate that the ecological attributes of an exotic strain of Z. radicans isolated from P. xylostella in Kenya may make it a more suitable biological control agent than a strain of the pathogen which was isolated locally. No plans are underway to release the Kenyan isolate into southeast Queensland.

Objective 1. Demonstration of the principles of IPM in Brassica crops under DPRK conditions.
Trials to demonstrate the principles of IPM were performed in summer white cabbage (Brassica oleracea) at three sites (Oryu Co-farm, Tae Sung Co-farm and Ssang Un Co-farm) in 2005. Pieris rapae, Plutella xylostella and Mamestra brassicae were again identified as the major pests of the crop and, as in previous years of the project, DPRK team members, farm managers and farm engineers were impressed by the results of IPM strategies for their management. The strategy is based on applications of Bacillus thuringiensis when pest thresholds are reached. Crop yields were significantly higher when managed by the IPM strategy than when managed by standard Co-farm practices. At all three trial sites members of work teams not involved with the project expressed a desire to become involved and requested supplies of Bacillus thuringiensis to manage their pests using this approach.

Objective 2. Wide-scale surveying for natural enemies of key insect pests in Brassica crops in DPRK
As in 2004, surveys for natural enemies of the key insect pests were limited to the three experimental sites at Tae Sung, Oryu and Ssang Un Co-farms. At all three sites P. xylostella larvae were attacked by Cotesia plutellae and Oomyzus sokolowskii and P. xylostella pupae were attacked by Diadromus collaris. For the third season in succession, the important P. xylostella larval parasitoid, Diadegma semiclausum, was not detected at any of the survey sites and it appears that this parasitoid is absent form the study area. In 2005 no surveys of the parasitoids attacking P. rapae larvae and pupae were conducted. Pitfall traps and intensive sampling of cabbage plants at the three study sites demonstrated that spiders and predatory coleoptera are the dominant groups of epigeal arthropod predators while spiders are the dominant group of foliar predators. The abundance of both groups of predators was significantly higher in IPM managed crops than in crops managed by standard Co-farm practice.

Objective 3. Assessment of the impact of natural enemies on key insect pests
Natural enemy exclusion studies at two sites studied in 2005 indicated that the combined activity of all natural enemies significantly reduced experimental pest populations at one site but not at the other. Overall, the impact of natural enemies on P. xylostella populations was very low. Populations of C. plutellae, the most significant P. xylostella natural enemy identified, lag behind those of the pest. This is probably due to the later arrival of the parasitoid in crop fields and its establishment is likely to be further compromised by the widespread use of broad spectrum insecticides on adjacent non-project fields.

Objective 4. Determination of EIL/ ETs for key pests at different crop growth stages
EIL/ETs employed in the project to date are based on the "standard insect" threshold system developed in ACIAR project CS2/1998/089. These thresholds have been very effective to date and, due to the very limited communication which has been possible between DPRK and Australian scientists, no modifications were experimentally tested in 2005. Based on the successful experiments conducted (2003-2005) field testing of higher intervention thresholds at Tae sung and Oryu Co-farms was identified as an objective for final experiments in the 2006 summer white cabbage crop. These experiments were undertaken in DPRK (April- July, 2006) but no data has yet been forwarded to Australia.

Objective 5. Analysis and interpretation of project data
Detailed discussions regarding analysis and interpretation of project data collected in 2005 were conducted at a meeting of Australian and DRPRK project staff in Hangzhou, China in November 2005. The meeting was extremely useful for both Australian and DPRK scientists; 2005 season data were reviewed in detail and appropriate experimental designs and analyses for experiments to be conducted in 2006 were discussed. However, the meeting (the first time that scientists from both countries were able to meet since May 2004) was a poor substitute for the planned exchange visits and collaborative research activities.

Objective 6. Investigation of endemic natural enemies of early season Brassica pests and the potential for the release of mass reared beneficial insects in Australia
In previous years field studies have indicated that Crocidolomia pavonana suffers only limited mortality from endemic natural enemies in southeast Queensland. In the current reporting period research focused on the movement of C. pavonana from plants on which egg masses were laid to neighbouring plants. The movement of larvae between plants can be considerable and it is significantly affected by the planting density of seedlings; this has important implications for the formulation of appropriate intervention thresholds at different stages of crop phenology.

Objective 7. Refining IPM practices to minimise early season chemical insecticide use in Australian Brassica crops.
Following the successful completion of studies investigating imidacloprid treatment of Brassica seedling roots for the management of Hellula spp. and Bemisia tabaci earlier in the project, studies in the reporting period investigated the effectiveness of the fungal pathogen Beauveria bassiana against the C. pavonana and P. xylostella. In laboratory tests B. bassiana was shown to be an effective pathogen of P. xylostella but, even when applied at extremely high concentrations, it was not pathogenic to C. pavonana.