Screening Of Trichogramma Species/strains And Their Application Strategy For IPM In Paddy Fields Of The Greater Mekong Subregion

Trichogramma spp. are the most popular parasitoids being applied on a number of host crops. For the establishment of a Trichogramma-based rice IPM for the Greater Mekong Subregion, Trichogramma strains were collected from this region and a series of investigations were conducted to evaluate the performance of these strains. Nine Trichogramma strains were screened in the laboratory and three most promising strains were released in the paddy field with three different rates. Then, the toxicity of four commonly used planthopper-targetting insecticides were tested on adults and immature stages of T. chilonis (Cuijia),(Tc-Cuijia) in the laboratory. Moreover, Trichogramma release-based rice IPM was demonstrated in XinwuliVillage, JieshouTown, Xing’an County, Guangxi Zhuang Autonomous Region in2013.1. Evaluation for potential Trichogramma strains for control of the striped stem borer in the Greater Mekong SubregionTrichogramma species differ significantly in host specificity and performance of different strains also varies. Trichogramma collected from paddy fields in the Greater Mekong Subregions were evaluated for their performance on eggs of the striped stem borer (SSB), Chilo suppressalis Walker, in both laboratory and field tests to determine potential Trichogramma strains that can be employed in inundative release in an IPM program. In the laboratory tests, all strains showed higher parasitism rates on0-24h eggs (34.0%)than on the two older age groups (24.7%for24-48h and20.0%for48-72h), wasp emergence rate was also higher from parasitized0-24h SSB eggs (84.0%), while Trichogramma immature duration was significantly prolonged on0-24h SSB eggs. Parasitism rate differed among Trichogramma strains, T. chilonis Cuijia showing significantly higher parasitism rate (49.7%) than any other strains. In the field tests, parasitisms of sentinel SSB eggs by Trichogramma strains released at50,000,100,000, and200,000wasps per ha were low (below13.1%), with differences between strains being marginally significant. The highest parasitism was achieved by T. chilonis Cuijia strain at the high and medium release rates (13.1%and11.4%, respectively). Hence, it can be concluded that T. chilonis Cuijia strain released at100,000wasps per ha might be a cost-effective potential for field releases targeting the striped stem borer.2. Toxicity of insecticides targeting rice planthoppers to adult and immature stages of Trichogramma chilonisPlanthoppers-targeting insecticides, pymetrozine, thiamethoxam, buprofezin and nitenpyram, were tested under laboratory conditions for toxicity to adults and immatures of Trichogramma chilonis Ishii, using standard tests described by IOBC. In the dry film residue test, the insecticides all resulted in more than90%mortalities in T. chilonis adults and were ranked as moderately harmful. Persistent toxicity test revealed that nitenpyram was short-lived (<5d) and the other three insecticides were of slightly persistent toxicity (5-15d) to the wasp adults. Effects of the insecticides on egg, larval and prepupal stages of T. chilonis were investigated with striped stem borer as host. At the three stages of T. chilonis (within the host egg), all the insecticides reduced parasitism rate, but nitenpyram and pymetrozine applied at egg stage, buprofezin and nitenpyram at larval stage, and buprofezin and thiamethoxam at prepupal stage of T. chilonis reduced parasitism by less than30%in comparison with the control, and were thus ranked as harmless. Although insecticide treatments to the three immature stages of T. chilonis all reduced wasp emergence from host eggs, only thiamethoxam applied at larval stage and buprofezin at prepupal stage resulted in more than30%reduction in emergence rate as compared with the control and were categorized as harmful. Immature duration and sex ratio of emerged wasps were largely not affected by the insecticide treatments to the wasp immature stages. The data are of significance for IPM program incorporating inundative release of T. chilonis for control of lepidopteran rice pests where there is heavy co-occurrence of planthoppers.3. Demonstration of Trichogramma-based rice IPM in fieldsTrichogramma release-based rice IPM was demonstrated in Xinwuli Village, Jieshou Town, Xing’an County, Guangxi Zhuang Autonomous Region in summer and autumn rice seasons in2013, by comparison of incidence of natural enemies and planthopper, damaged leaves, damaged tillers, occurrence of sheath blight and rice blast, and grain yieldbetween farmer’s conventional practices and the Trichogramma-based IPM.Field survey was conducted weekly to the IPM and conventional rice field in both summer and autumn season rice (5surveys for each). More natural enemies were found in IPM plot than in conventional plot in both the summer rice (by51.4%for spiders,37.0%for rove beetles and233.3%green plant bugs per100hills) and autumn season (by19.7%for spiders,14.0%for rove beetles and86.7%for green plant bugs per100hills).Percentages of damaged leaves by rice leaf roller were below EIL on all sampling dates in both IPM and conventional plots in both summer and autumn rice (less than1.3%).Average percentages of dead heart were less than0.9%for both IPM and conventional plots in both summer and autumn rice. Average population of planthoppers per100hills was higher in IPM plot (513.9) than in conventional plot (167.2) in the summer rice, while in the autumn rice, the population size was not different (93.5for IPM plot and141.6for conventional plot), planthopper population was generally below EIL. Parasitism of rice leaf roller eggs was significantly higher in IPM plot (23.0%) than in conventional fields (18.0%) in the summer rice and in IPM plot (52.0%) than in conventional plot (7.0%) in the autumn rice. In the summer rice,1.4times less pesticide application was used in IPM plot (2times) than in conventional plot (3.4times), while2.4times less pesticide application was used in IPM plot (1time) than in conventional plot (3.4times) in the autumn rice. Rice yield was155.5kg/ha more in IPM plot than in conventional plot in the summer rice and374.6kg/ha more in IPM plot than in conventional plot in the autumn rice, but not significantly different between the treatments.