ABSTRACT
The experiment was conducted to determine the shelf life for 20, 40 & 60 days of different development stages of Trichogrammatoidea bactrae at three different temperatures (0,4,& 8 °C) with two light/dark regimes (9/15 light/dark hours & complete darkness). It was observed that under the conditions of this test, the best shelf life (>57% adult emergence) was obtained when pupae were held at 8 °C for any holding time tested. Among the environmental factors tested (temperature, holding time and photoperiod) temperature was the most important. T. bactrae might overwinter either in egg or pupal stage.
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DOI: 10.3923/jbs.2001.58.59
URL: https://scialert.net/abstract/?doi=jbs.2001.58.59
INTRODUCTION
Trichogrammatoidea spp. are all egg parasitoids of economically important Lepidoptera (Hutchison et al., 1990), however little is known about the genus. Nagaraja (1978), Hutchison et al. (1990) and Naranjo (1993), studied the biology of the T. bactrae, but its ecological requirements particularly the abiotic factors like temperature (Sharma and Chaudhary 1988, Phoofolo et al., 1995, Marco et al., 1997), humidity (Sharma and Chaudhary, 1988) and photoperiod (Yeargan and Barney, 1996) which play an important role in the development, distribution and establishment of an parasite/predator in the field are not reported.
T. bactrae was first described from specimens taken from lepidopterous pests on rice (Oryza sativa L.), Cabbage (Brassica oleracea Var.) and Corn (Zea mays L.). Hosts were generally stem, stalk, or pine shoot borers from Pyralidae and Olethreutidae. One specimen was taken from Trichopluia sp. (Hubner) (Noctuidae) eggs. All of these T. bactrae that described were recovered from India, Malaysia and Taiwan, but some other species of Trichogrammatoidea have also been found in Africa, Australia, Costa Rica, and the West Indies (Nagaraja, 1978). Paul Walker (Department of Entomology, University of Queensland) in 1984 discovered T. bactrae from Biloea, Queensland, Australia from Pectinophora scutigera (Holdaway) (Gelechiidae, a micro lepidoptera related to PBW) in cotton. T. bactrae is an easily reared PBW egg parasitoid (Hutchison et al., 1990). It may prove a good biological control agent against PBW in cotton (Nagaraja, 1978).
An attempt was made in the laboratory with two objectives:
1. | To determine the best combinations of ecological factors like temperature, humidity and photoperiod with best suitable immature stage (egg, larvae or pupae) that could provide longer storage period for mass production and storage of the parasitoid in shelf for field release to synchronize the parasitoid/host population for biological control of PBW in cotton areas of the world like Pakistan |
2. | To determine that how does the parasitoid over winter in agroecosystem of cotton |
MATERIALS AND METHODS
This experiment was conducted in the Department of Entomology, Plant Pathology and Weed science, New Mexico State University, Las Cruces, USA.
The experiment was replicated four times in a factorial split plot design with three temperatures (0, 4 and 8°C), two light/dark regimes (9/15 light/dark hours and Complete darkness), four developmental stages (1 day, 3 days, 6 days and 8 days PBW eggs parasitized by T. bactrae), three holding times (20, 40 and 60 days), and 55% constant relative humidity.
It was determined from the T. bactrae life table, studied in the same laboratory, that at 28°C the egg/larval stage lasted about 05 days, the pupal stage lasted about 04 days and adults emerged approximately 09 days after parasitization.
More than 16,000 PBW eggs were placed in a newly emerged T. bactrae colony. After one day, 30 randomly selected eggs were placed in an air tight (50×09 mm) petri dish. It was assumed that all PBW eggs were parasitized by T. bactrae. Seventy two petri dishes were prepared in the same way. Twenty four petri dishes were placed at each temperature 0, 4 and 8°C. The procedure was repeated 03, 06 and 08 days after parasitization in a split split plot design (SSPD). After 20, 40 and 60 days, 24 petri dishes were removed (04 from each treatment) and placed at 28°C at 55% RH and 11/13 photoperiod for emergence.
The emerged adults were counted for each treatment and analyzed by ANOVA (Analysis of Variance) through Statistical Analysis System, SAS, (SAS Institute, 1990) for the effects of temperature, development stage, photoperiod and holding duration on emergence. A Least Significance Difference (LSD) Test was used on significant interactions found by ANOVA.
Results and Discussion
High mortality occurred in the eggs which were placed 8 days after parasitization. Most eggs either hatched or died during different treatments or adults did not emerge at all after removal from the environmental chambers at 28°C. They were not analyzed.
Analysis of variance for rest of the treatments showed that all treatments (temperature, developmental stage, and holding time) had significant interactions except photoperiod. Tauber et al. (1986) and Yeargan and Barney (1996), reported that temperature could alter the critical photoperiod for the development of insect/mite.
Table 1: | Mean*1 Number and percent of Adult T. bactrae that Emerged after Holding Egg, Larval and Pupal Stages at 0, 4 and 8°C for 20, 40 and 60 days |
*1 | Mean are from four replicates (n = 30) |
*2 | Lower case letters indicate significant difference down the column |
*3 | Greek characters represent significance |
*4 | Numbers in brackets are percent emergence LSD values for same temperature was 0.47 and for different temperature was 0.792 at significance level of 0.05 |
Three different temperatures were tested in this study and there was not much difference among them thus this factor could not affect photoperiod and as a result tested photoperiod had no significant interaction not only with each other but also with other applied factors thus this factor was not further analyzed.
Among the environmental factors tested temperature was the most important as were observed by Phoofolo et al. (1995), Marco et al. (1997) and Shipp and Van Houten (1997). The results showed that under the conditions of this test, the best shelf life was obtained when pupae were held at 8°C for any holding time tested (Table 1).
Adult emergence was highest (>57%) when pupae were stored at 8°C for any holding time (Table 1). Sharma and Chaudhary (1988) also observed minimum mortality in pupal stage at difference temperatures in Heliothis armigera (Hubner) while Hutchison et al. (1990) found the same in T. bactrae.
Larval stages of T. bactrae at any temperature had minimum adult emergence (Table 1). Maximum mortality was reported by Sharma and Chaudhary (1988) and Hutchison et al. (1990). Thus it may infer that parasitoid's larvae may not have ability to survive well at low temperatures.
The egg stage is more tolerant than the larval stage. Sharma and Chaudhary (1988) and Hutchison et al. (1990) reported same. However pupal stage is the most tolerant stage in the life cycle of this parasitoid. This suggests that T. bactrae may over winter either in egg or pupal stage.
Since best results were observed at the highest temperature tested (8°C), there is a possibility of better results above 8°C. Shelf life may be further advanced with other combinations of environmental conditions.
The results of the experiment suggest that the parasitoid may be stored in pupal stage for at least three months for the mass release in favorable conditions to establish their population in the field. This may turn a good biological agent for different pest of cotton and rice as reported by Nagaraja (1978) and Hutchison et al. (1990).
REFERENCES
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