Vol. 24 (1) (March 2021) Insect Environment Response of pupal weight of stalk borer, Chilo auricilius Dudgeon (Crambidae: Lepidoptera) on biology of Tetrastichus howardi (Olliff) (Hymenoptera: Eulophidae) Anuj Kumar, Arun Baitha* and A. Kumar Division of Crop Protection ICAR-Indian Institute of Sugarcane Research, R.B. Road, Dilkusha, P.O. Lucknow-226 002, India *Corresponding author:[email protected] Abstract The biological attributes of Tetrastichus howardi (Olliff) (Eulophidae: Hymenoptera) were studied at 26 ± 2°C and 65 ± 5% relative humidity in the laboratory on different weighed pupae of sugarcane stalk borer, Chilo auricilius Dudgeon (Crambidae: Lepidoptera). The lowest value for the mean number of progeny per pupa was recorded as 41.17 progenies/pupa and increased with increase in weight of pupa. The maximum progeny (82.83 progenies/pupa) was obtained from pupal weight of more than 0.091g. The number of female also increased per pupa (37.67 to 77.50) as pupal weight increased. The female biased sex ratio (>90%) was observed in all ranges of weighed pupa. It can be inferred that higher numbers of adults in short period of time, a strong preponderance of females on more weighed pupae and gregarious development makes it possible to multiply T. howardi on sugarcane stalk borer pupae in the laboratory. Key words: Sugarcane, Chilo auricilius, pupa, weight, Tetrastichus howardi Introduction The success of biological control programmes depends on the mass rearing of parasitoids (Pastori et al., 2008 ; Pereira et al., 2009) and the specific hosts that are used for rearing, making it mandatory to study their biological interaction (Nakajima et al., 2012;Kumar et al., 2016). The development of mass-rearing methods depends on the knowledge of biological attributes i.e. sex ratio, reproductive potential, length of the life cycle (egg to adult), exposure periods of parasitoids to host and parasitoid sensitivity to abiotic factors, i.e. temperature, light, and humidity (Favero et al., 2013). Tetrastichus howardi (Olliff) (Eulophidae: Hymenoptera) is a gregarious and polyphagous endopupal parasitoid of sugarcane borers, show great potential as an effective bio- 63 Vol. 24 (1) (March 2021) Insect Environment agent (Baitha and Sinha, 2005; La Salle and Polaszek, 2007; Kumar, 2020). It parasitizes sugarcane borer pupae (Cherian and Subramaniam, 1940; Puttarudriah and Sastry, 1958; Vargas et al., 2011; Sankar and Rao 2016) in their galleries in sugarcane. The knowledge of biological attributes particularly on host size, weight, quality, etc. is of vital importance in the mass rearing of T. howardi on alternate hosts and developing strategies for their subsequent release in the field (Pereira et al., 2015; Kumar et al., 2018). Its polyphagous nature, high fecundity and ability to attack a wide range of hosts are considered as valuable for the biological control of sugarcane borers. Providing host pupa in a proper manner to have potential production with the desirable biological attributes requires knowledge about the various interactions between the host and parasitoids. The knowledge on host – parasitoid interaction, gives us a platform upon which the right choices of host to mass multiply the parasitoids. Sugarcane stalk borer, Chilo auricilius Dudgeon (Crambidae: Lepidoptera) is a specialized borer of sugarcane. In sugarcane, it extensively damages the mature cane stalk (Mazumder, 2020) and it is also known as “Tarai borer” due to its prevalence in the Tarai region (moist as well as cold area in the subtropical belt). The study was undertaken to rear T. howardi in the laboratory by using different weights of pupa of C. auricilius as well as to generate opportunities for studying the potential of this parasitoid in controlling C. auricilius on sugarcane crop. Materials and Methods The host pupa of stalk borer, Chilo auricilius was collected from sugarcane fields at Research Farm, IISR, Lucknow. Freshly formed pupa is thin, slender and yellowish –white or creamy yellow in colour and as it matures the colour changes to light brown. The pupal parasitoid, Tetrastichus howardi was maintained on pupae of sugarcane stalk borer, C. auricilius (Fig.1). Newly emerged mated females of T. howardi were kept singly in glass vials (15 x 2.5 cm). The weight of each stalk borer pupa was recorded on electric balance. Each individual female parasitoid was provided with a pupa of stalk borer. Fine streaks of honey- water solutions (1:1 v/v) were provided as adult food and the glass vials were plugged with cotton wool. The individual females were allowed for 24h parasitisation and then removed. The 64 Vol. 24 (1) (March 2021) Insect Environment experiment was conducted at 26 ± 2°C and 65 ± 5% relative humidity with five replications. The observations were taken after the emergence of parasitoid on the developmental period (from egg to adult), the number of progeny emerged per pupa, female emergence and sex-ratio (M: F). Stalk borer pupae Parasitised pupa by T. howardi Emergence of T. howardi Emergence of T. howardi Figure 1. Fresh pupa of C. auricilius, parasitised pupa and emergence of T. howardi The sex of adult parasitoids was determined by assessing the morphological characteristics of their antennae and abdomen (LaSalle, 1994). The data (except sex ratio) were subjected to analysis of variance (ANOVA) at 5% probability. Results and Discussion On stalk borer pupa, developmental period varied from 17.33 to 17.83 days and it was not influenced by weighed pupae. The period of development of this parasitoid on different hosts is variable, but generally, the cycle lasts from 14 to 20 days (Puttarudriah and Sastry 1958, Favero et al., 2013). The lowest variation on duration of the cycle (egg-adult) of T. howardi on C. 65 Vol. 24 (1) (March 2021) Insect Environment auricilius indicates that host pupae are suitable for the development. The production of progeny per pupa was recorded lowest as 41.17 and increased with increase weight of pupa (Table 1). The maximum progeny (82.83 /pupa) was obtained from pupal weight with more than 0.091g. It may be associated with nutritional availability and size of the host. The weight of host pupa was correlated with the number of adults emerged (Nadarajan and Jayaraj, 1975). The smaller host pupa gave rise to less number of parasitoids whereas larger ones supported more parasitoids (Puttarudriah and Sastry 1958; Kfir et al., 1993; Baitha and Maurya, 2012). The limitation of space and deficiency of food materials in smaller pupa resulted in either low fecundity of females or greater mortality among immature stages or both. Parasitoids in general, determine the quality of host by its size and believed to contain more resources than small host (Godfray,1994; Islam and Copland 1997). Table 1. Response of host weight of stalk borer pupa on biological attributes of T. howardi Weight of stalk Development No. of No. of Female Sex Ratio borer pupa period progeny/ Female (%) (M:F) (gm.) (days) pupa < 0.050 17.7a 41.17 a 37.67 a 91.07 a 1:10.9 0.051 - 0.070 17.8 a 47.50 a 43.50 a 91.72 a 1:11.6 0.071 - 0.090 17.5 a 71.31b 66.30 b 92.95 a 1:14.1 >0.091 17.3 a 82.83 b 77.50 b 93.53 a 1:14.9 Means followed by different letters in the same column are significantly different (P<0.05) The number of female increased per pupa (37.67 to 77.50) as weight of pupa increased. The female biased sex ratio (>90%) was observed in all ranges of weighed pupa (Table 1). Uematsu (1981) observed that parasitoids may have the ability to modify sex ratio of the progeny according to host size. As weights of pupa increased, the sex ratio (M: F) also increased from 1:10.9 to 1:14.9. The large is more beneficial to the fitness of daughters than sons and selection would then favor wasps to lay daughter on large hosts and more sons in small hosts (Assem, 1971; Kobayashi and Shimada 2000; Harvey et al., 2004). 66 Vol. 24 (1) (March 2021) Insect Environment It can be inferred that higher numbers of adults in short periods of time, a strong preponderance of females on more weighed pupae and gregarious development make it possible to multiply T. howardi on field-collected sugarcane stalk borer pupae in the laboratory. Acknowledgement The authors are grateful to the Director, ICAR-Indian Institute of Sugarcane Research, Lucknow and Head, Division of Crop Protection for necessary facilities. The help rendered by Mr. Santosh Kumar Pandey, Sandeep Kumar Sharma and Arpit Maurya is also thankfully acknowledged. References Assem, J. Van Den.1971. Some experiments on sex ratio and sex regulation in the pteromalid, Lariophagus distinguendus. 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