Effect of temperature on the life cycle of Trilocha varians (Lepidoptera: Bombycidae) in Pakistan

Ficus benjamina is known as weeping fig, planted along roadsides in Pakistan to increase the aesthetic value of the country. It is native to tropical and sub-tropical regions of the world. In 2019, plants were infested by leaf eating caterpillar, identified as Trilocha varians. The larvae of the pest were caused up to 100% defoliation of F. benjamina. The aim of the recent study was to determine the life cycle of T. varians under two different environmental temperatures i.e. 26°C ± 1.0 controlled and uncontrolled 33°C ±2.0. The recent study was obtained that there was significant difference in the time taken for eggs, larval and pupal period of T. varians between high and low environmental temperatures. The life cycle of the test insect, T. varians was increased at low temperature and reduced in high temperature. The results showed that the fecundity of female ranged from 164 to 275 and 130-190 under controlled and uncontrolled conditions respectively. T. varians has complete metamorphosis and five larval stages. The last instar transferred into dark reddish colour prior to adult formation. The longevity of females and males was 10.0 ± 0.43 and 5.4±0.35 days, respectively. Pupa of the pest was obtect. Our present study results were effective for future management of T. varians in Pakistan.

. The plants can grow well in high temperature areas and it is grown to enhance the beauty of country and for landscaping purpose. These plants are planted alongside the roads to enhance the aesthetic value of many countries including Pakistan. It has medicinal value, used for the treatment of allergy and many other infections [2]. It has been reported that plant has anti-fungal and antitumor properties [3,4]. It is also used to remove the pollution and very toxic chemical like carbon monoxide and formaldehyde [5]. Several

Rearing and life cycle of Trilocha varians
The collected live insect stages were kept into transparent plastic jars and brought to Ecology Laboratory for rearing purpose. For rearing purpose, 10 plastic containers of 2L were purchased from nearby market and 10 larvae were placed in each container with natural diet, leaves of F. benjamina. Other stages such as pupae and eggs of pest were kept into separate plastic containers. Larvae were fed with ficus plants leaves until they reached at pupal stage.
After adult emergence, a pair of moths was placed into jar for collection of eggs and mating purposes. After mating eggs, leaves were examined for eggs. After eggs lying, eggs were placed into separate containers for larvae collection. Pest was reared under two different temperature i.e. controlled (26°C ± 1.0) and uncontrolled (33°C ± 2.0). When the eggs hatched out, larvae were released placed into containers and F. benjamina leaves were placed. On daily basis new leaves were provided for food and data regarding to eggs, larvae, pupa and adults recorded. Data was removed, if any stages like larvae or adults died during the study. Total of 15 and 9 specimens under controlled and uncontrolled condition respectively were successfully reared.

Statistical analysis
Data recorded regarding to developmental period of T. varians between controlled and uncontrolled conditions were analyzed by using Mann-Whitney test. Results and discussion Life cycle of T. varians reared at 26 0 C and 33 0 C temperatures T. varians was passes through different stages like eggs, larval stages (1 st , 2 nd , 3 rd and 4 th ), pupae and adults. All these stages were studied in the current experiment. Egg During the study, it was observed that 215 ± 32.87 eggs deposited by adult female in rows on the walls of containers while dorsal surface of the leaves in field conditions. The colour of eggs was change during the developmental time. Newly laid eggs were light yellow. Before hatching, colour of eggs were change from yellow to black. Shape of eggs was round flat, rounded at base and yellow in colour. The eggs were hatch within six days (Mean ± SE, 6.14 ± 0.47) and become larvae under controlled condition (Fig. 1). In the present study, eggs hatchability was recorded 95.50%. Under uncontrolled conditions (33°C ± 2.0), eggs hatchability took less time (Mean ± SE, 5.00 ± 0.76) for hatching than the controlled temperature.

Figure 1. Egg mass of T. varians on F. benjamina leaf
The significant differences in the time taken between the two temperatures, controlled and uncontrolled conditions for eggs to hatch were (N = 36, U = 70.00, p = 0.006, r = 0.50), larvae period (U = 14, N = 36, p ˂ 0.003, r = 0.70) and pupation period (N = 36, U = 62, p ˂ 0.05, r = 0.55). Larva Body of larvae was cylindrical with five and three pairs of abdominal and thoracic legs respectively. There was a caudal horn on each larva with length of 0.50mm. The dorsal and lateral sides of first instar larva were white and dark green respectively. The head of T. varians was black. Caudal horn on second instar larva was twice long than first instar larva. White powder was present on the whole body of second instar larva. Second instar larva was less moveable than the first instar. The length of caudal horn was longer in third and fourth while reduced in fifth instars. Newly emerged larvae were brown and after 24 hours change into greyish white till last instars. Last instars were resembled with the branches of ficus plants and difficult to find them. There were 5 th larval stages and duration of each stages 1 st , 2 nd , 3 rd , 4 th and 5 th of T. varians, last for 2.50 ±0.14, 3.27 ±0.28, 4.10 ±0.12, 4.95 ±0.15 and 6.99 ±0.25 days respectively. Before changing into pupae, larval stages were lasted about 19.5 days (Mean ± SE, 17.70 ± 2.50). Under uncontrolled conditions (33°C ± 2.0), larval stage was lasted for 11 days (Mean ± SE, 8.94 ± 2.99) before changed into pupa (Fig. 2).

Figure 2. T. varians larva feeding on F. benjamina leaf Pupa
Mature larva was covered itself into silken thread with boat shaped cocoon. During the whole study, colour of cocoon was change from white, bright yellow, light yellow and pinkish. Pupa of T. varians was obtect. Prior to emerging in adults, pupae took about five to six days (Mean ± SE, 6.70 ± 0.60). The period of life cycle become shorter due to high temperature under controlled conditions. The pupal period took four and a half days (mean ± SE, 3.00 ± 1.93) prior changed to adult (Fig.3).

Adult
In the recent study, it was observed that male was short lived as compared to female. Body parts such as head, thorax and abdomen of T. varians were dark reddish brown in colour. Mean longevity of both male and female was 6.6 ±0.01. and 12.00 ± 0.10 days respectively. The outer margins of forewings and hind wings of adult were pale reddish brown and greyish reddish brown in colour respectively (Fig. 4)  varians was at peak point in October to March and infestation rate also maximum during these months. In these months (October-March), developmental period was longer, larvae took more time to change into pupae, fed maximum plants and cause 100% defoliation. There was a long caudal horn on 8 th abdominal segment of early instars of T. varians. Same disruption had been described by other workers [3]. Pupation was taken placed into silken cocoon. Similar observations had been observed by earlier studies [12]. The developmental periods from eggs to larva, larva to pupa and pupa to adults under uncontrolled as well as controlled conditions were similar to earlier studies [9, 16,19].

Conclusion
The environmental conditions such as temperature was affected the life period of insect pests especially T. varians. The developmental time of pest was changed with variations in climate. This was the first study regarding life cycle of T. varians under two different temperatures in Pakistan. This study will be proved to be helpful for future pest control in Pakistan.