The first data on the biology of Ips stebbingi Strohmeyer, 1908 (coleoptera: curculionidae: Scolytinae), a pest of himalayan blue pine

The biological data were obtained mainly in Nowpora village (33°61.078’N, 075°18.700’E and elevation, 5920 ft.) in district Anantnag, Jammu and Kashmir. Based on the preliminary surveys, severe bark beetle infestations were observed in the study area, inhabited by almost 30–40-year-old blue pine trees. The sampling procedure for monitoring the I. stebbingi activity was adopted as per the methods of Buhroo and Lakatos (2007). By using trap logs and other infested branches of standing trees (Beaver 1967; Buhroo and Lakatos 2007; Khanday and Buhroo 2015), observations of the various life stages were made once or twice weekly throughout the experimental period. These trap logs were cut periodically from April to October each year from 2017 to 2018. Further information was obtained by careful removal of bark sections both in the field and in the laboratory. The eggs found in maternal galleries were exposed carefully and counted in their individual chambers. For measurement of galleries (both maternal and larval), a digital caliper scale was used (Khanday and Buhroo 2015). The correlation between the length of maternal galleries and the number of eggs deposited by beetle pests was worked out using the method of Zhang et al. (1992).

At the experimental site, the entrance holes that the newly emerged beetles started grooving were marked on one main branch and some twigs of a declining pine tree during May–June. After the marking dates, 15 beetle entries were dissected each day and examined for eggs to determine female maturation feeding period as per the method of Buhroo and Lakatos (2007).

Laboratory rearing of I. stebbingi was accomplished by placing infested logs (30–50 cm long and 5–10 cm in diameter) in three rearing boxes of similar design made up of glass with dimensions of 75 × 35 × 40 cm, 45 × 35 × 35 cm and 55 × 35 × 35 cm. The top face of each box was fitted with white muslin cloth. Each box could be opened from the top to facilitate exchange of logs. After every month, cut branches (20–40 cm long and 2–8 cm in diameter) from the host tree (P. wallichiana) were placed in the rearing boxes to induce fresh attack, 5–10 days before the emergence of adults in every generation. This enabled continuous rearing and examination of beetle development. A few infested logs were also debarked at regular intervals (10 days) to study various stages of the beetle under bark. Measurements of various developmental stages including egg, larva, pupa and adult were recorded. The development process and duration of beetle life stages were recorded and compared with the field results as per our earlier methods (Buhroo and Lakatos 2007; Khanday and Buhroo 2015).

Photographs were taken during the field study using Canon PowerShot SX60 camera fitted with macro lens (Raynox MSN-505, 37 mm; Yoshida Industry Co., Ltd, Tokyo, Japan). Analysis of digital images was done using ImageJ analysis software (Version 1.38f, 2006). For morphometric description of beetle life stages, images were taken with a Leica DFC295 camera (Leica Microsystems GmbH, Wetzlar, Germany) attached to a Leica M205A stereozoom binocular microscope having Leica Automontage Software (version 4.10). Spatial information regarding sample site was recorded in the form of latitude and longitude with the help of handheld global positioning system (GPS; Garmin eTrex 10, India).

Statistical analyses were performed using OriginPro software (version 2015). The gallery pattern and developmental stages were analysed using descriptive statistics (mean and standard deviation [SD]). The larval instars were separated from each other by head capsule measurements (Dyar 1890).

After host tree selection, the male of I. stebbingi was observed to form an initial gallery known as nuptial chamber (Fig. 1). Many female beetles (two to six) successively entered the nuptial chamber through the tunnel made by the male and after copulation, excavated their individual egg galleries radiating away from the central chamber (Fig. 1).

Figure 1.

Bark dissections for female maturation feeding (Fig. 2) showed that no eggs were collected from beetle entries on the first and second days; only 4/15 from 3-day-old entries yielded eggs, 9/15 from 4-day-old entries contained eggs, while 13/15 from 5-day-old entries contained eggs, but all the 15 of 6-day-old beetle entries contained eggs. This indicated that newly emerged females mostly fed and oviposited in 4–6 days in the field. The feeding sites were then continued into the maternal galleries.

Figure 2.

The gallery patterns are shown in Fig. 3. The average length of maternal galleries is 10.76 (±3.30 SD) cm (Fig. 3A, Tab. 1). Larval galleries radiate out from the maternal galleries. The average length of larval galleries is 3.83 (±0.63 SD) cm (Fig. 3B, Tab. 1). The larval tunnels are initially perpendicular to the maternal gallery, then radiate in different directions and can intersect (Fig. 3B). These tunnels are closely packed with the wood excreta passed out by the larvae during feeding.

Figure 3.

Data based on the length of the maternal gallery and the numbers of eggs deposited indicate that there is a positive correlation (y = 2.1686x – 2.315, r = 0.67) between the two variables (Fig. 4). The number of eggs increases linearly with maternal gallery length.

Figure 4.

The results of the present observations showed that I. stebbingi overwintered in adult stages in their respective galleries from the last week of October (Fig. 9). The adults remained inactive throughout the winter and resumed their activity from the second week of March onwards. The species produced three generations per year in Kashmir (Fig. 9). The first generation lasted from the last week of March to August, having a total life span of 124–156 days (Tab. 3). The second generation lasted from the second week of June to October, having a total life span of 101–136 days, while the third overwintering generation took 199–261 days and extended from August to May of the following year (Tab. 3). Laboratory observations also confirmed three generations with a little difference in developmental process and duration of insect stages.

Figure 9.