Effect of Age on Reproductive Behaviour of the Brown Planthopper, Nilaparvata lugens Stál (Hemiptera: Delphacidea)

The reared culture of N. lugens was taken from the Department of Entomology, Faculty of Crop Protection, Sindh Agriculture University, Tando Jam and further kept in wooden cages (90 x 42 x 42 cm) at 28 ± 2oC and 60-70 % relative humidity in the insectary during 2018-2019. The newly emerged adults were separated from the main culture to maintain their virginity. The sexes of adult insects were identified based on their genitalia and then kept in separate plastic jars having fresh rice seedlings inside it. Brachypterus males and females were taken to observe the effect of age in the mating behaviour of BPH. The male age (1 to 7 days) paired with 5 days female and female age (1 to 10 days) paired with 5 days male were selected. The insects were allowed to settle on two 30-40 days old rice plants with connected leaf blades (to permit interaction) under 100 W fluorescent lights. The mating behaviour of insects was observed between 1700 to 2100 hours. However, the efficiency of different aged male and female was observed in time with digital stop watch (SDW-219; Malaysia) based on male response time (MRT), male arrival time (MAT), male arresting time (MATt), number of times male extended genitalia (MEG), total pre-mating time (TPMT) and mating duration (MD) with naked eye as this study was based on physical behaviour of BPH regarding their mating efforts. The experiments were conducted in Complete Randomized Design (CRD) using five replications per treatment and analysed using one-way analysis of variance (ANOVA). Least significant difference (LSD) at 0.05 probabilities was used to separate the means with significant differences. In addition, two mating parameters such as total pre-mating time and successful mating percentage was correlated with male age using Pearson correlation coefficient (r). All analysis was done using Statistical analyser software (Statix 8.1).

The influence of the variable age of male in mating efforts of BPH was observed significantly different (MRT, F=26.59; MAT, F=16.39; MATt, F=8.50; MEG, F=27.86; MD F=4.02 and TPMT F=77.37 with dF=6, 28 at p<0.05). Each mating attempt or parameter was examined with uneven duration and observed influenced by male age (Table I). A maximum time to response (MRT) was observed in D1 and observed earlier as male age advanced. The BPH males responded with jerky walking steps up and down and sometimes they were observed stationary. However, the time noted for males of D1 to D5 was not significantly different except for D6 and D7 males with minimum time by D3 male. Such responses showed that different age pairing combinations played an imperative role in displaying variability in mating responses of BPH. A female’s behaviour is usually more complex than males as it invests more in offspring than males (Ayasse et al., 2001; Fortes and Consoli, 2011) thus its behaviour changes in accordance with the activity of its corpora allata with aging. After successful male arrival, male went for arresting time by female in which female scrutinised male thoroughly. During this period, male tried to connect its genitalia with female genitalia for successful copulation. Virgin males of variable age attempted a number of times to get over the female for mating but five days old virgin females took time and did not allow males swiftly. Nevertheless, male arresting time in virgin males of D3 to D7 was almost the same, though minimum time of 1.04±0.08 min was observed in D5. D1 male did not take maximum time under female arresting only, but it also extended genitalia maximum number of times that displayed maximum number of efforts (unsuccessful) attempted by young one day (D1) old male. However, more successful males were D5 to D7; those who extended one or two times their genitalia and were successfully accepted by females. This permitting act could be important for aging female

Means followed by different letters within the same row are significantly different (p≤0.05).

Means followed by different letters within the same row are significantly different (p≤0.05).

who already has a shortened preference window for the selection of best males thus allowing them to increase its reproductive potential. Whereas males do not often refuse copulation with vibrating females after locating them (Claridge et al., 1984), however this response could be affected by physiological factors like age or changes in environmental condition (Silva et al., 2012). In last, a minimum pre-mating time (3.39±0.17 min) was observed in D5 males with maximum mating duration of 1.92 ± 0.22 min in D6 old males. The mating duration was lower in early ages (D1 and D2) and reached at a peak in mid ages (D5 and D6) which later started to decrease a bit again in D7. In male cotton leafhopper A. devastans (Dist.), male Caribbean fruit flies Anastrepha suspensa (Loew) and in the previous study on male BPH, the effects of age on the sexual response of male have also been reported (Ichikawa, 1979; Kumar and Saxena, 1986; Aluja et al., 2009). This again highlights that too young and old males are not at the peak of mating efficiency and are less preferred by matured five days old females (Butlin, 1993; De Luca and Cocroft, 2011). Besides, the physical behaviour of BPH females did not show mating response during the first and second day of emerging (Table II). The first mating response by displaying female abdominal vibration (FAV) was noticed on the third day (D3) with a maximum calling latency of 12.1±1.5 mint. The results further showed that the imitativeness of females for courtship (calling latency) increased in terms of short period as older females responded early as compared to younger or middle age females. Similarly, the rejection rate also decreased (0.8 to 0.2) with increasing age (D7 to D10) of females which further assured less premating time in older females (4.2 to 1.1 min) as compared to young females but it also could be possible due to mating response of male partners. Meanwhile, overall rejection rate, FAV latency and pre-mating time were observed maximum in D3 females as compared to the rest of selected females. The correlation co-efficient also indicated strong with negative relationship (r= -0.92) between total premating time and male age and strong with a positive relationship (r=0.95) between male age and mating percentage (Table III). Female abdominal vibration is also seen as a guide for the male to locate the female depending upon the vibrating frequency (Ichikawa, 1979; De Luca and Cocroft, 2011). The maximum percentage of receptiveness was mostly observed in five to seven days old females and her willingness often correlated with male fitness (age). In BPH, females’ mate for a limited number of times, whereby two to three times of mating is quite sufficient for their entire life to fertilize their eggs (Mochida and Okada, 1979; Heong and Hardy, 2009). Therefore, they were found to be selective in choosing their partner; often scrutinizing either male size or male call to ensure the fittest male sires the progeny. Unlike females, males show post-copulatory mating response because they often can mate with a maximum of nine females within 24 h (Mochida and Okada, 1979; Heong and Hardy, 2009). Often, the aged female of nine days old showed less interest in long mating duration and was observed kicking and repelling the male to dislodge immediately after a short mating duration when paired with a different aged group of males.

It is concluded that all the mating parameters of both sexes were influenced by age. The best age for exhibiting maximum mating response was D5 for both adults.

We acknowledge the Department of Entomology for supporting this research work to the first author.

The authors have declared no conflict of interest.