Reproductive strategies in certain aphidophagous ladybird beetles

Abstract

Being the primary source of subsistence, agriculture is considered as the backbone of Indian economy. However, most agricultural crops are severely attacked by several insect pests including aphids that cause heavy losses to the crop yields. Synthetic pesticides are quite effective, but these chemicals also damage our environment and cause health hazards to human beings, livestock and other animals; besides several other problems. However, use of natural enemies in pest suppression (biocontrol) has gained increasing acceptance and popularity in recent years, being cost-effective, self sustaining, host/prey-specific, relatively safe to the non-target organisms and free from hazards of pollution and resistance in target species. Amongst natural enemies, predaceous ladybirds are the most successful group of insects. In order to facilitate mass multiplication and to enhance our understanding of ladybirds an attempt was made to investigate certain aspects of reproductive biology of two common occurring and locally abundant aphidophagous ladybirds, Coccinella septempunctata L. and Coccinella transversalis Fabricius. 1 Effect of multiple matings 1.1 Effect of multiple matings on mating behaviour In C. septempunctata, time for commencement of mating ((9.500.34 seconds), latent period (7.550.23 seconds), wriggling movement duration (26.80 1.14 minutes), number of bouts (261.304.00), and complete mating duration (69.20±0.99 minutes) were maximum when subjected to single mating. The respective values were minimum (5.900.31 seconds, 4.600.30 seconds, 21.800.71 minutes, 175.104.21 and 59.80±0.69 minutes) after 10 matings. However, interval between successive bouts was maximum (5.81±0.24 seconds) after 10 matings and minimum (4.88±0.21 seconds) after single mating. In C. transversalis, time for commencement of mating (7.70±0.39 seconds), latent period (7.21±0.26 seconds), wriggling movement duration (6.30±0.13 minutes), number of bouts (186.50±4.35), and complete mating duration (29.10±0.41 minutes) were the longest when subjected to single mating. These parameters were shortest (3.33±0.11 seconds, 3.44±0.18 seconds, 5.78±0.14 minutes, 136.30±4.43 and 22.50±0.80 minutes, respectively) after 10 matings. Interval between successive bouts was maximum (5.94±0.20 seconds) after 10 matings and minimum (4.19±0.14 seconds) after single mating. 1.2 Effect of multiple matings on reproductive attributes Females of C. septempunctata had highest fecundity (840.00±23.39 eggs) and egg viability (93.18±0.38%) after 10 matings and lowest (314.90±9.09 eggs and 86.44±0.50%, respectively) after single mating. Similarly, fecundity and egg viability in C. transversalis were highest (1046.00±22.28 eggs and 94.03±0.39%, respectively) after 10 matings and lowest (795.00±17.28 eggs and 87.22±0.25%, respectively) after single mating. 1.3 Effect of multiple matings on offspring development and survival Total development period of immature stages of both C. septempunctata and C. transversalis was maximum (15.81±0.21 and 15.120.23 days, respectively) in offspring of parents subjected to single mating and minimum (14.12±0.12 and 13.450.17 days, respectively) after 10 matings. Percent adult emergence and growth index were maximum (83.00±1.00%, and 10.66±0.28 per day for C. septempunctata; and 86.001.63%, and 11.420.18 per day for C. transversalis) after 10 matings and minimum (70.00±2.58%, and 8.14±0.24 per day for C. septempunctata; and 73.001.53%, and 8.750.21 per day, for C. transversalis) after single mating. Thus, the results suggest that multiple matings altered copulatory behaviour and improved reproductive attributes and growth, development and survival of offspring. 2 Effect of male mating history 2.1 Effect of male mating history on mating behaviour In C. septempunctata, time for commencement of mating, latent period, wriggling movement duration, number of bouts and complete mating duration were longest (9.20±0.19 seconds, 8.06±0.26 seconds, 25.50±1.14 minutes, 271.50±3.69 and 66.80±1.05 minutes, respectively) for unmated males and shortest (7.18±0.16 seconds, 6.79±0.13 seconds, 21.50±0.50 seconds, 204.50±4.94 and 60.60±1.78 minutes, respectively) for five times mated males. Interval between successive bouts was maximum for five times mated males and minimum for unmated males. In C. transversalis, time for commencement of mating (7.40±0.30 seconds), latent period (7.14±0.23 seconds), number of bouts (179.10±3.73), and complete mating duration (27.60±0.45 minutes) was longest in unmated males and shortest (5.17±0.12 seconds, 5.23±0.13 seconds, 127.10±5.73 and 22.00±0.80 minutes, respectively) in five times mated males. Interval between successive bouts was maximum (5.51±0.03 seconds) for five times mated males and minimum (4.05±0.14 seconds) for unmated males. 2.2 Effect of male mating history on reproductive attributes The fecundity and percent egg viability were maximum in C. septempunctata (317.30±10.30 eggs and 87.24±0.22%, respectively) and C. transversalis (827.30±13.25 eggs and 88.62±0.44%, respectively) when females mated with unmated males. These parameters were minimum (273.60±10.08 eggs and 81.92±0.26%, respectively, in C. septempunctata; and 705.60±15.66 eggs and 80.53±0.56%, respectively, in C. transversalis) when females were mated with five times mated males. 2.3 Effect of male mating history on offspring development and survival Offspring sired by five times mated male developed slowest (16.28±0.06 days in C. septempunctata and 15.92±0.08 days in C. transversalis) and fastest (15.64±0.07 and 15.23±0.07 days, respectively) when sired by unmated males. Maximum number of adults emerged from offspring of unmated males of C. septempunctata and C. transversalis (72.00±2.49% and 73.00±2.13%, respectively) and minimum (62.00±1.33% and 65.00±65.12%, respectively) from five times mated male. Thus, the male mating history significantly influenced copulatory behaviour, reproductive attributes and offspring growth, development and survival. Mated males resulted in lesser reproductive output and lower fitness of offspring. 3 Effect of mating frequency 3.1 Effect of single day mating frequency 3.1.1 Effect of single day mating frequency on mating behaviour The latent period (7.97±0.23 seconds), wriggling movement duration (24.60±0.96 minutes), number of bouts (259.20±9.43) and complete mating duration (65.00±1.61 minutes) in C. septempunctata were maximum at the mating frequency of 1 mating/day; values were shortest (5.61±0.22 seconds, 20.90±0.59 minutes, 128.30±5.66 and 43.90±2.05 minutes, respectively) at 3 matings/ day. Interval between successive bouts was maximum (5.74±0.18 seconds) for 3 matings/day and minimum (4.59±0.27 seconds) for 1 mating/ day. Latent period (6.39±0.27 seconds), wriggling movement duration (6.39±0.27 seconds), number of bouts (6.70±0.17 minutes) and complete mating duration (26.20±0.53 minutes) were maximum at the mating frequency of 1 per day in C. transversalis. 3.1.2 Effect of single day mating frequency on reproductive attributes Fecundity and egg viability in C. septempunctata were maximum (413.80±11.04 eggs and 89.15±0.56%, respectively) after 3 matings/ day and minimum (335.40±20.70 eggs and 86.88±0.56%, respectively) after 1 mating/ day. In C. transversalis, fecundity and egg viability were maximum (865.70±18.19 eggs and 90.23±0.45%, respectively) after 5 matings/day and minimum (785.90±13.55 eggs and 87.78±0.50%, respectively) after 1 mating/ day. 3.1.3 Effect of single day mating frequency on offspring development and survival Total development period of immature stages of C. septempunctata and C. transversalis was maximum (15.76±0.12 and 15.110.21 days, respectively) after 1 mating and minimum after 3 matings in C. septempunctata (15.17±0.09 days) and 5 matings in C. transversalis (14.210.13 days). The percent adult emergence in C. septempunctata was maximum (73.00±2.25%) after 3 matings/day and in C. transversalis, it was maximum (75%±2.25%) after 5 matings/day and minimum (71.00±2.46 and 73.00±1.52%, respectively) in both ladybirds after 1 mating/ day. Thus, increase in mating frequency modified copulatory behaviour and enhanced the reproductive output and the offspring had higher growth, development and survival. 3.2 Effect of mating frequency on different days 3.2.1 Effect of mating frequency on different days on reproductive attributes Fecundity and egg viability were highest for 3 matings/10 dayss (506.6020.09 eggs and 91.500.25%, respectively) in C. septempunctata and for 5 matings/10 dayss (965.0914.09 eggs and 93.440.57%, respectively) in C. transversalis. Fecundity and egg viability were lowest for 3 matings/ day (413.8011.04 eggs and 89.150.55%, respectively) in C. septempunctata and 5 matings/day (865.7018.19 eggs and 90.230.45%, respectively) in C. transversalis. 3.2.2 Effect of mating frequency on different days on offspring development and survival Total development period of immature was longest for three matings (15.240.07 days) in C. septempunctata and for five matings (14.260.10 dayss) in C. transversalis within 1 day. It was shortest (14.570.08 days in C. septempunctata and 13.490.09 days in C. transversalis) within 10 days. Thus, multiple matings spread over 10 dayss led to increased reproduction and faster growth, and development and higher immature survival of offspring than multiple matings on a day. 4 Age based mate choice and effect on reproduction and offspring development and survival 4.1 Effect of age on mate choice Young (χ2 = 11.55; P = 0.003; d.f. =1 and χ2 = 9.50; P = 0.008; d.f. =1) and middle aged (χ2 = 20.66; P < 0.0001; d.f. =1 and χ2 = 17.55; P < 0.0001; d.f. =1, respectively) females preferred middle aged males as mates in both C. septempunctata and C. transversalis, respectively. Similarly, young (χ2 = 9.55; P = 0.004; d.f. =1 and χ2 = 6.88; P = 0.032; d.f. =1, respectively) and middle aged (χ2 = 16.88; P < 0.0001; d.f. =1 and χ2 = 13.55; P = 0.001; d.f. =1,, respectively) males preferred middle aged females as mates. 4.2 Effect of mate age on mating behaviour Wriggling movement duration (27.40±0.72 and 8.60±0.31 minutes), number of bouts (297.10±6.92 and 200.70±6.69), and complete mating duration (71.70±1.54 and 29.70±0.76 minutes) were maximum in middle aged females pairs of C. septempunctata and C. transversalis, respectively. These values were minimum (18.00±0.58 minutes, 191.80±11.88 and 57.80±1.36 minutes for C. septempunctata and 5.60±0.31 minutes, 108.50±6.01 and 18.40±0.70 minutes for C. transversalis, respectively) in old aged pairs. 4.3 Effect of mate age on reproductive attributes Fecundity and egg viability were maximum (400.10±13.21 eggs and 90.01±0.64% in C. septempunctata and 893.00±26.61 eggs and 91.11±0.64% in C. transversalis, respectively) in middle aged pairs of C. septempunctata and C. transversalis. Both values were minimum (207.80±5.07 eggs and 74.92±1.39% in C. septempunctata; and 417.00±20.44 eggs and 76.04±1.10% in C. transversalis, respectively) in old pairs. 4.4 Effect of mate age on offspring development and survival Total development period of immature stages was maximum (17.70±0.33 and 17.39±0.18 days, respectively) for old aged mating pairs and minimum (14.24±0.18 and 13.57±0.27 days, respectively) for middle aged mating pairs of C. septempunctata and C. transversalis, respectively. Percent adult emergence was maximum (81.00±3.14% in C. septempunctata and 81.00±1.80% in C. transversalis) for middle aged mating pairs and minimum (54.00±1.63% in C. septempunctata and 55.00±1.67% in C. transversalis) for old aged mating pairs. Thus, middle aged adults were the preferred mates, which may be attributed to the enhanced reproductive output and fitter offspring production. 5 Effect of prey species on life history traits 5.1 Effect of prey species on reproductive attributes The fecundity was highest when the females were fed on A. pisum (1609.90±28.92 eggs in C. septempunctata and 1379.30±49.40 eggs in C. transversalis) and lowest when fed on H. setariae (1216.10±39.40 eggs in C. septempunctata and 955.70±31.01 eggs in C. transversalis). 5.2 Effect of prey species on fertility life table The net reproductive rates, intrinsic rates of increase and finite rates of increase in C. septempunctata and C. transversalis were highest (1014.20, 0.21 and 1.23 day-1; and 774.96, 0.23 and 1.26 day-1, respectively) when provided with A. pisum. 5.3 Effect of prey species on offspring development and survival Total development period of immature stages was longer on H. setariae in C. septempunctata (15.900.33 days) and C. transversalis (16.360.27days) and shorter (13.710.29 and 14.450.30 days, respectively) on A. pisum. Percent adult emergence was higher on A. pisum (85.002.24 in C. septempunctata and 78.002.49 in C. transversalis) and lower on H. setariae (691.80% in C. septempunctata and 68.002.00% in C. transversalis). 5.4 Effect of prey species on mortality life table The percent overall mortality of immature stages of C. septempunctata and C. transversalis prior to adult stage was highest on H. setariae (31.00% and 32%, respectively) and lowest (15.00% and 22%, respectively) on A. pisum. Thus, the highest reproductive attributes and best growth, development and immature survival of offspring were recorded on A. pisum and least on H. setariae. 6 Combined effect of body size and prey species on life history traits 6.1 Effect of body size on mate choice Both C. septempunctata and C. transversalis displayed body size based mate choice. Large (χ2 = 12.8; P < 0.0001; d.f. = 1 and χ2 = 9.8; P = 0.002; d.f. = 1, respectively) and small females (χ2 = 7.2; P = 0.007; d.f. = 1 and χ2 = 7.2; P = 0.007; d.f. = 1, respectively) of C. septempunctata and C. transversalis preferred large males as mates. Similarly, large males (χ2 = 5.0; P = 0.025; d.f. = 1 and χ2 = 5.0; P = 0.025; d.f. = 1, respectively) preferred large females as mates. No significant preference was shown by small males for the females of large and small body sizes. 6.2 Effect of body size and prey species on reproductive attributes Lowest pre-oviposition period, highest oviposition period, fecundity, egg viability and reproductive time ratio were recorded in larger mating pairs of C. septempunctata on A. pisum (10.90±0.50 days, 55.50±1.61 days, 1607.00±44.46 eggs, 90.08±0.78% and 2.36±0.08, respectively) and (6.90±0.41 days, 53.50±1.13 days, 1691.00±77.23 eggs, 90.41±0.80% and 2.90±0.17, respectively) of C. transversalis on A. craccivora. In C. septempunctata, reproductive rate (29.08±0.82) was highest in larger pairs on A. pisum and males (71.40±0.98 days) and females (79.10±1.71 days) of larger pairs lived longer. The larger pairs in C. transversalis reported highest reproductive rate (31.52±1.05) and larger males (68.60±0.95 days) lived longer. The females in larger pairs had highest longevity (72.40±1.09 days) when fed on A. craccivora. 6.3 Effect of body size and prey species on fertility life table The net reproductive rate, intrinsic rate of increase and finite rate of increase were highest in larger pairs of C. septempunctata on A. pisum (1016.46, 0.20 day-1 and 1.22 day-1, respectively) and of C. transversalis on A. craccivora (1022.04, 0.24 day-1, 1.26 day-1, respectively). Mean generation time (34.70 days) and doubling time (2.30 days) were lowest in larger pairs of C. septempunctata on A. pisum. In C. transversalis, mean generation time (28.61 days) was lowest in smaller pairs on A. pisum, whereas doubling time (2.14 days) was lowest in larger pairs on A. craccivora. 6.4 Effect of body size and prey species on offspring development and survival Total development period was longest for offspring of smaller pairs of C. septempunctata on A. craccivora (15.84±0.26 days) and of C. transversalis on A. pisum (15.64±0.25 days). It was shortest for offspring of larger pairs of C. septempunctata on A. pisum (13.70±0.26) and of C. transversalis on A. craccivora (13.28±0.24 days). Percent pupation, percent adult emergence, developmental rate, growth index and sex ratio were recorded maximum for offspring of larger pairs of both the ladybirds. 6.5 Effect of body size and prey species on mortality life table The percent overall mortality of immature stages was highest in smaller pairs of C. septempunctata on A. craccivora (39.00%) and of C. transversalis on A. pisum (40.00%). It was lowest in larger pairs of C. septempunctata on A. pisum (16.00%) and of C. transversalis on A. craccivora (17.00%). Thus, highest reproductive attributes and best growth, development and immature survival of offspring were recorded in larger pairs of C. septempunctata on A. pisum and C. transversalis on A. craccivora. The values were least in smaller pairs of C. septempunctata on A. craccivora and C. transversalis on A. pisum. 7 Effect of prey quantity on life history traits 7.1 Effect of prey quantity on reproductive attributes Pre-oviposition period C. septempunctata and C. transversalis was longest (19.00±0.42 and 9.20±0.49 days, respectively) on scarce prey and shortest (11.30±0.52 and 6.40±0.40 days, respectively) on abundant prey condition. Oviposition period of C. septempunctata and C. transversalis was longest (54.50±1.76 and 55.10±1.75 days, respectively) on abundant prey and shortest (40.30±1.54 and 38.50±2.14 days, respectively) on scarce prey condition. Fecundity and percent egg viability were highest (1546.60±41.61 eggs and 89.17±0.98% for C. septempunctata and (1604.10±45.61eggs and 90.82±0.80 % for C. transversalis, respectively) on abundant prey and lowest (784.90±30.15 eggs and 81.23±1.34% for C. septempunctata; and 794.60±30.84 eggs and 82.72±0.67 for C. transversalis, respectively) on scarce prey. 7.2 Effect of prey quantity on fertility life table The net reproductive rate, intrinsic rate of increase and finite rate of increase in C. septempunctata and C. transversalis were highest (977.35, 0.20 and 1.23; and 1037.01, 0.21 and 1.24, respectively) on abundant prey and lowest (362.90, 0.15 and 1.17; and 358.02, 0.20 and 1.23, respectively) on scarce prey. Generation time and doubling time of C. septempunctata were highest (37.20 days and 2.54 days, respectively) on scarce prey and lowest (33.89 days and 2.29 days, respectively) on abundant prey. In C. transversalis, generation time was highest (31.71) with lowest doubling time (2.21) on abundant. It was lowest (28.22) with highest doubling time (2.26) on scarce prey. 7.3 Effect of prey quantity on offspring development and survival Total development period of immature stages of C. septempunctata and C. transversalis was longest (17.29±0.19 and 16.21±0.14 days, respectively) on scarce prey and shortest (14.05±0.16 and 13.29±0.13 days, respectively) on abundant prey. Percent adult emergence of C. septempunctata (75.00±4.35%) and C. transversalis (79.00±4.09%) was maximum on abundant prey and minimum (56.00±4.99 for C. septempunctata and 57.00±4.99for C. transversalis) on scarce prey. 7.4 Effect of prey quantity on mortality life table The percent overall mortality of immature stages of C. septempunctata and C. transversalis prior to adult stage was highest (44.00 and 43.00%, respectively) on scarce prey and lowest (25.00 and 21.00%, respectively) on abundant prey. Thus, highest reproductive attributes and best growth, development and immature survival of offspring were recorded on abundant prey and least on scarce prey. In brief, it may be concluded that for successful mass multiplication of C. septempunctata and C. transversalis, larger middle aged females should be given, sufficient number of matings on different days with unmated larger middle aged males, reared on abundant supply of the most suitable prey species.