Rearing method and life-table data for the cocoa mirid bug Sahlbergella singularis Haglund (Hemiptera: Miridae)

The mirid bug Sahlbergella singularis feeds on cocoa pods and shoots, causing considerable crop losses. As laboratory experimentation requires numerous insects, this study aimed at improving available rearing method of S. singularis for Cameroon. Fifty second to fifth nymphal stages were collected at a cocoa farm and reared to the adult stage on cocoa pods in an insectary (T = 24.7 ± 0.9°C, RH = 84.5 ± 6.8%, photoperiod: 12 : 12 L : D). Newly emerged females were confined for 5-6 days on cocoa twigs for sexual maturation and each female paired with a male for 24 h. The pairs were returned to the field and enclosed in mousseline sleeves on attached cocoa pods, for egg laying. After 16 days (expected egg lifetime), the sleeve cages were checked daily to detect newly hatched nymphs. Then, the pods were collected and brought to the insectary, where nymphs continued to emerge and develop into adults. Our method allowed the production of 14.6 ± 6.7 nymphs per female per generation, for 15 consecutive generations. Nymphal survival was calculated to be 68.2% and the mean duration of the nymphal development was measured at 22.7 ± 3.1 days. The rearing performance was evaluated using life-table calculations. The net reproductive rate (R₀) was 6.59; the intrinsic rate of increase (r) was 0.037 per female per day with a population doubling time (Td) of 18.9 days. On average each female contributed 9.70 individuals to the population given a mean generation time (Tc) of 52.1 days. The percentage of reproductive females and the mean number of nymphs per female were significantly different between generations, with 86.8% and 18.1% in generation G7 as compared to 45.8% and 8.4% for generation G5, respectively. As rainfall showed concordant variations during the period of investigation, we discuss the impact of this factor on mirid fecundity.