Abstract
The fecundity of the pseudococcid predators Nephus includens (Boheman) and N. bisignatus (Kirsch) (Coleoptera: Coccinellidae), fed on Planococcus citri Risso (Hemiptera: Pseudococcidae), was studied at several constant temperatures (15, 20, 25, 30, 32.5 and 35°C). With additional data for the development of the immature stages, life-fecundity tables were constructed and some population parameters calculated. The average total fecundities of N. includens at the above temperatures were 49.2, 97.8, 162.8, 108.5, 87.4 and 31.1 eggs/female, and average longevities 99.5, 84.7, 69.5, 61.1, 49.6 and 30.1 days, respectively. The net reproductive rates (Ro) were 8.0, 32.2, 60.7, 32.6, 20.7 and 2.6 females/female, and the intrinsic rates of increase (rm) 0.014, 0.041, 0.083, 0.086, 0.077 and 0.024 females/female/day, respectively. The average total fecundities of N. bisignatus at 15, 20, 25, 30 and 32.5 ¿C were 54.7, 72.1, 96.9, 56.0 and 22.8 eggs/female, and average longevities 116.1, 108.7, 71.8, 68.8 and 43.7 days, respectively. The net reproductive rates (Ro) were 13.9, 26.4, 31.3, 15.2 and 3.6 females/female and the intrinsic rates of increase (rm) were 0.017, 0.035, 0.060, 0.051 and 0.024 females/female/day, respectively. The survival of females at each temperature was fitted using a Weibull distribution [S(t) = exp(-(t/b)c)]. Furthermore two mathematical models [Enkegaard equation: F = (a+b+x).e(c+d.x), Analytis equation: F = a.(x-xmin)n .(xmin- x)m] were fitted to the fecundity data.
Highlights
Nephus bisignatus (Boheman) and N. includens (Kirsch) (Coleoptera: Coccinellidae) are important indigenous predators of mealybugs (Homoptera: Pseudococcidae) in Greece (Argyriou et al, 1976; Kontodimas, 1997)
There are rare data on the fecundity of N. bisignatus or N. includens, Tranfaglia & Viggiani (1972) report that females lay 150.6 eggs and live for 74 days at 25–27°C when fed on P. citri
In the present study the fecundities of the two predators were examined under laboratory conditions and used to obtain the following life table parameters: age specific survival and fecundity, reproductive value, expected remaining life time, net reproductive value, intrinsic rate of increase, mean generation time, finite rate of increase and doubling time
Summary
Nephus bisignatus (Boheman) and N. includens (Kirsch) (Coleoptera: Coccinellidae) are important indigenous predators of mealybugs (Homoptera: Pseudococcidae) in Greece (Argyriou et al, 1976; Kontodimas, 1997). In the present study the fecundities of the two predators were examined under laboratory conditions and used to obtain the following life table parameters: age specific survival and fecundity, reproductive value, expected remaining life time, net reproductive value, intrinsic rate of increase, mean generation time, finite rate of increase and doubling time. Two mathematical models were fitted to the fecundity data and the survival of adult females were described using the Weibull distribution.
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