Integrating temperature-dependent life table data into Insect Life Cycle Model for predicting the potential distribution of Scapsipedus icipe Hugel & Tanga

Abstract

Scapsipedus icipe Hugel and Tanga (Orthoptera: Gryllidae) is a newly described edible cricket species. Although, there is substantial interest in mass production of S. icipe for human food and animal feed, no information exists on the impact of temperature on their bionomics. Temperature-dependent development, survival, reproductive and life table parameters of S. icipe was generated and integrated into advanced Insect Life Cycle Modeling software to describe relative S. icipe population increase and spatial spread based on nine constant temperature conditions. We examined model predictions and implications for S. icipe potential distribution in Africa under current and future climate. These regions where entomophagy is widely practiced have distinctly different climates. Our results showed that S. icipe eggs were unable to hatch at 10 and 40°C, while emerged nymphs failed to complete development at 15°C. The developmental time of S. icipe was observed to decrease with increased in temperature. The lowest developmental threshold temperatures estimated using linear regressions was 14.3, 12.67 and 19.12°C and the thermal constants for development were 185.2, 1111.1- and 40.7-degree days (DD) for egg, nymph and pre-adult stages, respectively. The highest total fecundity (3416 individuals/female/generation), intrinsic rate of natural increase (0.075 days), net reproductive rate (1330.8 female/female/generation) and shortest doubling time (9.2 days) was recorded at 30°C. The regions predicted to be suitable by the model suggest that S. icipe is tolerant to a wider range of climatic conditions. Our findings provide for the first-time important information on the impact of temperature on the biology, establishment and spread of S. icipe across the Africa continent. The prospect of edible S. icipe production to become a new sector in food and feed industry is discussed.

Fig 1. Sex ratio of Scapsipedus icipe adults that emerged from the last instar nymph reared at different constant temperature regimes.

Fig 2. Temperature-dependent developmental rate of Scapsipedus icipe.

(A) Egg; (B) Nymphs; (C) Pre-adult. Observed values are the solid points, with bars representing the standard deviation of the mean. Fitted models are the straight line for linear regression and a solid curved line for the Logan and Allahyari models. Dashed lines above and below represent the upper and lower 95% confidence bands.

Fig 3

Temperature-dependent mortality rates of immature life stages of Scapsipedus icipe: egg (A), Nymph (B), and pre-adult (C). Fitted curves: Wang 2 model (A, B), and Wang 3 (C). Dashed lines represent the upper and lower 95% confidence.

Fig 4

Mean (±SE) body length (A) and wet weight of Scapsipedus icipe females and males at six constant temperatures, respectively (B). Different letters indicate a significant difference while the same letters indicate no significant difference using Student-Newman-Keul’s test (P < 0.05).

Fig 5

Temperature-dependent total egg production (A) and age-related cumulative proportion of egg production (B). Age of the females at 50% oviposition is indicated. Dots represent data points. The upper and lower 95% confidence intervals of the model are indicated.

Fig 6

Temperature-dependent senescence rates (day 1) for Scapsipedus icipe adult females (A) and males (B). Fitted curves of senescence rates: Hilbert and logan 3 model (A) and Exponential simple Model (red solid line) (B). Bars represent the standard deviation of the median senescence rate.

Fig 7

Life table parameters of Scapsipedus icipe estimated through model prediction over a range of six constant temperatures: [A] Intrinsic rate increase, rm; [B] net reproduction rate, Ro; [C] gross reproductive rate, GRR; [D] mean generation time, T; [E] Finite rate of increase, 𝜆 and [F] doubling time, Dt.

Fig 8

Current [A] and future [B] spatial mapping of Scapsipedus icipe establishment according to ILCYM model prediction in Africa.

Fig 9. Mass production of Scapsipedus icipe under optimum rearing condition of 30°C (i.e. highest total fecundity (3416 individuals/female/generation), highest intrinsic rate of natural increase (0.075 days), highest net reproductive rate (1330.8 female/female/generation) and shortest doubling time (9.2 days).