Development of Necrobia ruficollis (Fabricius) (Coleoptera: Cleridae) under Different Constant Temperatures

Abstract

Necrobia ruficollis (Fabricius, 1775) (Coleoptera: Cleridae) is an important cosmopolitan storage pest, and also frequently appears on highly decomposed and skeletonized corpses. It is a forensically important species expected to indicate a longer postmortem interval (PMI). Therefore, we investigated the development of N. ruficollis at five constant temperatures between 22 °C and 34 °C. Under temperatures of 22, 25, 28, 31, and 34 °C, the mean (±SD) developmental durations from eggs to adults were 93.00 ± 1.63, 70.67 ± 0.94, 65.33 ± 3.40, 47.33 ± 0.94, and 56.66 ± 8.73 days, respectively. According to the developmental time and accumulated degree hours results, an isomorphen diagram and thermal summation model were generated. The calculated values of developmental threshold temperature and accumulated temperature constant were estimated by a linear model to be 14.51 ± 0.52 °C and 684.12 ± 33.85 degree days, respectively. Lower developmental thresholds, intrinsic optimum temperature, and upper lethal developmental threshold temperature were estimated by a nonlinear model to be 14.61, 25.90, and 34.94 °C. Morphological indexes of larvae were obtained by in vivo measurements. A growth curve and an equation of the relationship between development time and body length were simulated. In addition, the widths of the head capsules and the distance between the urogomphi of larvae at different instars were determined by cluster analysis. Classifiers were created and validated by linear discriminant analysis. These results provide important basic developmental data for using N. ruficollis to estimate the minimum postmortem interval (minimum PMI). However, this study was only conducted under constant temperature, and the applicability of these data to variable temperature conditions needs to be further confirmed.

Keywords: Necrobia ruficollis; development; forensic entomology; in vivo measurement; instar determination.

Figure 1

A schematic diagram of Necrobia ruficollis larval measurement. The two-way arrow highlights the indicators measured in this study, wherein (a) represents head capsule width, (b) represents distance between urogomphi, and (c) represents larval body length.

Figure 2

Isomorphen diagram of Necrobia ruficollis. The duration of each development event (hatching, 1st ecdysis, 2nd ecdysis, 3rd ecdysis, chamber formation, pupation, and adult emergence) is plotted against the time from oviposition to the onset of each event. Each curve corresponds to a particular development event. The error bar represents the SD.

Figure 3

Thermal summation models of different development stages of Necrobia ruficollis. ● represents the data used in the regression analysis, while ○ represents the eliminated data. The solid line represents the regression line. The gray area represents the 95% confidence interval.

Figure 4

Nonlinear thermodynamic Optim SSI models of the seven developmental stages of Necrobia ruficollis circles indicate data points. The curved line indicates the developmental rate predicted by the Optim SSI model of Shi et al. [46]. The three open squares denote the predicted mean developmental rates at T_L, T_Φ, and T_H. The black circles denote the data used for the linear fitting by the reduced major axis, whereas the white circles were the data excluded from the linear fitting.

Figure 5

Larval body length of Necrobia ruficollis changes with time at five constant temperatures.

Figure 6

Isomegalen diagram of Necrobia ruficollis. Each contour represents a specific larval body length.

Figure 7

The cluster analysis diagram of head capsule width and cercus spacing at each instar of Necrobia ruficollis larvae under different constant temperatures. There are four instars of Necrobia ruficollis larvae, so the category of cluster analysis was set to four. Through cluster analysis, the larval head capsule width and cercus spacing were divided into four categories. Each blue ellipse represented one instar; ○, △, +, and × represented first, second, third, and fourth instar, respectively.