Influence of Temperature on the Interaction for Resource Utilization Between Fall Armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae), and a Community of Lepidopteran Maize Stemborers Larvae

Abstract

Intra- and interspecific interactions within communities of species that utilize the same resources are characterized by competition or facilitation. The noctuid stemborers, Busseola fusca and Sesamia calamistis, and the crambid stemborer, Chilo partellus were the most important pests of maize in sub-Saharan Africa before the recent "invasion" of fall armyworm (FAW), Spodoptera frugiperda, which currently seriously limits maize yields in Africa. This new pest is interacting with the stemborer community at the larval stage in the use of maize resources. From a work done by Ntiri et al. [13] on the influence of temperature on the larval intra- and interspecific resources utilization within the community of Lepidoptera stemborers involving B. fusca, S. calamistis, and C. partellus, there is a need to update this study by adding the new pest, S. frugiperda, in order to understand the effect of temperature on the larval interactions of all these four species under the context of climate change. The influence of temperature on intra- and interspecific larval interactions was studied in the same protocol of Ntiri et al. [13] using artificial stems kept at different constant temperatures (15 °C, 20 °C, 25 °C, and 30 °C) in an incubator and assessing survival and relative growth rates of each species in single and multi-species experiments. After the inclusion of FAW into the experiments, with regard to relative growth rates, both intra- and interspecific competition was observed among all four species. With regard to survival rates, cannibalism can also explain the intra- and interspecific interactions observed among all four species. Interspecific competition was stronger between the stemborers than between the FAW and the stemborers. Similar to lepidopteran stemborers, temperature affected both survival and relative growth rates of the FAW as well. Regardless of the temperature, C. partellus was superior in interspecific interactions shown by higher relative growth and survival rates. The results suggest that the FAW will co-exist with stemborer species along entire temperature gradient, though competition and/or cannibalism with them is weak. In addition, temperature increases caused by climate change is likely to confer an advantage to C. partellus over the fall armyworm and the other noctuids.

Keywords: fall armyworm; interactions; intra- and interspecific; maize stemborers; temperature.

Figure 1

Effects of diet type, larval stage and rearing substrates on the survival (A) and relative growth rate (B) of fall armyworm larvae. Means (±SE) with different letters are significantly different, determined using linear model (GLM) with binomial error distribution. Significant differences were separated using Tukey’s multiple comparisons tests performed with lsmeans R package [21], following generalized linear model (GLM) with binomial errors distribution. For relative growth rate (RGR), means (±SE) were separated with lsmeans R package [21] with p-value adjustment method False Discovery Rate (FDR) [22] following analysis of variance (ANOVA) after constructing general linear models.

Figure 2

Comparison of survival (A) and relative growth rate (B) of S. frugiperda (FAW), B. fusca (Bf), S. calamistis (Sc), and C. partellus (Cp) in single-species combinations at different constant temperatures. Means (±SE) with different letters are significantly different, determined using Tukey’s multiple comparisons tests performed with lsmeans R package [21], following generalized linear model (GLM) with binomial error distribution for survival or False Discovery Rate (FDR) [22] with lsmeans R package [21], following analysis of variance (ANOVA) after constructing general linear models for relative growth rates. Small letters were used to compare means between temperatures for each species and capital letters to compare means between species for each temperature.

Figure 3

Comparison of survival of S. frugiperda (FAW), B. fusca (Bf), S. calamistis (Sc), and C. partellus (Cp) in multi-species combinations at different constant temperatures. Means (±SE) with different letters are significantly different, determined using Tukey’s multiple comparisons tests performed with lsmeans R package [21], following generalized linear model (GLM) with simple binomial procedure. A = FAW+Bf, B = FAW+Sc, C = FAW+Cp, D = FAW+Bf+Cp, E = FAW+Sc+Cp, F = FAW+Sc+Bf, G = FAW+Sc+Bf+Cp.

Figure 4

Comparison of relative growth rates of S. frugiperda (FAW), B. fusca (Bf), S. calamistis (Sc), and C. partellus (Cp) in multi-species combinations at different constant temperatures. Means (±SE) with different letters are significantly different, determined using False Discovery Rate (FDR) [22] with lsmeans R package [21], following analysis of variance (ANOVA) after constructing general linear models. A = FAW+Bf, B = FAW+Sc, C = FAW+Cp, D = FAW+Bf+Cp, E = FAW+Sc+Cp, F = FAW+Sc+Bf, G = FAW+Sc+Bf+Cp.

Figure 5

Comparison of survival (A) and relative growth rate (B) between single-species and multi-species combinations of S. frugiperda (FAW), B. fusca (Bf), S. calamistis (Sc), and C. partellus (Cp) under different constant temperatures. Statistical comparisons were only made between single- and corresponding multi-species pairings (see Table 5 and Table 6). Means (±SE) were compared using Tukey’s multiple comparisons tests performed using with lsmeans R package [21], following generalized linear model (GLM) with simple binomial procedure for survival or false discovery rate [22] following analysis of variance (ANOVA) after constructing general linear models for relative growth rates.