In experiment 1, the significance difference (f = 26.1, df = 23, p < 0.00) was found in egg cannibalism of different larval instars of C. carnea (Fig. 2). Second and third instar larvae expressed 1.6 and 2.3-fold higher egg cannibalism, respectively, and found more voracious toward conspecific eggs than the first instar larvae.
In experiment 2, in the presence of host eggs, the rate of egg cannibalism varied greatly with a significant difference among the first and second instar larvae (Fig. 3). Earlier instar larvae (first instar (t = 5.7, df = 14, p < 0.00) and second instar (t = 3.5, df = 14, p = 0.003)) were committed significant egg cannibalism, regardless of the presence of host eggs, indicating the attraction to conspecific eggs was not influenced by the presence of host eggs. However, the third instar larvae were equally consumed conspecific eggs and host eggs (t = − 1.6, df = 14, p = 0.132).
In experiment 3, both second and third instar larvae were evaluated for egg cannibalism in the presence of conspecific larvae (Fig. 4). Lone focal second instar larvae expressed low egg cannibalism (20.6 ± 1.1). However, focal larvae in the presence of neighboring larvae 1, 2, 4 and 8 expressed 1.2, 1.3, 1.3 and 1.8-fold increase in egg cannibalism, respectively. Likewise, during the assay of third instar, focal larvae held alone continued to exhibit low cannibalism (33.9 ± 2.5), but those held in the presence of conspecific larvae 1, 2, 4 and 8 become 1.1, 1.3, 1.6 and 1.6-fold more cannibalistic, respectively. Egg cannibalism changed significantly with increase in numbers of neighboring larvae (second instar = f = 31.6, df = 39, p < 0.00; third instar = f = 23.6, df = 39, p < 0.00). Results of comparison between control and each number of neighboring larvae were found significant in both (second and third) instar, except when held with single neighbor.
In experiment 4, nonsignificant difference was recorded in egg cannibalism when C. carnea larvae were held in two separate arenas for each type (related and unrelated) of eggs (p = 0.736) (Fig. 5). However, conspecific eggs of the other parents (unrelated) were significantly more preferred to cannibalize than the eggs of the same parents (related) (p < 0.00).
Behavioral response
In the test combination of C. carnea eggs vs. S. cerealella eggs, time proportion spent by the first instar of C. carnea in both novel arms was statistically similar (t = 0.14, df = 19, p = 0.894) and no preference was found toward different eggs (Figs. 6 and 7). Likewise, nonsignificant difference was found in speed (t = − 0.79, df = 19, p = 0.441) and as well as in the distance (t = 1.4, df = 19, p = 0.187) traveled by first instars in both novel arms provided with C. carnea and S. cerealella eggs. However, behavioral preference to C. carnea eggs was recognized by the second and third instar larvae, where they spent more than half of the total time in the particular novel arm. Speed of second instar larvae remained similar in both novel arms (t = − 0.68, df = 19, p = 0.502) but the significant difference was detected in third instar larvae (t = 7.9, df = 19, p < 0.00). Distance traveled by second instar was significantly higher (t = 6.2, df = 19, p = 0.00) in the novel arm provided with C. carnea eggs than the other arm with S. cerealella eggs, while nonsignificant difference was found in the distance traveled by third instar larvae (t = 0.8, df = 19, p = 0.430).
Furthermore, in the second (eggs from related parents vs. eggs from unrelated parents) test combination, second instar C. carnea larvae preferred eggs of unrelated parents over eggs of unrelated parents (t = − 13.06, df = 19, p = 0.00) (Figs. 8 and 9). Speed (t = − 2.03, df = 19, p = 0.66) and distance (t = 0.56, df = 19, p = 0.58) traveled in both novel arms were found similar.