Life History Plasticity and Gregarious Cocooning Behavior of the Wild Silkmoth Cricula trifenestrata Helfer (Lepidoptera: Saturniidae) on a Novel Host Plant, Cinnamon, in Thailand

Abstract

Cricula trifenestrata Helfer was recently documented on cinnamon (Cinnamomum spp.), a novel host plant in Thailand. We compared life history and behavior under natural field, semi-natural caged, and laboratory conditions on cinnamon, plus opportunistic collection from hog plum (Spondias pinnata). Laboratory rearing significantly extended development (62.30 ± 3.68 days) versus field conditions (56.30 ± 1.83 days, p < 0.001) through delayed egg and pupal stages, indicating life history plasticity. We discovered density-dependent oviposition plasticity (linear arrangements in field: 155.6 ± 84.9 eggs/batch; clustered in laboratory) and novel gregarious cocooning behavior, where 85.1% of individuals (n = 47 sites) aggregated to form communal clusters with unique reticulated architecture. Female cocoon shell ratio (CSR) was significantly higher in laboratory (5.02 ± 0.72%) and hog plum cohorts (5.30 ± 0.30%) than field conditions (3.92 ± 0.51%, p = 0.002). Opportunistic rearing yielded >2 kg fresh cocoons, with clusters reaching 0.220 kg. These findings establish biological baselines for C. trifenestrata Helfer on cinnamon, reveal sophisticated social behaviors expanding lepidopteran sociality concepts, and demonstrate commercial potential for sustainable sericulture integrated with pest management.

Keywords: Lepidoptera; Saturniidae; behavior; cinnamon; cocoon traits; life history; sericulture; wild silkmoth.

Figure 1

Geographic location of the study sites. (A) Map of Thailand indicating the locations of Chaiyaphum Province (field site) and Maha Sarakham Province (laboratory site). (B) The field site, Tanyachai Orchard, in Khon San District, Chaiyaphum. (C) The location of the Centre of Excellence for Silk Innovation at Mahasarakham University, Maha Sarakham. Base maps from Wikipedia Commons: “Chaiyaphum Province” and “Thailand_Maha_Sarakham_location_map.svg,” accessed 15 December 2024.

Figure 2

Experimental setups for rearing C. trifenestrata Helfer. (A) The mature cinnamon tree in the mixed-fruit orchard that served as the host for the wild population (field observation). (B) The semi-natural rearing cage (2 × 2 × 2 m) enclosing a young cinnamon tree. (C) A representative laboratory rearing container with young-instar larvae feeding on cinnamon leaves.

Figure 3

Life stages and key morphological features of C. trifenestrata Helfer. (A) Adult female depositing eggs (scale bar = 5 mm). (B) Egg string showing individual eggs laid in a linear arrangement (scale bar = 5 mm). (C) First-instar larva (scale bar = 5 mm). (D) Second-instar larva (scale bar = 5 mm). (E) Third-instar larva (scale bar = 1 cm). (F) Fourth-instar larva (scale bar = 1 cm). (G) Fifth-instar larva (scale bar = 1 cm). (H) Pupa (dorsal and ventral views) (scale bar = 1 cm). (I) Adult male (showing quadripectinate antennae) (scale bar = 1 cm). (J) Adult female (showing bipectinate antennae) (scale bar = 1 cm).

Figure 4

Oviposition plasticity in C. trifenestrata Helfer. (A) Linear arrangement of eggs on a leaf margin in the field (scale bar = 1 cm). (B) Close-up view of eggs laid in a linear arrangement on a leaf margin in the field (scale bar = 5 mm). (C) Clustered eggs from a laboratory rearing, showing a disorganized arrangement and variable sizes (scale bar = 5 mm). (D) Newly hatched larvae emerging from a laboratory egg cluster, illustrating the dense and irregular egg mass (scale bar = 5 mm). (E) Multiple egg clusters of varying sizes from laboratory conditions on black background, demonstrating the range of cluster formations (scale bar = 5 mm).

Figure 5

Gregarious feeding by early-instar C. trifenestrata Helfer larvae. (A) Early-instar larvae exhibiting collective feeding behavior in a natural field setting (scale bar = 3 cm). (B) Early-instar larvae forming dense clusters on the underside of a host plant leaf in a natural field setting (scale bar = 3 cm). (C) A close-up of a larval group under laboratory conditions, showing detailed morphology of the individual caterpillars (scale bar = 1 cm).

Figure 6

Controlled re-aggregation experiments demonstrating active gregarious behavior in 1st-instar C. trifenestrata Helfer larvae. (A) Manual transfer showing initial scattered distribution immediately after placement (scale bar = 3 cm). (B) Temporary exploration phase with larvae separating into two groups around leaf perimeter (scale bar = 3 cm). (C) Complete re-aggregation into single feeding cluster within 30 min, demonstrating preference for group feeding over individual foraging (scale bar = 3 cm).

Figure 7

Mass synchronous molting behavior in C. trifenestrata Helfer larvae. (A) First-instar larvae entering molting phase with immobilized postures in close proximity (scale bar = 1 cm). (B) Active molting process showing characteristic brown head capsules (old exuviae) being shed during 1st-to-2nd-instar transition, demonstrating coordinated ecdysis and group cohesion during vulnerable developmental phase (scale bar = 1 cm).

Figure 8

Aggregation of late-instar C. trifenestrata Helfer larvae in the laboratory. (A) Larvae grouping and feeding on host plant foliage (scale bar = 5 cm). (B) A close-up view of a dense aggregation of late-instar larvae on host plant branch tip (scale bar = 5 cm). (C) A pre-pupal aggregation of final-instar larvae on a single leaf immediately prior to the commencement of aggregated cocooning site selection, where each individual spins its own cocoon within the cluster (scale bar = 5 cm).

Figure 9

Gregarious feeding and pre-pupal aggregation of last-instar C. trifenestrata Helfer larvae on a cinnamon tree under natural field conditions. (A) A characteristic feeding aggregation of late-instar larvae on the host plant leaves (scale bar = 5 cm). (B) Larvae migrating down the trunk of the tree to form a pre-pupal aggregation site at the base for the construction of a cocoon cluster (scale bar = 10 cm).

Figure 10

Mass downward migration of 5th-instar C. trifenestrata Helfer larvae from a hog plum tree to the ground. (A) Overall view of 5th-instar larvae descending the trunk of a hog plum tree to aggregate (scale bar = 8 cm). (B) Close-up view of a dense aggregation of 5th-instar larvae migrating down the trunk of a hog plum tree (scale bar = 8 cm).

Figure 11

The process of cocoon cluster formation through gregarious cocooning by C. trifenestrata Helfer larvae. (A) Early aggregation of final-instar larvae initiating a shared silk matrix that forms the foundational framework of the cocoon cluster (scale bar = 3 cm). (B) Completed fresh cocoon cluster, showing its characteristic reticulated (net-like) structure (scale bar = 3 cm). (C) Dense aggregation of final-instar larvae collectively spinning an extensive silk matrix, reinforcing the developing cocoon cluster (scale bar = 3 cm). (D) Mature, weathered cocoon cluster attached to a dried leaf, with a section removed to reveal the individual pupal cells within (scale bar = 3 cm).

Figure 12

Cocoon cluster size distribution in C. trifenestrata Helfer. (A) Solitary cocoons (14.9% frequency) (scale bar = 5 cm). (B) Small clusters (2–3 cocoons, 48.9% frequency) (scale bar = 3 cm). (C) Small medium clusters (3–5 cocoons) (scale bar = 3 cm). (D) Medium cluster (8–10 cocoons) (scale bar = 5 cm). (E) Medium cluster (≈10 cocoons) in circular formation (scale bar = 5 cm). (F) Large medium cluster (15+ cocoons) (scale bar = 5 cm). (G) Large cluster in field conditions (31–100+ cocoons, 17.0% frequency) (scale bar = 8 cm). (H) Individual cocoons extracted from single cluster (34 total) showing individual cocoon structure and pedunculate stalks, demonstrating that each larva constructs its own separate cocoon within the aggregated site (scale bar = 5 cm).

Figure 13

A representative portion of the bulk cocoon harvest obtained from the opportunistic rearing of the hog-plum-derived cohort. Larvae were provided with cinnamon leaves in captivity until pupation.

Figure 14

Examples of communal cocoon clusters from the hog-plum-derived cohort, illustrating their structure and harvest weight. (A) Several elongated clusters with a combined weight of 0.360 kg. (B) A single, large, basket-shaped communal cocoon cluster weighing 0.220 kg.