Abstract
Millipede assassin bugs are a diverse group of specialized millipede predators. However, the feeding behavior of Ectrichodiinae remains poorly known, especially how the mouthpart structures relate to various functions in feeding. In this study, fine morphology of the mouthparts and feeding performance of Haematoloecha nigrorufa (Stål, 1867) was observed and described in detail for the first time. The triangular labrum is divided by a conspicuous transverse membrane into a strongly sclerotized basilabrum and a less sclerotized distilabrum. Fifteen types of sensilla are distributed on the mouthparts. Each mandibular stylet has an expanded spatulate apex and about 150 approximately transverse ridges on the external middle side; these help in penetrating the ventral trunk area and the intersegmental membranes of millipede prey. The right maxilla is tapered. On the internal surface are a row dorsal short bristles near the apex and a row of ventral bristles preapically. A longitudinal row of long lamellate structures extend proximate for a considerable distance, lie entirely within the food canal, and bear several short spines and short bristles. There is no obvious difference between males and females in the distribution, number, and types of sensilla on mouthparts. The adult feeding process involves several steps, including searching and capturing prey, paralyzing prey, a resting phase, and a feeding phase. The evolution of the mouthpart morphology and the putative functional significance of their sensilla are discussed, providing insight into the structure and function of the mouthparts adapted for millipede feeding.
Highlights
Mouthparts are the feeding organs of insects [1,2,3] and morphological variation in mouthparts generally corresponds well to their different feeding requirements [4,5]
The main elements of the mouthparts of H. nigrorufa are similar to other reduviid species and include the two-part labrum, three-segmented labium (Figure 1A–C), and stylet fascicle (Sf) composed by two separated mandibular stylets (Md) and two interlocked maxillary stylets (Mx) (Figure 1B)
In this study of the mouthpart structures in the Reduviidae (Ectrichodiinae) species H. nigrorufa, we focused on detailed morphological features that may be related to their unique adaptation for millipede-feeding
Summary
Mouthparts are the feeding organs of insects [1,2,3] and morphological variation in mouthparts generally corresponds well to their different feeding requirements [4,5]. The types and quantities of various sensilla are closely related to the feeding habits of insects. The mouthpart complex in Hemiptera is often called the “rostrum”, “sucking beak”, or piercing-sucking mouthparts [10]. During the long-term evolutionary history of Hemiptera, the components of this feeding apparatus have been clearly modified to serve their unique functions in different groups of bugs [11,12,13,14,15,16] and specialized to various sources of food [17]. Heteroptera, as compared to other groups of hemipterans (Cicadomorpha, Fulgoromorpha, Sternorrhyncha, and Colleorrhyncha) display a wider array of trophic and morphological diversity [12]
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