Research Article |
Corresponding author: David N. Honsberger ( dnh8@hawaii.edu ) Academic editor: Michael Ohl
© 2024 David N. Honsberger, Karl N. Magnacca, J. Hau‘oli Lorenzo-Elarco, Mark G. Wright.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Honsberger DN, Magnacca KN, Lorenzo-Elarco JH, Wright MG (2024) Life history of two new species of Prorops (Hymenoptera, Bethylidae) ectoparasitic on adult Hypothenemus eruditus beetles (Curculionidae, Scolytinae) in Hawai‘i. Journal of Hymenoptera Research 97: 1221-1256. https://doi.org/10.3897/jhr.97.138113
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Aspects of the life history and biology of two Prorops spp. are explored, Prorops maya sp. nov. and Prorops umiehu sp. nov. Aspects of their behavior are deduced through dissection of plant material and through the use of “phloem sandwich” style observation chambers. Both were found to be ectoparasitoids of adult Hypothenemus eruditus beetles. They thus show a novel feeding behavior as, along with a Plastanoxus sp., the only bethylids known to parasitize the adult stage of their hosts, and the only known ectoparasitoids of adult scolytids. Searching, stinging, host feeding, and oviposition behaviors are reported and illustrated with photographs and video. Oviposition occurs on the ventral side of the membraneous region between the pro- and mesothorax of the beetle, and larvae feed through this location. The projection on the frons, a defining character of the genus Prorops, is observed to function as a tongue and groove mechanism with which the adult female pushes on the edge of the prothoracic sclerite of the host beetle while maintaining use of its mandibles to chew on the membrane underneath for host feeding and in preparation for oviposition. Defensive action of a Hypothenemus sp. against the wasp's sting by clamping down on the intruding ovipositor between its pro- and mesothorax is also reported, though this behavior was only observed once and thus its generality is uncertain.
Functional morphology, host defense, macadamia, parasitoid Hymenoptera, Scolytinae
There are currently eleven known species in the genus Prorops (Hymenoptera: Bethylidae), including the two described here. Members of this genus can be distinguished from other members of Scleroderminae by having a distinct snout, a projection of the anterior part of the frons that is either a singular projection with a median groove, or is separated into two distinct projections on either side (
Known from Madagascar. No recorded hosts.
Known from Central Cardamom, Cambodia. No recorded hosts.
A parasitoid of Hypothenemus hampei (Ferrari, 1867), the coffee berry borer. Prorops nasuta has been imported from its native range in Africa to much of the coffee growing world as a biological control agent. It enters coffee berries, host feeds on all immature stages, stings and paralyzes the adult stage, and is an ectoparasitoid on the pupal and late instar larval stages (
Known from Trinidad island, Trinidad and Tobago. No recorded hosts.
Known from Louisiana, USA; and Guanabara, Brazil. It has been found associated with loblolly pine (Pinus taeda L.) (Pinaceae) in Louisiana where it is possibly a parasitoid of Dendroctonus frontalis Zimmerman, 1868.
Known from Aichi Prefecture, Japan. No recorded hosts.
Known from Madagascar. No recorded hosts.
In addition to the validly described species above, in an unpublished PhD dissertation
Both species explored in the present study and described herein were found attacking Hypothenemus eruditus Westwood, 1836 (Curculionidae: Scolytinae). This is currently the only known host for both of the species. Hypothenemus eruditus is regarded as a supergeneralist, found inhabiting dead wood of a wide variety of tree species over a large taxonomic range, and has even been recorded from fungi (
Specimens collected from wood and other plant parts were examined and photographed using a Leica MZ16 stereomicroscope or Macropod Pro imaging system. Specimens were also dissected, examined, and photographed using an Olympus CX31 compound microscope. Terminology relating to morphological characters follows
Morphometrics of the head were measured as in Fig.
LH Length of head; longitudinal line even with posterior of vertex to tip of snout.
LH\S Length of head not including snout; longitudinal line even with posterior of vertex to base of mandible.
VOL Vertex-ocular line; longitudinal line even with posterior of vertex to even with posterior margin of eye.
LE Length of eye; posterior margin to anterior margin of compound eye.
LHAE Length of head above bottom of eye; longitudinal line even with posterior of vertex to even with anterior margin of compound eye.
LHBE Length of head below bottom of eye; longitudinal line even with anterior margin of compound eye to tip of snout.
WH Width of head; maximum width of head including eyes.
WF Width of frons; minimum distance between compound eyes on frons.
BEM Bottom of eye to mandible; longitudinal line from even with anterior margin of compound eye to base of mandible.
WOT Width of ocellar triangle; distance between the outer margins of the posterior ocelli.
OOL Ocellar-ocular line; shortest distance from margin of posterior ocellus to margin of compound eye.
AOL Lateral ocellar line; shortest distance between margin of lateral ocellus and anterior ocellus
POL Posterior ocellar line; shortest distance between inner margins of posterior ocelli.
AOT Angle between lines joining middle of anterior ocellus and middle of each posterior ocellus.
LPD Length of metapectal-propodeal disc; distance along median line from anterior margin of metapectal-propodeal complex to declivity, measured in plane perpendicular to overall surface of disc.
WPD Width of metapectal-propodeal disc; greatest transverse distance between lateral marginal carinae or lateral edges of disc, posterior of propodeal spiracles; measured in plane perpendicular to overall surface of disc.
Ratios and measurements were among those typically used in Bethylidae and the genus Prorops, with the addition of LHBE : LHAE, which gives a sense of the relative length of the snout and may be useful in the genus Prorops. Body length was obtained by adding the length of the head from the apex of the snout to the occipital foramen, the occipital foramen to the anterior of the tegula, the anterior of the tegula to the petiole, and the petiole to the apex of the abdomen, to give the full body length if the body including the head were outstretched. Measurements were made on dried, point mounted specimens. Ranges of coloration reported cover that observed for live individuals and fresh or air dried specimens, and may be outside this range depending on preservation method.
Wood and other plant parts containing Scolytinae were collected in forest, agricultural, and urban environments, and returned to a laboratory for dissection under a microscope.
Behavior was also observed using “phloem-sandwich” style observation chambers, consisting of thin sheets of plant material compressed between a sheet of plexiglass and a sheet of aluminum, the same apparatus used and described in
DNA was extracted from adult wasps using the Qiagen DNeasy Blood and Tissue Kit (Qiagen, Inc., Valencia, Ca, USA), and the CO1 gene was amplified using the primers in Folmer et al. (1994). This was done for two adults of P. maya sp. nov., collected from fallen T. orientalis branches in the upper reaches of Mānoa Valley, O‘ahu, Hawai‘i, and described subsequently. The resulting sequences were identical and are reported in GenBank Accession # PP498809.
Specimens are deposited in the following museums:
UHIM University of Hawai‘i Insect Museum, Honolulu, Hawai‘i, USA
Females can be distinguished from other described Prorops spp. by the dark colored head and metasoma contrasting with the orange mesosoma; snout apically bifid and with mesal sulcus; head including snout approximately 1.1 times as long as wide; fore wing with vein 2r-rs+Rs distinct; metapectal-propodeal disc longer than wide in dorsal view, and with lateral carina. Males can be distinguished by the same set of characters except the coloration which is less pronounced than in the females, the head and metasoma brown and the mesosoma lighter yellow-brown.
Prorops maya females and males can be differentiated from the other species known from Hawai‘i, Prorops umiehu sp. nov., by the fore wing with vein 2r-rs+Rs distinct (fore wing with 2r-rs+Rs absent in P. umiehu); female head only slightly longer than wide (head substantially longer than wide in females of P. umiehu); metanotum continuous posterior to mesoscutellum in dorsal view (mesoscutellum covers metanotum medially in P. umiehu); mandible more narrow and bidentate (mandible wider and tridentate in P. umiehu); clypeus with dorsal and ventral margins more acutely rounded (clypeus dorsal margin more broadly rounded and ventral margin less curved in P. umiehu); metapectal-propodeal complex with lateral marginal carina (lateral marginal carina weaker or absent in P. umiehu); females by the more distinct coloration, with the mesosoma orange and the head and metasoma dark brown (head and mesosoma of similar reddish-brown color, sometimes mesosoma lighter but only slightly, in P. umiehu females).
Female (Figs
Head
(Figs
Mesosoma
(Figs
Legs
(Fig.
Fore wing
(Fig.
Metasoma
(Figs
Male (Fig.
Holotype
(Fig.
Allotype
(Fig.
Paratypes
: 7 ♀, 1 ♂; all with same data as holotype (2 ♀ UHIM, 1 individual with wings removed; 3 ♀, 1 ♂
This beautiful wasp is named after Maya Honsberger, a wonderful and beautiful human being. It has also been elusive for us to find, all individuals found on only one occasion, as with Maya, for whom it is also rare to find as wonderful a wife as her. The name is to be treated as a noun in apposition.
For the Hawaiian common name, mai‘apala (lit., ripe banana) was selected. Mai‘a (general term for banana) is similar in sound and spelling to the species name maya and also one of the favorite foods of Maya Honsberger, combined with the similarity of the yellow and brown coloration of the wasp to a ripe (pala) banana.
This species is known from the island of O‘ahu in Hawai‘i, where it is likely adventive. Based on its limited abundance and distribution, it is probably a recent arrival.
Hypothenemus eruditus (Coleoptera: Scolytinae); see Biology section.
Females can be distinguished from other described Prorops spp. by the combination of: head and mesosoma orangish-brown to reddish-brown; fore wing without vein 2r-rs+Rs; snout bifid and with mesal sulcus; head including snout approximately 1.3 times as long as wide; metapectal-propodeal disc approximately 1.2 times longer than wide in dorsal view, and without distinct lateral carina. Males can be distinguished by the same set of characters as the females except for coloration and morphometrics of the head: body darker in color, brownish; head including snout approximately 1.1 times as long as wide.
Prorops umiehu can be differentiated from Prorops maya by lack of vein 2r-rs+Rs in the fore wing (2r-rs+Rs distinct in P. maya); metapectal-propodeal complex and mesoscutellum overlapping medially, dividing metanotum in dorsal view (metanotum continuously visible posterior to mesoscutellum in P. maya); female head 1.3 times as long as wide, male head 1.1 times as long as wide (head 1.1 times as long as wide in both sexes of P. maya); mandible wide and tridentate, though dorsal tooth small and inconspicuous (mandible more narrow and bidentate in P. maya); clypeus with anterior margin broadly rounded, posterior margin slightly emarginate (anterior margin acutely rounded, posterior margin sinusoidal in P. maya); metapectal-propodeal complex without distinct lateral marginal carina (lateral marginal carina more distinctly conspicuous in P. maya); female with head and mesosoma of similar orange-red-brown color (dark brown head and metasoma contrasting with orange mesosoma in P. maya female).
Female (Figs
Mesosoma
(Figs
Legs
(Fig.
Fore wing
(Fig.
Metasoma
(Figs
Male (Figs
As in female but with the following differences: Head more square than in female, length to width ratio approximately 1.1; eye larger and more bulging; ocelli more widely placed; vertex only weakly concave; 2nd through 9th antennal flagellomeres longer and more cylindrical; coloration typically darker with head and metasoma brown, mesosoma slightly lighter brown. Genitalia: See Fig.
Holotype
(Fig.
Allotype
(Figs
Paratypes
: 18 ♀, 5 ♂. Hawaiian Islands, O‘ahu, Kahana Bay;21.5573°N, 157.8781°W, 15 m; 27.viii.2021; ex Trema orientalis branches; D. Honsberger (1 ♀, 1 ♂
The species name is Hawaiian, ‘umi‘ehu (lit., blonde mustache). When the head is viewed anteriorly (Fig.
This species is known from the islands of O‘ahu, Moloka‘i, Maui, and Hawai‘i in the Hawaiian Islands, where it is likely adventive, and from the United Arab Emirates near Al Ajban, Emirate of Abu Dhabi (
Hypothenemus eruditus and Hypothenemus seriatus (Coleoptera: Scolytinae); see Biology section.
Note that males of P. rakan, P. mandibularis, P. “sp. 23”, and P. “sp. 24” are currently unknown.
1 | Fore wing without vein 2r-rs+Rs, or 2r-rs+Rs vein very faint, reduced to fold | 2 |
– | Fore wing with distinct vein 2r-rs+Rs emanating from pterostigma | 4 |
2 | Snout with median groove but not clearly bifid, instead rounded or trifid apically; notauli present | P. obsoleta (♀♂) |
– | Snout clearly bifid apically (ends in two distinct lobes); notauli absent | 3 |
3 | LH subequal to WH; metapectal-propodeal disc wider than long, LPD:WPD ≈ 0.9 (both sexes); AND if female, vertex slightly incurved in face view; if male, vertex nearly straight in face view | P. impotens (♀♂) |
– | Metapectal-propodeal disc longer than wide, LPD:WPD ≈ 1.25; vertex distinctly incurved in face view (both sexes); AND if female, LH:WH ≈ 1.3; if male, LH:WH ≈ 1.1 | P. umiehu (♀♂) |
4 | Snout divided into two widely separated arms not contiguous basally or apically | P. sparsa (♀♂) |
– | Snout divided or with median groove, but contiguous at least basally | 5 |
5 | Snout with median groove but rounded apically, not clearly bifid | 6 |
– | Snout clearly bifid apically (ends in two distinct lobes | 7 |
6 | LH:WH ≈ 1.6, and LH\S also distinctly greater than WH; LHAE:LHBE ≈ 2.9; mandible tridentate; lengths of first four antennomeres with ratio of 10:3:1:2; head with vertex somewhat straight | P. petila (♀♂) |
– | LH:WH ≈ 1.3, and LH\S subequal to WH; snout long, LHAE:LHBE ≈ 1.3; mandible bidentate; first four antennomeres in ratio of 3.5:1.6:1.1:1.0; head with vertex incurved medially | P. mandibularis (♀) |
7 | LH:WH ≈ 1.4, first four antennomeres in ratio of 5:2:1:1; mandible tridentate | P. rakan (♀) |
– | LH subequal to WH | 8 |
8 | In females, mesosoma, mandible, snout, and basal region of antenna bright orange to reddish brown, in distinct contrast with metasoma and remainder of head almost black; in males, head and metasoma brown, mesosoma light brown. In both sexes, LPD distinctly greater than WPD, disc shiny with lateral carina, declivity also smooth and shiny with lateral carina at least anteriorly; mesonotum with only a few setae, usually just 2 on each side of median line of mesoscutellum; metanotum visible as continuous narrow band posterior to mesoscutellum in dorsal view; LH:WH ≈ 1.1; LHAE:LBHE ≈ 3–3.5 | P. maya (♀♂) |
– | Coloration entirely dark brown to black; WPD subequal to or greater than LPD, disc without lateral marginal carina; mesonotum with few to many setae on both anteromesoscutum and mesoscutellum; mesoscutellum covers metanotum medially | 9 |
9 | Head widest across eyes, narrowing between eye posterior margin and vertex; WPD slightly greater than 1.5 times LPD; LH:LE ≈ 2.4; LHAE:LHBE ≈ 2.5; mesonotum setose, including medially; mesoscutum with slightly rough texture, metapectal-propodeal disc smooth and glassy; head with vertex strongly incurved |
P. “sp. 23” [of |
– | Width of head just anterior to vertex subequal to or slightly greater than width across eyes; WPD distinctly less than 1.5 times LPD; LH:LE > 2.5; LHAE:LHBE < 2.0 | 10 |
10 | Vertex only somewhat incurved, such that anterior ocellus slightly posterior to top of compound eye in full face view; WH:LE ≈ 2.5; LH:LE ≈ 2.9; LHAE:LHBE ≈ 1.9; WH:LHBE ≈ 1.4; metapectal-propodeal disc only slightly wider than long, WPD:LPD ≈ 1.1, disc with rough texture; mesoscutum and scutellum setose, including medially | P. nasuta (♀♂) |
– | Vertex strongly incurved, such that anterior ocellus slightly anterior to top of compound eye in full face view; eyes smaller, so that WH:LE ≈ 3.3; LH:LE ≈ 2.4; LHAE:LHBE ≈ 1.3; WH:LHBE ≈ 1.7; metapectal-propodeal disc substantially wider than long, WPD:LPD ≈ 1.3, disc smooth and glassy; mesoscutum less setose, with few or no setae medially on mesoscutum |
P. “sp. 24” [of |
Prorops maya has been found parasitizing H. eruditus adults in Trema orientalis (gunpowder tree) branches in Mānoa Valley at the foot of the Ko‘olau Mountains on O‘ahu island (21.3288°N, 157.7930°W, 154 m) (Fig.
Hypothenemus eruditus beetles paralyzed and parasitized by P. maya or P. umiehu in T. orientalis branches. All photographs are of naturally occurring situations, taken while peeling bark from branches found in a forested region of Mānoa Valley on O‘ahu (21.3288°N, 157.7930°W, 154 m). Some beetles, such as each of the three in (a), are clearly parasitized with a P. maya or P. umiehu larva feeding through the membranous region of the beetle ventrally between the pro- and mesothorax, the posterior of the larva wrapped around the beetle. All larvae of P. maya and P. umiehu found in this study were observed to feed in this way. Prorops pupae, empty pupal cocoons, and more developing larvae are also visible in (b,c,d). Eggs of a thrips species that may scavenge on the remains can also be seen placed on top of beetles in (d). All beetles in these pictures were not moving, either paralyzed or killed presumably by P. maya or P. umiehu. Note that, in contrast to Fig.
Prorops umiehu has been found parasitizing H. eruditus in T. orientalis branches and D. regia seed pods in Mānoa, O‘ahu island, and Hypothenemus seriatus in macadamia nut husks in Waimānalo, O‘ahu (Figs
Prorops umiehu developing immatures. Photographs are of naturally occuring situations, taken while dissecting plant material collected from field environments a P. umiehu larva on H. eruditus from D. regia pods collected from the campus of UH Mānoa b pupating P. umiehu having completed its larval stage on H. eruditus in D. regia pods from UH Mānoa c, d P. umiehu larvae on H. eruditus from D. regia from UH Mānoa e macadamia husk from Waimānalo, O‘ahu with its inner layer peeled, showing pupating P. umiehu having developed on the H. seriatus adults next to them.
Development of P. maya and P. umiehu immature stages has been observed to occur on H. eruditus adult beetles in chambers and galleries the beetles excavate below the surface of the plant material (Figs
Typical placement of pupae when development occurs in a narrow tunnel environment. The parasitoid larva feeds on the adult beetle through the ventral membranous region between the pro- and the mesothorax. The growth of the larva and its subsequent construction of a pupal chamber forces these two sections of the beetle apart, and pupating larvae are typically found concealed between them. In these pictures, the white material near or around the parasitoid immature is what remains of the pupal cocoon it had constructed after the tunnel was broken open by peeling apart the plant material. Photographs are of naturally occurring situations, taken of plant material collected outdoors a, b Prorops sp. prepupa (a) and pupa (b) between two halves of an H. eruditus beetle in an H. eruditus tunnel in a T. orientalis branch collected from Mānoa Valley on O‘ahu; c: Prorops umiehu pupa in a D. regia pod from a tree on the campus of the University of Hawai‘i at Mānoa. Note the position of the pupal cocoon relative to the beetle in (c), not the larva itself which was moved as the pod was peeled apart. Such placement was more common in T. orientalis branches where scolytid tunnel systems were often more linear, but atypical in D. regia pods possibly due to the less linear and more confused organization of beetle feeding in these pods, but in (c) developed in this way due to the topography in the certain section where the beetle was parasitized.
The growth of the larva, positioned as it is, forces the two halves of the beetle apart. If development occurs in a tunnel, there is nowhere for this extra volume to go except to expand along the length of the tunnel. Thus between the growth of the wasp larva, the increased brittleness of the beetle after having been desiccated by the feeding of the larva, and the activity involved in creation of a pupation area by the wasp prepupa, the beetle splits apart and pupating wasps are often found in-between the two parts of the beetle, with the beetle's head and prothorax on one side of the pupating larva and the rest of the beetle on the other (Fig.
Field collections have indicated that oviposition and larval development occurs exclusively on the adult stage of the beetle, and the laboratory tests subsequently described that present P. maya and P. umiehu adult females with a variety of life stages of H. eruditus have resulted in parasitism of only adult beetles. Larval development of laboratory reared P. umiehu from egg to adult eclosion is pictured in Fig.
Development of P. umiehu on H. eruditus. The beetle was parasitized by a P. umiehu adult female entered into the observation chamber described in the text containing H. eruditus beetles on a piece of D. regia pod with channels cut into it with a knife. The parasitized beetle was then moved into a small hole carved into a wood substrate and covered with a piece of glass slide cover to mediate humidity and to create an enclosed environment to facilitate construction of a pupal cocoon by the prepupa. Time elapsed after presence of an egg was first observed on the beetle are noted in the photographs. The emerged adult is the allotype.
When parasitized beetles were found in T. orientalis branches, nearly all the beetles in the gallery were either paralyzed or parasitized (see Fig.
In D. regia pods, the pattern of patch use within a gallery system seems to be different. It seems to be much more sparse than in the T. orientalis branches, with only a small proportion of individuals in a gallery section either paralyzed or parasitized. This was observed only for P. umiehu (n > 15); P. maya has thus far only been found in T. orientalis branches. While this could be a result of differences in behavior between the two species, it appears more likely that this could be because the geometry of H. eruditus gallery systems tends to be different in these two plants. In T. orientalis branches, H. eruditus use only the thin phloem layer, and tend to construct a somewhat round chamber that extends in two dimensions under the bark, though this chamber eventually branches into a network of tunnels as the second and subsequent generations of beetles develop in the wood. Thus, at least in the earlier stages of beetle activity in the wood, their population tends to be somewhat localized in an uncomplex shape. In D. regia pods, the tissue the beetles use as a food source is thick enough relative to the size of the beetles to accommodate movement in three dimensions. Instead of forming a chamber, the beetle galleries take on a topologically more complex pattern, eventually creating a sponge-like network of tunnels spread through the material. The population of beetles inhabiting these tunnels tends to be more spread out within this maze of tunnels. Such variability in the gallery system created by H. eruditus among different host plants has been previously reported by
Observed behaviors were largely similar between P. maya and P. umiehu. While differences in behavior presumably exist, none of the general aspects of behavior and observations recorded here were distinct enough to be clearly associated with one species or the other. Typical observed behavior was as follows, and unless noted otherwise, the below observations apply similarly to both species.
General searching behavior (Video 1: https://vimeo.com/688211081, Video 2: https://vimeo.com/691136279): The wasps quickly moved through the tunnels in the wood, holding their antennae straight, vibrating and feathering them over the surfaces. This position of the antennae is in contrast to Allobethylus ewa (Bridwell, 1920), another bethylid observed in separate studies using the same apparatus, which holds its antennae curved while antennating the surface of a wood substrate or beetles within it, which may function to increase the contact area of the antenna against surfaces with pits or other irregular texture (D. Honsberger, pers. obs.). The Prorops spp. showed clear interest upon finding a beetle, and when immature and adult beetles were present together, the wasps seemed to take preferential interest in the adults, and subsequent stinging, malaxation, chewing, and host feeding behaviors were initially focused on them.
Upon encountering an active H. eruditus adult beetle, a female wasp was observed to typically examine and antennate it, often climbing somewhat on top of the beetle in doing so. This was most often followed by an attempt at stinging the beetle, or more rarely, the wasp would either move away and explore elsewhere or repeatedly bite the beetle with its mandibles seemingly with the objective of attempting to move it. Stinging was typically followed by a quick exploration of the beetle and the area around it, and then often by a chewing behavior and host feeding, these actions covered in more detail below. The beetle was typically then abandoned and the wasp moved through the arena and was arrested by the presence of additional beetles on which it performed similar behaviors. Beetles that had previously been stung and paralyzed were often re-encountered by the wasps, who would examine them, occasionally sting them again, and often perform additional chewing or host feeding. Prorops umiehu, if taking interest in a larva or pupa, was observed to exhibit a similar progression of stinging and host feeding as with an adult.
The wasps were observed to adeptly turn themselves around in the tight space of a tunnel. Similar behavior has been observed in other parasitoids living in concealed tunnel environments using the same apparatus, such as Acerocephala hanuuanamu (
Aspects of the behavior of P. maya in laboratory observation chambers. The apparatus is the same as in Fig.
Stinging
(Figs
Stinging and chewing behavior of P. umiehu in laboratory observation chambers a the observation chamber used in this study with a piece of D. regia pod tissue having been naturally infested by H. eruditus sandwiched between the aluminum and plexiglass b, c P. umiehu stinging H. eruditus adult females d profile view of a P. umiehu female next to H. eruditus, showing the groove formed between the snout dorsally and the mandibles ventrally which acts as a mechanism for holding the edge of the prothoracic sclerite of its host e the wasp grasps the abdomen of the beetle with its legs and pushes forward on the sclerite with this structure to expose the membranous region between the pro- and mesothorax of the beetle, while maintaining use of the mandibles for chewing on the stretched membrane. This was observed, as in (e), for the purposes of host feeding on adults having previously been stung and paralyzed, and was also observed during preparation for oviposition (shown in Fig.
An adult or immature beetle that was successfully stung slowed down over the next few minutes before becoming more or less motionless, making only marginal twitchy movements. After a few days, such subtle twitching movements were still observed, including in beetles having been oviposited on. This implies that the chemicals injected by the wasp are paralytic and do not necessarily kill the beetle. This may maintain the integrity of the nutrition and water content of the beetle as its young develops on it (
Chewing, oviposition, host feeding, and function of the snout
(Figs
Oviposition by P. umiehu on H. eruditus in a laboratory observation chamber. The apparatus in which this occurred is the same as that pictured in Fig.
All eggs observed both in the laboratory observation chambers and field collected wood from both species were placed at the same location on the adult beetles: transversely oriented on the ventral side of the membraneous region of articulation between the pro- and mesothorax. Thus one use of the chewing behavior was apparently to prepare the host for oviposition, though its exact function was not clear: it could possibly be to cut the membrane so that the gap between the pro- and mesothorax would remain open and present an accessible area for oviposition and egg development; to cut open the tissue so that the emerging larva would be able to penetrate the membrane and feed; to cut the ventral nerve cord; for the adult to taste the beetle's hemolymph to assess its quality as a host; or alternatively, simply for the adult to host feed on the beetle. Adult Sclerodermus harmandi (Buysson, 1903) (Hym.: Bethylidae) have been observed to chew holes through the cuticle of their host larvae through which their offspring feed as larvae (
The act of oviposition (Video 3: https://vimeo.com/688588477) was only observed once, for P. umiehu. An H. eruditus adult previously stung, paralyzed, and likely chewed on as evidenced by the separation between the pro- and mesothorax greater than normal for a beetle that had simply been stung, was approached by the wasp and its actions were observed for the 2.5 hours leading up to oviposition. In this time, the wasp initially explored the beetle and the surrounding area, focusing much of its attention near the junction of the pro- and mesothorax, and attempted to subtly manipulate the beetle's position in the tunnel by grabbing the body of the beetle with its mandibles. The wasp then remained motionless in the tunnel, its body oriented opposite that of the beetle, the two touching head to head. This was followed by a short chewing interval, after which the wasp reassumed its position motionless in the tunnel with the beetle for approximately 1.5 hours. The wasp then resumed its exploration of the beetle, short chewing intervals, and subtle manipulations of the beetle's position, followed by an extended chewing event on the membrane along the midline of the beetle. It then explored the area and the beetle, repeating short but vigorous chewing intervals. The wasp then after a few attempts grabbed the beetle and repositioned it approximately a body length away in a slightly wider section of the tunnel. This was followed by one more vigorous chewing event, after which the wasp turned around and reached the apex of her metasoma into the gap between the pro- and mesothorax. The wasp remained in this position for about 10 minutes, her metasoma pulsating slightly. Then, over about 30 seconds, the wasp slowly moved the apex of her metasoma transversely across the crevice and the egg was visible emerging. The wasp slowly withdrew and became active again, exploring the vicinity for a few minutes and then left the area. The next day, the wasp was observed again in the tunnel in the same position as that in which it had remained motionless for extended intervals prior to oviposition, this time for at least 30 minutes as if host guarding, but did not maintain that position.
The chewing behavior was commonly observed on paralyzed adult beetles for both Prorops spp., and in the vast majority of observed instances were not followed by oviposition. Many of these interactions seemed to be for the purpose of host feeding, but it was unclear if some also were for the purpose of oviposition but on a host that was eventually rejected. Chewing by both species was also observed to occur on immature stages that had previously been stung. Since no eggs or developing larvae were ever observed on an immature stage, chewing on pupae and larvae was presumably not for the purpose of oviposition, but instead for host feeding.
Intraspecific interactions were also observed. When encountering each other in open space, the wasps typically ignored each other. Females in the action of stinging or chewing were typically not interrupted by passing conspecifics, which might explore the beetle with their antennae. They were observed to be somewhat affected, though not to show any overt aggression, if both were exploring the same beetle adult or immature: if the wasps came in contact with each other, they would move slightly apart.
Defense against stinging by a Hypothenemus sp. (Fig.
Defense by Hypothenemus sp. male against a stinging attempt by P. umiehu. The identity of the beetle is unknown, but is not H. eruditus a position immediately prior to contact of stinger. Note that the beetle is in a relaxed state, with the gap between the pro- and mesothorax slightly open b The beetle quickly clamps down after contact, trapping the apex of the metasoma of P. umiehu, and maintains that position for approximately 3.5 minutes, during which time the wasp was not visibly agitated but was unable to extricate itself. The beetle appeared to remain healthy and active in the subsequent hours, seemingly unaffected by the stinging attempt. These actions are also shown in Video 4: https://vimeo.com/688212175.
Patch use : Almost all beetles entered into the observation chambers with P. maya or P. umiehu females were motionless within 12 hours (n = 3 for P. maya, n = 3 for P. umiehu), helping to confirm the observation in field collected wood that P. maya, and potentially P. umiehu as well, typically attacks more or less the whole host patch at least in geometrically simple environments such as those with which they were presented. In one instance where the details were more precisely recorded, five H. eruditus and the one unidentified Hypothenemus sp. male which showed the defensive behavior were inserted into the observation chamber in naturally bored H. eruditus galleries in D. regia pods with two P. umiehu adult females. All five H. eruditus were stung and paralyzed within two hours.
Given that the congeneric Prorops nasuta is a parasitoid of the coffee berry borer H. hampei, and of the known species of Prorops it seems close at least morphologically to P. maya females, and H. eruditus and H. hampei are also congenerics, we investigated whether P. maya would take any interest in the coffee berry borer. To test this, wasps were released into the same apparatus described above that successfully resulted in stinging, chewing, host feeding, and parasitism of H. eruditus, with H. eruditus adults and immatures switched out with H. hampei adults and immatures (Video 5: https://vimeo.com/691136424). No interest was observed, and the wasps even seemed to show slight repulsion, upon encounter briefly antennating the beetles and then quickly moving on. No stinging, chewing, host feeding, or parasitism was observed. Given this lack of interest, no further tests were done.
Prorops maya and P. umiehu are ectoparasitoids of adult H. eruditus beetles living below the surface of wood. Both species enter tunnels bored by the scolytid in the plant material, and sting, paralyze, oviposit, and develop as an ectoparasitoid on the adults. Prorops maya and P. umiehu are, as far as we are aware, along with a Plastanoxus sp. found to parasitize Euwallacea fornicatus by
The vast majority of parasitoids of Scolytinae whose biology are known reproduce only on immature host stages (
Because P. maya and P. umiehu were found parasitizing nonnative beetles in nonnative trees, the host beetles in a tribe with no native species, and Prorops is not otherwise known in Hawai‘i, Hawai‘i is not likely part of the native range of either species. It may also be unlikely the native host of these species is H. eruditus: their pattern of host use was not observed to be efficient and H. eruditus showed a lack of defensive behavior against attack, while potentially effective defensive behavior was shown in another Hypothenemus sp.
While P. maya seemed to parasitize or paralyze nearly every H. eruditus beetle in a gallery system in T. orientalis branches, most unconnected active beetle gallery systems in a contiguous piece of wood appeared untouched, containing healthy populations of beetles. Because the environment where we have observed this species is likely not its native environment, to which it is presumably best adapted, such sparse host use could potentially result from inefficient searching behavior due to lack of adaptation to the exact host or environmental cues present. Or, possibly, this sparse and spatially disparate use of galleries could result from adaptation to an environment where its natural enemies tend to search in a spatially contiguous manner, e.g. by walking along a branch. Observed sporadic gallery use could also be related to low population density of the parasitoids, and restricting oviposition to a single gallery system and incapacitating all other occupants could also be related to brood guarding, though such behavior was not convincingly observed for these species.
Finally, we make a note about morphology. Prorops is the only genus in Scleroderminae with a projection on its frons, a synapomorphy that can be used to identify the genus. This, in combination with the large mandibles, has previously been suggested to possibly function as a means of digging through hard substrate (
Additional video materials: Video 1: Searching, stinging, chewing, and host feeding behavior by Prorops maya on Hypothenemus eruditus: https://vimeo.com/688211081; Video 2: Searching, stinging, chewing, and host feeding behavior by P. umiehu on H. eruditus: https://vimeo.com/691136279; Video 3: Oviposition by P. umiehu on H. eruditus: https://vimeo.com/688588477; Video 4: Defense by Hypothenemus sp. male against a stinging attempt by P. umiehu: https://vimeo.com/688212175; Video 5: Response of P. maya to the coffee berry borer, H. hampei: https://vimeo.com/691136424.
These studies were helped immensely by Maya Honsberger, who made this project very enjoyable and contributed observations, insights, and support. We thank our coworkers Abdulla Ali, Michelle Au, Conrad Gillett, Mitchell Logan, Ali Miarkiani, Robert Sakuda, Vanessa Goodman, and Laura Doucette for their support. We acknowledge that this research took place on the mokupuni (island) of O‘ahu in the ahupua‘a (land division) of Waikīkī in the moku (district) of Kona, Kamananui in the moku of Waialua (now Wahiawā), Kahana in the moku of Ko‘olauloa, and Waimānalo in the moku of Ko‘olaupoko, the ancestral and traditional land of Native Hawaiian people. We are very grateful to USDA, HDoA and Hatch project HAW09041-H, administered by CTAHR, for their funding.