Acrapex azumai Sugi (Lepidoptera: Noctuidae)

This stemborer was discovered in Itoshima, Fukuoka Prefecture, on Kyushu Island, Japan, in Aug 2013, when several plants in an undisturbed patch of I. cylindrica were observed with brown central tillers, a symptom often referred to as “dead-heart” in crop grasses. Further inspection revealed insect boring damage in the lower stem, and 1 or 2 circular holes (about 2–3 mm in diameter) from the stem tunnel to the exterior of the stem. Three mature lepidopteran larvae were found in tunnels, 2 of which were reared to adulthood and identified as A. azumai (Takasu et al. 2014). Previous to our finding, A. azumai had only been collected as an adult in Japan with no records of larval hosts. Because stemborers of gramineous crops (rice, sugarcane, sorghum, corn) have extensively been investigated in Japan (Kishino 1970; Kiritania 1990; Khan et al. 1991; Ishikawa et al. 1999; Kim 1999; Nagayama et al. 2004; Sallam 2006) and A. azumai had not previously been reported from these cultivated grasses, it may have a narrow host range. Larvae (56) of A. azumai were collected from the same location in Itoshima in Aug 2014. All larvae were approximately the same size and thought to be in the final instar, suggesting discrete generations. One pupa was found at the bottom of a stem tunnel near the soil level.

The larvae were placed in vials with 6- to 8-cm-long pieces of cogongrass stem and artificial diet, and hand-carried to the Fort Pierce quarantine facility. They continued to be reared in vials with both artificial diet and cut stem pieces, the latter of which were replaced every 2 to 3 d. The majority of larvae burrowed in the diet, whereas a few entered stems. Only 4 individuals (7%) completed development; 1 had deformed wings and 1 emerged several days after the first 3 to emerge had died. Two of the adults emerged on the same day and were placed together in a 4 L plastic container with cut cogongrass stems (about 20 cm) held upright in moist sand. The deformed adult that emerged was added 3 d later. The 3 adults died after 4 d, and the stems were removed and inspected. Five egg batches with 160 eggs in total were found in leaf sheaths. Eggs were held in Petri dishes (60 × 14 mm) on moistened filter paper and as they eclosed, neonates were transferred to whole plants (n = 24 neonates) or to 6- to 8-cm-long stem pieces (n = 128). Stem pieces were changed every 2 to 3 d, but no larvae developed beyond the 3rd instar. Whole plants that had been inoculated were dissected after 2 wk, but no larvae were recovered. Additional shipments of A. azumai larvae were received at the Fort Pierce quarantine in Nov 2015 (11 larvae) and Dec 2015 (6 larvae) but were not successfully colonized.

Table 1.

Locations and dates of foreign surveys for insect herbivores of cogongrass.

Acrapex azumai also was collected from cogongrass on Ishigaki Island in far southern Japan in Jun 2015. A shipment of 30 A. azumai larvae from Ishigaki was received at the Fort Pierce biological control quarantine laboratory in Jun 2015, but the shipment was delayed in transit for several days and the larvae arrived in poor condition. Only 4 individuals pupated, from which 2 moths emerged. No mating was observed and no eggs were obtained.

Contarinia sp. (Diptera: Cecidomyiidae)

This gall midge causes a dead-heart symptom similar to that produced by Acrapex species. The midge was collected from the Ito campus of Kyushu University and several other locations in Fukuoka and Saga prefectures on Kyushu Island in late Jul to early Aug 2013. Dissection of plants revealed a spiraling deformity of the central tiller 4 to 15 cm above ground level. In several stems, a small pinkish larva was found near the deformity. No adults were reared, but larvae were identified as a Contarinia sp. Plant deformity in response to feeding by members of the genus Contarinia has been reported (Bardner et al. 1971; Brewer et al. 1994), and in sunflowers is thought to be associated with elevated levels of auxin (Brewer et al. 1994). As many cecidomyiid midges have narrow host ranges (Gagné 1989; Yukawa 2000; Gagné 2004), the midge found in cogongrass may warrant further investigation as a potential biological control agent.

Orseolia javanica Kieffer & van Leeuwen-Reijinvaan (Diptera: Cecidomyiidae)

A previous study in West and Central Java, Indonesia, identified the stem gall midge O. javanica as a potential biological control agent of cogongrass (Mangoendihardjo 1980). Limited host range testing with cultivated rice, 2 wild Oryza species., corn, sorghum, and 2 other noncultivated grasses, Paspalum conjugatum P. J. Bergius (Cyperales: Poaceae) and Penisetum polystachyon (L.) Schultes (Cyperales: Poaceae), suggested a narrow host range with midges surviving only in cogongrass. According to Mangoendihardjo (1980), midges held in cages with cogongrass plants laid 98% of their eggs on the soil and 2% on plant stems. Most eggs were viable, but very few larvae were able to successfully enter the plant. Once inside stems, larval feeding induced the formation of a stem gall, in which 1 larva developed and pupated. After gall formation, infested stems ceased development and senesced after the emergence of adult midges. During visits to West Java in May 2015 and Feb 2016, stem galls were abundant along bunds separating rice paddies in Cianjur District. Galls, along with stem crowns, roots, and pieces of rhizome, were removed from the soil and placed in clear acrylic tubes (5.08 cm in diameter, 30 cm in length) sealed with plastic caps and transported inside coolers to the Fort Pierce quarantine laboratory. The 2015 collection was maintained in 8 groups of approximately 30 galls each, held in acrylic plastic containers (19 × 14 × 10 cm).

Of 247 galls collected, only 3 midges (1%) emerged, 2 females and 1 male. The females died several days before the male emerged so there was no opportunity for mating and colony establishment. Three species of parasitoids emerged from galls, including Platygaster orseoliae Buhl (Hymenoptera: Platygastridae), Prospicroscytus mirficus Girault (Hymenoptera: Pteromalidae), and an Aprostocetus sp. (Hymenoptera: Eulophidae) (Buhl & Hidayat 2016). In 2016, midges emerged from 14 of 215 galls (6.5%) collected in Feb, including 6 that emerged and died during transport. The other 8 adults (2 females and 6 males) emerged within the first 2 d in quarantine and were placed together in a cage with cogongrass plants. No mating or oviposition was observed and all midges died within 24 h of emergence. Plants were held for 6 wk but no galls formed, indicating a failure to obtain progeny. From this collection, a subset of galls (n = 71) was held individually to allow calculation of parasitism. Aprostocetus sp., P. orseoliae, and an unidentified eupelmid emerged from 26 (37%) galls.

Emmalocera sp. (Lepidoptera: Pyralidae)

This stemborer was collected at 1 location in Laguna Province and 1 location in Quezon Province during a survey in Jul 2013. Its closest match in GenBank was E. latilimbella (Ragonot), but with only a 93% sequence similarity and an “E” value of 0.0. Emmalocera latilimbella is only known from Australia and Papua New Guinea (BOLDSYSTEMS 2016; Global Information System on Pyraloidea 2016), and a literature search revealed no records of larval host plants. With a 93% similarity, it seems unlikely that the borer is E. latilimbella, but based on similarity among other Lepidoptera (Kim et al. 1999; Cognato 2006), it is probably in the genus Emmalocera.

Chilo sp. (Lepidoptera: Crambidae)

During a survey in the Philippines in Mar 2015, crambid larvae were found boring in the stems of cogongrass near Binan, Laguna Province, causing damage similar to that described above for Acrapex species. Based on the CO1 gene, the closest species in GenBank was Chilo partellus (Swinhoe), a notorious pest of corn and sorghum in southern Asia and East and southern Africa (Kfir et al. 2002; Sharma et al. 2007) that is not known to occur in the Philippines. However, the sequence similarity was only 92% (E value = 0.0), suggesting that the insect was not C. partellus. This was confirmed by morphological identification as a Chilo sp., but taxonomically distinct from C. partellus. A collection of 30 larvae was sent to the Fort Pierce quarantine facility, where they were placed on cut stems of cogongrass. Although all the larvae appeared to be mature when collected, several did not pupate until late May and early Jun, suggesting that they may have been in aestivation at the time of collection, which was during the dry season in Luzon. Two individuals reached the adult stage in mid- Jun but efforts to establish a colony were unsuccessful.

Acrapex yakoba Le Ru (Lepidoptera: Noctuidae)

Le Ru and colleagues have been investigating lepidopteran stemborers associated with native grasses in East and Central Africa for the past 13 yr (Le Ru et al. 2006), and they have discovered 4 species in the genus Acrapex that have only been collected from cogongrass (Le Ru et al. 2014). In Feb 2013, 580 larvae of A. yakoba were collected from several patches of cogongrass in the Njombe region of southwestern Tanzania. Of the total collection, 490 larvae were taken to the laboratories of the International Center of Insect Physiology and Ecology (ICIPE) in Nairobi, Kenya, whereas 90 larvae were hand-carried to the Fort Pierce quarantine laboratory. In Fort Pierce, 27% of larvae pupated and of those, 10 produced adults, which were placed in a 4 L plastic cage with cut stems of cogongrass. No mating was observed, but 206 eggs were laid in leaf sheaths in groups of 1 to 64. In total, 21 eggs eclosed and neonate larvae were placed on an artificial diet. All larvae died before molting to the 2nd instar. In Nairobi, 25% of larvae pupated, 16 adults emerged and laid 336 eggs, of which 170 eclosed (46%). Neonate larvae were placed on an ICIPE-developed diet (Onyango & Ochieng' Odero 1994), but none completed development.

Acrapex syscia Fletcher (Lepidoptera: Noctuidae)

In May 2014, A. syscia larvae were collected from cogongrass during a survey in southwestern Uganda. Larvae were either hand-carried to ICIPE laboratories in Nairobi, Kenya (482 larvae), or to the University of Florida biological control quarantine laboratory in Fort Pierce, Florida (88 larvae). At ICIPE, 452 larvae were placed on the same artificial diet as used for A. yakoba and the remaining 30 were placed on live cogongrass plants. Larval consumption of the artificial diet was poor compared with the feeding of A. yakoba and less than 9% pupated. A few adults (22 females and 21 males) emerged but several were malformed, and few emerged at the same time. Only 2 couples were paired, but no eggs were produced. Out of the 30 larvae placed on cogongrass plants, there was no evidence of colonization after 2 to 3 wk; after 7 to 8 wk, the plants were dissected and no larvae were recovered.

In Florida, 88 larvae were received alive in quarantine, of which 10 were placed on each of 4 whole plants whereas the remaining larvae were placed in vials on artificial diet (Frontier Agricultural Sciences, Product F9775B). From the larvae placed on whole plants, only 2 adults emerged, whereas 5 adults successfully developed on artificial diet. All adults were placed in one 4 L plastic cage with 4 to 6 cut stems of cogongrass (about 20 cm long) held upright in wet sand. Stems were inspected daily and replaced. In total, 158 eggs were collected in 4 batches and placed in Petri dishes with moistened filter paper. None of the eggs hatched, possibly due to lack of fertilization.

Acrapex subalbissima Berio (Lepidoptera: Noctuidae)

During surveys in the Kipengere and Uzungwa mountains of Tanzania, Le Ru et al. (2014) found A. subalbissima only in cogongrass. They stated that it is a “markedly hygrophilous species found along banks of rivers and streams.” No attempt was made to initiate a laboratory colony of A. subalbissima.

Acrapex mitawa Le Ru (Lepidoptera: Noctuidae)

Le Ru et al. (2014) discovered A. mitawa in the Ruvuma region of Tanzania and only found it in cogongrass, despite sampling several other grasses. Like A. subalbissima, it was found in cogongrass growing in moist areas along river and stream banks and in marshes. No attempt was made to establish a laboratory colony of this species.