Oryctes virus--time for a new look at a useful biocontrol agent

The introduction of Oryctes virus into outbreak areas of the rhinoceros beetle, Oryctes rhinoceros (Coleoptera: Scarabaeidae), has been a major success for "classical" biocontrol with a virus and has led to a dramatic reduction in palm damage in many areas of the Asia/Pacific region. In recent years, however, there have been new reports of high levels of rhinoceros beetle damage to palms. Damage has been especially intense in SE Asia following the introduction of no-burn polices for land clearance and replanting, but outbreaks have also been reported from some Pacific Islands where control seems to have diminished over time. SE Asian studies show that there is considerable genetic variation among endemic Oryctes virus isolates and studies in new island release areas have shown rapid evolution of the virus. The consequences of such genetic variation are in need of further study. Furthermore, the taxonomic position of the virus is unclear, with its removal from the Baculoviridae to an "unassigned' virus, reflecting its novel characteristics. Genomic sequencing could help resolve the taxonomy of the virus and provide a basis for studying strain variation. Oryctes virus has achieved wide success in the past without the benefit of molecular analysis and identification techniques. In order to fully take advantage of this unique pathogen for protection of palms, a renewed, coordinated effort centered on genetic selection and distribution of effective strains is required.     

The Oryctes virus: its detection, identification, and implementation in biological control of the coconut palm rhinoceros beetle, Oryctes rhinoceros (Coleoptera: Scarabaeidae)

In view of the increasing and devastating damage by rhinoceros beetle (Oryctes rhinoceros) to coconut palms in the middle of last century, many efforts were made to find an efficient natural control factor against this pest, which could not be controlled by pesticides. The basic procedures of these monitoring programmes are outlined together with the final detection of a virus disease in oil palm estates in Malaysia in 1963. In extensive laboratory studies, the virus was isolated and identified as the first non-occluded, rod-shaped insect virus, morphologically resembling the baculoviruses. Infection experiments clarified the pathology, histopathology, and virulence of the virus and demonstrated that the virus was extremely virulent to larvae after peroral application. These findings encouraged the first pilot release of virus in 1967 in coconut plantations of Western Samoa where breeding sites were contaminated with virus. Surprisingly, the virus became established in the Samoan rhinoceros beetle populations and spread autonomously throughout the Western Samoan islands. As a consequence, there was a drastic decline of the beetle populations followed by a conspicuous recovery of the badly damaged coconut stands. This unexpected phenomenon could only be explained after it was shown that the adult beetle itself is a very active virus vector and thus was responsible for the efficient autodissemination of the virus. The functioning of the beetle as a 'flying virus factory' is due to the unique cytopathic process developing in the midgut after peroral virus infection. Pathological details of this process are presented. Because of the long-term persistence of the virus in the populations, rhinoceros beetle control is maintained. Incorporation of virus into integrated control measures and successful virus releases in many other countries are recorded.     

The epizootiology of the baculovirus of the coconut palm rhinoceros beetle (Oryctes rhinoceros) in Tonga

The incidence and distribution of the baculovirus of the coconut palm rhinoceros beetle was determined in Tongatapu, Tonga, 7 years after being first introduced. Surveys showed the virus to be spread throughout the beetle population, affecting 14.6% of breeding sites and over 84% of all adult beetles taken. Counts of damaged palms and of breeding site occupancy indicated that beetle numbers had remained at low levels. It appears that the virus has the potential for long-term control of beetle populations in these habitats.     

Establishment of a loop‐mediated isothermal amplification system for on‐site diagnosis of Oryctes rhinoceros nudivirus in Allomyrina dichotoma (Coleoptera: Scarabaeidae)

The Korean insect industry is rapidly developing, with the Korean horn beetle Allomyrina dichotoma as one of the most popular insects kept as pets. Korean horn beetles reared in local farms are suffering from Oryctes rhinoceros nudivirus (OrNV). In a nationwide investigation on the early death of young larvae due to this virus, 70 to 77% mortality was found. It was also confirmed that several larvae collected from some wild horn beetle habitats were infected with the virus. Thus, it was concluded that the virus could be transmitted vertically from an infected adult to the offspring and that the OrNV disease is a very serious threat to the wild horn beetle in Korea. With local farmers expecting that an early detection technique would be helpful for the quick removal of infected larvae, an on‐site diagnosis method for the viral disease using loop‐mediated isothermal amplification (LAMP) assay was thus tested. To avoid the DNA extraction process, the LAMP assay used a 50‐fold diluted hemolymph was set for diagnosis standardization and convenient on‐site application to infected larvae from local farms. A. dichotoma larvae were assayed for the OrNV infectivity with LAMP primers targeting the OrNV_gp102 gene. To evaluate the LAMP specificity, two bacterial pathogens, Bacillus thuringiensis and Serratia marcescens, causing disease in A. dichotoma were tested along with OrNV. The positive results were detected only from the OrNV‐infected larvae.     

Social media posts suggest that coconut rhinoceros beetle has established in the Western hemisphere

The coconut rhinoceros beetle (CRB: Oryctes rhinoceros L.) is one of the most damaging pests of coconut and oil palms in the Asia/Pacific region but has not been reported from the Western Hemisphere. Here, we report a possible establishment of CRB in Nayarit, Mexico, based on an analysis of social media reports and photographs indicating the presence of the beetle and the distinctive v-shaped notches in palm fronds caused by the beetle feeding. CRB populations are destructive once established, therefore, urgent actions are required to contain the pest and prevent damage to coconut and oil palm in the Americas.     

The epizootiology of two pathogens of the coconut palm rhinoceros beetle

Two diseases of Oryctes rhinoceros caused by Metarrhizium anisopliae and a virus were introduced from Western Samoa into Tongatapu, Kingdom of Tonga, in 1969 and 1970, respectively. The fungus remained at a low incidence and did not significantly affect the beetle population. The virus disease developed to epizootic levels within 5 months and spread across the island in 15 months. The beetle population was monitored through palm damage surveys, which confirmed that the population was considerably reduced by the disease.The greater impact of the virus was attributed to its much higher power of dispersal through infected beetles.The experiment supports the view that the reduction in beetle numbers recorded previously in Western Samoa was caused by a virus epizootic.     

Susceptibility of a native and an exotic lady beetle (Coleoptera: Coccinellidae) to Beauveria bassiana

The exotic multicolored Asian lady beetle, Harmonia axyridis, became established and recently spread across much of North America and southern Canada. In a habitat now used by both the invading H. axyridis and a native lady beetle, Olla v-nigrum, we discovered that the native lady beetle was commonly infected by Beauveria bassiana; whereas, the exotic H. axyridis, was not. Laboratory assays revealed that B. bassiana isolates collected from naturally infected O. v-nigrum were pathogenic to adult O. v-nigrum but not to adult H. axyridis. In contrast, the GHA strain of B. bassiana was not significantly pathogenic to O. v-nigrum nor H. axyridis. Late-season field collections revealed significantly higher B. bassiana infection of O. v-nigrum than H. axyridis. Our results lead us to hypothesize that low susceptibility of H. axyridis to B. bassiana (found to infect O. v-nigrum) may provide an intraguild advantage to H. axyridis over O. v-nigrum; this may also occur with other species of native lady beetles and other endemic entomopathogens in different habitats and regions.     

Ecological methods for adult populations of Oryctes rhinoceros (Coleoptera, Scarabaeidae)

ABSTRACT. 1. For comparing assessment methods, O.rhinoceros (L.) populations were monitored in five 30–50 ha plots in southern Luzon, Philippines. No consistent correlations were found between number of beetles caught in traps, amount of palm damage and number of breeding sites. Apparently, plots were too small to account for fast dispersal of beetles.
2. Coconut cap traps baited with ethylchrysanthemumate attracted O.rhinoceros adults searching for breeding sites. Several factors were identified influencing catches but trapping was found to be unsuitable for accurately assessing pest populations.
3. A new method which gives estimates on the monthly number of O.rhinoceros attacks on coconut palms, was tested in the Maldives. Palms are climbed about once a year and the sequence of fronds, the number and the position of beetle cuts are recorded.
4. Reduction with age of the length of three teeth on the fore tibia of O. rhinoceros adults was studied in the Philippines. The data was insufficient to obtain a clear correlation between age and length of teeth.
5. The observations indicated that in the Philippines after leaving their site of pupation, O.rhinoceros adults spend about 5 weeks feeding on coconut palms. This is followed by a period of about 7 weeks in breeding sites and, on occasion, additional visits to palms. With these estimates it was possible to relate palm damage records with numbers of feeding adults.     

Experimental evidence of bark beetle adaptation to a fungal symbiont

The importance of symbiotic microbes to insects cannot be overstated; however, we have a poor understanding of the evolutionary processes that shape most insect–microbe interactions. Many bark beetle (Coleoptera: Curculionidae, Scolytinae) species are involved in what have been described as obligate mutualisms with symbiotic fungi. Beetles benefit through supplementing their nutrient‐poor diet with fungi and the fungi benefit through gaining transportation to resources. However, only a few beetle–fungal symbioses have been experimentally manipulated to test whether the relationship is obligate. Furthermore, none have tested for adaptation of beetles to their specific symbionts, one of the requirements for coevolution. We experimentally manipulated the western pine beetle–fungus symbiosis to determine whether the beetle is obligately dependent upon fungi and to test for fine‐scale adaptation of the beetle to one of its symbiotic fungi, Entomocorticium sp. B. We reared beetles from a single population with either a natal isolate of E. sp. B (isolated from the same population from which the beetles originated), a non‐natal isolate (a genetically divergent isolate from a geographically distant beetle population), or with no fungi. We found that fungi were crucial for the successful development of western pine beetles. We also found no significant difference in the effects of the natal and non‐natal isolate on beetle fitness parameters. However, brood adult beetles failed to incorporate the non‐natal fungus into their fungal transport structure (mycangium) indicating adaption by the beetle to particular genotypes of symbiotic fungi. Our results suggest that beetle–fungus mutualisms and symbiont fidelity may be maintained via an undescribed recognition mechanism of the beetles for particular symbionts that may promote particular associations through time.     

The effect of re-release of Oryctes rhinoceros baculovirus in the biological control of rhinoceros beetles in Western Samoa

The Rhinoceros Beetle Project in Western Samoa has developed and successfully applied biological methods to control the rhinoceros beetle, a serious pest of coconut palms, by using two specific pathogens, a baculovirus (Family Baculoviridae), and an entomopathogenic fungus, Metarhizium anisopliae. The application of virus particularly has markedly suppressed the beetle population and helped revive the copra industry. The virus disease had established itself in the wild beetle population several years after its introduction at a level between 30 and 50%. At the same time an increase in beetle numbers and damage to palm trees was experienced. Therefore, a continuous release of virus into beetle-infested areas was proposed. It was argued that, considering the relatively high level of “natural” virus incidence, further releases of virus into the population would be futile. In a combined research and control program, virus was again re-released into the wild beetle population which was already virus infected. The results show that through re-release the virus level can be raised and the number of beetles and consequently the damage can be reduced. The techniques of the control methods are described. The virus release is very easy and cheap; it requires no chemicals, no special equipment, and it is particularly recommended in situations where breeding places are inaccessible or other methods such as plantation sanitation are either impossible or economically impractical. Above all, the methods are absolutely safe from the standpoint of environmental protection.     

Inhibitory Effect of Bursaphelenchus mucronatus (Nematoda: Aphelenchoididae) on B. xylophilus Boarding Adult Monochamus alternatus (Coleoptera: Cerambycidae)

Inhibitory effects of Bursaphelenchus mucronatus on the number of B. xylophilus carried by an adult Monochamus alternatus were investigated using artificial pupal chambers. When pupal chambers were infested with either B. xylophilus or B. mucronatus, the load of B. xylophilus onto the beetle was greater (P < 0.001) than that of B. mucronatus. However, within the pupal chamber there was no difference in the abundance of the third-stage dispersal juveniles, which would molt to the fourth-stage dispersal juveniles to board beetles. The nematode load on beetles that emerged from pupal chambers infested with both Bursaphelenchus species was smaller (P = 0.015) than that of beetles with B. xylophilus alone but greater (P < 0.001) than that of beetles with B. mucronatus alone, suggesting an inhibitory effect of B. mucronatus. As a result of this study, the rate of inhibition of B. mucronatus on molting of third-stage dispersal juveniles of B. xylophilus to fourth-stage dispersal juveniles was 0.65, which resulted in great inhibition on boarding beetles at a rate of 0.7.     

Horizontal Transmission of Bursaphelenchus xylophilus between Sexes of Monochamus alternatus

Four experiments were conducted using nematode-infested and nematode-free adults of the cerambycid beetle, Monochamus alternatus, to determine horizontal transmission pathways of Bursaphelenchus xylophilus. When nematode-infested beetles of one sex and nematode-free beetles of the opposite sex were paired in containers for 48 or 72 hours, the number of nematodes carried by nematode-free beetles tended to increase with increased number of nematodes carried by nematode-infested beetles. The nematodes acquired by "nematode-free" beetles could be transmitted to pine. A female beetle that received 13 nematodes from a male transmitted one nematode to a Pinus densiflora bolt via an oviposition wound. When the nematode-infested and nematode-free beetles were observed continuously, it was observed that the number of nematodes carried by nematode-free beetles at the end of the first sexual mounting increased as the number of nematodes carried by nematode-infested beetles just before mounting increased. The number of nematodes transferred to nematode-free beetles was positively related to duration time of mounting. There was no difference in transmission efficacy between male-to-female transmission and female-to-male transmission. The horizontal transmission pathways are discussed relative to the persistence of B. xylophilus in resistant pine forests and the control of pine wilt disease.     

Transmission of Bursaphelenchus xylophilus through Oviposition Wounds of Monochamm carolinensis (Coleoptera: Cerambycidae)

Transmission of pinewood nematode through Monochamus carolinensis oviposition wounds was documented. Nematode transmission was measured as the average number of nematodes isolated per oviposition wound excavated and also as the percentage of oviposition wounds from which nematodes were isolated. The influence of three factors that might affect nematode transmission was investigated: age of the beetle vector, number of nematodes carried per beetle, and egg deposition in the oviposition wound. Only the number of nematodes carried by the beetle was found to have a significant effect on transmission. Nematodes were transmitted more frequently and in slightly greater numbers by beetles carrying more nematodes. The influence of pinewood on nematode exit from beetles were investigated by comparing nematode exit from beetles placed over pine chips with those placed over distilled water. Nematodes exited in greater numbers and at a higher frequency from beetles over pine chips than from beetles over distilled water. Apparently, the nematodes are able to detect a factor from the pine chips that promotes their exit from the beetles.     

An Opportunistic Bacterial Pathogen, Pseudomonas alcaligenes , May Limit the Perpetuation of Oryctes Virus, a Biocontrol Agent of Oryctes rhinoceros L.

Pseudomonas alcaligenes was detected at a high concentration (10 9 -10 10 cells mL -1 ) in the haemolymph of some dead Oryctes rhinoceros grubs collected from its breeding sites in the three southern districts, viz. Alleppey, Quilon and Kottayam of Kerala State, India. In a laboratory colony maintained for production of Oryctes virus, an important biocontrol agent of this major coconut pest, approximately 52% of the grubs succumbed to septicaemia with similar symptoms. The bacterium was found to be a component of the gut microflora of healthy grubs. Occurrence of the viral infection naturally or when induced in the laboratory in the O. rhinoceros grubs, appeared to be one of the biotic stress factors for P.alcaligenes to become an opportunistic pathogen. A preponderance of this bacterial infection in field populations during the periods when natural viral infection in grubs was above average, agrees with this observation. This finding becomes significant as infection by the opportunistic bacterial pathogen, P. alcaligenes , reduces the production of Oryctes virus inoculum in nature and limits the field-perpetuation of this viral biocontrol agent.     

Microbial pathogens of the coconut pest Oryctes rhinoceros: influence of weather factors on their infectivity and study of their coincidental ecology in Kerala,India

The rhinoceros beetle, Oryctes rhinoceros L., is an economically important pest of the coconut palm. Management of this pest has been accomplished using microbial agents viz., Oryctes virus (OrV) and an entomofungal pathogen Metarhizium anisopliae. Recently an opportunistic bacterial pathogen Pseudomonas alcaligenes has also been noticed to cause septicaemia in the grubs when under stress. To unravel the influence of abiotic weather factors and the interactions amongst these microbial pathogens, a 3 year study was conducted from September 1996 to August 1999 in three of the southern districts of Kerala, India. Of the 6627 grubs and 307 adults collected from various breeding sites of the pest, 5% of the grubs and 22% of the adults had natural virus infection, 3% larvae died of M. anisopliae mycosis and 20% larvae succumbed to bacterial septicaemia. Oryctes virus infection in grubs and adults was negatively correlated to minimum temperature (correlation co-efficient, r = –0.4, and –0.6 respectively, sample size, n = 0). Increase in relative humidity increased the fungal activity (r = 0.8) whereas, maximum temperature had a negative impact (r = –0.7). Occurrence of virus infection in grubs and adults was positively correlated (r = 0.6), supporting the contention of active transmission of the virus pathogen between these two stages. The bacterial septicaemia in the grubs was marginally correlated with virus infection and P. alcaligenes undermined the efficiency of the virus pathogen.     

Molecular identification and first documentation of seven species of Carpophilus Stephens (Nitidulidae: Carpophilinae) in oil palm ecosystem,Peninsular Malaysia

Sap beetles are commonly found in many agricultural systems worldwide. In Malaysia, sap beetles are less documented despite their abundance in oil palm plantations. The similarities in the morphology of the sap beetle makes the identification process difficult from the same genus. This study aims to determine of composition of the sap beetle species from the genus Carpophilus, to identify the species of sap beetles and to document the DNA barcode for those species collected from the oil palm plantation, which has never been done before. DNA of seven species of sap beetles within the subfamily Carpophilinae have been successfully amplified using cytochrome oxidase subunit I marker (COI) namely C. hemipterus (Linnaeus), C. maculatus Murray, C. mutilatus Erichson, C. marginellus Motschulsky, C. sp. 1, C. nepos Murray and C. obsoletus Erichson represented 21, 12, 33, 8, 9, 6 and 11%, respectively from the total number collected. The sequences were analysed and a tree was constructed based on Neighbor-Joining (NJ) analysis with Meligethes thalassophilus chosen as an outgroup. All of the samples showed 90–100% similarities in BOLD and BLAST analyses. NJ trees constructed show that each sap beetle species collected from the study site located at their specific lineages on the tree. Interestingly, the DNA barcoding described in this study is the first to document barcoding data of sap beetles genus Carpophilus in Malaysia and this can be a helpful tool in updating the taxonomic and molecular status of the sap beetles in Malaysia.     

Giant rhinoceros beetle Golofa claviger (Linnaeus) (Coleoptera: Melolonthidae: Dynastini) is damaging North Brazilian oil palm plantations

The oil palm is an economically important crop cultivated in the North of Brazil. Damage caused by insects is one of the main causes of reduced productivity for the oil palm. Before this research, only the beetles of the family Curculionidae were considered to be oil palm pests in Brazil. However, for the first time, we report on the damage caused by a giant rhinoceros beetle to oil palm plantations in Pará, Brazil. The beetle was identified as Golofa claviger (Linnaeus, 1771), which has a single record in Brazil (Pará) but is widely distributed in South America. The species occurs in an unprecedentedly high abundance of local specimens. The attacks are concentrated on the central cluster of young palms. Feeding behavior is identified as the main cause of the damage as the beetles use their mouthparts to rip the plant tissues, causing wedge-shaped cuts on young fronds that have not yet unfurled. After an attack, the leaflets of the unfurled fronds are partially destroyed.     

Susceptibility of lady beetles (Coleoptera: Coccinellidae) to entomopathogenic nematodes

We investigated differential susceptibility of lady beetles to entomopathogenic nematodes, for two reasons: (1) to estimate potential nontarget effects on natural lady beetle populations, (2) to compare the susceptibility of exotic versus native lady beetle species. We hypothesize that successful establishment of some exotically introduced arthropods may be due, in part, to a lower susceptibility relative to competing native species. In laboratory studies, we compared the pathogenicity, virulence, and reproductive capacity of Heterorhabditis bacteriophora and Steinernema carpocapsae among two native (Coleomegilla maculata and Olla v-nigrum) and two successfully established exotic (Harmonia axyridis and Coccinella septempunctata) lady beetles, and a known susceptible lepidopteran host, Agrotis ipsilon. After 1 and 2 days of exposure to either nematode species, mortality of A. ipsilon was higher than in all lady beetles. Thus, we predict that nematode field applications would have significantly less impact on lady beetle populations than on a susceptible target pest. Additionally, the impact of soil-applied nematodes may be lower on lady beetles than on soil-dwelling hosts because the former spends relatively less time on the soil. Exotic lady beetles were less susceptible to nematode infection than native species. Reproductive capacity data also indicated lower host suitability in H. axyridis, but not in C. septempunctata. Overall, the hypothesis that low susceptibility to pathogens in certain exotic lady beetles may have contributed to competitive establishment was supported (especially for H. axyridis). Additional studies incorporating different hosts and pathogens from various geographic locations will be required to further address the hypothesis.     

Per cent emergent weight: A roadmap to adult rhinoceros beetle,Oryctes rhinoceros,behaviour

Adult rhinoceros beetles, Oryctes rhinoceros L., leave their pupal chambers, take their first flight, and die at well-defined ratios of their wet weight and their adult emergent weight. In addition, the beetles feed in a cyclical manner that is variable with time; however, each feeding event is well defined by a constant ratio of their weight just prior to feeding and their adult emergent weight. The ability to accurately estimate the emergent weight of field collected beetles, and therefore calculate the percentage emergent weight at the time of capture, makes these correlations useful in ecological studies and may be extended to other insects.     

Temporal Pattern of Pinewood Nematode Exit from the Insect Vector Monochamus carolinensis

Laboratory-reared Monochamus carolinensis (Olivier) were used to study the temporal pattern of pinewood nematode dauer larval exit from this beetle vector. Exit rates of dauer larvae were determined by comparing the mean number of dauer larvae carried by adult beetles 0, 7, 14, or 21 days after emergence from the log in which they developed. Density of dauer larvae was highest in beetles on the day of their emergence and dropped slowly through the subsequent age classes. The rate of nematode exit was low during the first week (4.5%) and higher during weeks 2 (20.5%) and 3 (13.1%). A total of 38.1% of the initial dauer larvae exited the beetles during the 3-week observation period.