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Plantwise Technical Factsheet

African white rice borer (Maliarpha separatella)

Host plants / species affected
Andropogon tectorum
Oryza (rice (generic level))
Oryza barthii
Oryza longistaminata (perennial wild rice)
Oryza punctata (wild rice)
Saccharum
Sorghum
List of symptoms/signs
Stems  -  dead heart
Stems  -  internal feeding
Whole plant  -  cut at stem base
Whole plant  -  external feeding
Whole plant  -  internal feeding
Whole plant  -  plant dead; dieback
Symptoms

M. separatella infests rice for most of its growth, attacking tillers and tunnelling in the internodes. These activities increase with the maturity of the crop (Njokah et al., 1982). Early rice, which provides the highest crop yield, is heavily attacked by M. separatella, and although later rice is only minimally infested, this increases through progression of the season (Breniere et al., 1962). The damage caused by this stem borer is said to be unique among rice stem borers because it rarely causes deadhearts or whiteheads (Heinrichs and Barrion, 2004). Small, circular cavities are made in the stem, which is not pierced (Heinrichs and Barrion, 2004). Breniere (1969), studying plant damage by M. separatella in Cote d’Ivoire, concluded that an increase in cropping density and high levels of Nitrogen fertilizer application would likely lead to an increase in the level of damage caused by M. separatella (see the section on Cultural Control and Sanitary Measures).

Rice plants have a whitish, fragile portion at the base when grown in deep water, which, combined with feeding by M. separatella and water pressure at a depth of 3 m, results in the damaged part of the plant detaching; infested stems are seen floating on the water surface and hills are missing (Akinsola, 1980; Heinrichs and Barrion, 2004).

Prevention and control

Cultural Control and Sanitary Measures

Several authors have investigated various factors for the cultural control of M. separatella in rice ecosystems, including rotting of stubble; using trap crops; adjusting planting date and adjusting planting density (e.g. Breniere et al., 1962; Ukwungwu, 1984; Nwilene et al., 2011).

Breniere et al. (1962) stated that flooding after harvest to ensure rotting of the stubble, or early cultivation where the soil was pulverized and dry plant clumps were buried, were recommended for control of M. separatella in Madagascar. Planting dry-season crops and allowing cattle to graze and trample the stubble are also important control measures to be adopted as part of an integrated control programme (Appert, 1967).

The use of trap crops has also been suggested as an effective method in the battle to control stem borers in southwest Nigeria (Nwilene et al., 2011). Nwilene et al. (2011) investigated the resistant status of upland NERICA rice varieties and the effectiveness of using maize as a trap crop against stem borers, including M. separatella. Intercropping rice and maize is widely used in Nigerian upland rice cultivation and the authors reported a significant reduction in stemborer attack on rice when NERICA rice was intercropped with maize, compared to plots that were intercropped with cassava or monocrops.

Planting date is also something to consider in controlling insect pests, including M. separatella. Ukwungwu (1984) reported that rice planted in February, March and April in Nigeria was more prone to infestation by M. separatella compared to rice planted in August. In the following year, infestation was high in the February, April and May crops, and again low in the August crop. Predicting peak populations of pests, with regard to seasons (e.g. Ukwungwu, 1987), is a useful tool in helping to control insect pests such as stem borers.

The effect of planting density on pest incidence was studied in western Kenya, where it was found that the intensity of damage by stem borers, including M. separatella, was the same at two densities studied (Ho and Kibuka, 1983a). When plots received a higher dose of fertilizer, the percentage of empty grains due to pest infestation was higher. The authors concluded that high-density planting was not economically viable, since yield did not increase with dense planting.

Biological Control

During a study by Appert (1967) to investigate the ecology and control of this pest in Madagascar, it was stated that the indigenous parasites of M. separatella were not effective enough for use in biological control. This is also true of biological control methods that rely on ingestion, such as pathogenic species, because stem borers such as M. separatella spend the larval stage within plant stems, rendering this method ineffective (see the review by Nickel, 1964).

Nickel (1964), in a review of biological control of rice stem borers including M. separatella, suggested that firstly steps should be taken to determine natural control factors of stem borers, as well as ecological studies of parasites proposed for control in their native environment, and evaluation post-release. This is the basis of determining the efficacy of any biological control programme.

Chemical Control

Breniere et al. (1962) stated that chemical control of M. separatella was not economically viable in Madagascar due to the lack of damage the pest caused to rice in this country. It is also said to be too expensive in Kenya, except in irrigated lowland rice (Ho and Kibuka, 1983c).

During a study by Appert (1967) to investigate the ecology and control of this pest in Madagascar, it was found that the use of fertilizer lead to accelerated growth of the plants and subsequent early pest attack, but this declined as the plants became more bushy and less attractive to females (see the section on Reproductive Biology), which moved on to less dense vegetation in unfertilized plots.

In a later study by the same author (Appert, 1970), it was stated that insecticide application is economical when the number of egg masses per sampling unit of 1 m x 1 m, taken every 10 days from 20 DT, is higher than 3.5.

The synthetic insecticide isofenphos (Randrianangally, 1990; Lafleur, 1994) has been tested for its efficacy against M. separatella and in some cases compared with the effects of neem (e.g. Lafleur, 1994). For example, while neem was found to be ineffective against M. separatella in Burkina Faso and yield of rice could be increased with the use of synthetic insecticides, the latter reduced the natural control of other rice pests, suggesting an integrated approach is necessary to improve the efficacy of control methods.

Experiments have also been conducted to investigate the effects of different formulations of neem for the control of pests including M. separatella (e.g. Ho and Kibuka, 1983b; Amaugo et al., 2005). Ho and Kibuka (1983b) reported that the percentage of stems infested with M. separatella was significantly lower in plots treated with neem cake and urea-neem cake than untreated plots and those treated with neem oil. However, the number of whiteheads in the plots did not significantly differ. Plots treated with neem cake and urea-neem cake produced the highest grain and straw yields, indicating a potential for the input of neem to control this stem borer.

Host Resistance (incl. vaccination)

Rice varieties resistant (e.g. Malinga, 1985; Nwilene et al., 2011; Kega et al., 2013) or moderately resistant (Anon., 1974) to M. separatella have been reported. Susceptibility is related to stem and leaf width, the capacity of forming new tillers and the duration and earliness of plant development (Appert, 1967).

Kega et al. (2013) studied the management of M. separatella using resistant rice cultivars and entomopathogenic nematodes in Mwea, Kenya. The authors concluded that this would be a viable method to control M. separatella as part of an integrated approach.

IPM

Baumgartner at al. (1990) studied rice production in Madagascar using a multiple regression model and used this to estimate the effects of various production factors, including pest control. Regional differences, quality of irrigation, planting density and dates of planting were all found to be important factors for consideration. Results indicated that weed control and insecticides only had a positive effect on yield when applied to fields that had high yield potential.

Monitoring and Surveillance (incl. remote sensing)

Cork et al. (1991) analysed ovipositor washings of female M. separatella and found 3 electrophysiologically active (EAG-) compounds, which they subsequently used in fields trials in Sierra Leone. Two of the EAG-active compounds attracted male moths in the field, showing promise for use in monitoring M. separatella.

Appert (1967) reported that light traps for assessing distribution and infestation levels were less accurate than counts of egg masses. When the number of egg masses exceeded 5 per m2, artificial control was said to be economically viable during the susceptible period, between the last 10 days of tillering and the end of flowering. Using egg mass counts to determine economic threshold was also reported by Delucchi et al. (1996), working in Madagascar.

Related treatment support
Pest Management Decision Guides
Kimani, A.; Ndung'u, B. N.; Ndung'u, J.; CABI, 2014, English language
CABI; CABI, 2017, English language
CABI; CABI, 2015, English language
Kimani, A.; Ndung'u, B. N.; Ndung'u, J.; Otipa, M.; CABI, 2014, Swahili language
 
External factsheets
Integrated Pest Management Extension Guide, Ministry of Food and Agriculture, 2004, English language
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