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CURRENT STATUS OF HABITAT MANIPULATION FOR NATURAL ENEMIES AND PEST MANAGEMENT IN JAPAN

Hisashi Nemoto
Institute of Crops and field,
Saitama Prefectural Agriculture and Forestry Research Center
Kubojima, Kumagaya, Saitama, 360-0831 Japan
Email: nemoto.hisashi@pref.saitama.lg.jp

ABSTRACT

The actual application of IPM remained limited in Japan. There is little spread of habitat manipulation except experiments with eggplants and cabbages. The ecological responses of pest populations to pest control tactics, with an emphasis on the phenomena of resistance and resurgence that often occur using pesticides are explored. Spread of habitat manipulation is difficult if it does not solve a problem of a pesticide in Japan. The solutions by conservation biological control with selective pesticide in these pesticide problems are showed. And insect pests on eggplants surrounded with aphid banker plants without pesticides are well controlled by natural enemies. This can become a clue of solution.

Keywords: IPM, selective insecticide, resistance, resurgence, conservation biological control,
     aphid banker plant

INTRODUCTION

Even if Japanese Government pushes forward "Environmental-Friendly Farming (= Sustainable Agriculture)" since 1999, Japan is still the most country in the OECD's list of total pesticide (active ingredients) use per arable and permanent crop area. The actual application of IPM remained limited because most farmers and extension workers were not interested in IPM. There are some researches of habitat manipulation, but there is little dissemination of information happening to farmers.

It is the reason why the average age of farmers is high (62.2-year-old in 2000 and 65.8-year-old in 2010), and an average cultivated area per one farmhouse is small with 1.8 ha in Japan (The Ministry of Agriculture, Forestry and Fisheries. 2008). So, IPM was considered a complicated activity for most farmers. Likewise, pest control could easily be achieved through the use of pesticides in order to obtain higher yields and decreasing cosmetic damage to crop products. Also, the government still encouraged pesticide use in order to obtain higher yields.

In 2002 a lot of illegal pesticide use was discovered in Japan, and the pesticide suppliers were arrested. Japanese agricultural products suppliers and consumers were worried about pesticide residues. After that, the amount of shipment of biological insecticides derived from naturally occurring arthropods and microorganisms increased and the researcher's interest was applied to IPM. This can be regarded as the first phase of IPM in Japan.

Pesticides have long overshadowed the importance of natural enemies in pest management programs. The high efficacy, easy accessibility, and consistent performance of chemical controls have made them the tool of choice for growers in managing their pest problems. But frequent outbreaks of secondary pest after pesticide applications and the increasing prevalence of pesticide resistance in various pests have pointed out the risks of unilateral reliance on pesticides (Ruberson, et al. 1998). The IPM concept initially embraced the combined use of natural enemies and pesticides to manage pest (Stern et al., 1959). This idea later evolved to include coordinated use of all possible viable tactics, including pesticides, natural enemies, host plant resistance, cultural controls, and other biologically based methods (Smith et al., 1976).

There is little spread of habitat manipulation during the beginning of the research. And experiments with eggplants and cabbages are known on habitat manipulation inconsiderably in Japan (Nagai and Date, 2000; Masuda and Miyata, 2008; Masuda, 2009; Yamashita, 2010).

RESISTANCE AND RESURGENCE

Norris et al. (2003) warned about the key to management of the three Rs (resistance, resurgence or replacement) was implementation of mitigating strategies before they become a problem. Pest management practitioners seem to have great difficulty with this concept, despite the general acceptance that a manager must adopt IPM practices and not rely on a single control method (rotate mortality factors). Unless management of the three Rs is learned, and what is known is implemented, pest managers may eventually run out of options for pest control.

Brassica crops

Nemoto (1986, 1993a) pointed out the link of insecticides to diamondback moth (DBM) Plutella xylostella outbreaks on Brassica crops. Farmers did not know about biological control, and some farmers sprayed their crucifer fields as soon as they find a pest. Then insecticides killed off effective predators of DBM and other natural enemies. This lack of understanding of ecology meant that many farmers did not know that their Brassica fields were protected by the action of natural enemies.

The incidence of DBM increased after applications of methomyl in a cauliflower field compared with the untreated control in Saitama, Japan. Using cages covered with a mesh netting to artificially exclude natural enemies, the importance of the role of native natural enemies in the reduction of the DBM population was demonstrated. Then the role of predators and parasites was evaluated by artificially excluding them for the estimation of the DBM mortality. Brassica greens, on which DBM eggs were laid in the laboratory, were planted in the cabbage field. A cage was covered with 0.2-mm mesh netting to exclude all the predators and parasites. Another cage was covered with a vinyl film (except for the top) and treated with a sticky substance on the upper edges of the vinyl film to exclude ground-dwelling predators. This allows flying predators to invade the cage. After planting a brassica green with the DBM eggs in the plot, the number of larvae in the control plots decreased more rapidly than in the other two cages (Fig. 1), indicating the importance of natural enemies in the reduction of the DBM population. There is also a small difference in the numerical change of larvae of two cages, which indicates parasitoids did not always appear to be a key factor.

The predators of DBM were identified by immunological test. Field-collected lycosid spiders exhibited a possive reaction in the test, while few Labiduridae species and other suspected predators effected positively. The effect of methomyl on the predator populations was studied in the cabbage field. The numbers of lycosid spiders were reduced by the application of methomyl, while other predatory insects were not affected. P. astrigera was the most common lycosid in the cabbage field. The LC50 value to lycosid was around 10 ppm against about 7,500 ppm for the fourth instar DBM larvae using the dipping method, and about 20,000 ppm for the third instar larvae by feeding methomyl-contaminated cabbage leaves. Methomyl is generally sprayed at 450 ppm to control pests on Brassica. Methomyl was substantially less deadly to DBM than to the lycosid. Ground-dwelling predators like these spiders thus appear to be effective in reducing the DBM population (Fig. 2). Muckenfuss et al. (1992) reported that the parasitoid Diadegma insulare and indigenous communities of arthropod predators were the major mortality factors of the DBM larvae in South Carolina, USA.

Wagge (1989) stated that "Killing natural enemies is not a bad thing if, at the same time, the pesticide used makes up, in direct kill of pest, the natural enemy distribution which it eliminates". Resistance to an insecticide is an essential factor which induces a resurgence of the target insect pest. It is suggested that the application of methomyl may cause a resurgence of the insect population through the following mechanisms: (1) resistance to the insecticide; (2) differential mortality levels between DBM and its predator which is responsible for most of the pest mortality; and (3) stimulation of the reproductive potential (Nemoto, 1993a). The first two are the main factors inducing the resurgence of DBM in Japan. On the basis of these results, I consider that the pest management of Brassica spp. requires a non-chemical control approach and information to identify an insecticide which is selective in its target. The pesticide impact on indigenous communities of natural enemies needs to be investigated.

Eggplant

In 1990s, eggplant growth has been severely impaired in Japan by Thrips palmi and utmost efforts have been made to control this pest. The control of only one species of pest is not relevant to eggplants because this crop also requires simultaneous protection from other pests. In addition, the use of non-selective pesticides may actually cause a resurgence of T. palmi, Tetranychus spp., the cotton aphid Aphis gossypii (Nemoto, 1995a) and corn earworm Helicoverpa armigera. The use of imidacloprid, which is highly effective against pests such as A. gossypii and T. palmi, also causes a resurgence of spider mites (Nemoto, 1993b). The relationships between the various pests of eggplant and their natural enemies have remained unexplored except for that between T. palmi and its predators, Orius spp. (Kawamoto and Kawai, 1988; Nagai, 1993). Nemoto (1995) repeatedly sprayed eggplants with various pesticides to determine the effects of these substances on the populations of pests and their predators on the crop.

Permethrin, ethofenprox and imidacloprid wettable powder (except imidacloprid granule) strongly reduced the population density of Orius sauteri and O. minutus which are known to be predators of T. palmi (Nemoto, 1995). The population densities of coccinellid beetles and predators of aphids and spider mites were also reduced by treatment with permethrin. A. gossypii, populations exhibited two distinct peaks in the plot sprayed with permethrin and ethofenprox, and these peaks densities were much higher than those in the untreated plot after June. Thus there is a very high probability that pesticides like permethrin having a strong eradication effect on the natural enemies of pests actually are responsible for the resurgence of the pests (Fig. 3) (Nemoto, 1995). The densities of T. kanzawai treated with imidacloprid wettable powder were much higher than those in the untreated plot after June (Nemoto, 1993b). Meanwhile, milbemectin reduced the population density of T. kanzawai. Milbemectin showed a minimal adverse effect on predators such as Orius spp. and it had hardly any effect on the population densities of A. gossypii and T. palmi.

Japanese pear

Abnormal development of spider mites was observed after a frequent dispersion of synthetic pyrethroids, a non-selective insecticide, to Japanese pear (Fig. 4). Leaf dwelling predator like the predatory mites remarkably contributed to a decrease in the number of spider mites. It was recognized that the above case of resurgence for spider mites resulted from elimination of native natural enemies. Synthetic pyrethroids are very effective on fruit moths, tortrixes and stink bugs, but extremely harmful to predatory mites. Decrease of the number of natural enemy and decrease of chemical sensitivity to synthetic pyrethroid for spider mites are very important factors to explain the abnormal outbreak of spider mites. Resurgence often happens when a certain insecticide kills natural enemy while it does not affect a target pest.

Conservation biological control

Hassan (1989) introduced International Organization of Biological Control, West Palaearctic Regional Section (IOBC/WPRS) methodology for risk assessment of pesticide effects on natural enemies. The methodology requires choice of species tested, technology that same stage of natural enemies are mass-reared, and devices for testing pesticide effects. However, Integrated Pest Management (IPM) is not yet established in the cultivation of vegetables in many Asian countries because important natural enemies have not been identified, nor has pest-regulating power been determined. The IOBC/WPRS methodology is thus not applicable for Asian countries including Japan but is for those such as the EU.

To be effective, natural enemies may need access to alternative pray or hosts, adult food resources, overwintering habitats, constant/alternative food supply, and appropriate microclimates. Identifying the ecological factor necessary to favor even a few key natural enemies can be a time-consuming research endeavor (Landis and Wratten, 2002).

Brassica crops

Evaluation of the side effects by spraying a relatively small area repeatedly with an insecticide can be done even in Asian countries. This can also be done by recording seasonal changes in the abundance of all pests and their natural enemies with all available pesticides. On the basis of data from our field experiments, selective pesticide use on crops can enhance biological control.

Ground-dwelling predators such as lycosid spiders and the foliage-dwelling spiders C. octomaculatum and G. exsiccatum are important biotic mortality agents of immature stages of DBM. The power of natural enemies should be used in control because DBM has few effective insecticides and also, there were no non-chemical control methods for aphids and common cabbage worm in 1990s in Japan. Since these pests are a problem in unsprayed Brassica fields, they must be controlled by pesticides. On the basis of the results, it is possible to develop methods for control of these pests without adverse effect on their natural enemies.

There were a few effective natural enemies for the important insect pests in cabbage fields which were treated with non-selective pesticides. In the long-term, repeated insecticide treatment might affect the number of natural enemies. So in order to increase natural enemies, a white clover was arranged surrounding the cabbage and broccoli fields (Fig. 5, Fig. 6 and Fig. 7., Nemoto, 2003). As a result the frequency of an insecticide treatment was reduced into half compared to that of conventional treatment. But there are few refuges like hedges, overwintering habitats, constant/alternative food supply, and appropriate microclimates for effective natural enemies.

Eggplant

Nagai (1991, 1993) showed integrated control programs Thrips palmi on eggplants which used a selected insecticides. A sorghum barrier surrounding eggplant for a storm protect invasion of Thrips palmi into the eggplant field physically (Nagai and Date, 2000). Seasonal occurrence of Orius spp., predacious natural enemies of Thrips palmi, in eggplant fields and surrounding habitat of white clover were investigated. As a result, Orius sauteri dominated on white clover and eggplant in June (Ohno and Takemoto, 1997).

Imidacloprid granules, which are known to cause a resurgence of spider mites (Nemoto, 1993), were placed in each planting hole at a rate of 1 g per plant. The treated and untreated areas were each divided into two plots: one that had not been sprayed with chemicals, and the other that was sprayed with a solution of selective acaricides.

In the Imidacloprid granule treated area, the plot sprayed with selective acaricides, once a month showed a lower degree of infestation by the three pests, T. palmi, A. gossypii and T. kanzawai. But only treatment with Imidacloprid granules caused a resurgence of T. kanzawai from mid-July through mid-August in 1993. Aphid outbreaks occurred between May and June in untreated and selective acaricides-sprayed plot. Imidacloprid granules thus may be used effectively in combination with a solution of selective acaricides (Nemoto, 1995a). As a result the frequency of an insecticide treatment was reduced into half to one-eighth compared with the conventional treatment.

Insect pests on eggplants surrounded with forage corn in the organic farming in Saitama, Japan are well controlled by natural enemies (Fig. 8 and Fig. 9, Nemoto, 2007). In this case, forage corn becomes aphid banker plants of eggplants and physical barrier against female adults of owlet moths. Colonies of grass-feeding aphid species such as oat bird-cherry aphid Rhopalosiphum padi and/or the corn-leaf aphid Rhopalosiphum mcmaidis as a prey for the predator scymnid ladybugs are established on the forage corn. The ladybugs continually reproduce and emerge from the banker plants to suppress aphid pests such as Aphis gossypii and Myzus persicae. The natural enemies feed on both the eggplant pest and the grass-feeding aphid on the forage corn. The grass-feeding aphids did not injure the eggplants. In addition some refuges like hedges and overwintering habitats for effective natural enemies were left here. The eggplant field of the neighbor of organic farming was sprayed by chemical pesticides which included non-secretive pesticides by two times of frequency in a week. We recommended the farmer to change to secretive pesticides, after the reduction of spraying frequency from twice a week to two times in three months without a change of quantity of fruit to harvest.

Japanese pear

Mating disruptors have been utilized to suppress insect pest populations through either disruption of communication between the sexes and those that are not harmful to beneficialspecies. However, the mating disruptors were species specific, so it was difficult to use the mating disruptors by commercial growers. The new mating disruptor which was able to control multiple species of lepidopterous insect pests such as fruit moths and tortrixes was developed recently. These mating disruptors have no effect on other pests like aphids, spider mites and caterpillars which are non-target pests of the mating disruptors. We need to regulate these pests by selective pesticides. Fruit moths, tortrixes, stink bugs and aphid but non-selective insecticides easily kill predatory mite consequently causing resurgence of spider mites. Prevention and elimination of pests depending only on insecticide tends to bring about resurgence. There is a way to solve this problem by using the mating disruptor and selective pesticides. This method is expected to conserve natural enemies. But in the main producing center of the crops, there a few refuges like hedges, overwintering habitats, constant/alternative food supply, and appropriate microclimates for effective natural enemies and non-selective pyrethroid are still sprayed for stink bugs. These are left as problems in Japan.

CONCLUSION

Ecological responses of pest population to pest control tactics, with an emphasis on the phenomena of resistance, resurgence, and replacement - the three Rs of IPM - often occur when pesticides are used. These three Rs of pest management may be considered to account for the nearly inevitable downfall of all single-tactic approaches to pest management, and are major reasons why it is necessary to manage pests within an IPM framework. Overall submit is (Norris et al. 2003). The goal of Integrated Pest Management is to achieve economical protection from pest damage while minimizing hazards to crops, human health, and successful IPM has always followed an ecological approach (Kogan 1998).

The conservation biological control seeks to manipulate the environment to enhance the survival, fecundity, longevity, and behavior of natural enemies to increase their effectiveness in controlling pests (Landis and Wratten, 2002). But there is an extremely little habitat manipulation for natural enemies and a methodology for risk assessment of pesticide effects on natural enemies in Japan. Insect pests on eggplants surrounded with banker plants like forage corn (where some refuges are near) are well controlled by natural enemies without the use of chemical pesticides. We need to push forward these researches in the future. Japanese government begins to send in a fund on a research of habitat manipulation and seems to become one of the targets of the direct payment for habitat manipulation to farmers.

REFERENCE

  • Hassan S. A. (1989) Testing methodology and the concept of the IOBC/WPRS working group. In "Pesticides and non-target invertebrates, ed by P.C. Jepson". Intercept, Wimborne, UK." p. 1-18.
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  • Kogan, M. 1998. Integrated Pest Management: Historical Perspectives and Contemporary Developments. Annual Review of Entomology 43: 243-270.
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  • Masuda, T. 2009. Effects Cover of Living Mulch on Oviposition of Small White Pieris rapae crurcivora and Occurrence of Insect Pests in Cabbage Field. Annual Report of Plant Protection of North Japan. 60:208-211. (In Japanese).
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  • Nagai, K. and H. Date. 2000. Integrated control of Thrips palmi on eggplants in an open field utilizing sorghum barrier and indigenous natural enemies. Sin-gizyutu in Kinki and Tyugoku region 34: 45-46. (www.naro.affrc.go.jp/top/seika/1999/wenarc/kankyo/cgk99075.html). (In Japanese).
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Index of Images

  • Fig 1 Survivorship curves of immature stages of DBM within the different cages. (Nemoto, et al.1992)

    Fig 1 Survivorship curves of immature stages of DBM within the different cages. (Nemoto, et al.1992)

  • Fig. 2 Concentration-mortality curve of methomyl for the spider,

    Fig. 2 Concentration-mortality curve of methomyl for the spider,

  • Fig. 3 Effect of insecticide treatment on Tetranychus kanzawai populations on Eggplant. (Nemoto, 1995).

    Fig. 3 Effect of insecticide treatment on Tetranychus kanzawai populations on Eggplant. (Nemoto, 1995).

  • Fig. 4 Secondary outbreaks of spider mites after applications of the insecticides. (Nemoto, 2005)

    Fig. 4 Secondary outbreaks of spider mites after applications of the insecticides. (Nemoto, 2005)

  • Fig. 5 Effects of selective pesticides treatment on the DBM populations in broccoli fields. (Nemoto, 2003)

    Fig. 5 Effects of selective pesticides treatment on the DBM populations in broccoli fields. (Nemoto, 2003)

  • Fig. 6 The cabbage (left) and broccoli (right) field surrounding with a white clover. (Nemoto, 2003)

    Fig. 6 The cabbage (left) and broccoli (right) field surrounding with a white clover. (Nemoto, 2003)

  • Fig. 7 Effects of selective pesticides treatment on the DBM populations in broccoli fields. (Nemoto, 2003).

    Fig. 7 Effects of selective pesticides treatment on the DBM populations in broccoli fields. (Nemoto, 2003).

  • Fig. 8 The eggplant field surrounded with forage corn in the organic farming. (Nemoto, 2010)

    Fig. 8 The eggplant field surrounded with forage corn in the organic farming. (Nemoto, 2010)

  • Fig. 9 Oat bird-cherry aphid Rhopalosiphum padi on the forage corn. (Nemoto, 2010)

    Fig. 9 Oat bird-cherry aphid Rhopalosiphum padi on the forage corn. (Nemoto, 2010)

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