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Biological Control as a Pest Management Strategy

Several researches were carried out by different organisations in Mauritius to implement natural control in Mauritius as a component of the local Integrated Pest Management strategies. However, it can be observed that most of the natural foes which were introduced over the past few years are unable to match up with the expected efficacy on the field. Only a portion of the introduced natural enemies are very effective in pest control and maintaining their degree of infestation below the monetary threshold level, for example, natural foes used in sweets cane field are extremely effective and necessitates no pesticide and herbicide use to control pests thus, lowering the expense of sugar cane production. However, those fruit and vegetables planters in Mauritius that know about the principles of natural control tend to misjudge the use of natural control as a way of pest management, they are both right and wrong using ways.

Based on the info collected in this research, it can be plainly seen that the efficiency of natural foes differ from region to region. With regards to the natural enemy types, some are more effective in certain locations compared to others. Some natural opponents have the probable of being a very good effective natural control, however, it sometimes appears that their performance on field is not sufficiently reasonable. Before implementing a new biological control program, several procedures are followed to be able to pick the best performing natural foes. Risks to natural enemies' efficacy can be found in many varieties. The biggest threat and most common the first is the application and overuse of chemicals such as pesticides and insecticides. Based on the survey data obtained, it sometimes appears that most farmers apply pesticide every week. The usage of chemical substance pesticides has more than doubled in the past 10 years. The application and pesticide residuals are severe hazards to natural opponents, especially parasitic wasps, flies and predators. An example would be planter N01 where a sample of Plutella xylostella (L) was accumulated to judge the parasitoid Cotesia plutellae. The farmer employs selective pesticides and can be applied the very least amount on his contaminated plants and the speed of pesticide program is every 2 weeks.

The efficiency of Cotesia plutellae in his field was seen to be up to 50% that is, 1 / 2 of the larvae examined were parasitized by the wasp. On the other hand, another sample of Plutella xylostella (L) was gathered on planter's W02 field and the effectiveness of Cotesia plutellae assessed was found to be lower than the N01 sample, 16% respectively. In the survey data, it was seen that planter W02 makes use or a larger collection of chemicals and applies them weekly, the pace of pesticide request is doubly more for planter W02 than for N01. Another interesting observation made while carrying out the survey. It had been the way a few of the planters put together their pesticide solution, a few of them evidently use much more pesticide than the total amount recommended. A few of them tend to mix several pesticides together and made a pesticide "cocktail" out of them, making the ultimate solution have a broader range. Though the ready pesticide cocktail solution might be effective against the infestations, but it also has a poor effect on natural foes present on the field or the encompassing fields. Because of the "cocktail effect", it is possible that chemicals in the combination might interact to create an increase in its toxicity. This may be a reason for the low effectiveness of natural opponents. Farmer A may be taking good steps of IPM and using less chemicals, however the overuse and misuse of pesticides by the other close by farmer(s) will sure impact biological control on farmer's A field.

Another case came across with high natural foe efficacy is with sample W01 which consisted of Aphis gossypi gathered a Saint Martin, a town located in the Western world of Mauritius. The efficiency of the parasitoid wasp Lysiphlebus testaceipes was of 48%. The sample was collected over a calabash plant. That which was most interesting was that calabash had not been the planter's main crop, only a few trees and shrubs were planted at the area of the field and let to develop without caring for and no pesticide and other chemical substance application. This may be why the efficiency of the parasitoid was relatively high. An essential cause of biological control inability is the planter's frame of mind and knowledge about natural enemies and biological control. Most farmers surveyed had very good understanding of the pest threat they usually face, in addition they can identify the harm causing pest and use appropriate procedures. On the contrary, it was discovered that most of them (97%) do not have any knowledge on natural control, they didn't know the presence of beneficial organism handling damage leading to ones.

For this reason, they can not be expected to recognise and adopt traditional measures to maintain natural opponents, such as previously mentioned, reduce pesticide use, habitat management and improve biological and ecological aspects to enhance natural enemies such as removal of secondary opponents. It is believed that sensitisation by the responsible specialists is important to the planters in order to improve the overall IPM in Mauritius.

On the other hand, even if proper sensitisation is made to all planters, it could still be quite challenging to raise the natural enemy effectiveness. Most planters in Mauritius have a attitude which makes them disbelief in something they do not see using their own sight. Also, farmers will not be willing to get away from their traditions which were offered to them by their parents and grandparents. The use of chemicals in Mauritian agriculture is definately not being governed. Farmers say that their budget tend to be limited and they cannot take risks of striving something new due to the concern with it not being truly a success and of shedding everything. That is due to the fact that biological control does not completely eliminate the pest population however in truth it only reduces the pest level to a minimum acceptable level. Normally, this is undesirable to the farmer who wants to see his field totally free from any infestation. If no proper conservative actions and natural opponent monitoring are applied, another pest outbreak may occur inflicting losses to planters. They are reasons why planters in Mauritius would rather use pesticides as a way of pest control. Also, though most planters aren't willing to improve their traditional way of pest control, some of them are sometimes willing to adopt new IPM strategies to be able to regulate pests, like the use of bait traps and sticky traps, but those traps also work against natural foes, mostly little parasitic wasps. The right agricultural practices can also contribute in biological control inability, for example, crop rotation is a good way of lowering pest population, if the host plant essential for the pest success is not available, neither will be the infestations or their particular natural enemy. The usage of pest resistant varieties is also a sensible way to avoid pest outbreaks but is the crop is too resistant to pests, natural control will be very difficult to determine if no other resources of habitat and food are present.

Another aspect having an effect on natural adversary efficacy evaluated in this research was the climatic element in the different areas that is mainly the microclimate within different sites chosen for sample collection. It was found that climate change comes with an impact on insect phenology and the distribution of phytophagus pests especially Lepidoptera. This clarifies the rapid development and vast syndication of the pest Plutella xylostella throughout Mauritius. In the chi square test done and presented in stand 3. 8 in the previous section, it was discovered that the p-value to be less than 0. 05 for the natural opponent Cotesia plutella, meaning that the efficiency of the parasitoid would depend to the climatic factor in several region. Actually, both hymenoptera parasitoid assessed was seen to be dependent on climatic factors compared to the other natural opponents evaluated in the chi square test (Refer to Appendix 1).

This represents the difference in efficiency of the parasite around Mauritius. It was found by Nofemela, 2004 that the parasitoid Cotesia plutellae can develop on a variety of heat (8. 14oC - 33oC), thus, another deduction that can be made about the efficiency of Cotesia plutellae would be that the parasitoid density present in the different regions is not the same. In all circumstances of planter interviewed, it is available that the planters found an increase in heat and in change in rainfall routine and power. The planters also brought up that the warmer it is, the more the risk of an pest outbreak, for this reason, they usually apply more pesticides in summer season. It is concluded a changing (warming) climate and use of chemicals in agriculture are straight and positively related. Even though some pests became protected to pesticides and other chemicals, farmers still apply pesticides realizing that no results will be seen. To some extent, environment change will be responsible for the increasing overuse of chemicals and agriculture which can in turn lead to a reduction in biological control effectiveness. A change in insect phenology might also affect the sponsor and natural adversary synchrony, a fail in synchronisation with the host life cycle may cause drastic drop in biological control for reproductive failure.

Other factors that was seen to affect the efficacy of natural opponents was the coexistence of the infestation with other organisms which provide safety to the pest against natural foes. The two varieties of mealy bug researched, the Paracoccus marginatus and the Icerya seychellarum were seen to coexist with ants in all the infestations samples gathered. The ants harvest a product called honeydew from them which is secreted by the mealy bugs, and in return they provide coverage against natural foes, mainly predators. The effectiveness of the Paracoccus marginatus predator Exochomus laeviusculus is probably not the same on the field than the one evaluated in the lab, on the field, especially on papaya trees and shrubs where the Paracoccus marginatus examples were accumulated the mealy pests were found to be compacted on the trees, stems and super fruit, like a big white cottony lump. A waxy structure was present on all the mealy insect colonies, this may clarify why the infestation is being hard to control. The waxy compound stops chemicals to permeate in to the colony coating and natural enemies can only prey on the unhappy nymphs thinking around with no coverage. Also several types of ladybugs and other predators like spiders and sparrows were seen on a single tree. Such situations might make a competition among predators and the effectiveness of a picked predator for example the coccinelid Exochomus laeviusculus may not be the same compared to a scenario where the coccinelid is really the only predator preying on the infestation.

A suprisingly low parasitism rate was recorded for the parasitoid Cryptochetum monophlebi natural control of the pest Icerya seychellarum, this might be as a result of existence of ants, chemicals present in that one environment, but also, the Cryptochetum monophlebi being the order Diptera. It really is known that Dipterans will be the favourite food of lizards and some other insectivorous reptiles. Because of the presence of those reptiles on tree fruits, it can be a reason why the efficiency of the parasitoid is too low.

The effectiveness of the ladybug Nephaspis bicolor, predator of Aleurodicus dispersus was also evaluated in the lab and its efficiency, exactly like other natural foes examined was seen to alter from region to region. However the efficiency was seen to be very low, although no ants were present where in fact the Aleurodicus disperses test were collected, the effectiveness of the Nephaspis bicolor was as low as for the Exochomus laeviusculus. Coccinellid are far better when several of them are present, for a competent natural control using ladybugs, a higher population must be available and retained in the field throughout the crop cycle on which the pest is present. When no food is present, the ladybug beetle will tend to move away to some other area where in fact the pest exists or find another sources of food in order for the coffee lover not starve to death. Only if a few are present, they will only prey on a fewer amount of pests, making no differences to the pest population, also, they might get eaten up by parrots or lizards present on the field. However both the ladybugs examined are unbiased to the climatic factor present in the regions where they were gathered (P > 0. 05). This means that the locations from which these were collected does not have an effect on their efficacy.

Another facet of IPM for sustainable pest control would be the use of biopesticides, such as microbial pesticides and botanical pesticides. Only 32% of all the planters interviewed know about the availability of this type of pesticide. Many of them think they are expensive and ineffective. However, since biopesticides aren't manufactured locally, the price tag on the biopesticides is almost the same as for chemical pesticides. That is a reason why planters would prefer to buy chemical pesticide and don't take the risk of purchasing something they aren't sure about. Planters also think it is troublesome to prepare their own botanical pesticides using locally available plant life such as neem and citronella plus much more. Botanical pesticides do not damage the surroundings and the efficiency of natural enemies will be sure to be boosted if more planters adopt the utilization of biopesticides.

Another interesting observation made while control the results obtain. It was that the efficacy of natural foes evaluated in the different agro ecological areas selected does not change greatly. The efficacies are in the number of 15. 8% to 20. 2% respectively. It can be figured the natural foes evaluated have a good adaptability to the local climate, which really is a major characteristic for being a good natural adversary as failure to adapt to the climate and environmental factors is one of the factors in natural control inability. Nevertheless, it is detected the average efficiency is lower in very humid regions compared to sub humid regions. As mentioned early on, this might be because of the methods of the planters on the farm and also the difference in temps, causing changes in both natural opponent and the sponsor pest's phenology.

In crops producing fields in Mauritius, it was deducted that the use of natural foes works well to certain degree, however, not as effective to be able to control a infestations by themselves. This is the case in every area investigated whatever the land use diversities. The land use can also prove to be very identifying in biological control. An example is the pest Aleurodicus disperses, the sample (CO5) was gathered in Vacoas where the citrus trees were in a field located in a domestic area. The trees were found on the road aspect and were heavily infected near the stem and underneath the leaves. The beetle Nephaspis bicolor was scarce and incredibly difficult to count. On the other hand, sample CO8 of Aleurodicus disperses was gathered at Ripailles, the trees were within a field encircled by other vegetable fields and sugarcane. The tree was abundant with ladybug inhabitants, and the beetle Nephaspis bicolor could be easily accumulated. This shows that land use and vegetative cover comes with an impact on the presence of natural foes. For instance, maize areas have a positive influence on ladybug density present and thus, this explains the low pesticide utilization in maize vegetation (Zhou, 2014). Vegetative covered areas provide food and shelter for natural foes. An area of high vegetative cover will generally have greater densities of natural enemies compared to a region of low vegetative cover or bare land without vegetation by any means. Other vegetation or trees and shrubs have skills to attract some natural foes, so planting those trees on the field will tend to enhance biological control. Some farmers, especially large level farmers often wipe out their field to remove everything left after harvesting, this is an extremely bad strategy if we wish biological control to achieve success. With no vegetation to provide shelter, the beneficial organisms will tend to move to another habitat or perish out.

A good monitoring schedule must be setup in order to ensure the status of natural enemies and their effectiveness must be examined regularly. That is mainly to make certain that natural control is going on well and whether individuals intervention is required to provide a increase to the natural opponents in order to increase their performance. However, nothing of these appear to be there on the field where the evaluations were completed. Although a good method of foreign exploration and release of natural foes were done by local organisations, no more monitoring programs are carried out.

In some areas of the country, for example Saint Martin, Surinam and Belle Mare, in all which a pest sample was gathered, several small planters can be found advertisement a few large scale planters. Their field are close to each other and can be put together together to form a very large area for crop development. The efficiency of the respective natural foes was very low compared to the areas. The reason why might be because every single farmer makes use of their own kind of pesticides in their own private ways. And pesticides being put on such a sizable area will surely cause toxicity to the land and water resources found close by. Such a big amount of pesticide program decreases the density of the available natural foes. Less natural enemy density and failure to replicate will lead to a fewer amount of parasitized or preyed infestations.

Ladybug beetles have a tendency to be very good infestations destroyer as both larvae and men and women are voracious eater. However, a very interesting observation was made on a papaya tree infested with mealy insects. Several types of ladybugs were present on the tree. Some abnormal activities were discovered. A ladybug larva was seen feeding on another ladybug larva which was of an different species. Cannibalism may also be considered a factor of low effectiveness among coccinelid. This is an issue of host specificity and competition among pest predators. Regarding the parasitoids assessed no instances of hyperparasitism, multiparasitism or superparasitism was detected.

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