New Records of Mealybugs on Sprouted Potatoes in Storage at Kulumsa, South East Ethiopia - A Potential Future Threat for Potato Production

Potato has lived with several diseases and insect pests such as late blight and potato tuber moth for several decades. However, newly emerging insect pest known by the name 'mealybug' is recorded as a new threat for potato production in the highlands of Arsi, Southeast Ethiopia. This pest has never been observed in the area in the history of potato culture in which potato has been grown for many years. Therefore, awareness creation should be the primary step by which any respective stakeholders including potato growers, research institutions, ministry of agriculture; NGOS, etc. are informed about the importance of the pest. This will help to look for appropriate management options and take the necessary precautions before the pest becomes important in other areas in the country.

before the pest becomes a potential threat for potato production.

What did we observe in the potato store (DLS)?
The pest was not appearing on fresh tubers when it brought in to the store after harvest. However, it came into view later 4-5 month of storage when tubers were sprouting. The level of the infestation has increased with time as the pest multiplied rapidly feeding on the sap from sprouts. The insect had white mass of cottony like cocoon which appeared in different developmental stages (instars) having different body sizes ( Figure 1A). Adult Mealybug bodies are distinctly segmented and usually covered with wax. Older individuals may have wax filaments around their body margins. In some species the filaments are longer in the rear and can be used to help distinguish between different species. The pest forms white mass of thread like web on the surface of the sprouts, which is probably the protective case where the females lay their eggs inside ( Figure 1B). It is more likely to see high population of the pest on the sprouted tubers placed in piled thick layers as the pest likes to feed in colonies usually between tuber touches in protected areas. Besides, it was not uncommon to see honey dew like fluid on the surface of the tubers where the infestation was severe ( Figure 1D). In a bad infestation, their waxy excretions (also known as honeydew) encourages the development of sooty mold fungus which later causes tubers rotting. ( Figure 1C). From our observation, we could speculate that the pest can overwinter in the store hiding under barks and between touches of wooden materials used to construct the store and also on the underside of plastic boxes used to temporarily store and transport tubers ( Figure 2). Hence, there is high chance for the pest to make re-infestations in the stores whenever stored potatoes are sprouting and the environment is favorable.

Possible sources of the pest
It is still unclear whether the sources of the pest could either be from the field or the store itself. There should be some possible sources which we may probably suggest from our observation. Since the pest is less mobile and does not move long distance, the more likely source could be from seed tubers which are usually come from other places since there is always movement of seed tubes between research centers to exchange planting materials (sprouted tubers) for research purposes. Hence, it could be a suitable means by which the pest could move easily from one place to another and cause such kind of infestation in areas where the pest has never been before.
Journal of Biology, Agriculture and Healthcare www.iiste.org ISSN 2224-3208 (Paper) ISSN 2225-093X (Online) Vol.10, No.11, 2020 Figure 2. The underside of a plastic box, used to temporarily store and transport potato tubers from field to stores and vice versa. The pest uses to hide on the edges of the boxes until the next infestation. The arrows indicate the young of the pest hiding on the underside of the box.
The other likely source could be different plant harvests other than potato tubers which might bring the pest into the store. Since Mealybugs have a wide host range, it may come to the potato store with samples of different plant harvests, such as pumpkins, garlic, onions, shallots, seed spices, etc., which are temporarily kept in the stores.
It has been recorded from 154 plant species including field crops, vegetables, ornamentals, weeds, bushes and trees (Arif et al., 2009;Saini et al.,2009). Most of these belong to the family Malvaceae, Solanaceae, Asteraceae, Euphorbiaceae, Amaranthaceae and Cucurbitaceae, however, the economical damage has been observed on cotton, okra, tomato, sesame, sunflower and China rose (Arif et al., 2009).The oleander Mealybug, Paracoccus burnerae (Brain), occurs from Kenya to South Africa and attacks approximately 35 species of plants, including important food and beverage crops such as potatoes, olives and coffee (www.sel.barc.usda.gov/scalenet/scalenet.htm) (Johnson and Giliomee, 2011). Butternut, pumpkins and sprouting potatoes have been found to be suitable substrates for the mass rearing of various Coccoidea (Blumberg and Swirski, 1977;Elder and Smith, 1995), the super family to which Mealybugs belong. The Mealybug is a significant pest of many tropical and subtropical fruits, vegetables, and ornamental plants (Miller and Miller, 2002), and it has a wide host range, including Carica papaya L.  (Walker et al., 2006).

What measures were taken?
Since the infestation was accidental and occurred with no control options at hand, the first measure was to consult entomologist and take whatever possible options available so as to contain the pest in the store and prevent it from spreading to other areas. Hand picking and sanitation were the first measures undertaken to minimize the scale of the infestation and prevent it from spreading within the stores itself. Since there were no any research recommended insecticides at hand at the time of the outbreak, the only option other than hand picking and sanitation was to spray systemic insecticides such as Karate and Profit with a perception that Mealybugs are sap feeding insects. In addition, contact insecticide (Endosulfan) was applied in the storage to make sure that any harboring Mealybugs which are left on and between the wooden surfaces of the store are killed so as to minimize/ or avoid the next infestation. The measures helped at least to stop the pest from multiplying and spreading to healthy tubers within the store. Sooty mold funguses were developed on seed tubers severely infested by the pest ( Figure 1C) and were discarded from the store and buried in the soil. been rated as a major pest, since they play a dual role as pest and vector in field crops. During the last few decades, the Mealybugs, Rhizoecus amorphophalli has emerged as anxious pest infesting on stored tubers of elephant foot yam, taro and tannia (Palaniswami and Pillai,1979;Rajamma et al,. 2002Rajamma et al,. , 2006. This pest is also suspected as a vector of plant diseases (Culik and Gullan, 2005) and has a wide range of variation in morphological characters, biological adaptations and ecological adjustability (Hodgson et al.,2008). Integrated pest management of Mealybug could be the safest and cheapest method of pest control (Ahmad et al., 2003). However, the use of insecticides is inevitable to check the Mealybug outbreaks as compared to predators and parasitoids (McKenzie, 1967;Joshi et al., 2010). Several insecticides belonging to different groups have been documented as effective against potato tuber Mealybug.

Conclusion and recommendation
Since seed tubers are the basis for potato plant and determines the productivity of the crop, it has to be healthy and free from insect infestation such as Mealybugs. Since Mealybugs are less mobile insects, seed tubers are the most likely means by which the pest can be disseminated to other areas. Hence, there should be an assurance about the health of the seed before sourcing and transporting to other areas. As far as the pest is new in the area, it has to be studied immediately and look for appropriate measures. Verification of appropriate Mealybug management options from recommended packages and awareness creation among different stakeholders about the importance of the pest could be the primary assignment of the respective entomologists. Species identification should also be conducted side by side with the pest management efforts. Moreover, this could be an opportunity for other areas in the country to be aware that the pest is important and make the necessary precautions to avoid unnecessary movement of the pest from one area to another. We also recommend for the responsible government organizations to establish and thoroughly strengthen effective quarantine system to avoid the introduction of exotic insects like Mealybugs to our country and guarantee healthy agricultural production.