Tue Jun 24, 2014

by Rafique Bailey Ph.D. Entomology

Introduction

Hibiscus Mealy Bugs (HMB) are widespread throughout St Vincent; they are found on soursops, sugar apple, sorrel, okra, peanuts, guavas, bananas, plantains and their primary host Hibiscus spp. They can even attack forest trees such as the Blue Mahoe (Hibiscus elatus), Samaan (Samanea saman), Teak (Tectona grandis) and Gliricida spp., and as ocurred in Grenada and Trinidad in the recent past, many Blue Mahoe and Samaan trees have been killed from high infestations of HMB and by efforts to control this pest (Sagarra and Peterkin, 1999).{{more}}

The pest has about 200 hosts and is native to Asia, and was first detected in the Western hemisphere in Grenada in 1994. From there it spread to four Caribbean islands in 1995, seven islands in 1996, 17 islands in 1997, 20 islands in 1998, 21 islands in 1999 and 27 islands presently (Sagarra and Peterkin, 1999).

Female mealy bugs usually deposit 80 to 654 eggs in between four and eight days. The eggs hatch within three to nine days and a cycle is completed within a month. Newly hatched mealy bugs (crawlers) are highly mobile and are responsible for the high colonization rate of this insect. They move around until they find a suitable site on the plant or fruit, settle and start developing (Sagarra and Peterkin, 1999).

Some of the symptoms of mealy bug infestation include malformation of new shoots and leaves. Other symptoms include leaf curling, fruit malformation and bunchy top appearance due to shortening of the internodes. In heavy infestations, the plant can become completely defoliated leading to death. It can also cause sooty mold to develop on the leaves, thereby inhibiting photosynthesis. See Figures 1 and 2 of soursop fruits at Arnos Vale, St Vincent, infested with the Hibiscus Mealy Bug.

So, what are the economic costs of having this pest in our country? In 1997, USDA estimated that the economic losses exceeded US $3.5 million per year in Grenada and US $125 million per year in Trinidad and Tobago before control measures were implemented. An economic study conducted by L. Joe Moffit (1999) from the University of Massachussets showed that the economic risk to United States agriculture in the event of the invasion of the Hibiscus Mealy Bug is estimated to be approximately US $750 million per year in the absence of control measures (Sagarra and Peterkin, 1999). In St Vincent, there is clearly a resurgence of this pest; we have seen losses estimated to be in the thousands of dollars for March and April 2014, from the rejection of over 2,000 boxes of plantains and bananas shipped to Trinidad and Tobago. Trade in fresh fruits, vegetables and ornamental plants could also be affected if the population of HMB is not brought under control.

So, what have we learnt from our first encounter with the Hibiscus Mealy Bug? We know that it is an extremely invasive pest and because it was introduced without its natural enemies, its population exploded in most of the islands of the Caribbean causing tremendous losses to agriculture, forestry and horticulture in the affected countries. We know that the communication plan at the time was to spray, cut and burn; this did not go down well with some people because they did not want to cut down their beautiful hibiscus fences. We also know that chemical control did not work effectively as mealy bugs are protected by a waxy cuticle and they hide in small, hard to reach places on the plant. Therefore, populations re-emerged with more vigour two to three weeks after spraying (Sagarra and Peterkin, 1999).

We also learnt that Regional Biological Control Programs were initiated in several of the affected islands, with assistance from FAO, CABI Bioscience, CARDI, USDA and INRA. This proved to be the most effective method of controlling the HMB and it involved the introduction of the predatory beetle Cryptolaemous montrouzieri Mulsant and the parasitic wasp Anagyrus kamali Moursi. The following table shows the number of beetles that were released in some of the main Caribbean countries affected by HMB.

Source: Sagarra and Peterkin, 1999

The general strategy used for release of these biological control agents has been to release C. montrouzieri beetles when populations of mealy bugs are high. This is because a single predatory beetle can consume between 3,000-5,000 mealy bugs during its life time, and it is functionally more effective at high densities. On the contrary, introducing both species simultaneously may interfere with each other’s effectiveness, because the predator C. montrouzieri may feed on the parasitized stages of the Hibiscus Mealy Bug. The best practice would therefore be to first introduce the predator C. montrouzieri when the population of HMB is high and as the population of HMB decreases, the parasitoid A. kamali should be released to give a more sustainable and long-term control. In the case of St Vincent, a quantity of 85, 416 C. montrouzieri beetles were released and 25, 330 A. kamali parasitoid (Sagarra and Peterkin, 1999). It is reasonable to believe that because of the heavy use of pesticides in agriculture and horticulture, along with abiotic factors such as temperature and humidity, that most of these beneficial insects would have been destroyed over time. It is therefore necessary to restart a Classical Biological Control Program and to develop an effective communication plan for St Vincent to avoid farmers from spraying chemicals where biological agents have been released.

Conclusions

Invasive Alien Species (IAS), along with climate change are the two most important threats to our agriculture/fisheries sector, as well as our endemic biodiversity. These foreign species not only impact our ecosystems, but also affect the economy and trade. The experience gained from the biological control of the Hibiscus Mealy Bug in the Caribbean provides a model for future management of other IAS in the region. In this regard, why are the relevant Ministries of Government operating like it is business as usual? Why are there no serious efforts at public sensitization about IAS issues when there is lurking on the horizon Frost Pod Rot that affects cocoa (present on southern side of Venezuela), Red Palm Mite that affects coconuts (present in St Lucia), Giant African Snail that affects a wide range of crops (present in St Lucia) and Fusarium Wilt Tropical Race 4 that is devastating to Cavendish bananas (Asia, Middle-East and Africa)?