The challenge of biological control of Cosmopolites sordidus Germar (Col. Curculionidae): A review

Abstract

With growing human populations in Africa, Asia and South America, securing food production in tropical areas is increasingly important. Banana ranks 2nd in fruit production worldwide (FAO, 2018) and along with plantains is an essential component of the nutrition of a large population. The most important pest of banana and plantain is the banana root borer Cosmopolites sordidus (Gold et al., 2001; Okolle et al., 2009). Females of this weevil lay eggs in the lower pseudostem and corm, and larvae develop in the corm. This weakens the plant and can lead to dramatic losses, both directly because of toppling and indirectly because of lower yields and increased infections by plant pathogens (Gold et al., 2001). Damage caused by C. sordidus is difficult to assess, however, because the immature stages of the weevil are hidden in the pseudostem and corm and their detection requires destructive sampling (Vilardebo, 1973). Furthermore, because the damage is not immediately visible and because C. sordidus effects are partly indirect, the full extent of C. sordidus damage is often underestimated until toppling occurs. The banana weevil can be described as a K-selected species (Pianka, 1970), with a long holometabolan development (almost two months; Vinatier et al., 2009), a low fecundity (two eggs per week; Vinatier et al., 2009) and an extended lifespan (up to 4 years (Gold et al., 2001)). With these features, C. sordidus differs from pests like aphids, flies or moths that are typically rselected species that generate damage because of their ability to rapidly produce large numbers of offspring (Williamson, 1996). However, K-selected species may also be important pests (Duyck et al., 2007). Its K-selected characteristics should have consequences for the biological control of C. sordidus. Because of its slow rate of

Caught on camera: Field imagery reveals the unexpected importance of vertebrates for biological control of the banana weevil (Cosmopolites sordidus Col. Curculionidae)

“…We found vertebrates rather than invertebrates to be predators of adult weevils, and previous research indicated that invertebrates (such as ants or earwigs) are likely to be predators of the egg and larval stages of the weevil [ 41 ]. However, it has been hypothesized that eggs only remain accessible for predation during a relatively short time because they are rapidly covered with leaking latex after oviposition [ 39 ].…”

“…We found that all the predated weevils were consumed by vertebrates, although reports of predation of C . sordidus by vertebrates had previously been considered anecdotal [ 39 , 41 ]. For the first time, we provide the evidence that rodents ( S .…”

“…Because of this arthropod bias, the role of vertebrates in the regulation of C . sordidus is considered anecdotal [ 41 ].…”

First Evidence of Feeding-Induced RNAi in Banana Weevil via Exogenous Application of dsRNA

“…Cultural methods of control include the use of clean planting material [12], hot water treatment [3], weevil traps [13], and field sanitation [14]. While there have been great successes in the use of natural enemies to control other weevils [15,16], there are limits to the use with banana weevils [17], which were described as poor candidates for biological control [18]. Although success was reported in Cuba using predatory ants Tetramorium guineense [19] and Pheidole megacephala [20], this was not achieved elsewhere [1,21].…”

“…The various attempts to control banana weevils using cultural, chemical, and biological methods [17] have not been very effective because they are labor-intensive [13], expensive, or not environmentally friendly [29], and this has remained a substantial problem for millions of farmers in Africa. Therefore, the best IPM strategy under the circumstances would be the use of host plant resistance in combination with cultural control methods highlighting the need for resistant cultivars.…”