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14 June 2019 Does Prior Feeding Behavior by Previous Generations of the Maize Weevil (Coleoptera: Curculionidae) Determine Future Descendants Feeding Preference and Ovipositional Suitability?
Charles J. Stuhl
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The maize weevil Sitophilus zeamais (Motschulsky) (Coleoptera: Curculionidae) is an important pest of stored grains, predominantly corn (Zea mays), wheat (Triticum spp.), rice (Oryza spp.), and sorghum (Sorghum bicolor) (all Poaceae). In Africa, post-harvest grain losses of maize amounts to about US $4 billion annually, with an estimate of 10 to 88% loss of maize due to stored grain pests (FAO 2010; Ojo & Omoloye 2012). Current control methods are the application of an insecticide, cultural practices, and the development of resistant grain. Unfortunately, there is no effective trapping system for control of the maize weevil. Previous studies have indicated that the odors associated with the grains upon which the weevils feed, mate, and oviposit are known to be attractive. To better understand this behavior, a study was developed to investigate the weevil's attraction to dry grains with and without the presence of the commercial pheromone lure. The weevil's ability to develop on specific grains also was investigated. The weevils were reared on 4 types of grain to determine, if presented a choice, whether they would prefer the grain upon which their parents and they themselves fed as larvae. This research demonstrates that previous feeding did not influence the weevil's attraction to a certain grain. The isolation of key corn semiochemicals should be the focus in the development of an attractant for S. zeamais. These findings eliminate the need to develop individualized attractants that would have to be tailored to weevils feeding upon specific hosts.

Sitophilus zeamais (Motschulsky) (Coleoptera: Curculionidae), known as the maize weevil, are serious pests of stored grains worldwide, with the association between weevils and human food dating back about 10,500 yr (Obata et al. 2011). Both adults and larvae can survive on a wide variety of food substances but are known as a pest species primarily from their infestations of corn (Zea mays L.; Poaceae), wheat (Triticum spp.; Poaceae), rice (Oryza spp.; Poaceae), and sorghum (Sorghum bicolor [L.] Moench; Poaceae). These pests not only affect stored grains, but also infest grains prior to harvest (Ni et al. 2011; Vyavhare & Pendleton 2011). As such, new infestations in storage facilities occur after each harvest. In grain storage facilities, control of these weevils usually is done by application of insecticides when loaded into silos, or as a surface treatment after storage (Arthur & Throne 2003). The female weevil chews a hole in the grain and lays an egg inside the kernel. The hole is then sealed with a waxy secretion that creates a plug. This hardens, sealing the hole in the seed to protect the egg. The egg hatches and the larva consumes the valuable commodity. At the end of the life cycle, an adult weevil emerges from the grain. Control of this pest must be directed at the adult due to the immature's development within the grain, protected from pesticide exposure (Walgenbach et al. 1983). However, consumer preference, pesticide deregulation, and resistance have reduced the use of such treatments, making alternatives to chemical pesticides necessary (Vyavhare et al. 2018).

The attraction of insects to plants and other host organisms involves detection of specific semiochemicals, more notably specific ratios of semiochemicals. The isolation of these odors can be used as attractants for the control and monitoring of pest populations (Norin 2007). Male- and female-produced insect pheromones have been successfully isolated and are used for mating, aggregation, defense, and host recognition (El-Sayed et al. 2006). Male-produced sex attractants are referred to as aggregation pheromones, because they typically attract both sexes and have been reported in many species of Coleoptera, Dictyoptera, Hemiptera, and Orthoptera (Landolt 1997). The aggregation pheromone for the rice weevil, Sitophilus oryzae Schoenherr (Coleoptera: Dryophthoridae) and maize weevil, (4S, 5R)-5-hydroxy-4-methylheptan-3-one, has been identified (Phillips et al. 1985) and is currently used as the attractant for traps in indoor applications, particularly in household pantries. However, there is little information on the use of the pheromone for monitoring and control in large grain storage facilities or in the field. Additionally, little is known about the host produced volatiles that attract the maize and rice weevils. Therefore, there is a need to develop more effective semiochemical based attractants for these pests. For instance, the identification of the sex and aggregation pheromones for the boll weevil, Anthonomus grandis (Boheman) (Coleoptera: Curculionidae), played a crucial role in successful implementation of the boll weevil eradication program (Tumlinson et al. 1969). It has been shown that the pheromone, in combination with the green leaf volatile trans-2hexen-1-ol, enhanced pheromone trap captures. It also increased trap capture by extending the longevity of attractiveness of pheromone-baited traps. (Dickens 1989). This dynamic has been shown in many trapping systems for Coleoptera, such as the boll weevil. The synergistic effect of a sex or aggregation pheromone in conjunction with a host volatile (food or oviposition) greatly enhances attraction (Bartelt & Dowd 1991). Insect produced pheromones and host plant odors assist conspecifics for mating and locating feeding and oviposition sites. Aggregation pheromones for trapping are useful because both sexes may be captured in the trapping device (Burkholder 1990; Sato & Touhara 2008). The male boll weevils locate their host plant, feed, and then release an aggregation pheromone in their frass (Tumilson et al. 1969).

In insects, the location of a mate or a food source is dependent upon olfactory information. Their highly specialized structures can detect compounds with a high sensitivity, and initiate a behavioral response to the olfactory message received (Martin et al. 2011). These specialized structures allow phytophagous insects to selectively feed only on a limited number of plant species or generalist feeding on a diverse range of plants in many families