Is Elytral Color Polymorphism in Sweetpotato Weevil (Coleoptera: Brentidae) a Visible Marker for Sterile Insect Technique?: Comparison of Male Mating Behavior

Abstract

The sterile insect technique (SIT) is widely used for suppressing or eradicating target pest insect populations. In the eradication programs using the SIT, a large number of sterile insects are marked and released in the field. In Japan, Cylas fonnrmicarius (F.) group (Coleoptera: Brentidae) weevils are marked with a fluorescent powder dye to monitor the progress of such programs. However, this monitoring technique is not fully effective because of the disappearance or contamination of the dye. Therefore, an alternative marking method is required. Currently, a rare color morph such as piceous elytra (PE) is used for visible marking of C. formicarius group weevils. A PE-monomorphic strain has previously been established by artificial selection from a small locally distributed population; this can lead to reduced survival and genetic changes in behavioral traits due to inbreeding depression. In this study, we evaluated the survival rate and mating behavior of PE males of C. formicarius group. The characteristics of the PE males were similar to those of the wild strain (WS) males. Thus, we considered that PE males were suitable for visible marking in the eradication programs using the SIT.

First case of successful eradication of the sweet potato weevil, Cylas formicarius (Fabricius), using the sterile insect technique

“…The scarcity of the PE morph in the field is an advantageous factor when used as phenotypic maker for visible marking of sterile C . formicarius weevils during SIT application [ 39 , 45 ]. Therefore, from January 2010 to the later stage of this eradication program, the PE strain was used as a visible marker to mitigate any contamination or detachment of the powder markings.…”

“…Therefore, from January 2010 to the later stage of this eradication program, the PE strain was used as a visible marker to mitigate any contamination or detachment of the powder markings. The mating performance, survival, and dispersal ability of the PE males that were mass-reared in OPPPC did not differ from those of WS mass-reared males [ 39 , 40 ].…”

Eradication of sweetpotato weevil, Cylas formicarius, from Tsuken Island, Okinawa, Japan, under transient invasion of males

“…The establishment of efficient mass‐rearing strains for sterile insects is essential for the successful progress of the SIT (Parker et al, 2021). At the beginning of the project, a weevil with a bluish elytra colour morph, which is commonly observed in wild populations in Okinawa (Kawamura et al, 2005, 2009; Shiromoto et al, 2011, 2012), was employed as the mass‐reared strain (hereafter called wild strain; WS). The WS originated from adults collected at Yomitan Village, Okinawa Island, Japan (26°39′N, 127°74′E), in October 1997.…”

“…The founder population size was ~10,000 individuals. The WS were marked by a fluorescent powder dye (0.1 g/10,000 individuals) (Braze Orange; DayGlo Color Corp.) before release to distinguish them from wild insects when they were captured (Kawamura et al, 2009;Shiromoto et al, 2011Shiromoto et al, , 2012. However, the fluorescent dye can dissipate or be transferred to wild insects, causing misidentification of both wild and sterile individuals (Kawamura et al, 2009;Shiromoto et al, 2011;Shiromoto et al, 2012;Parker et al, 2021;Himuro et al, unpubl data).…”

“…The PE was established by a male and female adult collected at Yonaguni Island, Japan (24°28′06″N, 123°00′17″E) in July 2007, and a female adult with a piceous elytra colour morph obtained from the WS. Survival rate, mating duration and mating competitiveness are not significantly different between the WS and the PE (Shiromoto et al, 2011). with mesh lids, and ~1,800g of sweet potato root tubers were provided as the egg-laying substrate and food.…”