ABSTRACT

Anthonomus santacruzi Hustache (Coleoptera: Curculionidae) was released in South Africa in 2008 to curb the spread of the invasive alien weed Solanum mauritianum Scopoli (Solanaceae) and is widely established in warmer regions. In KwaZulu-Natal Province (KZN), where S. mauritianum populations are particularly abundant, weevil populations display seasonal peaks in autumn, thrive at coastal locations, but barely persist at colder inland locations. Besides substantial winter declines and poor compatibility with colder areas, native parasitoids may be constraining weevil populations. In this study, A. santacruzi populations were surveyed during late summer at six coastal and three inland sites in KZN to determine the levels of parasitism. Also, weevil population densities were compared with those recorded during post-release surveys conducted since 2015. Parasitoid recruitment was negligible, with <1% of weevil-infested buds parasitised. Significant differences in A. santacruzi numbers between 2016, 2018 and 2020 across the same nine sites were due to lower numbers in 2020, as a result of earlier sampling (i.e. two months before the autumn peak) than in preceding years. Four sites that were sampled during late summer in 2015 displayed significant increases in weevil abundance, but significant decreases in floral and fruit production, over the six years preceding 2020. The significant negative correlation between weevil densities and fruiting, across all sites surveyed between 2015 and 2020, suggests some impact, albeit moderate, on the weed’s reproductive output. Climatic limitations rather than recruited parasitoids are currently limiting the distribution and densities of A. santacruzi in KZN.

摘要

Anthonomus santacruzi Hustache（鞘翅目：仙茅科）于 2008 年在南非被释放，以遏制外来入侵杂草Solanum mauritianum Scopoli（茄科）的传播，并在较温暖的地区广泛种植。在夸祖鲁-纳塔尔省 (KZN)，S. mauritianum种群特别丰富，象鼻虫种群在秋季出现季节性高峰，在沿海地区茁壮成长，但在较冷的内陆地区几乎不存在。除了冬季大幅下降和与寒冷地区的兼容性差之外，本地寄生蜂可能会限制象鼻虫种群。在这项研究中，A. santacruzi夏末在 KZN 的六个沿海和三个内陆地点对种群进行了调查，以确定寄生水平。此外，将象鼻虫种群密度与自 2015 年以来进行的发布后调查期间记录的密度进行了比较。 寄生蜂的招募可以忽略不计，被寄生的象鼻虫感染的芽不到 1%。A. santacruzi 的显着差异2016 年、2018 年和 2020 年之间相同 9 个地点的数字下降是由于 2020 年的数字较低，这是由于采样时间比前几年提前（即秋季高峰前两个月）。在 2015 年夏末采样的四个地点显示，在 2020 年之前的六年中，象鼻虫丰度显着增加，但花卉和果实产量显着下降。 2015 年至 2015 2020 年，表明对杂草的繁殖产量有一些影响，尽管是温和的。气候限制而不是招募的寄生蜂目前限制了A. santacruzi在 KZN的分布和密度。