Differential parasitism of native and invasive widow spider egg sacs

During colonization, invasive species establish and spread to new locations, where they may have an advantage over native species. One such advantage may be avoidance of predators or parasites by means of better defences or due to lower suitability as a host. We conducted field surveys and lab behavioural experiments to investigate the differential susceptibility of two widow spider species—one native to Israel, the white widow spider Latrodectus pallidus, and one invasive species, the brown widow spider, Latrodectus geometricus—to an egg sac parasitoid wasp, Philolema latrodecti. In collections of egg sacs from six paired sites of L. geometricus and L. pallidus populations in the Negev Desert, Israel, we found higher parasitism rates on the egg sacs of the native L. pallidus. In no-choice trials, we found that wasps were more likely to parasitize and oviposited longer on L. pallidus egg sacs than on L. geometricus egg sacs. In two-choice tests with spider webs and egg sacs, parasitoids made first contact with L. pallidus webs more often and faster. After developing inside of L. pallidus egg sacs, more parasitoids emerged and were larger than those emerging from L. geometricus egg sacs. Potentially better defence of the L. geometricus egg sacs as well as the parasitoid’s fitness advantages gained from parasitizing L. pallidus egg sacs may explain the higher parasitism rate in the native species. Our results suggest that the invasion and establishment success of L. geometricus is due, in part, to its ability to escape parasitism.

Methods
These data are of field collections to determine parasitism rate by Philolema latrodecti of Latrodectus pallidus and Latrodectus geometricus egg sacs from six paired sites in the Negev Desert, Israel. Data of laboratory observations of P. latrodecti behaviours and parasitism in no-choice and choice tests are included, as well as parasitoid development, emergence, and body size. The data are raw values from lab observations and measurements.

在生物入侵过程中，外来入侵物种可在新定殖区域建立种群并扩散，且往往相较于本地物种具备竞争优势。这类优势的来源之一，便是通过更完善的防御机制，或是作为宿主的适宜性更低，从而规避天敌或寄生虫的侵染。

本研究针对两种寇蛛属（Latrodectus）蜘蛛——以色列本地种白寡妇蜘蛛（Latrodectus pallidus）与入侵种褐寡妇蜘蛛（Latrodectus geometricus）——对卵囊寄生蜂（Philolema latrodecti）的易感性差异，开展了野外调查与室内行为学实验。在以色列内盖夫沙漠的6组配对样地中采集两种蜘蛛的卵囊后发现，本地种L. pallidus的卵囊寄生率显著更高。无选择试验中，寄生蜂更倾向于在L. pallidus的卵囊上完成寄生，且产卵时长更长；双选择试验（同时提供蛛网与卵囊）中，寄生蜂首次接触L. pallidus蛛网的频率更高、耗时更短。相较于从L. geometricus卵囊中羽化的个体，在L. pallidus卵囊内发育的寄生蜂羽化数量更多、体型也更大。

褐寡妇蜘蛛卵囊可能具备更强的防御能力，且寄生本地种卵囊可让寄生蜂获得适合度优势，这或可解释本地种更高的寄生率。本研究结果表明，褐寡妇蜘蛛的入侵定殖成功，部分源于其能够有效规避寄生蜂的寄生。

## 方法
本数据集包含两类数据：一是野外采集所得的寄生率数据，样本为采自以色列内盖夫沙漠6组配对样地的L. pallidus与L. geometricus卵囊；二是室内观测得到的P. latrodecti行为与寄生相关数据，涵盖无选择试验、选择试验结果，以及寄生蜂的发育、羽化情况与体型测量数据。所有数据均为实验室观测与测量得到的原始数值。