Mosquito Consumption by Insectivorous Bats: Does Size Matter?

Insectivorous bats have often been touted as biological control for mosquito populations. However, mosquitoes generally represent only a small proportion of bat diet. Given the small size of mosquitoes, restrictions imposed on prey detectability by low frequency echolocation, and variable field metabolic rates (FMR), mosquitoes may not be available to or profitable for all bats. This study investigated whether consumption of mosquitoes was influenced by bat size, which is negatively correlated with echolocation frequency but positively correlated with bat FMR. To assess this, we investigated diets of five eastern Australian bat species (Vespadelus vulturnus Thomas, V. pumilus Gray, Miniopterus australis Tomes, Nyctophilus gouldi Tomes and Chalinolobus gouldii Gray) ranging in size from 4-14 g in coastal forest, using molecular analysis of fecal DNA. Abundances of potential mosquito and non-mosquito prey were concurrently measured to provide data on relative prey abundance. Aedes vigilax was locally the most abundant mosquito species, while Lepidoptera the most abundant insect order. A diverse range of prey was detected in bat feces, although members of Lepidoptera dominated, reflecting relative abundance at trap sites. Consumption of mosquitoes was restricted to V. vulturnus and V. pumilus, two smaller sized bats (4 and 4.5 g). Although mosquitoes were not commonly detected in feces of V. pumilus, they were present in feces of 55 % of V. vulturnus individuals. To meet nightly FMR requirements, Vespadelus spp. would need to consume ~600-660 mosquitoes on a mosquito-only diet, or ~160-180 similar sized moths on a moth-only diet. Lower relative profitability of mosquitoes may provide an explanation for the low level of mosquito consumption among these bats and the absence of mosquitoes in feces of larger bats. Smaller sized bats, especially V. vulturnus, are likely to be those most sensitive to reductions in mosquito abundance and should be monitored during mosquito control activities.

食虫蝙蝠常被推崇为蚊虫种群的生物防治（biological control）手段。然而，蚊虫通常仅占蝙蝠饮食的极小比例。鉴于蚊虫体型微小、低频回声定位（echolocation）对猎物探测能力造成的限制，且蝙蝠的野外代谢率（field metabolic rates, FMR）存在差异，蚊虫可能并非所有蝙蝠都能获取，或是取食蚊虫无法为其带来足够的能量收益。
本研究探讨了蚊虫取食行为是否受蝙蝠体型影响——蝙蝠体型与回声定位频率呈负相关，而与野外代谢率呈正相关。为验证这一假设，本研究以澳大利亚东部沿海森林中5种体型跨度为4~14克的蝙蝠为研究对象，分别为Vespadelus vulturnus Thomas, V. pumilus Gray, Miniopterus australis Tomes, Nyctophilus gouldi Tomes及Chalinolobus gouldii Gray，通过粪便DNA分子分析对其饮食组成进行探究。研究同时测定了潜在蚊虫猎物与非蚊虫猎物的丰度，以获取猎物相对丰度数据。当地最优势的蚊虫物种为警觉伊蚊（Aedes vigilax），而鳞翅目（Lepidoptera）为最优势的昆虫目。蝙蝠粪便中检测到多种类别的猎物，其中鳞翅目昆虫占主导地位，这与诱捕站点的猎物相对丰度情况相符。
蚊虫取食行为仅见于两种小型蝙蝠：V. vulturnus（体重4克）与V. pumilus（体重4.5克）。尽管V. pumilus的粪便中极少检测到蚊虫，但55%的V. vulturnus个体粪便中均检出蚊虫成分。为满足夜间野外代谢率需求，仅以蚊虫为食的Vespadelus属蝙蝠需捕食约600~660只蚊虫，而仅以体型相近的蛾类为食时则仅需捕食160~180只。蚊虫相对较低的取食收益，可解释为何这些蝙蝠对蚊虫的取食频率较低，以及体型更大的蝙蝠粪便中完全未检出蚊虫成分。小型蝙蝠（尤其是V. vulturnus）很可能是对蚊虫丰度下降最为敏感的类群，因此在蚊虫防治活动中应重点对其进行监测。