Intricate predatory decisions by a mosquito-specialist spider from Malaysia

Abstract

Paracyrba wanlessi is a southeast Asian jumping spider (Salticidae) that lives in the hollow internodes of fallen bamboo and preys on the larvae, pupae and adults of mosquitoes. In contrast to Evarcha culicivora, an East African salticid that is also known for actively targeting mosquitoes as preferred prey, there was no evidence of P. wanlessi choosing mosquitoes on the basis of species, sex or diet. However, our findings show that P. wanlessi chooses mosquitoes significantly more often than a variety of other prey types, regardless of whether the prey are in or away from water, and regardless of whether the mosquitoes are adults or juveniles. Moreover, a preference for mosquito larvae, pupae and adults is expressed regardless of whether test spiders are maintained on a diet of terrestrial or aquatic prey and regardless of whether the diet includes or excludes mosquitoes. Congruence of an environmental factor (in water versus away from water) with prey type (aquatic versus terrestrial mosquitoes) appeared to be important and yet, even when the prey were in the incongruent environment, P. wanlessi continued to choose mosquitoes more often than other prey.

Keywords: Spartaeinae; mosquitoes; perception; predatory specialization; prey preference; prey-choice behaviour.

Figure 1.

Lures made from the larvae and pupae of mosquitoes, showing how these prey types were mounted on cork discs. (a) Anopheles larva, mounted ventral side up, with head rotated 180°. (b) Culex larva, mounted in a head-down, almost-vertical posture, with the ventral surface of the larva's last abdominal segment on the top of the cork disc. (c) Culex pupa, mounted with the anterior ventral surface on top of the cork disc.

Figure 2.

(a) Apparatus used in prey-choice experiments when lures were in water and (b,c) when lures were away from water. Start of test: test spider in predator chamber and walks down to prey chamber. (c) Prey chamber sat inside a pit on top of a wooden platform. Two lures were present at any one time, and lures were moved during the test by using a sine-wave generator connected to a coil situated underneath the platform (held with a plastic stand; not shown). End of test: test spider attacks lure.

Figure 3.

Results from testing P. wanlessi with adult females of C. quinquefasciatus and a variety of non-mosquito terrestrial prey. Prey: lures presented to test spiders away from water. Simultaneous-presentation testing: n=30 for each pair of prey types (except when testing with Culex and mirid: n=25). Alternate-day testing: n=35. (a) All test spiders had been maintained on the standard terrestrial diet (no experience with mosquitoes; see table 2). (b) All test spiders had been maintained on a diet of C. capitata and unidentified Baetidae (no experience with mosquitoes or midges).

Figure 4.

Results from testing P. wanlessi with adult females from three mosquito species, A. aegypti (culicine), A. gambiae (anopheline) and C. quinquefasciatus (culicine). Mosquitoes either had received a blood meal or had been fed only sugar (glucose solution). All test spiders had been maintained on the standard terrestrial diet (no experience with mosquitoes; see table 2). Prey: lures presented to test spiders away from water. Simultaneous-presentation testing: n=60 for each pair of prey types. Alternate-day testing: n=35 for each pair of prey types.

Figure 5.

Results from simultaneous-presentation testing of P. wanlessi with adult females and adult males from three mosquito species: A. aegypti (culicine), A. gambiae (anopheline) and C. quinquefasciatus (culicine). All test spiders had been maintained on the standard terrestrial diet (no experience with mosquitoes; see table 2). Prey: lures presented to test spiders away from water. n=60 for each pair of prey types.

Figure 6.

Results from testing P. wanlessi with adult females from three mosquito species: A. aegypti (culicine), A. gambiae (anopheline) and C. quinquefasciatus (culicine). All test spiders had been maintained on the standard terrestrial diet (no experience with mosquitoes; see table 2). Prey: lures presented to test spiders away from water. Simultaneous-presentation testing: n=60 for each pair of prey types. Alternate-day testing: n=35 for each pair of prey types.

Figure 7.

Results from testing P. wanlessi with larvae and pupae of C. quinquefasciatus. All test spiders had been maintained on the standard aquatic diet (no experience with mosquitoes; see table 3). Prey: lures presented to test spiders in water. Simultaneous-presentation testing, n=60; alternate-day testing, n=35.

Figure 8.

Results from testing P. wanlessi with larvae or pupae from three mosquito species: A. aegypti (culicine), A. gambiae (anopheline) and C. quinquefasciatus (culicine). All test spiders had been maintained on the standard aquatic diet (no experience with mosquitoes; see table 3). Prey: lures presented to test spiders in water. Simultaneous-presentation testing: n=60 for each pair of prey types. Alternate-day testing: n=35 for each pair of prey types.

Figure 9.

Results from testing P. wanlessi with larvae or pupae of C. quinquefasciatus and with baetid naiads. All test spiders had been maintained on the standard aquatic diet (no experience with mosquitoes or with baetids; see table 3). Prey: lures presented to test spiders in water. Simultaneous-presentation testing: n=60. Alternate-day testing: n=35 for each pair of prey types.

Figure 10.

Results from simultaneous-presentation testing of P. wanlessi with larvae of C. quinquefasciatus and a variety of non-mosquito aquatic prey. All test spiders had been maintained on the standard terrestrial diet (no experience with mosquitoes or with any other aquatic prey; see table 2). Prey: lures presented to test spiders in water. n=25 for each pair of prey types.

Figure 11.

Results from testing P. wanlessi with two prey types: one, but not the other, being in its normal location (in or away from water). Test spiders had been maintained on the standard terrestrial diet (no experience with mosquitoes; see table 2). Prey: lures presented to test spiders. (a) Culex quinquefasciatus larvae or pupae paired with C. quinquefasciatus adult females. Both prey away from water. Simultaneous-presentation testing: n=60 for each pair of prey types. Alternate-day testing: n=35. (b) Anopheles gambiae larvae paired with A. gambiae adult females, and C. quinquefasciatus larvae or pupae paired with C. quinquefasciatus adult females. Both prey in water. Simultaneous-presentation testing: n=60 for each pair of prey types.

Figure 12.

Results from alternate-day testing of P. wanlessi with prey that were presented in water on one day and away from water on the other day. All test spiders had been maintained on the standard terrestrial diet (no experience with mosquitoes, baetids or spiders; see table 2). (a) Larvae or adult females of C. quinquefasciatus (n=45 for each pair). (b) Adult females of C. quinquefasciatus and Argyrodes sp. or baetid naiads (n=45 for each pair of prey types, except that n=35 when baetid naiads were away from water).