Effects of habitat loss and fragmentation on the abundance and species richness of aphidophagous beetles and aphids in experimental alfalfa landscapes

Abstract

Abstract. In agro-ecosystems, habitat loss and fragmentation may alter the assemblage of aphidophagous insects, such as foliarforaging (coccinellids) and ground-foraging predators (carabids), potentially affecting intraguild interactions. We evaluated how habitat loss (0, 55 and 84%), fragmentation (1, 4 and 16 fragments) and their combination affected the abundance and species richness of coccinellids and carabids, and aphid abundance, both in the short-term (summer: December to February) and over a longer time span (autumn: March to May), when different demographic mechanisms may participate. We created four types of 30 × 30 m patches (landscapes) in which alfalfa was grown: Control (1F -0%, 30 × 30 m patch of alfalfa with no fragmentation or habitat loss), 4F -55% (4 alfalfa fragments, with 55% total habitat loss), 4F -84% (4 alfalfa fragments, with 84% total habitat loss), and 16F -84% (16 alfalfa fragments, with 84% total habitat loss). Each landscape type was replicated five times. Insects were sampled by sweep-netting and pitfall traps, from December (summer) to May (autumn). Total abundance and species richness of carabids, in the short-term, was highest in the 16F -84% landscapes. Total abundance of adult coccinellids was similar among landscapes, but at the species level Hyperaspis sphaeridioides, in the short-term, and Adalia bipunctata, in the long-term, had their highest densities in fragments within landscapes with high habitat loss (84%), independently of habitat fragmentation. Species richness in the long-term was higher in the landscapes with 84% habitat loss. Among aphids, in the long term Aphis craccivora was less abundant in landscapes with high habitat loss and fragmentation (16-84%), while Therioaphis trifolii showed the opposite trend. These results suggest that habitat loss and fragmentation may increase the density and diversity of aphidophagous insects, while their effects on aphids are more variable.

Food Relationships

“…axyridis tracked aphid population dynamics more effectively than did adults of Col. maculata within and across experimentally fragmented landscapes with 10 -80% cover of red clover planted in clumped or fragmented fashion. Grez et al (2005Grez et al ( , 2008 assessed and distinguished between the effects of habitat loss and habitat fragmentation on population levels of ladybirds and aphids in differently fragmented plots of alfalfa.…”

Invasions by ladybugs, ladybirds, and other predatory beetles

“…These species include P. quatuordecimpunctata and Hippodamia variegata (Goeze) in northeastern North America (Day et al 1994;Ellis et al 1999;Finlayson et al 2008); Coccinella undecimpunctata L. and Adalia bipunctata (L.) in New Zealand (Dixon 2000); and Hippodamia convergens Guérin-Méneville and H. variegata (Goeze) in Chile (Grez et al 2008).…”

“…The introduced H. variegata may be replacing the indigenous Eriopis connexa (Germar) in alfalfa fields of central Chile. The former species was much rarer than the latter species in 1993 but this pattern had become reversed by 2008 (Grez 1997;Grez et al 2008;Grez et al in review).…”

Movement between crops and weeds: temporal refuges for aphidophagous insects in Central Chile

“…Hence, field edges can be important in modulating predator-prey interactions and the control of pest populations within crops (Grez et al, 2005). Habitat fragmentation can affect insect dispersal in the landscape, especially considering modern agricultural practices that modify the landscape significantly, eliminating natural or semi-natural vegetation where insect biological control agents may seek refuge (Grez et al, 2008).…”