Population variation in and selection for resistance to pyrethroid-neonicotinoid insecticides in the bed bug

Abstract

Pyrethroid resistance in bed bugs, Cimex lectularius, has prompted a change to combination products that include a pyrethroid and a neonicotinoid. Ten populations of bed bugs were challenged with two combination products (Temprid SC and Transport GHP). Susceptibility of these populations varied, with the correlated response of the two products indicating cross resistance. We imposed selection on three populations using label rate Temprid, and then reared progeny from unselected and selected strains. All selected strains were significantly less susceptible to Temprid SC than unselected strains. Temprid selected strains were also less susceptible to Transport. The pyrethroid component of Temprid showed a significantly higher LD50 in selected strains, but susceptibility to the neonicotinoid remained unchanged. Taken together these results indicate resistance to combination insecticides is present in field populations at levels that should be of concern, and that short-term selection affecting existing variance in susceptibility can quickly increase resistance.

Figure 1. Regression between proportion of bed bugs killed by residues of Temprid SC and Transport GHP for ten populations (1 corresponds with CIN1, 2 corresponds with CIN10, 3 corresponds with FD, 4 corresponds with FF1, 5 corresponds with LA1, 6 corresponds with LEX5, 7 corresponds with LEX7, 8 corresponds with LEX8, 9 corresponds with NY1 and 10 corresponds with RO1) of bed bugs at 1 to 14 d of exposure.

Data shown were corrected for control mortality.

Figure 2. Susceptibility to Temprid SC in selected and unselected lines from CIN1, LA1, and NY1.

In the parental generation adult bed bugs were exposed to residues of Temprid SC for intervals expected to kill 80% at 24 h after exposure for selected lines. Unselected lines were treated in the same way but without insecticide exposure. In each replicate of each strain there was a significant decrease (each χ² analysis had 1 df) in offspring mortality from the same exposure as parents received (see text for log linear analysis).

Figure 3. Susceptibility to Transport GHP in selected and unselected lines from CIN1 and LA1 showing cross resistance to Temprid SC.

In the parental generation, adult bed bugs were exposed to residues of Temprid SC for intervals expected to kill 80% at 24 h after exposure for selected lines. Unselected lines were treated in the same way but without insecticide exposure. NY1 was not evaluated because of insufficient numbers of test insects. In each replicate of both populations, there was a significant decrease (each χ² analysis had 1 df) in offspring mortality from Transport GHP exposure (see text for log linear analysis).

Figure 4. Probit regression data for the relationship between dose of β-cyfluthrin and mortality at 24 h for topical bioassays.

Open diamonds and dotted lines represent unselected strains; whereas solid squares and solid lines represent selected strains.

Figure 5. Probit regression data for the relationship between dose of imidacloprid and mortality at 24 h for topical bioassays.

Open diamonds and dotted lines represent unselected strains; whereas solid squares and solid lines represent selected strains.